Electrochemical measurement with additional reference measurement

Abstract

To provide a method and apparatus for measuring potential differences indicative of concentrations of one or more analyte ions in a sample, such as a liquid whole blood sample, which is more cost efficient, simpler and more accurate, enables working with smaller sample volumes, and is durable and less prone to breakdown.SOLUTION: The method comprises: measuring, with a reference ion measurement setup (104), a parameter indicative of a concentration of a reference ion in the liquid whole blood sample, where the reference ion measurement setup (104) is different from an electroanalytical measurement setup; and measuring, with an analyte ion measurement setup (105), potential differences directly or indirectly between solid-state working electrodes and between each of the solid-state working electrodes comprising an ion-selective electrode selective for an analyte ion and a solid-state reference electrode selective for the reference ion, where the analyte ion measurement setup is an electroanalytical setup. There is additionally presented an apparatus (100) and use of the apparatus.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for measuring parameters indicative of the concentration of an analyte ion in a liquid, more particularly to a method 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 liquid whole blood sample, and further to a corresponding device and the use of such a device. [Background technology]

[0002] Generally, being able to determine one or more potential differences indicative of one or more concentrations of one or more analyte ions in a sample, such as when 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 equipment, which may require large sample volumes, which may also have a limited service life, and / or be prone to failure.

[0003] Thus, there is a need for improved methods and 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 liquid whole blood sample, particularly improved methods and apparatus that are more cost-effective, simpler, more accurate, allow for operation with smaller sample volumes, and are more durable and / or less prone to malfunction. Summary of the Invention

[0004] It is an object of the present invention to provide an improved method and apparatus that overcomes at least some of the drawbacks of known methods and 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 liquid whole blood sample. Additionally or alternatively, it is an object of the present invention to provide an alternative to known methods and apparatus.

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

[0006] A potential advantage of the present invention is that it allows a reference ion measurement setup to eliminate the need for a reference electrode of known or predictably varying potential, for example, eliminating the need for a reference with a stable potential or eliminating the need for known or predictable conditions for a reference with a potential that varies with condition, which in turn may result in one or more of more cost-effective, simpler, and / or more accurate methods. is also more durable and / or less prone to failure and / or requires less specimen volume It may be possible to work with

[0007] A gist of the present invention can be viewed as recognizing that providing a constant, known, or predictably varying potential may advantageously replace measuring the concentration of a reference ion, which would reduce the need for a reference electrode (e.g., by not requiring the electrode to maintain a constant potential) and / or the need for a measurement solution such as liquid whole blood (e.g., by not requiring that parameters such as the concentration of the reference ion in the measurement solution be known or predictable).

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

[0009] As another example, instead of relying on a reference electrode that varies with conditions, and even relying on knowing or predicting the measurement conditions, it may be 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, via a setting for measuring pH. An advantage of measuring the reference ion concentration may be that it allows for increased accuracy in determining the concentration of the analyte ion, where the increased accuracy in determining the concentration of the analyte ion results from increased accuracy in the concentration of the reference ion due to the measurement being more accurate than assumed or predicted. Additionally, measuring the reference ion concentration may be considered advantageous in expanding the usability of the method to applications where conditions such as the concentration of the reference ion are unknown or unpredictable. For example, when relying on a known, constant concentration of a particular reference ion, or when relying on a situation in which the concentration of a particular reference ion behaves in a predictable manner, the selection of the reference ion is limited to reference ions (candidates) whose concentrations are known and constant or behave in a predictable manner. This can be disadvantageous for several reasons, including the fact that (reference) ion concentrations may not be truly constant between individuals (e.g., for different people) and / or that there may be no overlap between applicable reference ions and optimal ion-selective reference electrodes (in other words, the concentration of the reference ion for which the optimal reference electrode is specific may not be known, constant, or predictable, and therefore a less-than-optimal reference electrode may need to be employed). In contrast, in embodiments according to the present invention, the reference ion can be freely selected, for example, according to the optimal reference (ion-specific) electrode. This, in turn, may benefit the accuracy of the reference ion measurement setup, which, in turn, may benefit the overall accuracy of the determination of the analyte ion concentration.

[0010] 'Measuring one or more potential differences' should be understood as common in the art (where potential difference is an electrical potential difference), e.g., measuring one or more voltages, e.g., DC voltages. Measuring such potential differences can be performed, e.g., by potentiometry. In the case of multiple potential differences, it is understood that each potential difference should be measured between the reference electrode and the (respective) working electrode.

[0011] 'Indicating one or more concentrations of one or more analyte ions in the sample' may be understood as the method being configured so that the measured potential difference is indicative of the concentration of an ion or group of ions, respectively, in the sample.

[0012] 'Indicating concentration' may generally be understood as meaning that the concentration can be determined. For example, a potential difference - which is not itself a concentration - is measured, which makes it possible to determine the concentration. Determining the concentration may be understood as both detecting the presence (presence / absence) of an analyte qualitatively, e.g., a concentration above the detection limit, and determining the concentration quantitatively, e.g., an ordinal, interval, or ratio-type scale.

[0013] By 'reference ion' is understood any ion that may be naturally present in whole blood that 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, e.g., in a potentiometric setup. Reference ions are, for example, hydrogen ions (H + ), sodium ions (Na + ), potassium ions (K + ), calcium ions (Ca 2+ ), chloride ions (Cl - ), magnesium ions (Mg 2+ ), or bicarbonate or hydrogen carbonate ions (HCO3 - ) can be either

[0014] By 'reference ion measurement setup' is understood any setup in which a parameter indicative of the concentration of a reference ion (wherein generally a reference ion may be understood to be a single specific reference ion or a group of reference ions) can be determined, for example a setup arranged to optically probe a sample, such as a whole blood sample, and determine its optical parameter indicative of the reference ion concentration.

[0015] The reference ion measurement settings can be selective for a single ion or a group of ions. The reference ion measurement setup is somewhat (cross-)selective with respect to one or more interfering ions. However, a reference ion measurement setting may be understood to be more selective for one ion or group of ions compared to another ion or group of ions (e.g., a selectivity factor for interfering ions of less than 1.0, such as less than 0.9, for example less than 0.5, for example less than 0.1, such as 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, it may generally be advantageous for the cross-selectivity to be negligible or zero, so as to allow for the complete elimination of the need to consider cross-selectivity. If the cross-selectivity is non-zero, e.g., not negligible, e.g., if the cross-selectivity is sufficiently low (e.g., if the selectivity coefficient for the interfering ion is less than 1.0), it may still be possible to make corrections and take the cross-selectivity into account, and measurements may still be available, so it may still be advantageous if the cross-selectivity is below a certain threshold, e.g., the selectivity coefficient for 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 embodiment, the reference ion is a single specific ion or group of ions, with substantially no cross selectivity in either the reference ion measurement setup or the reference electrode. According to another embodiment, the reference ion is a single, specific ion or group of ions, and the reference ion measurement setup and / or reference electrode has cross-selectivities, each cross-selectivity being accounted for, for example, by measuring and / or estimating the respective concentrations of one or more interfering species and taking these one or more concentrations into account.

