Electrochemical measurement with additional reference measurement

Abstract

A method is provided for measuring one or more potential differences indicative of one or more concentrations of one or more analyte ions in a sample (102), e.g., a liquid whole blood sample, comprising measuring a parameter indicative of a concentration of a reference ion in the sample using a reference ion measurement setup (104), where the reference ion measurement setup (104) is different from the electroanalytical measurement setup, and measuring one or more potential differences directly or indirectly between each of one or more optionally solid-state working electrodes, said optionally solid-state working electrodes including an ion selective electrode selective for the analyte ion, and each of an optionally solid-state reference electrode selective for the reference ion, using an analyte ion measurement setup (105), where the analyte ion measurement setup is the electroanalytical setup. Additionally, an apparatus (100) and uses of said apparatus are provided.

Description

Technical Field

[0001] The present invention relates to a method for measuring a parameter indicating the concentration of an analyte ion in a liquid, and more particularly, to a method for measuring one or more potential differences indicating one or more concentrations of one or more analyte ions in a sample such that the sample is a liquid whole blood sample, and further to a corresponding device and the use of such a device.

Background Art

[0002] Generally, being able to determine one or more potential differences indicating one or more concentrations of one or more analyte ions in a sample such that the sample is a liquid whole blood sample is advantageous for a number of reasons, but doing so can involve expensive, complex, and / or inaccurate devices, which may also require a large sample volume, and which may further have a limited service life and / or be prone to failure.

[0003] Accordingly, there is a need for an improved method and apparatus for measuring one or more potential differences indicating one or more concentrations of one or more analyte ions in a sample such that the sample is a liquid whole blood sample, in particular, an improved method and apparatus that is more cost-effective, simpler, more accurate, enables working with a smaller sample volume, and is further more durable and / or less prone to failure.

Summary of the Invention

[0004] It is an object of the present invention to provide an improved method and apparatus that overcome at least some of the drawbacks of known methods and apparatuses for measuring one or more potential differences indicating one or more concentrations of one or more analyte ions in a sample such that the sample is a liquid whole blood sample. Additionally, or alternatively, it is an object of the present invention to provide an alternative to known methods and apparatuses.

[0005] According to a first aspect, the present invention provides a method for measuring one or more potential differences indicative of the concentration of one or more analyte ions in a sample, such that the sample is a liquid whole blood sample, and optionally further determining the concentration of one or more analyte ions, said method comprising the steps of: - optionally providing an apparatus according to a second aspect; - measuring a parameter indicative of the concentration of reference ions in the sample using a reference ion measurement setting, wherein the reference ion measurement setting (104) is different from an electroanalytical measurement setting and optionally further determining the reference ion concentration, and - measuring directly or indirectly, using an analyte ion measurement setting, one or more potential differences indicative of the concentration of one or more analyte ions in the sample between: i. each of one or more working electrodes, such as one or more solid working electrodes, each of said working electrodes comprising an ion-selective electrode that is selective for analyte ions, and ii. a reference electrode, such as a solid reference electrode that is selective for reference ions, wherein the analyte ion measurement setting is an electroanalytical setting, such as a potential difference measurement setting, and - optionally determining the concentration of one or more analyte ions.

[0006] A possible advantage of the present invention is that it allows the reference ion measurement setting to eliminate the need for a reference electrode with a known or predictably varying potential, e.g., eliminating the need for a reference with a stable potential or the need to know or predict the conditions for a reference with a potential that varies with conditions, which in turn may lead to one or more more cost-effective, simpler, and / or more accurate methods, which may further be more durable, less prone to failure, and / or able to work with a smaller sample volume.

[0007] The gist of the present invention is considered to be recognized in that providing a constant, known or predictably varying potential can advantageously be replaced by measuring the concentration of a reference ion, which reduces the requirement for a reference electrode (e.g., by not requiring the electrode to maintain a constant potential) and / or the requirement for a measurement solution such as liquid whole blood (e.g., by not requiring parameters such as the concentration of the reference ion in the measurement solution to be known or predictable).

[0008] Instead of relying on a reference electrode of a nominally known potential with an aqueous electrode such as a standard hydrogen electrode (SHE), it may be possible to have a solid ion-selective electrode such as a pH-sensitive solid electrode as a reference (and further having a reference measurement setup for measuring pH). Aqueous reference electrodes are circumstantial, expensive, may take up space (e.g., by means of a liquid-liquid junction and a separate electrolyte solution chamber), and may have a limited service life due to ion loss from the electrolyte chamber to the sample and / or rinse solution. Furthermore, the ion loss itself can cause problems of contamination of the sample and / or rinse solution, which can introduce measurement errors and loss of accuracy. The ion leakage of the aqueous reference electrode may require a large distance between the working electrode and the reference electrode, which in turn can increase the size and require a larger sample volume (where in certain cases such as for neonates and / or intensive care patients, a large volume can be particularly disadvantageous for whole blood samples).

[0009] As another example, instead of relying on a reference electrode that varies depending on conditions, or instead of relying on further knowing or predicting the measurement conditions, it is possible to have an ion-selective electrode, such as a pH-sensitive solid electrode, as a reference and measure the reference ion concentration, for example, through settings for measuring pH. The advantage of measuring the reference ion concentration may be that it enables an increase in the accuracy of determining the concentration of the analyte ion, where the increase in the accuracy of determining the concentration of the analyte ion results from an increase in the accuracy of the concentration of the reference ion due to the measurement being more accurate than an assumption or prediction. Additionally, expanding the usability of the method for applications where conditions such as the concentration of the reference ion are not known or cannot be predicted can be considered an advantage of measuring the reference ion concentration. For example, when relying on a known constant concentration of a specific reference ion, or when relying on a situation where the concentration of a specific reference ion behaves in a predictable manner, the selection of the reference ion is limited to reference ions (candidates) whose concentration is known and constant or behaves in a predictable manner. This can be disadvantageous for several reasons, including that the (reference) ion concentration may not be truly constant between individuals (e.g., with respect to different humans), and / or there may be no overlap between the reference ions applicable in this way and the optimal ion-selective reference electrodes (in other words, because the concentration of the reference ion for which the optimal reference electrode is specific is not known, not constant, or not predictable, it may be necessary to employ a sub-optimal reference electrode). In contrast, in aspects according to the present invention, the reference ion can be freely selected, for example, according to an optimal reference (ion-specific) electrode. This may in turn result in a benefit to the accuracy of the reference ion measurement setting, which may in turn result in a benefit to the overall accuracy regarding the determination of the analyte ion concentration.

[0010] 'Measuring a potential difference of 1 or more' should be understood as, for example, measuring a voltage of 1 or more such as a DC voltage, as is common in the art (where the potential difference is an electrical potential difference). Such measurement of the potential difference can be performed, for example, by potential difference measurement. In the case of a plurality of potential differences, it is understood that each potential difference should be measured between a reference electrode and the (respective) working electrode.

[0011] 'Indicating one or more concentrations of one or more analyte ions in a sample' can be understood as the method being configured such that the measured potential difference indicates the concentration of the ions or group of ions in the sample, respectively.

[0012] 'Indicating a concentration' can generally be understood as being able to determine the concentration thereby. For example, a potential difference - which itself is not a concentration - is measured, and this enables the determination of the concentration. Determining the concentration can be understood as both qualitatively detecting the presence (yes / no) of the analyte, for example, a concentration above the detection limit, and quantitatively determining the concentration, for example, on both an ordinal, interval, or ratio type scale.

[0013] 'Reference ion' is understood to be any ion that can potentially exist naturally in whole blood and is applicable as a reference ion in the sense that a (reference) electrode selective for said (reference) ion can be used as a reference electrode, for example, in a potential difference measurement setting. Reference ions can be, for example, hydrogen ions (H + ), sodium ions (Na + ), potassium ions (K + ), calcium ions (Ca 2+ ), chloride ions (Cl - ), magnesium ions (Mg 2+ ), or bicarbonate ions (HCO3 - ).

[0014] 'Reference ion measurement setting' refers to any setting that can determine a parameter indicating the concentration of a reference ion (where, in general, the reference ion can be understood to be a single specific reference ion or a group of reference ions), for example, a setting arranged to optically explore a sample such as a whole blood sample and determine its optical parameter indicating the reference ion concentration.

