Method for determining the lithium content in a biological fluid

Abstract

Method for determining an amount of lithium contained in a biological fluid, said method comprising the steps consisting in adding, to a biological fluid sample of known volume, a given volume of a discriminating solution, the effect of which is to obtain a biological fluid solution buffered at a pH of between 6 and 8 and to bring about precipitation of at least a portion of the cations contained in the biological fluid sample except for the lithium Ions. The method further comprises the steps consisting in depositing a given volume of biological fluid solution onto an active layer (2) of an optode (1), said active layer comprising a chemical transducer of which at least one optical property is modified In the presence of lithium ions in the biological fluid solution, in measuring at least one characteristic of at least one light wave emitted or reflected by the active layer of the optode and in determining, from the at least one measured characteristic and from calibration data, an amount of lithium contained in the biological fluid.

Description

[0001] DESCRIPTION

[0002] Method for determining the level of lithium in a biological fluid

[0003] Technical field

[0004] The present invention relates to the field of determining the quantity of Lithium contained in biological or bodily fluids by means of an optode.

[0005] The present invention relates, in particular, to the monitoring of Lithium levels, at home, by people suffering from mood disorders and receiving lithium-based treatment such as, but not limited to, bipolar disorder or in combination with other treatments for resistant depressive disorders.

[0006] State of the prior art

[0007] The state of the art is known to us as a product sold by FISIC under the trade name "Medimate Multireader." This device allows a user to measure their lithium levels in the body. The measurement is accurate because it is based on electrophoresis. However, the analysis requires the collection of a blood sample from the user, which is an invasive procedure.

[0008] The use of an optode for determining lithium levels in biological fluids is also known in the prior art. Albero et al., “Novel flow-through bulk optode for spectrophotometric determination of lithium in pharmaceuticals and saliva,” Sensors and Actuators B, 145, (2010) 133-138 describes the determination of lithium concentration in saliva using an optode by spectrophotometry.

[0009] An aim of the invention is, in addition, to propose a method for determining the level of Lithium in a biological fluid:

[0010] - allowing the determination of the Lithium level at a concentration lower than 5 mM, and / or

[0011] - to determine the salivary lithium level, and / or

[0012] - at low cost, and / or

[0013] - simple to implement, and / or

[0014] - allowing the user to carry out the process himself and at home. Presentation of the invention

[0015] For this purpose, a method is proposed for determining a quantity of Lithium contained in a biological fluid. The method comprises the steps of:

[0016] - obtain, from a sample of biological fluid of known volume, a solution of biological fluid buffered to a pH between 6 and 8, noted step A,

[0017] - adding, into the biological fluid solution, a given volume of a discriminating solution having the effect of causing precipitation of at least part of the cations contained in the biological fluid solution with the exception of the Lithium ions, noted step B,

[0018] - depositing a volume, preferably a given volume, of biological fluid solution on an active layer of an optode; said active layer comprises a chemical transducer of which at least one optical property is modified in the presence of Lithium ions in the biological fluid solution, noted step C,

[0019] - measuring at least one characteristic of at least one light wave emitted or reflected by the active layer of the optode, preferably by the chemical transducer,

[0020] - determine, from at least one measured characteristic and from calibration data, a quantity of Lithium contained in the biological fluid.

[0021] The biological fluid solution may be any solution, liquid or viscous, preferably aqueous, containing Lithium ions.

[0022] Steps A, B may be implemented in any chronological order. Preferably, step C is implemented subsequently to steps A and B.

[0023] Preferably, steps A and B constitute a single step consisting of adding, to a sample of biological fluid of known volume, a given volume of a discriminating solution having the effect of:

[0024] • to obtain a solution of biological fluid buffered to a pH between 6 and 8, and

[0025] • to cause precipitation of at least some of the cations contained in the biological fluid sample with the exception of Lithium ions.

[0026] Preferably, the discriminating solution has the effect of precipitating the bi-cations contained in the biological fluid solution, in particular the Magnesium and Calcium ions. Preferably, the discriminating solution has the effect of precipitating the monocations contained in the biological fluid solution, with the exception of the Lithium ions, in particular the Potassium and Sodium ions. Preferably, the discriminating solution has the effect of precipitating all the cations, with the exception of the Lithium ions, contained in the biological fluid solution.

[0027] Preferably, obtaining a biological fluid solution buffered at a pH between 6 and 8 has the effect of overcoming the influence of at least a portion of the cations contained in the biological fluid solution, preferably the bi-cations, preferably the Calcium and Magnesium ions, and the mono-cations, with the exception of the Lithium ions, contained in the biological fluid solution, preferably the Potassium and Sodium ions, on the capture of Lithium by the active layer of the optode.