[0018] An 'electroanalytical measurement setup' is understood as is common in the art, e.g., a setup for an electroanalytical method, e.g., where 'electroanalytical method' refers to a method for chemical analysis, e.g., For example, electroanalysis is a method that allows for the determination of parameters indicative of the concentration of reference ions and / or analyte ions in a liquid sample by electrolysis, where 'electrolysis' is understood as commonly understood in the art, e.g., a method for producing a chemical change by applying an electric potential and / or passing an electric current through an electrolyte. More specifically, electroanalysis is understood to determine parameters indicative of the concentration of analyte ions and / or reference ions by measuring the electric potential (volts) and / or current (amperes) in an electrochemical cell containing the analyte ions and / or reference ions. Electroanalysis uses electrically conductive probes called electrodes to make electrical contact with the analyte solution. Electrodes are used in conjunction with an electrical or electronic device to which they are attached to measure parameters of the solution. The measured parameters relate to the identity of the analyte ions or reference ions and / or the amount of the analyte ions or reference ions in the solution. Electroanalytical methods include potentiometry, amperometry, conductometry, electrogravimetry, voltammetry (and polarography), and coulometry.

[0019] By 'the reference ion measurement setting is different from the electroanalytical measurement setting', it is understood that a reference ion measurement setting exists and is applied to the method, but belongs to a group of measurement settings that is different with respect to the group of electroanalytical measurement settings. An advantage of this may be that while electroanalytical measurement settings generally require a reference electrode, this need can be omitted for measurement settings that are different from electroanalytical measurement settings. In addition, once a parameter indicative of the concentration of the reference ion in a sample has been determined, it is then possible to benefit from the advantages of electroanalytical methods (e.g., potentiometry) for the purpose of determining a parameter indicative of one or more concentrations of one or more analyte ions in a sample, i.e., a potential difference, without the need for a reference electrode with a predetermined, known potential.

[0020] In some embodiments, the reference ion measurement setup is selected from the group of measurement setups that rely on the measurement of optical parameters (e.g., light, emitted light and / or optical properties of a sample investigated by, for example, 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 mode (QCM-D)).

[0021] For example, the reference ion setup can be a setup for determining a 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 is common in the art, e.g., to irradiate at least a portion of the sample with light and receive at least a portion of the (emitted) light therefrom, where the received light allows information (e.g., concentration) about an analyte (e.g., reference ion) therein to be derived. In another example, the reference ion measurement setup can be a setup based on measuring mechanical properties (e.g., dissipation) and / or mass, e.g., a setup using a quartz crystal microbalance sensor with dissipation measurement capabilities (QCM-D) to measure mass and / or dissipation, or a setup based on measuring magnetic parameters, such as measuring mass (in dynamic mode) and / or stress (in static mode) using a microcantilever, or measuring the magnetic field of labeled magnetic particles using a Hall sensor. It is contemplated that a parameter indicative of the concentration of a reference ion may be measured directly or indirectly, including by measuring effects such as conformational changes in macromolecules induced by the reference ion, or effects such as the rate of adsorption or desorption of relatively heavy molecules from a surface affected by the reference ion, from which an indirect measure of the concentration of the reference ion is obtained.

[0022] Generally, references throughout this application to 'visual', 'optical', etc. refer to electromagnetic radiation such as light having a wavelength(s) within the range of 380 nm to 750 nm. It can be generally understood that this is done in this manner.

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

[0024] By 'measuring a parameter indicative of the concentration of a reference ion in a sample using a reference ion measurement setup' it is understood that a parameter is determined by the reference ion measurement setup, which parameter makes it possible to determine the concentration of the reference ion in the sample, for example wherein said parameter is the intensity of (emission) light within a particular wavelength.

[0025] By 'directly or indirectly measuring one or more potential differences' it may be understood that each potential difference may be determined directly between two points, such as directly between the working and reference electrodes, for example via a (possibly high impedance) voltmeter between the working and reference electrodes, or indirectly, for example where each of the potential differences between the working and reference electrodes is measured with respect to a third electrode and the potential difference between the working and reference electrodes is subsequently determined, and thus is (only) measured indirectly.

[0026] A 'working electrode' is understood as is common in the art, eg, an electrode with which analyte ions can react and where this reaction can be measured. An 'ion selective electrode' (ISE) is understood as is common in the art. An ISE can be selective for a single ion or group of ions. More specifically, an ISE is an electrochemical sensor or electrode that allows potentiometric determination of the activity of a particular ion in the presence of other ions. An ISE can include an ion-selective membrane that allows passage of only selected ions (considering possible some cross-selectivity, as described below) to a conductive inner electrode. An ISE can include electrodes that are somewhat (cross-)selective for one or more interfering ions. However, an ISE can be understood to be more selective for one ion or group of ions compared to another ion or group of ions (e.g., a selectivity coefficient for an interfering ion of 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] A 'membrane' may be wholly or partly solid, but may contain a plasticiser (e.g. where the remainder is partly or wholly liquid), for example comprising at least 20 volume / volume percent (v / v%) solids, such as comprising at least 40 v / v% solids, for example comprising at least 60 v / v% solids, such as comprising at least 80 v / v% solids, for example comprising at least 90 v / v% solids, such as comprising at least 95 v / v% solids, for example comprising at least 99 v / v% solids, for example being completely solid.