[0015] The reference ion measurement setting can be selective with respect to a single ion or a group of ions. The reference ion measurement setting is somewhat (cross-)selective with respect to one or more interfering ions. However, the reference ion measurement setting can be understood to be more selective with respect to a certain ion or group of ions as compared to another ion or group of ions (for example, the selectivity coefficient of the interfering ion is less than 1.0, for example less than 0.9, for example less than 0.5, for example less than 0.1, for example less than 0.07, for example less than 0.05, for example less than 0.03, for example less than 0.02, for example less than 0.01).

[0016] For example, in order to make it possible to completely omit the need to consider cross-selectivity, it may generally be advantageous for the cross-selectivity to be negligible or zero. If the cross-selectivity is not zero, for example, cannot be ignored, for example, if the cross-selectivity is sufficiently low (for example, when the selectivity coefficient of the interfering ion is less than 1.0), it may still be possible to perform corrections and take cross-selectivity into account, and the measurement may still be usable. Therefore, it may still be advantageous when the cross-selectivity is less than a certain threshold, for example, when the selectivity coefficient of the interfering ion is less than 1.0, for example less than 0.9, for example less than 0.5, for example less than 0.1, for example less than 0.07, for example less than 0.05, for example less than 0.03, for example less than 0.02, for example less than 0.01.

[0017] According to one aspect, the reference ion is a single specific ion or a group of ions, and there is substantially no cross-selectivity in either the reference ion measurement setting or the reference electrode. According to another aspect, the reference ion is a single, specific ion or group of ions that has cross-selectivity with respect to the reference ion measurement setting and / or the reference electrode, and each cross-selectivity is explained, for example, by measuring and / or estimating the respective concentration of one or more interfering species and taking into account these one or more concentrations.

[0018] 'Electroanalytical measurement setting' is understood to be common in the art and is, for example, a setting of an electroanalytical method. Here, 'electroanalytical method' is a method for chemical analysis, for example, a method that enables determination of parameters indicating the concentration of reference ions and / or analyte ions in a liquid sample by an electrolytic method. Here, 'electrolytic method' is understood to be common in the art and is, for example, a method for causing a chemical change by applying a potential and / or passing an electric current through an electrolyte. More specifically, it is understood that an electroanalytical method determines parameters indicating the concentration of analyte ions and / or reference ions by measuring the potential (volts) and / or current (amperes) in an electrochemical cell containing analyte ions and / or reference ions. An electroanalytical method uses an electrically conductive probe called an electrode to make electrical contact with the analyte solution. The electrodes are used in combination with the electrical or electronic devices to which they are attached to measure the parameters of the solution. The parameters measured are related to the identity of the analyte ions or reference ions and / or the amount of analyte ions or reference ions in the solution. Electroanalytical methods include potential difference measurement, current measurement, conductometry, electrogravimetry, voltammetry (and polarography), and coulometry.

[0019] "The reference ion measurement setting is different from the electroanalytical measurement setting" means that there is a reference ion measurement setting that is applied to the method but is understood to belong to a different group of measurement settings with respect to the group of electroanalytical measurement settings. This advantage may be that while electroanalytical measurement settings generally require a reference electrode, the need for it can be omitted for measurement settings that are different from electroanalytical measurement settings. In addition, once a parameter indicating the concentration of reference ions in a sample is determined, then, without the need for a reference electrode having a predetermined known potential, it becomes possible to obtain the benefits from the advantages of electroanalytical methods (e.g., potential difference measurement), i.e., to determine parameters indicating the concentration of one or more analyte ions in the sample, i.e., the potential difference.

[0020] In some embodiments, the reference ion measurement setting is selected from the group of measurement settings that rely on the measurement of optical parameters (e.g., light, e.g., emitted light and / or optical properties of a sample examined by fluorescence, chemiluminescence, refractive index or absorption), mass parameters (e.g., quartz crystal microbalance (QCM)), magnetic field parameters (e.g., by a Hall sensor combined with labeled magnetic nanoparticles), stress parameters (e.g., using a microcantilever) or dissipation parameters (e.g., by a quartz crystal microbalance with dissipation monitoring (QCM-D) having a dissipation mode).

[0021] For example, the reference ion setting can be a setting for determining the reference ion concentration of a sample, such as a whole blood sample, by optical probing of the sample, such as with an optical pH sensor. 'Optical probing' is understood as being common in the art and relates, for example, to irradiating at least a part of the sample with light and receiving at least a part of the (emitted) light therefrom, where the received light enables derivation of information (such as concentration) regarding an analyte (such as a reference ion) therein. In another example, the reference ion measurement setting can be a setting based on measurement of mechanical properties (such as dissipation) and / or mass, for example, a setting using a quartz crystal microbalance sensor (QCM-D) having a dissipation measurement capability for measuring mass and / or dissipation, or measurement of mass (in the dynamic mode) and / or stress (in the static mode) using a microcantilever, or a setting based on measurement of magnetic parameters such as measurement of the magnetic field of labeled magnetic particles using a Hall sensor. It is included that a parameter indicating the concentration of the reference ion can be measured directly or indirectly, since an action such as a conformational change in a polymer induced by the reference ion or an action such as the adsorption rate or desorption rate of relatively heavy molecules from a surface affected by the reference ion is measured, from which an indirect measure of the concentration of the reference ion is obtained.

[0022] Generally, when referring throughout this application to 'visual', 'optical', etc., it can generally be understood that this is done with reference to electromagnetic radiation such as light having a wavelength (s) within the range of 380 nm to 750 nm.

[0023] In some embodiments, the reference ion measurement setting is a setting that relies on a measurement principle different from that of electroanalytical techniques. For example, the different measurement principle relies on an effect (e.g., optical property, mechanical property, or mass change) different from an effect (e.g., potential or current) measurable by electroanalytical techniques (e.g., potential difference measurement, coulometry, voltammetry). A possible advantage of this can be reducing or eliminating the risk of damaging the sample, such as the risk of extracting ions from red blood cells, which can be a risk in chronopotentiometry. Another possible advantage is eliminating the need for a reference electrode of known potential.

[0024] 'Measuring a parameter indicative of the concentration of reference ions in a sample using a reference ion measurement setting' is understood to mean that the parameter is determined by the reference ion measurement setting and that the parameter enables the determination of the concentration of reference ions in the sample. For example, here the parameter is the intensity of (emitted) light within a specific wavelength.

[0025] 'Measuring one or more potential differences directly or indirectly' is understood to mean that each potential difference can be determined directly between two points, such as directly between a working electrode and a reference electrode via a (possibly high-impedance) voltmeter between the working electrode and the reference electrode, or indirectly. For example, each of the potential differences between the working electrode and the reference electrode is measured with respect to a third electrode, and the potential difference between the working electrode and the reference electrode is then determined and thus measured (only) indirectly.

[0026] A 'working electrode' is understood to be common in the art, e.g., an electrode at which analyte ions can react and where this reaction can be measured. 'Ion-selective electrode' (ISE) is understood to be common in the art. An ISE can be selective for a single ion or a group of ions. More specifically, an ISE is an electrochemical sensor or electrode that enables the determination of the potential difference of the activity of a specific ion in the presence of other ions. An ISE may include an ion-selective membrane that allows passage only of the selected ion (taking into account some possible cross-selectivity as described below) to a conductive internal electrode. An ISE may include an electrode that is somewhat (cross-)selective for one or more interfering ions. However, an ISE can be understood to be more selective for a particular ion or group of ions as compared to another ion or group of ions (e.g., the selectivity coefficient for an interfering ion is less than 1.0, e.g., less than 0.9, e.g., less than 0.5, e.g., less than 0.1, e.g., less than 0.07, e.g., less than 0.05, e.g., less than 0.03, e.g., less than 0.02, e.g., less than 0.01).

[0027] 'Membrane' is completely or partially solid, but can also contain a plasticizer (e.g., here, the remaining part is partially or completely liquid), e.g., contains at least 20 volume / volume percent (v / v%) solids, e.g., contains at least 40 v / v% solids, e.g., contains at least 60 v / v% solids, e.g., contains at least 80 v / v% solids, e.g., contains at least 90 v / v% solids, e.g., contains at least 95 v / v% solids, e.g., contains at least 99 v / v% solids, e.g., is completely solid.