[0028] Preferably, the biological fluid may be blood or saliva. In the context of self-monitoring of lithium levels at home, saliva is preferably the preferred biological fluid.

[0029] Preferably, the method does not include an invasive step of collecting the biological fluid sample. The method may include a step of obtaining a biological fluid.

[0030] The term "given" can be defined as determined or known.

[0031] Preferably, the at least one optical property is modified in comparison to the amount of Lithium in the biological fluid solution. Preferably, the at least one optical property is modified proportionally or not but bijectively to the amount of Lithium in the biological fluid solution.

[0032] An optical property or characteristic of at least one light wave can be understood as a luminous intensity, a hue, an absorption or a luminescence.

[0033] It can be understood by the at least one characteristic of the at least one light wave at least one variation of at least one characteristic of the at least one light wave.

[0034] The optical property of the transducer may be an emission and / or a variation of an emission and / or a stopping of an emission of at least one light wave by the chemical transducer.

[0035] The characteristic of the at least one light wave emitted or reflected by the active layer can be defined as the optical property of the active layer.

[0036] The calibration data may be stored data. The calibration data may be a calibration curve or function or a value or correspondence table. Preferably, the step of obtaining the buffered biological fluid solution is carried out by adding a volume, preferably a given volume, of a buffer solution not comprising cations, with the exception of Hydronium ions, preferably not comprising bi-cations, in particular Magnesium and Calcium, more preferably not comprising mono-cations, in particular Sodium and Potassium ions, into the biological fluid sample.

[0037] Preferably, the step of measuring the at least one characteristic of at least one light wave emitted or reflected by the active layer of the optode is carried out by means of an optical measuring device. The optical measurement, by the optical measuring device, can be carried out by transmission or by reflection.

[0038] The step of adding a given volume of discriminating solution to the biological fluid solution may have the effect of causing desolvation of at least some of the cations contained in the biological fluid solution with the exception of lithium ions.

[0039] The method may comprise, prior to the step of adding the discriminating solution, a step of filtering the biological fluid solution or the biological fluid on a porous membrane having a cut-off threshold less than or equal to 50 pm.

[0040] Preferably, the discriminating solution is a buffer solution not comprising cations except Hydronium ions.

[0041] Preferably, the discriminating solution is a buffer solution not comprising di-cations.

[0042] Preferably, the discriminating solution is a buffer solution not comprising mono-cations except Hydronium ions.

[0043] Preferably, the discriminating solution is a buffer solution not comprising Magnesium and Calcium ions.

[0044] Preferably, the discriminating solution is a buffer solution not comprising Sodium and Potassium ions.

[0045] Preferably, the buffer solution is a pH 7 buffer solution of tris(hydroxymethyl)aminomethane:HCl. Preferably, the molar ratio of tris(hydroxymethyl)aminomethane:HCl is

[0046] 1:1.

[0047] The buffer solution may be a buffer solution of or comprising or based on Tricine or N-(2-Hydroxy-1,1-bis(hydroxymethyl)ethyl)glycine, bicine or [Bis(2-hydroxyethyl)amino]acetic acid, HEPES or 4-(2-hydroxyethyl)-1-piperazine ethanesulfonic acid or MES or 2-(N-morpholino)ethanosulfonic acid.

[0048] Preferably, the discriminating solution is an aqueous solution comprising oxalate ions at a concentration greater than or equal to 1 milliMolar (mM), or 1 mmol.l -1 , preferably at 5 mM.

[0049] The concentration of oxalate ions in the discriminating solution may be between 1 mM and the solubility limit of oxalic acid in water. Preferably, the concentration of oxalate ions in the discriminating solution is 5 mM.

[0050] Preferably, the at least one characteristic of the at least one light wave emitted or reflected by the active layer of the optode comprises, preferably is, a hue value of the active layer.

[0051] The hue of the solution can be the Hue value in a color space or system, for example HSL or HSV.

[0052] Preferably, the method comprises a step of processing the at least one measured characteristic of the at least one light wave emitted or reflected by the active layer of the optode in which the at least one measured characteristic comprises a set of colorimetric values ​​in a colorimetric space, for example CIE XYZ, or another space, for example HSV, obtained from, or which is a function of, the CIE XYZ colorimetric space.

[0053] The set of colorimetric values ​​may be, or may be represented as, a chromaticity diagram.

[0054] Preferably, the at least one measured characteristic comprises three colorimetric values. The set of colorimetric values ​​may comprise hue and / or saturation and / or luminance.

[0055] Preferably, the method comprises a step of converting the at least one measured characteristic of the at least one light wave originating from, preferably emitted or reflected by, the active layer into a three-dimensional colorimetric space.

[0056] Preferably, the step of processing the at least one measured characteristic comprises:

[0057] - a change of reference, within the color space, carried out on the two XY dimensions, then

[0058] - a projection on the Y axis of the color space of the measured colorimetric values.