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

[0029] A reference electrode can be somewhat (cross)selective to one or more interfering ions. However, a reference electrode is more selective for one ion or group of ions than another ion or group of ions. It can be understood to be more selective for the group (e.g., a selectivity coefficient for interfering ions of 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' may be understood to be an ion whose concentration is of interest and / or to be determined. According to some embodiments, a method is provided in which each of the one or more working electrodes is a solid (ion-selective, working) electrode and / or the reference electrode is a solid (ion-selective, reference) electrode. A 'solid' electrode is understood as is common in the art. More specifically, by a solid ion-selective electrode is understood an ion-selective electrode comprising an ion-selective membrane and a conductive inner electrode, in which there is little or no liquid between the membrane and the conductive inner electrode, e.g., between the side of the membrane facing the conductive inner electrode and the side of the conductive inner electrode facing the membrane. By 'little or no' liquid, one can understand a volume of liquid that is less than 10 times the volume of the membrane, e.g., less than 5 times the volume of the membrane, e.g., less than 2 times the volume of the membrane, e.g., less than the volume of the membrane, e.g., less than 0.5 times the volume of the membrane, e.g., less than 0.1 times the volume of the membrane, e.g., less than 0.01 times the volume of the membrane. Additionally or alternatively, the conductive internal electrode may be understood to be in contact with or in close proximity to the membrane such that the percentage of the distance from the conductive internal electrode to the opposite side of 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 may be understood to be positioned to be in close proximity to or allow close proximity to 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] A 'conductive internal electrode' may be understood as a solid component in which an electrochemical reaction takes place, which is electrically conductive and which is coupled to an analytical device such as a (high-impedance) voltmeter. An (electrically) conductive internal electrode is therefore understood to form part of a solid electrode. A conductive electrode may comprise one or more different materials, where one or more of the different materials may comprise a non-solid substance, e.g., a liquid, and / or may be susceptible to liquid uptake, e.g., where the conductive internal electrode forms a matrix comprising a solid material. A conductive internal electrode may be fully or partially solid (e.g., where the remaining portion is partially or fully liquid), e.g., comprising at least 50 v / v % solid material, e.g., comprising at least 60 v / v % solid material, e.g., comprising at least 70 v / v % solid material, e.g., comprising at least 80 v / v % solid material, e.g., comprising at least 90 v / v % solid material, e.g., comprising at least 95 v / v % solid material, e.g., comprising at least 99 v / v % solid material, e.g., completely solid.

[0032] According to one embodiment, a method is provided in which each of the one or more working electrodes is a solid electrode and wherein the reference electrode is a solid reference electrode. A potential advantage of this may be that it overcomes disadvantages associated with non-solid (aqueous or liquid-liquid) electrodes, such as large size, large cost, electrolyte contamination or consumption, fragility, and / or erroneous measurements, such as those due to electrolyte leakage (from aqueous, liquid-liquid electrodes) and affecting the measurement (at the working electrode).

[0033] According to one aspect, a method is provided that includes determining one or more concentrations of one or more analyte ions in a sample based on: i. the concentration of the reference ion, and ii. A potential difference of 1 or more.

[0034] An advantage of this is that one or more concentrations of one or more analyte ions may be determined, and / or said determination(s) may be made with greater accuracy by taking into account the concentrations of the reference ions (as determined in a reference ion measurement setup), e.g., rather than just relying on assumed—and possibly probed (e.g., by adding a certain amount of reference ion)—concentrations of the reference ions. The determination of the concentrations of the analyte ions may be made by calculating the concentrations, e.g., by utilizing the Nernst equation.

[0035] For purposes of determining one or more concentrations 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 the analyte ion:

[0036] [ka]

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

[0038] Regarding the pH example:

[0039] [ka]

[0040] where cH1 = cH (i.e., hydrogen ions H+ (concentration of HCl), and for sample 2 cH2 = cH. The same method is used for electrolytes, e.g., for cK:

[0041] [ka]

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

[0043] Derivation of the formula for N_fac(X): Between sample 1 and sample 2, using pH as reference:

[0044] [ka]

[0045] It can be reformulated as:

[0046] [ka]

[0047] By calculating N_fac(X), the value of N_fac(pH) can be estimated, for example, as 57 mV (e.g., based on prior knowledge of the electrode half-cell slope). Optionally, a set of optimal calibration solutions ("best"), e.g., solutions with the same or nearly the same pH value, can be used to obtain N_fac(pH) with the following formula:

[0048] [ka]

[0049] "Best" may refer to an optimal set of solutions, e.g., N_fac(X) for two solutions having the same or nearly the same pH value, where the average of the two values for n_Fac(pH) is calculated and used for further calculations.

[0050] Since the pH for the (unknown) sample is unknown and may be different with respect to the calibration solution, this pH difference must be calculated into a voltage (millivolt (mV) value) that is subtracted to account for the different electrolyte concentrations. For example, an applicable formula for calculating the correction potential Pot.corr is:

[0051] [ka]

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

[0053] [ka]

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

[0055] [ka]

[0056] According to one embodiment, a method is provided in which one or more potential differences depend on the reference ion concentration in the sample.Therefore, it can be understood that one or more potential differences can 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.An advantage can be that this need can be eliminated.

[0057] According to one embodiment, a method is provided in which determining one or more concentrations of one or more analyte ions in a sample is based on an expression that reflects and / or incorporates the dependence of one or more potential differences on the concentration of a reference ion in the sample. For example, the reference ion concentration can affect one or more potential differences as described in the above expression, and this same dependence of one or more potential differences can be incorporated into an expression for 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 certain 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 completely, taken into account in the same way, e.g., by reducing, minimizing, or eliminating the effect of the reference ion concentration on the (determined) one or more concentrations of the analyte ions in the sample. 'Reflecting and / or incorporating' may be understood to include the same or similar terms (which may be negative or inverse terms to negate the effect) in the expression, as in the expression representing the effect of the reference ion concentration on one or more potential differences.

[0058] According to one embodiment, 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 may be that it eliminates the need to separate fractions of the (original) whole blood sample, such as to provide plasma or serum. The term "whole blood" is understood as commonly used in the art, such as blood from a human or animal from which naturally occurring components have not been removed (e.g., unprocessed blood). More specifically, whole blood may refer to blood composed of plasma and cellular components. Plasma occupies approximately 50%-60% of the volume, and 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 from a human subject, but may also refer to whole blood from an animal. The term "blood plasma" or "plasma" refers to the liquid portion of blood and lymph, which constitutes about half of the volume of blood (e.g., about 50%-60% by volume). Plasma is devoid of cells. It contains all clotting factors, especially fibrinogen, and is about 90%-95% water by volume. Plasma components include electrolytes, lipid metabolites, markers, such as those related to infection or tumors, enzymes, substrates, proteins, and additional molecular components.

[0059] According to one embodiment, a method is provided that includes aspirating a sample, such as aspirating a 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 may be that a controlled portion of the sample can be aspirated, e.g., aspirated and analyzed. In a further embodiment, measurements at the reference ion measurement setting and measurements at the analyte ion measurement setting are each performed on an aspirated portion of the sample. A potential advantage of this may be that the (same) aspirated portion of the sample can be subjected to both types of analysis, thereby reducing or eliminating the risk of differences between (sub)sample portions.