[0028] 'Reference electrode' is understood to be common in the art and can be used, for example, as a reference point for the measurement of the potential difference for each of one or more working electrodes.

[0029] The reference electrode can be somewhat (cross-)selective to one or more interfering ions. However, it can be understood that the reference electrode is more selective to a certain ion or group of ions as compared to another ion or group of ions (for example, the selectivity coefficient for interfering ions is less than 1.0, for example less than 0.9, for example less than 0.5, for example less than 0.1, for example less than 0.07, for example less than 0.05, for example less than 0.03, for example less than 0.02, for example less than 0.01).

[0030] An 'analyte ion' can be understood to be an ion in which there is interest in its concentration and / or which is to be determined. According to one aspect, there is provided a method in which each of one or more working electrodes is a solid (ion-selective, working) electrode and / or the reference electrode is a solid (ion-selective, reference) electrode. The'solid' electrode is understood as being common in the art. More specifically, a solid ion-selective electrode is an ion-selective electrode including an ion-selective membrane and a conductive internal electrode, in which there is little or no liquid between the membrane and the conductive internal electrode, for example, between the side of the membrane facing the conductive internal electrode and the side of the conductive internal electrode facing the membrane. By 'little' liquid, a liquid volume less than 10 times the volume of the membrane, for example, less than 5 times the volume of the membrane, for example, less than 2 times the volume of the membrane, for example, less than the volume of the membrane, for example, less than 0.5 times the volume of the membrane, for example, less than 0.1 times the volume of the membrane, for example, less than 0.01 times the volume of the membrane can be understood. Additionally, or alternatively, the conductive internal electrode is in contact with or in proximity to the membrane such that the percentage of the distance from the conductive internal electrode to the opposite side of the membrane that is conductive, the distance from the internal electrode to the membrane, is less than 90%, for example, less than 75%, for example, less than 50%, for example, less than 25%, for example, less than 10%, for example, less than 5%, for example, less than 2%, for example, less than 1%, for example, less than 0.1%. Additionally, or alternatively, the conductive internal electrode is arranged to be able to be close to or approach the sample such that the distance between the conductive internal electrode and the sample is less than 1 mm, for example, less than 0.75 mm, for example, less than 0.5 mm, for example, less than 0.25 mm, for example, less than 0.1 mm, for example, less than 0.03 mm, for example, less than 0.01 mm, for example, less than 0.003 mm.

[0031] 'Conductive internal electrode' refers to a solid sub-component where an electrochemical reaction occurs, which is conductive and can be understood as being coupled to an analytical device such as a (high-impedance) voltmeter. Thus, an (electrically) conductive internal electrode is understood to form part of a solid electrode. The conductive electrode can include one or more different materials, where one or more of the different materials can include a non-solid substance, such as a liquid, and / or can be susceptible to uptake of a liquid. For example, here the conductive internal electrode forms a matrix containing a solid material. The conductive internal electrode is completely or partially solid (e.g., here the remaining part is partially or completely liquid), for example containing at least 50 v / v% solid material, for example at least 60 v / v% solid material, for example at least 70 v / v% solid material, for example at least 80 v / v% solid material, for example at least 90 v / v% solid material, for example at least 95 v / v% solid material, for example at least 99 v / v% solid material, for example completely solid.

[0032] According to one aspect, there is provided a method where each of one or more working electrodes is a solid electrode and where the reference electrode is a solid reference electrode. A possible advantage of this is that it overcomes the drawbacks associated with non-solid (aqueous or liquid-liquid) electrodes, such as large size, high cost, contamination or consumption of the electrolyte, vulnerability and / or incorrect measurements, such as those due to electrolyte leakage (from aqueous, liquid-liquid electrodes) and affecting the measured value (at the working electrode).

[0033] According to one aspect, there is provided a method comprising determining one or more concentrations of one or more analyte ions in a sample based on the following: i. The concentration of a reference ion, and ii. One or more potential differences.

[0034] The advantages thereof can be that the concentration(s) of one or more analyte ions is / are determined and / or that said determination(s) can be made with (more) high accuracy by taking into account the concentration of a reference ion (as determined in a reference ion measurement setting), for example, not only relying on the hypothesized - and possible search for (e.g., by addition of an amount of reference ion) - concentration of the reference ion. The determination of the concentration of the analyte ion can be made by calculating the concentration, for example, by using the Nernst equation.

[0035] For the purpose of determining the concentration(s) of one or more analyte ions in a sample, the following framework can be relied upon. The Nernst equation gives the relationship between the potential and the concentration of an analyte ion:

[0036]

Chemical formula

[0037] where N_fac is the slope of the half - cell (Nernst coefficient), for example, here, X = cH + , cK + , cNa + , cCa ++ or cCl - (where 'c' indicates 'the concentration of'), and hereinafter, the '+' and '-' can be omitted. For example, cK means cK + , that is, the concentration of potassium ions; here, an element, for example, K does not have the prefix c, and it is simply the parameter K (potassium). Due to the differences between samples, E0 is removed.

[0038] Regarding the example of pH:

[0039]

Chemical formula

[0040] where, for sample 1, cH1 = cH (i.e., the hydrogen ion H+ For sample 2, cH2 = cH (where cH is the concentration). For the electrolyte, in the same way, for example, for cK:

[0041] [Chemical formula]

[0042] It is as follows. For N_fac(pH) = the Nernst coefficient for parameter pH, and similarly for N_fac(X): the Nernst coefficient for parameter X (where X represents the electrolyte), the equations can be expanded. These equations should be used by calculating the concentration of the analyte in the sample and respectively by calculating the correction potential (see below).

[0043] Derivation of the formula for N_fac(X): Using pH as a reference between sample 1 and sample 2:

[0044] [Chemical formula]

[0045] It can be reformulated into the following equation:

[0046] [Chemical formula]

[0047] By calculating N_fac(X), the value of N_fac(pH) can be estimated, for example, to be 57 mV (for example, based on prior knowledge of the gradient of the half-cell of the electrode). Optionally, a set of optimal calibration solutions ("highest"), for example, solutions having the same or approximately the same pH value, can be used to obtain N_fac(pH) having the following equation:

[0048] [Chemical formula]

[0049] "Highest" may refer to N_fac(X) for a set of solutions that may be optimal in some cases, for example, two solutions having the same or nearly the same pH value, where for n_Fac(pH), the average value of those two values is calculated and used for further calculations.

[0050] Since the pH for a (unknown) sample is unknown and may be different for calibration solutions, this pH difference must be calculated to be a voltage (millivolt (mV) value), which is subtracted by the calculation of different electrolyte concentrations. For example, the applicable formula for the calculation of the correction potential Pot.corr is the following formula:

[0051]

Chemical formula

[0052] A new potential can be calculated for an example where the concentration of the analyte ion is to be determined, where 'cal1' is the calibration liquid and'sample' is the unknown sample:

[0053]

Chemical formula

[0054] The electrolyte concentration (mM) can be calculated as follows:

[0055]

Chemical formula

[0056] According to one aspect, a method is provided in which one or more potential differences depend on the reference ion concentration in a sample. Thus, it can be understood that one or more potential differences may depend on the ion concentration in the sample, for example, by eliminating the need for a reference electrode with a known or predictably varying potential. The advantage may be that this need can be eliminated.

[0057] According to one aspect, a method is provided that determines one or more concentrations of one or more analyte ions in a sample based on an expression that reflects and / or incorporates a dependence of one or more potential differences on a reference ion concentration in the sample. For example, the reference ion concentration may affect one or more potential differences as described in the above expression, and this same dependence of the one or more potential differences can be incorporated into an expression regarding electrolyte concentration (see, e.g., the last expression above representing ’cXsample’). In other words, the reference ion concentration can affect one or more potential differences in a particular way (e.g., by a logarithmic term), but in an expression for determining one or more concentrations of one or more analyte ions, this dependence is at least partially, e.g., partially or fully, accounted for by reducing, minimizing, or eliminating the effect of the reference ion concentration on the (determined) one or more concentrations of analyte ions in the sample in the same way. By ’reflecting and / or incorporating’ it can be understood that the same or similar terms (which can be negative or inverse terms to cancel the effect) are included in the above expression as in the expression representing the effect of the reference ion concentration on one or more potential differences.