[0059] The change of reference can be a rotation step, in the CIE XYZ color space, preferably reduced to two dimensions, denoted XY, by an angle between 35° and 60° of the measured colorimetric values. The change of reference can be a principal component analysis or any other transformation.

[0060] Preferably, the step of processing the at least one measured characteristic is carried out on two colorimetric values ​​from the set of colorimetric values.

[0061] The change of reference, within the color space, can be carried out on the three dimensions of the XYZ color space.

[0062] According to the invention, an optode is also proposed, preferably for determining the quantity of Lithium contained in a biological fluid, comprising:

[0063] - a white support made of chemically inert material,

[0064] - an active layer resting on the support, said active layer comprises a chemical transducer arranged so that at least one optical property is modified in the presence of a specific ionic species, preferably Lithium ions,

[0065] - a black layer of chemically inert material comprising at least one opening forming a well arranged to receive a solution to be analyzed intended to be in contact with the active layer.

[0066] Chemically inert can be understood to mean a material which does not interfere or interferes little with the biological fluid or the medium containing the biological fluid and / or does not degrade or degrades little the optode, in particular the active layer of the optode.

[0067] It can be understood by chemically inert biocompatible. It can be understood by biocompatible a material which does not interfere with and / or does not degrade the biological environment or the environment comprising the biological fluid with which it is intended to be put in contact.

[0068] It can be understood as resting on the immobilized support, hanging, attached or fixed to the support.

[0069] It can be understood as specific, determined, or particular.

[0070] Preferably, the chemically inert material is a polymer.

[0071] Preferably, the black layer of chemically inert material rests, at least in part, preferably in full, on the active layer.

[0072] Preferably, the active layer of the optode comprises an ionophore and a chromophore.

[0073] The active layer may further comprise an additive, for example a lipophilic anionic additive.

[0074] Preferably, the chemically inert material is poly(methyl methacrylate) (PMMA).

[0075] The chemically inert material can be Teflon.

[0076] The chemically inert material can be inorganic. The chemically inert material can be a ceramic.

[0077] Preferably, the optode according to the invention is suitable, more preferably is particularly suitable, more preferably is designed and particularly advantageously is specially designed, for implementing the method for determining a quantity of Lithium contained in a biological fluid according to the invention.

[0078] Any characteristic of the optode according to the invention can be directly transposed to the determination method according to the invention and vice versa.

[0079] According to the invention, there is also proposed a use of an aqueous solution comprising oxalate ions at a concentration greater than 1 mM, preferably 5 mM, and having a pH greater than or equal to 6 for the determination of the quantity of Lithium contained in a biological fluid. The concentration of oxalate ions in the aqueous solution may be between 1 mM and the solubility limit of oxalic acid in water. Preferably, the concentration of oxalate ions in the aqueous solution is 1 mM.

[0080] It may be understood by "aqueous comprising oxalate ions at a concentration greater than 1 mM and having a pH greater than or equal to 6 for the determination of the quantity of Lithium contained in a biological fluid", the use of said aqueous solution for the preparation of a biological fluid solution intended to be analyzed to determine the quantity of Lithium it contains.

[0081] Description of figures

[0082] Other advantages and particularities of the invention will appear on reading the detailed description of implementations and embodiments which are in no way limiting, and the following appended drawings:

[0083] [Fig. 1a] FIGURE 1a is a schematic representation of an embodiment of a portable optical measuring device coupled to the optode according to the invention in a configuration capable of carrying out a measurement of the optical properties of the optode, [Fig. 1b] FIGURE 1b is a schematic representation of the portable optical measuring device decoupled from the optode,

[0084] [Fig. 2] FIGURE 2 is a schematic representation of an optode illustrating the variation in hue of the active layer of the optode as a function of the Lithium concentration,

[0085] [Fig. 3a] FIGURE 3a is a representation of the xy components of the CIE xyY color space obtained from multispectral data measured on an optode according to the invention,

[0086] [Fig. 3b] FIGURE 3b is an enlargement of the xy components of the CIE xyY color space shown in FIGURE 3a,

[0087] [Fig. 4] FIGURE 4 is a representation of the data obtained by processing the XY components of the CIE XYZ color space shown in FIGURES 3a and 3b,

[0088] [Fig. 5] FIGURE 5 is a representation of an optode comprising a single well according to the invention.

[0089] Description of the embodiments

[0090] The embodiments described below being in no way limiting, it will be possible in particular to consider variants of the invention comprising only a selection of the described characteristics, isolated from the other described characteristics (even if this selection is isolated within a sentence comprising these other characteristics), if this selection of characteristics is sufficient to confer a technical advantage or to differentiate the invention compared to the state of the prior art. This selection comprises at least one characteristic, preferably functional without structural details, or with only a part of the structural details if this part only is sufficient to confer a technical advantage or to differentiate the invention compared to the state of the prior art.