[0060] According to one embodiment, a method is provided in which the reference ion measurement setup is based on an optically measurable parameter, e.g., a reference ion-sensitive indicator (which changes one or more optical properties, e.g., 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) depending on the concentration of the reference ion), e.g., a measurement principle based on a pH-sensitive luminescence indicator, and the measurement principle of the analyte ion measurement setup is a potentiometric measurement principle. This advantage is due to the fact that potentiometric measurements, which require specific electrodes and / or conditions, are not possible. It may be that drawbacks associated with constant measurement principles can be overcome in whole or in part by using, for example, optically based measurement principles, which may in effect obviate the need to establish a known potential via, for example, an aqueous liquid-liquid reference electrode.

[0061] By 'measurement principle' may be understood a principle for measuring concentration that relies on the measurement of a particular parameter such as (electrical) voltage or (optical) absorbance or light intensity. According to one embodiment, a method is provided in which measuring one or more potential differences includes measuring one or more potential differences exclusively, e.g., directly, between solid electrodes, e.g., directly between a solid working electrode and a solid reference electrode. An advantage of this can be that only solid electrodes are included, e.g., aqueous liquid-liquid electrodes (and their associated disadvantages) are excluded. By 'exclusively' with respect to between solid electrodes, it is understood that only the potential difference between the solid electrodes is measured, but 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 the solid reference electrode and a 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, e.g., by inserting a (high-impedance) voltmeter between the solid working electrode and the solid reference electrode.

[0062] According to one embodiment, a method is provided in which measuring the concentration of a reference ion in a sample using a reference ion measurement setup comprises optical measurement. By 'optical measurement' is understood any measurement that measures any of the optical parameters, such as absorbance, reflectance, fluorescence, refractive index, luminous flux, absorption, and wavelength. An advantage of optical measurement may be that it can be performed without damaging red blood cells. Another potential advantage may be that it is independent of electroanalytical techniques and therefore provides an alternative to electroanalytical techniques. Another potential advantage may be that it eliminates the need for a known potential, such as that provided by an aqueous liquid-liquid reference electrode.

[0063] According to one embodiment, the reference ion is a hydrogen ion, e.g., H + , sodium ions, e.g., Na + , or potassium ions, e.g., K + A method is provided in which: A potential advantage of using hydrogen ions as a reference ion is that they can be assumed to be present in many samples, e.g., whole blood samples in particular; A potential advantage of using sodium ions as a reference ion is that they can be present in relatively high concentrations (e.g., they are the major ionic component in human plasma, e.g., the ionic component with the highest concentration in human plasma); they can be measured optically, e.g., using a (possibly readily available) sodium ion-sensitive fluorophore; sodium ion concentration correlates with ionic strength (hence, using sodium ions as a reference ion will include and exclude the effects of ionic strength); and / or they (e.g., their concentration) can be relatively stable in, e.g., human plasma (e.g., absolute and / or relative fluctuations can be relatively small); A potential advantage of using potassium ions as a reference ion is that they can be present in relatively high concentrations (e.g., they are the major ionic component in human plasma, e.g., the ionic component with the second highest concentration in human plasma).

[0064] According to one embodiment, the optical measurement is performed using a pH-dependent optical parameter P oThe change in an optical parameter (e.g., absorbance, reflectance, fluorescence, refractive index, or color) with a change in pH (dpH), dP o , dP o A method is provided in which the pH / dpH has a local and / or global maximum within the pH interval [7;8], e.g., within the pH interval [7.2, 7.6], e.g., at or about 7.4. A potential advantage of this is that the maximum sensitivity can therefore be in the region where the pH of whole (human) blood is expected. Thus, the accuracy of the determination of pH (or hydrogen ion concentration), and therefore the concentration of one or more analytes, is increased.

[0065] According to one embodiment, the reference ions are ions naturally occurring in (human) whole blood, such as One of the following methods is provided: - Hydrogen ions, e.g., H + , -sodium ions, e.g. Na + , - Potassium ions, e.g., K + , -Calcium ions, e.g., Ca 2+ , -chloride ions, e.g. Cl - , -Magnesium ions, e.g. Mg 2+ ,or -Bicarbonate ion, e.g. HCO3 - .

[0066] In this case, the reference ion can be measured directly on the whole blood without the need for the addition of an ion to serve as the 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 the sample being a liquid whole blood sample, comprising: a reference ion measurement setup arranged to measure a parameter indicative of the concentration of a reference ion (wherein the reference ion measurement setup (104) is different from the electroanalytical measurement setup); and -Analyte ion measurement settings including: i. one or more optionally solid-state working electrodes, each of said optionally solid-state working electrodes comprising an ion-selective electrode that is selective for an analyte ion; and ii. a reference electrode selective for a reference ion, optionally comprising a solid-state ion-selective electrode; wherein the analyte ion measurement setup is an electroanalytical setup, such as a potentiometric setup; and wherein the analyte ion measurement setup is arranged to directly or indirectly measure one or more potential differences between: i. each of the one or more working electrodes; and ii. Reference electrode.

[0067] In embodiments, each of the one or more working electrodes is a solid electrode and / or the reference electrode is a solid reference electrode. The analyte ion measurement setup and the reference ion measurement setup can be rigidly connected and / or the device can include an enclosure, e.g., a single enclosure, e.g., a single enclosure that encompasses and surrounds the analyte ion measurement setup and the reference ion measurement setup.

[0068] The analyte ion measurement setting and the reference ion measurement setting can be arranged to probe the sample in the same measurement chamber in the device. This can be advantageous for keeping the required sample volume to a minimum, since the sample only needs to fill a single measurement chamber. In addition, since the sample does not need to be introduced into different measurement chambers, handling, rinsing, cleaning, etc. can be simplified.

[0069] According to one embodiment, a device is provided, wherein the reference ion measurement setup comprises an optical sensor, e.g., an optical instrument for measuring a parameter indicative of the concentration of the reference ion, e.g., wherein the optical sensor is arranged to perform measurements, which include measuring an optical parameter Po (e.g., absorbance, reflectance, fluorescence, refractive index, or color), which is pH-dependent, and wherein a change in the optical parameter dPo with a change in pH dpH, dPo / dpH, has a local and / or global maximum within a pH interval of [7;8], e.g., within a pH interval [7.2, 7.6], e.g., at or about 7.4. For example, the optical sensor may measure one or more optical properties, e.g., 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), depending on the concentration of the reference ion, e.g., based on a reference ion-sensitive indicator, e.g., based on a pH-sensitive luminescent indicator. For example, it can be an optical pH sensor that changes the wavelength in the 700-900 nm range.