[0058] According to one aspect, a method is provided in which the sample is a liquid whole blood sample. A potential advantage of the sample being a whole blood sample can be that it obviates the need to separate fractions of the (original) whole blood sample, such as providing plasma or serum. The term "whole blood" is understood as is common in the art, such as blood from which naturally occurring components from a human or animal (optionally collected therefrom) have not been removed (e.g., untreated blood). More specifically, whole blood can refer to blood composed of plasma and cellular components. Plasma occupies approximately 50% - 60% of the volume, and the cellular components occupy approximately 40% - 50% of the volume. The cellular components are erythrocytes (red blood cells), leucocytes (white blood cells), and thrombocytes (platelets). Preferably, the term "whole blood" refers to whole blood of a human subject, but can also refer to whole blood of an animal. The term "blood plasma" or "plasma" refers to the liquid portion of blood and lymph, which constitutes approximately half of the volume of blood (e.g., approximately 50% - 60% by volume). Plasma is cell-free. It contains all the clotting factors, particularly fibrinogen, and contains approximately 90% - 95% by volume of water. Plasma components include electrolytes, lipid metabolites, markers, such as markers for infectious diseases or tumors, enzymes, substrates, proteins, and additional molecular components.

[0059] According to one aspect, a method is provided that includes aspirating a sample, such as aspirating the sample at a sample inlet of an apparatus such as the apparatus according to the second aspect, thereby generating an aspirated portion of the sample. A potential advantage of this can be that a controlled portion of the sample can be aspirated, e.g., can be aspirated and analyzed. In a further aspect, each of the measurement in the reference ion measurement setting and the measurement in the analyte ion measurement setting is performed on the aspirated portion of the sample. A potential advantage of this can be that the (same) aspirated portion of the sample is subjected to both types of analysis, and thus the risk of differences between (sub-)sample portions can be reduced or eliminated.

[0060] According to one aspect, a method is provided in which the reference ion measurement setting is based on a measurement principle based on an optically measurable parameter, such as a reference ion sensitivity indicator (which varies one or more optical properties, such as absorption (e.g., in the wavelength range of [400;1200] nm, e.g., in the wavelength range of [500;1100] nm, e.g., in the wavelength range of [600;1000] nm, e.g., in the wavelength range of [700;900] nm) according to the concentration of the reference ion), e.g., based on a pH-sensitive luminescence indicator, and the measurement principle of the analyte ion measurement setting is a potential difference measurement principle. The advantage of this is that the disadvantages associated with the potential difference measurement principle, which require specific electrodes and / or conditions, can be completely or partially overcome, for example, by using an optically based measurement principle, which can, in fact, obviate the need to establish a known potential, for example, via an aqueous liquid-liquid reference electrode.

[0061] The'measurement principle' can be understood as a principle for measuring concentration that relies on the measurement of a specific parameter such as (electrical) voltage or (optical) absorbance or light intensity. According to one aspect, a method is provided in which measuring one or more potential differences includes exclusively measuring one or more potential differences between solid electrodes, for example, directly, for example, directly between a solid working electrode and a solid reference electrode. The advantage of this can be that only solid electrodes are included, for example, excluding aqueous liquid-liquid electrodes (and related disadvantages). By 'exclusively' for solid electrodes, it is understood that only the potential difference between the solid electrodes is measured, although the potential difference between the solid working electrode and the solid reference electrode can be measured as the sum or difference between the potential differences between the solid working electrode and a third solid electrode and between the solid reference electrode and the third solid electrode, respectively. By 'directly', it is understood that the potential difference is measured directly between the solid working electrode and the solid reference electrode, for example, by inserting a (high impedance) voltmeter between them.

[0062] According to one aspect, a method is provided for measuring the concentration of a reference ion in a sample using a reference ion measurement setting, which includes optical measurement. 'Optical measurement' is understood to be any measurement that measures any one of optical parameters, such as absorption rate, reflectance, fluorescence, refractive index, light beam, absorption, and wavelength. An advantage of optical measurement may be that it can be carried out without damaging red blood cells. Another possible advantage may be that it is independent of electroanalytical techniques and thus provides an alternative to electroanalytical techniques. Another possible advantage may be that it eliminates the need for a known potential, such as a known potential provided by an aqueous liquid-liquid reference electrode.

[0063] According to one aspect, a method is provided in which the reference ion is a hydrogen ion, such as H + , a sodium ion, such as Na + , or a potassium ion, such as K + . A possible advantage of using a hydrogen ion as a reference ion may be that it can be assumed to be present in many samples, such as especially in whole blood samples. A possible advantage of using a sodium ion as a reference ion may be that it can be present at a relatively high concentration (for example, it is the main ionic component in human plasma, for example, it is the ionic component with the highest concentration in human plasma), that it can be measured optically, for example, using a sodium ion-sensitive fluorophore (which may be readily available in some cases), that the sodium ion concentration correlates with the ionic strength (thus using a sodium ion as a reference ion will include and exclude the influence of the ionic strength), and / or that it (for example, its concentration) may be relatively stable in human plasma, for example, the absolute and / or relative variations may be relatively small. A possible advantage of using a potassium ion as a reference ion may be that it can be present at a relatively high concentration (for example, it is the main ionic component in human plasma, for example, it is the second highest concentration ionic component in human plasma).

[0064] According to one aspect, the optical measurement is an optical parameter P that depends on pH omeasuring (for example, absorption rate, reflectance, fluorescence, refractive index, or color), and a change dP in an optical parameter with a change dpH in pH o , dP o / dpH has a local and / or global maximum within a pH interval of [7;8], for example within a pH interval [7.2, 7.6], for example at or about 7.4. A possible advantage of this is that the maximum sensitivity can be in the region where the pH of whole (human) blood is expected. Thus, the accuracy of determining the pH (or hydrogen ion concentration), and thus the concentration of one or more analytes, is increased.

[0065] According to one aspect, there is provided a method in which the reference ion is an ion that naturally exists in whole (human) blood, for example any of the following: - hydrogen ion, for example H + , - sodium ion, for example Na + , - potassium ion, for example K + , - calcium ion, for example Ca 2+ , - chloride ion, for example Cl - , - magnesium ion, for example Mg 2+ , or - bicarbonate ion, for example HCO3 - .

[0066] In this case, the reference ion can be measured directly on whole blood without the need for the addition of an ion that functions as a reference ion. According to a second aspect, there is provided an apparatus for measuring one or more potential differences indicative of one or more concentrations of one or more analyte ions in a sample, such as a sample that is a liquid whole blood sample, comprising: - a reference ion measurement setting arranged to measure a parameter indicative of the concentration of a reference ion (where the reference ion measurement setting (104) is different from the electroanalytical measurement setting) and - an analyte ion measurement setting comprising: i. In the case of 1 or more, each of the working electrodes being solid, and in the case of the working electrodes being solid as described above, each includes an ion-selective electrode which is selective for analyte ions, and ii. A reference electrode including an ion-selective electrode which is solid and selective with respect to reference ions, - Wherein the analyte ion measurement setting is an electroanalytical setting such as a potential difference measurement setting, and wherein the analyte ion measurement setting is arranged to directly or indirectly measure 1 or more potential differences between: i. Each of 1 or more working electrodes, and ii. The reference electrode.

[0067] In a plurality of aspects, each of the 1 or more working electrodes is a solid electrode and / or the reference electrode is a solid reference electrode. The analyte ion measurement setting and the reference ion measurement setting can be rigidly connected, and / or the device can include an enclosure, for example a single enclosure, for example a single enclosure that encompasses and surrounds the analyte ion measurement setting and the reference ion measurement setting.

[0068] The analyte ion measurement setting and the reference ion measurement setting can be arranged to probe a sample in the same measurement chamber in the device. This can be advantageous for minimizing the required amount of sample since the sample only needs to fill a single measurement chamber. Additionally, handling, rinsing, cleaning, etc. can be simplified since there is no need to direct the sample to different measurement chambers.

[0069] According to one aspect, an apparatus is provided, where the reference ion measurement setup includes an optical sensor, e.g., an optical device for measuring a parameter indicating the concentration of a reference ion. For example, here the optical sensor is arranged to perform the measurement, which includes measuring an optical parameter Po (e.g., absorbance, reflectance, fluorescence, refractive index or color), which is pH-dependent, where the change dPo in the optical parameter associated with a change dpH in pH, dPo / dpH has a local and / or global maximum within a pH interval of [7;8], e.g., within a pH interval of [7.2, 7.6], e.g., at 7.4 or at about 7.4. For example, the optical sensor can be an optical pH sensor based on, e.g., a pH-sensitive luminescent indicator, e.g., based on a reference ion-sensitive indicator (changing one or more optical properties, e.g., absorbance (e.g., in a wavelength range of ]400;1200[ nm, e.g., in a wavelength range of ]500;1100[ nm, e.g., in a wavelength range of ]600;1000[ nm, e.g., in a wavelength range of ]700;900[ nm) according to the concentration of the reference ion).

[0070] The reference ion - sensitive indicator may have a maximum or minimum value of optical properties such as the absorption maximum in a wavelength region, for example, within a wavelength region greater than 400 nm, or greater than 500 nm, or greater than 600 nm, or greater than 700 nm, and / or less than 1200 nm, or less than 1100 nm, or less than 1000 nm, or less than 900 nm, e.g., in the wavelength region of ]400;1200[ nm, for example, in the wavelength region of ]500;1100[ nm, for example, in the wavelength region of ]600;1000[ nm, for example, in the wavelength region of ]700;900[ nm. The advantages of a reference ion - sensitive indicator having a maximum or minimum value of optical properties within such a wavelength region are that hemoglobin absorption is minimal within 600 - 1000 nm, and / or interference with other sensors is limited (because the wavelengths in this region are long enough not to interact / decompose with entities (e.g., ionophores) in other sensors present in the device), and / or scattering by lipid particles is limited (because the wavelengths in this region are long enough to be less susceptible to scattering by relatively small lipid particles in samples such as biological samples like whole - blood samples).

[0071] According to one aspect, there is provided a device in which the reference ion is any of the following: - Hydrogen ion, e.g., H + 、 - Sodium ion, e.g., Na + 、 - Potassium ion, e.g., K + 、 - Calcium ion, e.g., Ca 2+ 、 - Chloride ion, e.g., Cl - 、 - Magnesium ion, e.g., Mg 2+ 、or - Bicarbonate ion, e.g., HCO3 - 。

[0072] Each of the listed reference ions is an ion that naturally exists in (human) whole blood. In this case, the reference ions can be measured directly on whole blood without the need for the addition of ions that function as reference ions.

[0073] According to one aspect, there is provided an apparatus further comprising: - A data processing device including a processor configured as follows: i. Determining one or more concentrations of one or more analyte ions in a sample based on: 1. The concentration of a reference ion, and 2. One or more potential differences.

[0074] By implementing the data processing device, the determination of one or more concentrations of one or more analyte ions can be performed in a faster, automated, and / or more reliable manner. According to one aspect, there is provided an apparatus further comprising: - A sample handling system including: ○ A sample inlet, for example, the sample inlet including a suction system, ○ A measurement chamber (for example, a sample handling system of a certain volume, where the sample is placed while measurements of parameters indicating the concentration of a reference ion and / or one or more potential differences are being made), for example, where both a reference ion measurement setting (104) and an analyte ion measurement setting (105) are arranged for measurements on the sample while in the measurement chamber.

[0075] ○ One or more fluid channels, for example, microfluidic channels, fluidically connecting the sample inlet and the measurement chamber. A possible advantage is that the handling of the sample can be performed in a more hygienic, safe, automated, reliable, and / or repeatable manner. The'sample handling system' can generally be understood as a system that receives and handles a sample, for example, transporting it from the sample inlet through one or more fluid channels to the measurement chamber.

[0076] According to one aspect, an apparatus is provided in which a sample handling system further includes the following: - One or more valves, such as valves that enable segmented transport of a sample through a sample handling system, such as in the form of a sample plug, where said valves are optionally controlled by a data processing device, such as a data processing device.

[0077] A possible advantage is that the valve can enable segmented transport, such as transport where the sample moves through at least a part of the sample handling system (e.g., from the sample inlet to the measurement chamber) as a plug and / or without mixing with the liquid in front of and / or behind the sample.

[0078] According to one aspect, an apparatus is provided where, for analyte ions that are monovalent ions, the analyte ion concentration accuracy is less than 20%, such as less than 15%, such as less than 10%, such as less than 7%, such as less than 5.4%, such as less than 5%, such as less than 3.5%, such as less than 2.7%. The advantage of such low (where 'low' accuracy is understood to mean less deviation from the true value) accuracy is that a more accurate estimation of the concentration can be achieved, which in turn can enable improved diagnosis, improved evaluation of treatment efficacy, or improved estimation of the physiological and / or nutritional state of a subject (e.g., a patient or person from whom a blood sample has been taken). 'Accuracy' is understood as is common in the art and is, for example, the error that would exist between the actual ('true') value, such as the true concentration of analyte ions in this context, and the measured value, such as the concentration of analyte ions in the output of the apparatus and / or determined by the apparatus in this context.

[0079] According to one aspect, an apparatus is provided, where the apparatus, for example the entire apparatus, is capable of determining the concentration of one or more analyte ions in a sample based on one or more potential differences, with respect to one or more analyte ions each being a monovalent ion, with an accuracy regarding one or more true concentrations of less than 20%, such as less than 15%, such as less than 10%, such as less than 7%, such as less than 5.4%, such as less than 5%, such as less than 3.5%, such as less than 2.7%. It should be understood that the determination of the analyte ion concentration based on both a parameter indicating the concentration of reference ions and a potential difference indicating the concentration of analyte ions, for example the entire apparatus, allows for a low accuracy with respect to the determination of the analyte ion concentration. Furthermore, it should be understood that the accuracy is determined with respect to the true value of the concentration.

[0080] According to one aspect, an apparatus is provided, wherein the accuracy of the reference potential (i.e., the combined accuracy of both the reference ion measurement setting and the reference electrode (i.e., taking into account the cumulative error), which is selective with respect to the reference ion), as determined by a reference electrode (which may be solid in some cases), is less than 10%, such as less than 7.5%, such as less than 5%, such as less than 3.5%, such as less than 2.7%, such as less than 2.5%, such as less than 1.75%, such as less than 1.35% with respect to analyte ions that are monovalent ions. The advantage of such a low (where 'low' accuracy is understood to mean less deviation from the true value) accuracy of the reference potential, i.e., of the reference ion measurement setting and the reference electrode, is that a more accurate estimate of the reference potential is provided, which in turn can enable improved accuracy regarding the concentration of analyte ions, which can in turn enable improved diagnosis of a subject (e.g., a patient or person from whom a blood sample has been taken), evaluation of improved treatment efficacy, or estimation of an improved physiological and / or nutritional state. 'Accuracy' is understood as is common in the art, for example, the error that would exist between the actual ('true') value of the reference potential (e.g., the 'true' potential difference between the potential in the bulk portion of the sample and the potential in the conductive internal electrode within the reference electrode) and the reference potential determined based on the concentration of the reference ion, which is derived from a parameter indicating the concentration of the reference ion as determined by the potential at the reference ion measurement setting and the reference electrode (e.g., the potential subtracted from the potential difference between the working electrode and the reference electrode to obtain the potential difference between the potential in the bulk portion of the sample and the potential in the conductive internal electrode within the working electrode) in this context.

[0081] According to one aspect, an apparatus is provided, wherein - the analyte ion concentration accuracy is less than 20%, such as less than 15%, such as less than 10%, such as less than 7%, such as less than 5.4%, such as less than 5%, such as less than 3.5%, such as less than 2.7% with respect to analyte ions that are monovalent ions, and - the proportion of the analyte ion concentration accuracy due to the reference ion measurement setting and the reference electrode is less than 50%, such as less than 40%, such as less than 30%, such as less than 20%, such as less than 10%. For example, here, the analyte ion concentration accuracy is less than 10%, and the proportion of the analyte ion concentration accuracy due to the reference ion measurement setting and the reference electrode is less than 30%, for example less than 25%, for example less than 20%. The advantage of this is that an analyte ion concentration accuracy lower than 10% is accurate enough for most purposes, and the relatively low proportion due to the reference ion measurement setting and the reference electrode leaves room for the realistic accuracy (or lack thereof) from other sources, for example, from the ion-selective working electrode.