[0070] The reference ion-sensitive indicator may have a maximum or minimum value of an optical property, such as an absorption maximum, in a wavelength region having a wavelength 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, for example, within 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. An advantage of a reference ion-sensitive indicator having a maximum or minimum of its optical property within such a wavelength region may be that hemoglobin absorption is minimal within 600-1000 nm, and / or that interference with other sensors is limited (because wavelengths in this region are long enough not to interact / degrade with other sensor entities (e.g., ionophores) present in the device), and / or that scattering by lipid particles is limited (because wavelengths in this region are long enough not to be subject to scattering by relatively small lipid particles in samples such as in biological samples such as whole blood samples).

[0071] According to one aspect, there is provided an apparatus wherein the reference ion is one of the following: - Hydrogen ions, e.g., H + , -sodium ions, e.g. Na + , - Potassium ions, e.g., K + , -Calcium ions, e.g., Ca 2+ , -chloride ions, e.g. Cl - , -Magnesium ions, e.g. Mg 2+ ,or -Bicarbonate ion, e.g. HCO3 - .

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

[0073] According to one aspect, there is provided an apparatus further comprising: -a data processing device, comprising a processor configured as follows: i. Determine one or more concentrations of one or more analyte ions in the sample based on: 1. The concentration of the reference ion, and A potential difference of 2.1 or more.

[0074] By implementing a 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: -Sample handling system including: a sample inlet, for example comprising a suction system, a measurement chamber (e.g. a volume of the sample handling system in which the sample is placed while measurements of parameters indicative of the concentration of reference ions and / or one or more potential differences are made), e.g. where both the reference ion measurement setup (104) and the analyte ion measurement setup (105) are arranged for measurements on the sample while it is in the measurement chamber.

[0075] One or more fluidic channels, e.g. microfluidic channels, fluidically connecting the sample inlet and the measurement chamber. A potential advantage may be that sample handling may be performed in a more hygienic, safe, automated, reliable and / or repeatable manner. A 'sample handling system' may generally be understood as a system that is able to receive and handle a sample, e.g. transport it from a sample inlet to a measurement chamber via one or more fluid channels.

[0076] According to one aspect, there is provided an apparatus wherein the sample handling system further comprises: - one or more valves, e.g. valves allowing segmented transport of the sample through the sample handling system, such as in the form of a sample plug, said valves optionally being controlled by a data processing device, e.g.

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

[0078] According to one embodiment, a device is provided, wherein, 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 as less deviation from the true value) accuracy is that a more accurate estimation of concentration may be achieved, which in turn may allow for improved diagnosis, improved evaluation of treatment effects, or improved estimation of the physiological and / or nutritional status of a subject (e.g., a patient or person from whom a blood sample was taken). 'Accuracy' is understood as is common in the art, and refers to, for example, the error that may exist between the actual ('true') value, e.g., in this context, the true concentration of the analyte ion, and the measured value, e.g., in this context, the concentration of the analyte ion at the output of and / or determined by the device.

[0079] According to one embodiment, a device is provided, wherein the device, e.g., the entire device, enables determination of 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% of the true concentration of one or more analyte ions, each of which is a monovalent ion. It should be understood that the device, e.g., the entire device, i.e., determination of analyte ion concentration based on both a parameter indicative of the concentration of a reference ion and a potential difference indicative of the concentration of an analyte ion, allows for a low accuracy in determining 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 embodiment, a device is provided, wherein the accuracy of the reference potential as determined by the (optionally solid-state) reference electrode (i.e., the total accuracy (i.e., taking into account cumulative errors) of both the reference ion measurement setup and the reference electrode, which is selective with respect to the reference ion), with respect to an analyte ion that is a monovalent ion, is less than 10%, such as less than 7.5%, for example less than 5%, for example less than 3.5%, for example less than 2.7%, for example less than 2.5%, for example less than 1.75%, for example less than 1.35%. An advantage of such a low (where 'low' accuracy is understood as less deviation from the true value) accuracy of the reference potential, i.e., of the reference ion measurement setup and reference electrode, is that a more accurate estimate of the reference potential is provided, which in turn may allow for improved accuracy with respect to the concentration of the analyte ion, which in turn may allow for improved diagnosis, improved evaluation of treatment effects, or improved estimation of the physiological and / or nutritional status of a subject (e.g., a patient or person from whom a blood sample is taken). 'Accuracy' is understood as is common in the art, e.g., the actual value of the reference potential. is understood in this context as the error that may exist between the ('true') value of the reference potential (e.g. the "true" potential difference between the potential in the bulk of the sample and the potential in the conductive inner electrode in the reference electrode) and the reference potential determined on the basis of the concentration of the reference ion derived from parameters indicative of the reference ion measurement settings and the concentration of the reference ion determined by the potential at the reference electrode (e.g. the potential that is subtracted from the potential difference between the working and reference electrodes to obtain the potential difference between the potential in the bulk of the sample and the potential in the conductive inner electrode in the working electrode).

[0081] According to one aspect, an apparatus is provided, comprising: the analyte ion concentration accuracy is less than 20%, such as less than 15%, for example less than 10%, such as less than 7%, for example less than 5.4%, for example less than 5%, such as less than 3.5%, for example less than 2.7% for analyte ions that are singly charged ions; the percentage of analyte ion concentration accuracy derived from the reference ion measurement setup and 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 that comes from the reference ion measurement setup and reference electrode is less than 30%, e.g., less than 25%, e.g., less than 20%. The advantage of this is that an analyte ion concentration accuracy of less than 10% may be sufficiently accurate for most purposes, and the relatively low proportion that comes from the reference ion measurement setup and reference electrode leaves room for realistic accuracy (or lack thereof) from other sources, such as from the ion-selective working electrode.

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

[0083] According to one aspect, an apparatus is provided, comprising: - each of one or more working electrodes; and -Reference electrode The distance between (e.g., center-to-center) is 10 mm or less, such as 5 mm or less, for example 3 mm or less, such as 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 less (idle) time must pass between measurements on different samples, for example when utilizing a sample chamber that can be rinsed more quickly (e.g., because the sample chamber has a smaller volume).