[0082] The advantage of such low (where 'low' accuracy is understood to mean less deviation from the true value) accuracy is that a more accurate estimate of the concentration can be achieved, which in turn enables improved diagnosis of the subject (for example, the patient or person from whom the blood sample was taken), evaluation of improved treatment efficacy, or assessment of improved physiological and / or nutritional status. 'Accuracy' is understood as is common in the art, for example, the error that would exist between the actual ('true') value, for example, the concentration of the analyte ion, and the indicated value, for example, the concentration of the analyte ion, in the output of the device and / or as determined by the device.

[0083] According to one aspect, a device is provided, where: - each of one or more working electrodes, and - the reference electrode The distance (for example, the center-to-center distance) between them is 10 mm or less, for example 5 mm or less, for example 3 mm or less, for example 1 mm or less, for example 1 mm or less. A possible advantage is that (simply) a relatively small sample volume is required. Another possible advantage is that, for example, when using a sample chamber that can be rinsed more quickly (for example, because the volume of the sample chamber is smaller), the (idle) time that must be passed between measurements on different samples is less.

[0084] According to one aspect, there is provided an apparatus in which the gradient of a reference ion half-cell is at least 10%, such as at least 25%, such as at least 50%, such as at least 75%, such as at least 80%, such as at least 90%, such as at least 95%, such as at least 97% with respect to the theoretical gradient of the reference ion according to the Nernst equation. The advantage of having a relatively large gradient can be that an off-the-shelf ISE (which can be used as the working electrode itself) that functions properly and sufficiently (since the reference ion measurement setting allows for taking into account the gradient / sensitivity) can be used as the reference electrode. The gradient of the reference ion half-cell is understood as the proportionality constant between the measured potential and the (logarithm of the) reference ion concentration. For example, here, the measured electrode potential E is related to the activity of the ion species by the Nernst equation: E = E0 + 2.3xRT / (nF)logA where E0 = a constant for a given cell, R = the gas constant, T = the temperature in Kelvin, n = the ion charge, F = the Faraday constant, A is the activity, and x is a coefficient that takes into account the possibility that the gradient coefficient may deviate from the coefficient given by RT / nF, which can be called the ideal gradient coefficient. For example, when measuring potassium ions (i.e., n = +1), the gradient coefficient at 298 K (25 °C) has a value of 59.16 mV, and the gradient coefficient at 37 °C has a value of 61.54 mV. For example, when x = 0.1, the gradient of the reference ion half-cell is 10% with respect to the theoretical (ideal) gradient of the reference ion according to the Nernst equation.

[0085] According to a third aspect, there is provided the use of the apparatus according to the second aspect, where the apparatus is used to measure one or more potential differences indicative of one or more concentrations of one or more analyte ions in a sample (e.g., the sample is a liquid whole blood sample), and is used, for example, to determine one or more concentrations of one or more analyte ions in the sample based on, for example, the concentration of a reference ion and one or more potential differences.

[0086] In the context of a point-of-care measurement system (also referred to in the art as a 'bedside' system) and similar laboratory environments, blood gas analysis is often performed by a user who may not be trained, for example, in the use of a blood gas analyzer, such as a nurse.

[0087] According to a fourth aspect (or an aspect of the third aspect) of the present invention, there is provided the use of an apparatus according to a second aspect of the present invention for point-of-care (POC) analysis, such as the determination of the concentration of one or more analytes in one or more samples, such as a sample that is a liquid whole blood sample.

[0088] POC measurements are also referred to in the art as 'bedside' measurements. In this context, the term 'point-of-care measurement' should be understood to mean a measurement performed very close to the patient, i.e., a measurement not performed in a laboratory. Thus, according to this aspect, the user of an apparatus such as a blood gas analyzer performs the measurement of a whole blood sample in a handheld blood sample container close to the patient from whom the blood sample is taken, for example, in a room housing the patient's bed or ward, or in a room close to the same hospital department. In such use, the level of expertise of the user is often diverse, from novice to experienced, and thus the ability of a blood gas analyzer to automatically output instructions that match the skills of each individual user based on sensor input is particularly beneficial in such an environment.

[0089] The first, second, third, and fourth aspects of the present invention can each be combined with any of the other aspects. These and other aspects of the present invention will be apparent from, and will be described with reference to, the embodiments described below.

[0090] The method, apparatus, and use according to the present invention will be described in more detail herein with reference to the accompanying drawings. The drawings illustrate one way of implementing the invention and should not be construed as limiting to other possible embodiments within the scope of the set of appended claims.

[0091] Preferred embodiments of the present invention are thought to be described in more detail in connection with the accompanying drawings, and more specifically: **Brief Description of the Drawings**

[0092]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

[0093] FIG. 1 is a schematic diagram of an apparatus 100 for measuring one or more potential differences indicative of one or more concentrations of one or more analyte ions in a sample 102, for example a liquid whole blood sample, and includes the following: - arranged (234) to measure a parameter indicative of the concentration of a reference ion, where the reference ion measurement setting is a reference ion measurement setting 104, 304 different from an electroanalytical measurement setting such as an optical sensor, and - analyte ion measurement settings 105, 305 including the following: i. one or more, optionally solid, working electrodes 352, each of said optionally solid working electrodes 352 including an ion - selective electrode selective for analyte ions, ii. a reference electrode 350 including an ion - selective electrode selective for reference ions and optionally solid, where the analyte ion measurement setting is an electroanalytical setting such as a potential difference measurement setting, And here, the electrochemical measurement settings 105, 305 are arranged to measure directly or indirectly one or more potential differences (236) between: iii. each of the one or more working electrodes 352, and iv. the reference electrode 350.

[0094] The reference ion measurement settings 104, 304 and the electrochemical measurement settings 105, 305 are depicted as being in separate measurement chambers or being included within separate measurement chambers, but in an alternative embodiment, they may both explore the sample in the same measurement chamber 354.

[0095] The reference ion measurement settings 104, 304 in the schematic example include something optical, such as an optical pH sensor, and further include the following: - A data processing device 106 including a processor configured as follows: i. Determine (238) one or more concentrations of one or more analyte ions in the sample based on the following: 1. The concentration of the reference ion, 2. One or more potential differences.

[0096] The apparatus of the schematic diagram of FIG. 1 further shows a sample handling system including the following: ○ A sample inlet 112 ○ A measurement chamber 354 ○ One or more fluid channels 114, such as microfluidic channels, fluidically connecting the sample inlet and the measurement chamber(s).

[0097] The described device further includes a digital storage device 116 (for storing data related to the control and / or calculations of the data processing device, for example), and a user interface 118, where the user interface includes an output unit 120 (which is a display unit in the described embodiment) arranged to visually output information related to operating the device and / or information representing the concentration of one or more analyte ions in the sample 102, and an input unit 122 (such as a keyboard for providing information about the identity of the sample 102 to the device, for example). The thin line arrows indicate the flow of information such as the parameter indicating the concentration of the reference ions flowing from the reference ion measurement settings 104, 304 to the data processing device 106, one or more potential differences flowing from the electrochemical measurement settings 105, 305 to the data processing device 106, the concentration of one or more analyte ions in the sample flowing from the data processing device 106 to the user interface 118 (more specifically, the output unit 120), and the user input flowing from the input unit 122 to the data processing device 106.

[0098] Figure 2 shows a method 200 for measuring one or more potential differences (starting at block 230 and ending at block 240), showing the concentration of one or more analyte ions in a sample 102, which may be a liquid whole blood sample in some cases, and optionally further determining the concentration of one or more analyte ions, the method including the following steps: - Optionally, provide the sample 102 to the sample inlet 112 of the device 100 as described in FIG. 1 and / or according to a second aspect of the present invention (232) - Measure the concentration of the parameter indicating the reference ions in the sample 102 using the reference ion measurement settings 104, 304 (234), where the reference ion measurement settings 104 are different from the electroanalytical measurement settings and optionally further determine the reference ion concentration, - Measure directly or indirectly one or more potential differences between the following using the analyte ion measurement settings (236): iii. each of the working electrodes 352 above 1 (for example, one or more solid working electrodes, each of the working electrodes including an ion-selective electrode that is selective for analyte ions) and iv. a reference electrode 350, such as a solid reference electrode that is selective for reference ions, wherein the analyte ion measurement setting is an electroanalytical setting such as a potential difference measurement setting, and - optionally, determining (238) one or more concentrations of one or more analyte ions.

[0099] FIG. 3 shows examples of electrochemical measurement settings 105, 305 and reference ion measurement settings 104, 304. More specifically, the figure shows a reference electrode 350 and a working electrode 352 partially within a measurement chamber 354, an (electrochemically (high impedance)) voltmeter 356 between the reference electrode 350 and the working electrode 352, and an (inlet) fluid channel 314 arranged to enable a sample to be introduced into the measurement chamber 354, for the electrochemical measurement settings 105, 305. The portions of the reference electrode 350 and the working electrode 352 are similar, but for simplicity only, the reference electrode 350: a case 360 including an insulating sealant 362 surrounding a conductor 364 electrically connected to a conductive internal electrode 366 disposed on the other side of a membrane 368 with respect to the interior of the measurement chamber 354 (where a sample may be present during use) will be described. The center-to-center distance 370 between the reference electrode 350 and the working electrode 352 is also shown.

[0100] FIG. 3 also shows reference ion measurement settings 104, 304 in the form of an optical pH sensor, including an optical analysis unit 358 that is partially present within the measurement chamber 354 and may include one or more light sources and one or more photodetectors and optionally one or more optical filters.

[0101] Figure 4 shows an enlarged view of the conductive internal electrode 366 and the film 368 (e.g., of the working electrode 352 or the reference electrode 350). The drawing further shows that there may be a gap 472 between the conductive internal electrode 366 and the film 368. Further, the drawing shows the distance 474 from the conductive internal electrode 366 to the opposite side of the film 368, which is also the distance between the conductive internal electrode 366 and the sample 102 (or the measurement chamber 354 in which the sample 102 may be present during use). Further, the figure shows the distance 476 from the conductive internal electrode 366 to the film 368.

Example

[0102] A human (non-smoker) blood sample 102 was adjusted to a total hemoglobin concentration of 15 g / dL and a pH value of approximately 7.6 using a gas (SAT100) that ensures oxygen saturation, where the CO2 level in the gas controls the pH.

[0103] The pH measurement of the blood sample 102 was performed using five ABL725 (Radiometer, Copenhagen, Denmark) electroanalytical blood gas analyzers. The measurement was repeated four times with each ABL725 electroanalytical blood gas analyzer. The results can be seen in Table I (where n in “ABL725-n” indicates the instrument number n).

[0104]

Table 1

[0105] The pH measurement 234 of the blood sample 102 was further carried out using ten NPT7 (Radiometer, Copenhagen, Denmark) optical blood gas analyzers 104, 304. The measurement was repeated four times with each NPT7 optical blood gas analyzer. The results can be seen in Table II and Table III (“#m.” indicates the number of the measurement, and n in “NPT-n” indicates the number of the device), where the entries in Table II each represent a different NPT7 measurement, and the entries in Table III each represent the deviation or error from the average value determined by five ABL725 measurements in the same round of measurement (by degassing CO2 and subsequent pH change) to remove the interference from the drift in the sample 102.

[0106]

Table 2

[0107]

Table 3

[0108] To evaluate the impact on accuracy by replacing the completely electro-analytical method and apparatus with the apparatus 100 and method 200 according to the aspects of the present invention, a total of 40 sums or errors were formed, and each sum is the sum of the error from the NPT7 measurement value and the error from the ABL725 measurement value (where the ABL725 data set was replicated to match the double-sized NPT7 data set).

[0109] Assuming that the electrical analytical method and settings depend entirely on the perfect reference electrode 352 (for the purpose or to provide a conservative estimate), the impact on the accuracy introduced in aspects of the present invention is the error on the optical pH measurement 234 of the NPT7 devices 104, 304 (corresponding to the error introduced by the reference ion measurement settings) and the error introduced by the solid ion-selective pH electrode of the ABL725 device (corresponding to the error introduced by the reference electrode of the analyte ion measurement settings), which can be estimated as the sum. It is noted that depending on the signs of these errors, they can either sum up or (fully or partially) cancel each other out.

[0110] Figure 5 shows an overview of these sums in a graph having the systems 1 - 10 (formed by the NPT7 devices 104, 304 and the ABL725 device respectively) and four different measured values (“#m.1”, “#m.2”, etc.) for each system. It can be seen that all errors are less than 1.60 mV, the errors are generally about 1.0 mV, and the average of the absolute values is 0.888 mV. For a Nernst coefficient of 60 mV, this would correspond to an impact on the accuracy of the analyte ion measurement of 3.47% for monovalent ions and 6.93% for divalent ions. When corrected for the average value of the system, these values can be reduced to 2.7% and 5.4% for monovalent and divalent ions respectively. Assuming that the analyte ion-selective working electrode introduces errors below the same order of magnitude, the accuracy of the method or device according to the present invention can be estimated to be approximately 2.7 - 5.4% for monovalent analyte ions and approximately 5.4 - 10.8% for divalent analyte ions. * (10 (0.888mV / 60mV) -1)

[0111] Although the present invention has been described in connection with specific embodiments, it should in no way be construed as being limited to the presented examples. The scope of the present invention is indicated by the set of appended claims. In the context of the claims, the terms "comprising" or "comprises" do not exclude other possible elements or steps. Also, references such as "a" or "an" should not be construed as excluding a plurality. The use of reference signs in the claims regarding the elements shown in the drawings should also not be construed as limiting the scope of the present invention. Further, the individual features recited in different claims may, in some cases, be advantageously combined, and the recitation of these features in different claims does not exclude the possibility and advantage of combining the features. This specification includes the disclosure of the following invention. [Item 1] A method for measuring one or more potential differences indicating one or more concentrations of one or more analyte ions in a sample such that the sample is a liquid whole blood sample, said method comprising the following steps: - Measuring a parameter indicating the concentration of a reference ion in the sample using a reference ion measurement setting, where the reference ion measurement setting is different from an electroanalytical measurement setting, and - Using an analyte ion measurement setting to directly or indirectly measure one or more potential differences indicating one or more concentrations of one or more analyte ions in the sample between: i. Each of one or more working electrodes, each including an ion-selective electrode that is selective for the analyte ion, and ii. A reference electrode that is selective for the reference ion, where the analyte ion measurement setting is an electroanalytical setting such as a potential difference measurement setting. [Item 2] The method according to Item 1, wherein each of the one or more working electrodes is a solid electrode and / or the reference electrode is a solid reference electrode. [Item 3] The method according to Item 1 or 2, comprising the following: i. The concentration of the reference ion, and ii. One or more potential differences to determine one or more concentrations of one or more analyte ions in the sample. [Item 4] The method according to any one of Items 1 to 3, wherein the one or more potential differences depend on the reference ion concentration in the sample. [Item 5] The method according to Items 3 and 4, wherein determining the one or more concentrations of the one or more analyte ions in the sample is based on an expression that reflects and / or incorporates the dependence of the one or more potential differences on the reference ion concentration in the sample. [Item 6] The method according to any one of Items 1 to 5, wherein the sample is a liquid whole blood sample. [Item 7] The method according to any one of Items 1 to 6, comprising aspirating the sample, such as aspirating the sample at the sample inlet of an apparatus such as the apparatus according to any one of Items 11 to 17, thereby generating an aspirated portion of the sample, and each of the measurement using the reference ion measurement setting and the measurement using the analyte ion measurement setting being performed on the aspirated portion of the sample. [Item 8] The method according to any one of Items 1 to 7, wherein measuring the concentration of the reference ion in the sample using the reference ion measurement setting includes an optical measurement. [Item 9] The method according to any one of Items 1 to 8, wherein the reference ion is a hydrogen ion, for example H+, a sodium ion, for example Na+, or a potassium ion, for example K+. [Item 10] The method according to Item 9, wherein the optical measurement includes measuring an optical parameter Po that depends on pH, and the change dPo of the optical parameter and dPo / dpH with a change dpH in pH have a local and / or global maximum value within a pH interval of [7;8], for example within a pH interval of [7.2, 7.6], for example at or about 7.4. [Item 11] An apparatus for measuring one or more potential differences indicating one or more concentrations of one or more analyte ions in a sample, such as a liquid whole blood sample, comprising: - A reference ion measurement setting arranged for measuring a parameter indicating the concentration of a reference ion, the reference ion setting being different from an electroanalytical measurement setting, and - An analyte ion measurement setting including: i. One or more, optionally solid, working electrodes, each of the optionally solid working electrodes including an ion-selective electrode that is selective for analyte ions, the optionally solid working electrodes, and ii. A reference electrode including an ion-selective electrode that is selective for the reference ion and is optionally solid, wherein the analyte ion measurement setting is an electroanalytical setting such as a potential difference measurement setting, and wherein the analyte ion measurement setting is arranged to directly or indirectly measure one or more potential differences between: v. Each of the one or more working electrodes, and vi. The reference electrode; An apparatus comprising. [Item 12] The apparatus according to Item 11, wherein the reference ion measurement setting includes an optical sensor. [Item 13] The apparatus according to any one of Items 11 to 12, further comprising: - A data processing device including a processor configured for: i. Determining one or more concentrations of the one or more analyte ions in the sample based on: 1. The concentration of the reference ion, and 2. One or more potential differences An apparatus comprising. [Item 14] The apparatus according to any one of Items 11 to 13, further comprising: - A sample handling system including: ○ A sample inlet including, for example, a suction system, a sample inlet, ○A measurement chamber, for example, a measurement chamber arranged for measurement on a sample while both a reference ion measurement setting and an analyte ion measurement setting are in the measurement chamber. ○One or more fluid channels, such as microfluidic channels, fluidically connecting the sample inlet and the measurement chamber. An apparatus comprising the above. [Item 15] The apparatus according to any one of Items 11 to 14, wherein for the analyte ions that are monovalent ions, the accuracy is less than 20%, for example less than 15%, for example less than 10%, for example less than 7%, for example less than 5.4%, for example less than 5%, for example less than 3.5%, for example less than 2.7%. [Item 16] The apparatus according to any one of Items 11 to 15, wherein the apparatus, for example the whole apparatus, is capable of determining one or more concentrations of one or more analyte ions in a sample based on one or more potential differences with an accuracy of less than 20%, for example less than 15%, for example less than 10%, for example less than 7%, for example less than 5.4%, for example less than 5%, for example less than 3.5%, for example less than 2.7% with respect to one or more true concentrations for the one or more analyte ions that are monovalent ions. [Item 17] The apparatus according to any one of Items 11 to 16, comprising the following: - Each of one or more working electrodes, and - The reference electrode The distance between them is 10 mm or less, for example 5 mm or less, for example 3 mm or less, for example 1 mm or less, for example 1 mm or less. [Item 18] Use of the apparatus according to any one of Items 11 to 17, wherein the apparatus is used to measure one or more potential differences indicating one or more concentrations of one or more analyte ions in a sample such as the sample which is a liquid whole blood sample.