[0084] According to one embodiment, a device is provided in which the slope of the reference ion half-cell is at least 10%, e.g., at least 25%, e.g., at least 50%, e.g., at least 75%, e.g., at least 80%, e.g., at least 90%, e.g., at least 95%, e.g., at least 97% of the theoretical slope of the reference ion according to the Nernst equation. The advantage of having a relatively large slope may be that a normal, fully functional, pre-fabricated ISE (which may be used as the working electrode itself) may be used as the reference electrode (since the reference ion measurement settings allow for the slope / sensitivity). The slope of the reference ion half-cell is understood to be the proportionality constant between the measured potential and the (logarithm of) reference ion concentration, e.g., where the measured electrode potential E is related to the activity of the ionic species according to the Nernst equation: E=E0+2.3xRT / (nF)logA where E0 = constant for a given cell, R = gas constant, T = temperature in Kelvin, n = ionic charge, F = Faraday constant, A = activity, and x is a factor that accounts for possible deviations of the slope coefficient from that given by the formula RT / nF, which may be referred to as the ideal slope coefficient. For example, when measuring potassium ions (i.e., n = +1), the slope coefficient at 298 K (25°C) has a value of 59.16 mV, and the slope coefficient at 37°C has a value of 61.54 mV. For example, if x = 0.1, the slope of the reference ion half-cell is 10% relative to the theoretical (ideal) slope of the reference ion according to the Nernst equation.

[0085] According to a third aspect, there is provided a use of a device according to the second aspect, wherein the device 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), e.g., to determine one or more concentrations of one or more analyte ions in the sample, e.g., based on the concentrations of reference ions and one or more potential differences.

[0086] In the context of point-of-care measurement systems (also referred to in the art as 'bedsite' systems) and similar laboratory environments, blood gas analysis is often performed by users, e.g., nurses, who may not be trained users in the use of blood gas analyzers.

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

[0088] POC measurements are also referred to in the art as 'bedsite' measurements. In this context, the term 'point-of-care measurement' should be understood to mean a measurement performed in close proximity to the patient, i.e., not in a laboratory. Thus, according to this embodiment, a user of a device, such as a blood gas analyzer, performs a measurement of a whole blood sample in a handheld blood sample container near the patient from whom the blood sample is taken, e.g., in the room or ward housing the patient's bed, or in a nearby room in the same hospital department. In such uses, the user's level of expertise often varies from novice to experienced, and therefore the ability of a blood gas analyzer to automatically output instructions based on sensor inputs that match each individual user's skill level is particularly beneficial in such environments.

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

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

[0091] Preferred embodiments of the present invention will now be described in more detail with reference to the accompanying drawings, in which: [Brief explanation of the drawings]

[0092] [Figure 1] FIG. 1 is a schematic diagram of an apparatus 100; [Figure 2] FIG. 2 illustrates a method 200, [Figure 3] FIG. 3 shows an example of an electrochemical measurement apparatus 305 and a reference ion measurement setup 304. [Figure 4] FIG. 4 shows an enlarged view of the conductive inner electrode 366 and membrane 368; [Figure 5] FIG. 5 shows a schematic diagram of systems 1-10 (formed by NPT7 instruments 104, 304 and ABL725 instruments, respectively) and a graphical representation of the total (deviation / error) of four different measurements ("#m.1", "#m.2", etc.) for each system. DETAILED DESCRIPTION OF THE INVENTION

[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, e.g., a liquid whole blood sample, including: - arranged to measure a parameter indicative of the concentration of a reference ion (234), where the reference ion measurement setup is a reference ion measurement setup 104, 304 that is different from the electroanalytical measurement setup, such as an optical sensor; and an analyte ion measurement setup 105, 305, including: i. one or more optionally solid-state working electrodes 352, each of said optionally solid-state working electrodes 352 comprising an ion-selective electrode selective for an analyte ion; ii. a reference electrode 350 selective for a reference ion and optionally comprising a solid-state ion-selective electrode; wherein the analyte ion measurement setup is an electroanalytical setup, such as a potentiometric setup; and wherein the electrochemical measurement setup 105, 305 is configured to measure (236) one or more potential differences directly or indirectly between: iii. each of the one or more working electrodes 352; and iv. Reference electrode 350.

[0094] Although the reference ion measurement setup 104, 304 and the electrochemical measurement setup 105, 305 are depicted as being contained in or within separate measurement chambers, in alternative embodiments, they may both probe a sample in the same measurement chamber 354.

[0095] The reference ion measurement setup 104, 304 in the schematic example includes an optical one, such as an optical pH sensor, and further includes: 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: 1. Concentration of the reference ion, A potential difference of 2.1 or more.

[0096] The apparatus of the schematic diagram of FIG. 1 further shows a sample handling system including: ○Sample inlet 112 ○ Measurement chamber 354 One or more fluidic channels 114, e.g., microfluidic channels, fluidically connecting the sample inlet and measurement chamber(s).

[0097] The depicted device further includes a digital storage device 116 (e.g., for storing data relevant to the control and / or calculations of the data processing device), a user interface 118, where the user interface includes an output unit 120 (in the depicted embodiment, the output unit is a display unit) and an input unit 122 (e.g., for displaying the identity of the sample 102) arranged to visually output information relevant to operating the apparatus and / or information representative of one or more concentrations of one or more analyte ions in the sample 102. The thin arrows indicate information flows such as a parameter indicative of the concentration of a reference ion flowing from the reference ion measurement setup 104, 304 to the data processing device 106 and one or more potential differences flowing from the electrochemical measurement setup 105, 305 to the data processing device 106, one or more concentrations of one or more analyte ions in the sample flowing from the data processing device 106 to the user interface 118 (more particularly to the output unit 120), and user input flowing from the input unit 122 to the data processing device 106.

[0098] FIG. 2 illustrates a method 200 (starting at block 230 and ending at block 240) for measuring one or more potential differences to indicate one or more concentrations of one or more analyte ions in a sample 102, which is optionally a liquid whole blood sample, and optionally further to determine one or more concentrations of one or more analyte ions, said method including the steps of: Optionally, providing (232) a sample 102 to the sample inlet 112 of the device 100, as described in FIG. 1 and / or in accordance with the second aspect of the present invention. - measuring (234) the concentration of a parameter indicative of a reference ion in the sample 102 using a reference ion measurement setup 104, 304, where the reference ion measurement setup 104 is different from the electroanalytical measurement setup and optionally also determines the reference ion concentration; -using an analyte ion measurement setup to directly or indirectly measure one or more potential differences (236) between: iii. each of one or more working electrodes 352 (e.g., one or more solid-state working electrodes, each of said working electrodes comprising an ion-selective electrode selective for an analyte ion); and iv. a reference electrode 350, such as a solid reference electrode that is selective with respect to a reference ion; wherein the analyte ion measurement setup is an electroanalytical setup, such as a potentiometric setup; and Optionally, determining one or more concentrations of one or more analyte ions (238).