Explanation of Symbols

[0112] 100 Device 102 Sample 104 Reference Ion Measurement Setting 105 Analyte Ion Measurement Setting (Electrochemical Measurement Setting) 106 Data Processing Device 112 Sample Inlet 114 Fluid Channel 116 Digital Memory Device 118 User Interface 120 Output Unit 122 Input Unit 200 Method 230 block 232 provide 234 measure 236 measure 238 determine concentration 240 block 304 reference ion measurement setting 305 analyte ion measurement setting (electrochemical measurement device) 314 fluid channel 350 reference electrode 352 working electrode 354 measurement chamber 356 voltmeter 358 optical analysis unit 360 case 362 insulating sealant 364 conductor 366 conductive internal electrode 368 film 370 center-to-center distance 472 gap 474 distance 476 distance

Claims

1. A method for measuring one or more potential differences indicative of one or more concentrations of one or more analyte ions in a sample, said method comprising the following steps: - Measuring a parameter indicative of the concentration of a reference ion in the sample using a reference ion measurement setting, wherein the reference ion measurement setting is different from an electroanalytical measurement setting, and - Measuring directly or indirectly one or more potential differences indicative of one or more concentrations of one or more analyte ions in the sample using an analyte ion measurement setting between: i. Each of one or more working electrodes, each of said one or more working electrodes comprising an ion-selective electrode selective for an analyte ion, and ii. A reference electrode selective for a reference ion, the analyte ion measurement setting being an electroanalytical measurement setting, measuring the concentration of the reference ion in the sample using the reference ion measurement setting comprising an optical measurement, said optical measurement comprising measuring an optical parameter Po that depends on pH, the change dPo of the optical parameter with a change dpH of pH, dPo / dpH having a local and / or global maximum within a pH interval of [7;8].

2. The method according to claim 1, wherein each of said one or more working electrodes is a solid electrode and / or said reference electrode is a solid reference electrode.

3. The method according to claim 1 or 2, comprising: i. The concentration of the reference ion, and ii. One or more potential differences to determine one or more concentrations of one or more analyte ions in the sample.

4. The method according to any one of claims 1 to 3, wherein said one or more potential differences depend on the concentration of the reference ion in the sample.

5. The method according to claims 3 and 4, wherein determining the one or more concentrations of the one or more analyte ions in the sample is based on and / or incorporates an equation that reflects the dependence of the one or more potential differences on the concentration of the reference ions in the sample.

6. The method according to any one of claims 1 to 5, wherein the sample is a liquid whole blood sample.

7. The method according to any one of claims 1 to 6, comprising aspirating a sample, thereby generating an aspirated portion of the sample, wherein each of the measurement using the reference ion measurement setting and the measurement using the analyte ion measurement setting is performed on the aspirated portion of the sample.

8. The method according to any one of claims 1 to 7, wherein the reference ion is a hydrogen ion, a sodium ion, or a potassium ion.

9. An apparatus for measuring one or more potential differences indicative of one or more concentrations of one or more analyte ions in a sample, comprising: - A reference ion measurement setting arranged to measure a parameter indicative of the concentration of a reference ion, the reference ion measurement setting being different from an electroanalytical measurement setting, and - An analyte ion measurement setting comprising: i. One or more, optionally solid, working electrodes, each of the optionally solid working electrodes comprising an ion-selective electrode that is selective for analyte ions, and ii. A reference electrode comprising an ion-selective electrode that is selective for the reference ion and is optionally solid, wherein the analyte ion measurement setting is an electroanalytical measurement setting, and wherein the analyte ion measurement setting is arranged to measure one or more potential differences directly or indirectly between: v. Each of the one or more working electrodes, and vi. The reference electrode; and comprising The reference ion measurement setting includes an optical sensor, the optical sensor is arranged for measuring an optical parameter Po that depends on pH, and the change dPo of the optical parameter and dPo / dpH with a change dpH in pH are set to have local and / or overall maximum values within a pH interval of [7; 8]. Device.

10. The device according to claim 9, further comprising the following: - A data processing device including a processor configured for the following: i. Determining one or more concentrations of the one or more analyte ions in the sample based on the following:

1. The concentration of the reference ion, and 2. One or more potential differences Device.

11. The device according to claim 9 or 10, further comprising the following: - A sample handling system including the following: ○ Sample inlet, ○ Measurement chamber, ○ One or more fluid channels fluidly connecting the sample inlet and the measurement chamber, Device.

12. The device according to any one of claims 9 to 11, wherein, with respect to the analyte ions that are monovalent ions, the accuracy is 2.7% or more and less than 20%. Device.

13. The device according to any one of claims 9 to 12, wherein the device is capable of determining one or more concentrations of one or more analyte ions in a sample based on one or more potential differences with an accuracy of 2.7% or more and less than 20% with respect to one or more true concentrations for the one or more analyte ions that are monovalent ions. Device.

14. The device according to any one of claims 9 to 13, further comprising the following: - Each of one or more working electrodes, and - The reference electrode An apparatus in which the distance therebetween is 10 mm or less.

15. The use of an apparatus according to any one of claims 9 to 14, wherein the apparatus is used for measuring one or more potential differences indicative of one or more concentrations of one or more analyte ions in a sample.

16. An apparatus according to any one of claims 9 to 14, wherein the sample is a liquid whole blood sample.

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