[0099] 3 shows examples of electrochemical measurement setups 105, 305 and reference ion measurement setups 104, 304. More specifically, the figure shows electrochemical measurement setups 105, 305 including a reference electrode 350 and a working electrode 352 partially within a measurement chamber 354, a (high-impedance) voltmeter 356 electrically connected between the reference electrode 350 and the working electrode 352, and an (inlet) fluid channel 314 positioned to allow sample introduction into the measurement chamber 354. Portions of the reference electrode 350 and the working electrode 352 are similar, but for simplicity only, the reference electrode 350 will be described in terms of a case 360 including an insulating seal 362 enclosing a conductor 364 electrically connected to a conductive inner electrode 366 positioned on the other side of a membrane 368 relative to the interior of the measurement chamber 354 (where a sample may reside during use). The center-to-center distance 370 between the reference electrode 350 and the working electrode 352 is also shown.

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

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

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

[0103] pH measurements of blood samples 102 were performed on five ABL725 (Radiometer, Copenhagen, Denmark) electroanalytical blood gas analyzers. Measurements were repeated four times on each ABL725 electroanalytical blood gas analyzer. The results can be seen in Table I (where "ABL725-n" indicates the instrument number).

[0104] [Table 1]

[0105] pH measurements 234 of the blood samples 102 were also performed using ten NPT7 (Radiometer, Copenhagen, Denmark) optical blood gas analyzers 104, 304. Measurements were repeated four times on each NPT7 optical blood gas analyzer. The results can be seen in Tables II and III (where "#m." indicates the measurement number and "n" in "NPT-n" indicates the instrument number), where each entry in Table II represents a separate NPT7 measurement, and each entry in Table III represents the deviation or error from the mean value determined by five ABL725 measurements in the same round of measurements (by CO2 degassing and subsequent pH change) to remove interference from drift in the sample 102.

[0106] [Table 2]

[0107] [Table 3]

[0108] To assess the impact on accuracy of replacing a fully electroanalytical method and apparatus with the apparatus 100 and method 200 according to an embodiment of the present invention, 40 sums or errors were formed, each sum being the sum of the error from the NPT7 measurements and the error from the ABL725 measurements. (where the ABL725 dataset was replicated to match the double-sized NPT7 dataset).

[0109] Assuming (for purposes of, or to provide a conservative estimate) that a fully electroanalytical method and setup relies on a full reference electrode 352, the impact on accuracy introduced by embodiments of the present invention can be estimated as the sum of the error on the optical pH measurement 234 of the NPT7 instrument 104, 304 (corresponding to the error introduced by the reference ion measurement setup) and the error introduced by the solid-state ion-selective pH electrode of the ABL725 instrument (corresponding to the error introduced by the reference electrode in the analyte ion measurement setup). It is noted that, depending on the signs of these errors, they can add up or cancel each other out (fully or partially).

[0110] Figure 5 shows a summary of these summaries in a graph with systems 1-10 (formed by NPT7 instruments 104, 304 and ABL725 instruments, respectively) and four different measurements for each system ("#m.1", "#m.2", etc.). It can be seen that all errors are less than 1.60 mV, the errors are generally around 1.0 mV, and the average of the absolute values is 0.888 mV. For a Nernst coefficient of 60 mV, this is 100% * (10 (0.888mV / 60mV) -1) would correspond to an accuracy impact on the analyte ion measurement of 3.47% for monovalent ions and 6.93% for divalent ions. Correcting for the system mean, 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 of the same order of magnitude or less, the accuracy of a method or apparatus 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.

[0111] Although the present invention has been described with reference to specific embodiments, it should not be construed as being limited to the examples presented in any way. The scope of the present invention is indicated by the set of appended claims. In the context of the claims, the term "comprising" or "comprises" does not exclude other possible elements or steps. Moreover, references such as "a" or "an" should not be construed as excluding a plurality. The use of reference signs in the claims for elements shown in the drawings should also not be construed as limiting the scope of the present invention. Furthermore, individual features recited in different claims can in some cases be advantageously combined, and the recitation of these features in different claims does not exclude that combination of features is not possible or advantageous. This specification includes the disclosure of the following inventions. [Item 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, wherein the sample is a liquid whole blood sample, said method comprising the steps of: - measuring a parameter indicative of the concentration of a reference ion in the sample using a reference ion measurement setup, wherein the reference ion measurement setup is different from the electroanalytical measurement setup; and -using an analyte ion measurement setup to measure one or more potential differences indicative of one or more concentrations of one or more analyte ions in the sample directly or indirectly between: i. each of one or more working electrodes, the one or more working electrodes including an ion-selective electrode that is selective for an analyte ion; and ii. a reference electrode that is selective with respect to a reference ion; A method wherein the analyte ion measurement setting is an electroanalytical setting, such as a potentiometric 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: i. the concentration of the reference ion, and ii. A potential difference of 1 or more determining one or more concentrations of one or more analyte ions in the sample based on [Item 4] The method according to any one of Items 1 to 3, wherein the one or more potential differences depend on the concentration of the reference ion in the sample. [Item 5] The method described in 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 of any one of Items 1 to 6, comprising aspirating the sample, such as by aspirating the sample at a sample inlet of an apparatus such as the apparatus of any one of Items 11 to 17, thereby generating an aspirated portion of the sample, and wherein each of measurements using the reference ion measurement configuration and measurements using the analyte ion measurement configuration are 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 comprises optical measurement. [Item 9] The method according to any one of items 1 to 8, wherein the reference ion is a hydrogen ion, such as H+, a sodium ion, such as Na+, or a potassium ion, such as K+. [Item 10] The method according to Item 9, wherein the optical measurement comprises measuring a pH-dependent optical parameter Po, and wherein the change in the optical parameter dPo with a change in pH dpH, dPo / dpH, has a local and / or global maximum value within a pH interval of [7;8], for example within a pH interval [7.2, 7.6], for example at or around 7.4. [Item 11] 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 setup arranged to measure a parameter indicative of the concentration of a reference ion, the reference ion measurement setup being different from the electroanalytical measurement setup; and -Analyte ion measurement settings including: i. one or more, optionally solid-state, working electrodes, each of said, optionally solid-state, working electrodes comprising an ion-selective electrode that is selective for an analyte ion; and ii. a reference electrode selective for a reference ion, optionally comprising a solid-state, ion-selective electrode; wherein the analyte ion measurement setting is an electroanalytical setting, such as a potentiometric setting; and wherein the analyte ion measurement setup is configured 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; 1. An apparatus comprising: [Item 12] The device according to item 11, wherein the reference ion measurement setup includes an optical sensor. [Item 13] The device according to any one of items 11 to 12, further comprising: -a data processing device comprising 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 Potential difference of 2.1 or more 1. An apparatus comprising: [Item 14] The device according to any one of items 11 to 13, further comprising: -Sample handling system including: a sample inlet, which may include, for example, a suction system; a measurement chamber, in which e.g. both the reference ion measurement setup and the analyte ion measurement setup are arranged for measurement on the sample while it is in the measurement chamber, one or more fluidic channels, e.g. microfluidic channels, fluidically connecting the sample inlet and the measurement chamber, 1. An apparatus comprising: [Item 15] The device according to any one of items 11 to 14, wherein the accuracy for the analyte ion being a monovalent ion 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 device according to any one of Items 11 to 15, wherein the device, for example the entire device, enables determination of one or more concentrations of one or more analyte ions in a sample based on the 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% of the true concentration of the one or more analyte ions, each of which is a monovalent ion. [Item 17] The device according to any one of items 11 to 16, - each of one or more working electrodes; and -The reference electrode wherein the distance between is 10 mm or less, such as 5 mm or less, for example 3 mm or less, such as 1 mm or less, for example 1 mm or less. [Item 18] Use of the device according to any one of items 11 to 17, wherein the device is used to measure one or more potential differences indicative of one or more concentrations of one or more analyte ions in a sample, such as the sample being a liquid whole blood sample. [Explanation of symbols]

[0112] 100 devices 102 samples 104 Reference Ion Measurement Settings 105 Analyte ion measurement settings (electrochemical measurement settings) 106 Data processing device 112 Sample inlet 114 Fluid Channel 116 Digital Storage Devices 118 User Interface 120 output units 122 input units 200 ways 230 blocks 232 provided 234 Measurements 236 measurements 238 Determine the concentration 240 blocks 304 Reference Ion Measurement Settings 305 Analyte ion measurement setup (electrochemical measurement device) 314 Fluid Channel 350 Reference electrode 352 Working electrode 354 Measurement Chamber 356 Voltmeter 358 Optical Analysis Unit 360 cases 362 Insulating sealing material 364 Conductors 366 Conductive internal electrode 368 Membrane 370 center distance 472 Gap 474 distance 476 distance

Claims

1. 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, wherein the sample is a liquid whole blood sample, said method comprising the steps of: - measuring a parameter indicative of the concentration of a reference ion in the sample using a reference ion measurement setup, wherein the reference ion measurement setup is different from the electroanalytical measurement setup; and - using an analyte ion measurement setup to measure one or more potential differences indicative of one or more concentrations of one or more analyte ions in the sample directly or indirectly between: i. each of one or more working electrodes, wherein each of the one or more working electrodes comprises an ion-selective electrode that is selective for an analyte ion; and ii. a reference electrode that is selective for a reference ion; A method wherein the analyte ion measurement setting is an electroanalytical setting, such as a potentiometric setting.

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

3. 3. The method of claim 1 or 2, comprising: i. the concentration of the reference ion, and ii. A potential difference of 1 or more determining one or more concentrations of one or more analyte ions in the sample based on

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

5. 5. The method of claims 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 concentrations 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. 18. A method according to any one of claims 1 to 6, comprising aspirating the sample, such as by aspirating the sample at a sample inlet of an apparatus, such as the apparatus of any one of claims 11 to 17, thereby producing an aspirated portion of the sample, and wherein measurements using the reference ion measurement configuration and measurements using the analyte ion measurement configuration are each performed on the aspirated portion of the sample.

8. The method of any one of claims 1 to 7, wherein measuring the concentration of the reference ion in the sample using the reference ion measurement setup comprises optical measurement.

9. 9. The method according to any one of claims 1 to 8, wherein the reference ions are hydrogen ions, e.g. H ＋ , sodium ions, e.g., Na ＋ , or potassium ions, e.g., K ＋ That's the method.

10. 10. The method of claim 9, wherein the optical measurement comprises a pH-dependent optical parameter P ｏ measuring the change in the optical parameter dP with the change in pH dpH; ｏ , dP ｏ / dpH has a local and / or global maximum within the pH interval [7;8], such as within the pH interval [7.2, 7.6], for example at or around 7.

4.

11. 1. 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 the sample being a liquid whole blood sample, comprising: a reference ion measurement setup arranged to measure a parameter indicative of the concentration of a reference ion, the reference ion measurement setup being different from the electroanalytical measurement setup; and - Analyte ion measurement settings including: i. one or more, optionally solid-state, working electrodes, each of said, optionally solid-state, working electrodes comprising an ion-selective electrode that is selective for an analyte ion; and ii. a reference electrode that is selective for a reference ion, optionally comprising a solid-state, ion-selective electrode; wherein the analyte ion measurement setting is an electroanalytical setting, such as a potentiometric setting; and wherein the analyte ion measurement setup is configured 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; 1. An apparatus comprising:

12. 12. The apparatus of claim 11, wherein the reference ion measurement setup includes an optical sensor.

13. The device according to any one of claims 11 to 12, further comprising: A data processing device including a processor configured to: 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 Potential difference of 2.1 or more 1. An apparatus comprising:

14. 14. The device according to any one of claims 11 to 13, further comprising: - A sample handling system including: a sample inlet, which may include, for example, a suction system; a measurement chamber, in which e.g. both the reference ion measurement setup and the analyte ion measurement setup are arranged for measurement on the sample while it is in the measurement chamber, one or more fluidic channels, e.g. microfluidic channels, fluidically connecting the sample inlet and the measurement chamber, 1. An apparatus comprising:

15. 15. An apparatus according to any one of claims 11 to 14, wherein for analyte ions that are singly charged ions the accuracy is less than 20%, such as less than 15%, for example less than 10%, such as less than 7%, for example less than 5.4%, such as less than 5%, for example less than 3.5%, such as less than 2.7%.

16. 16. An apparatus according to any one of claims 11 to 15, wherein the apparatus, e.g. the entire apparatus, enables one or more concentrations of one or more analyte ions in a sample to be determined based on the one or more potential differences with an accuracy of less than 20%, such as less than 15%, for example less than 10%, such as less than 7%, for example less than 5.4%, such as less than 5%, for example less than 3.5%, for example less than 2.7% of the one or more true concentrations for the one or more analyte ions, each being a monovalent ion.

17. 17. The device according to any one of claims 11 to 16, comprising: - each of one or more working electrodes; and - the reference electrode; is 10 mm or less, such as 5 mm or less, for example 3 mm or less, such as 1 mm or less, for example 1 mm or less.

18. 18. Use of a device according to any one of claims 11 to 17, wherein the device is used to measure one or more potential differences indicative of one or more concentrations of one or more analyte ions in a sample, such as the sample being a liquid whole blood sample.

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