[0091] With reference to FIGURES 1 to 4, the method for determining the amount of Lithium contained in a liquid is presented. The embodiment relates to the determination of the amount of Lithium in biological fluids and, in particular but not limited to, in saliva. Saliva is a fluid that does not require a delicate or invasive sampling step and its collection can therefore be carried out at home by the user himself. Mood stabilizing agents are among the various molecules existing to treat bipolar disorders. Clinically, the main actions that qualify a molecule as a mood stabilizer are its effects at both ends of the mood spectrum (depression and mania) and its ability to maintain euthymia by preventing future mood instability. According to these factors, lithium is the best mood stabilizing agent and therefore the reference one.The advantage of the method according to the invention is that it is designed so that a user can implement it at home without the intervention of a third party and can measure his Lithium level when necessary, obtaining results quickly. However, the method can also be implemented by a third party.

[0092] Saliva is preferably mechanically filtered through a membrane filter; membranes with cutoffs of 0.45 μm and 0.8 μm were used. A volume of 1 ml of filtered saliva was used according to the non-limiting embodiment. The use of a membrane filter is not limiting and other filtration means could also be used.

[0093] Sodium, potassium, magnesium and calcium cations are present in most biological fluids. The inventors observed that the variability of the cation concentration from one biological fluid sample to another modifies the operating point of the optode used for optical measurement and therefore makes the determination of the lithium concentration unreliable. The use of a chelator, EDTA (ethylenediaminetetraacetic acid), to complex these cations has proven inconclusive. Also, to overcome this problem, the method comprises the step of obtaining a biological fluid solution by adding a given volume of a discriminating solution to the biological fluid sample, here filtered saliva, of known volume. According to the embodiment, 1 ml of discriminating solution is added to 1 ml of filtered saliva.Saliva may contain residues and the filtration step aims to eliminate these in order to improve the reproducibility and reliability of the subsequent measurement carried out on optode 1. In practice, a volume of between 100 and 500 μl of saliva will be preferred.

[0094] According to the embodiment, the discriminating solution is a Tris / HCl buffer solution at pH 7 containing Sodium Oxalate at a concentration of 50 mM. Ammonium Oxalate is preferred in that it does not add additional Sodium ions.

[0095] The use of this discriminating solution makes it possible to obtain a biological fluid solution buffered to a pH between 6 and 8. In this way, the exchanges between the Lithium and the reactive surface of the optode are maximized, which makes it possible to optimize the colorimetric variation of the active layer 2 and therefore the detection sensitivity of Lithium. In addition, the use of this discriminating solution also has the effect of removing the mono-cations, in particular the Calcium and Magnesium ions, from the biological fluid solution and thus making the determination of the Lithium level more reliable. Preferably, the mixture is conveyed via fluidic channels or tubing from the filtration zone to the well(s) 6 of the optode 1.

[0096] The use of this discriminating solution also has the surprising effect of causing precipitation of at least some of the cations contained in the biological fluid sample with the exception of Lithium ions. In particular, the use of the discriminating solution makes it possible to effectively precipitate the di-cations contained in the biological fluid sample, in particular Magnesium and Calcium ions, and thus make the determination of the Lithium level even more reliable.

[0097] After mixing the discriminating solution and the biological fluid sample, 30 to 40 pL of the resulting biological fluid solution are then placed in a circular well 6 of an optode 1. The bottom of the well 6 is formed by the active layer 2 of the optode 1. The solution is left in contact with the active layer 2 for between two and five minutes before the optical measurement is carried out. The active layer 2 of an optode 1 comprises a chemical transducer of which at least one optical property is modified in the presence of lithium ions in the biological fluid solution.

[0098] The measurement of at least one characteristic of at least one light wave originating from, i.e. emitted or reflected by, the active layer 2 of the optode 1 is then carried out, then the determination of the quantity of Lithium contained in the biological fluid from the at least one measured characteristic and from calibration data of the optode 1. According to the non-limiting embodiment, a calibration curve may constitute the calibration data.

[0099] According to the embodiment, the lithium concentration in the sample is determined by colorimetric analysis of the active layer 2 of the optode 1. The measurement of the characteristic of the light waves coming from the active layer 2 of the optode 1 is carried out by a portable optical measuring device 7 illustrated in FIGURES 1a and 1b. The optical measuring device 7 is arranged to cooperate with the optode 1. The optical measuring device 7 is intended to be reversibly coupled with the well 6 of an optode 1. The optical measuring device 7 comprises a light source 8 and a multispectral sensor 9 of model AS7341 sold by the company AMS® which measures the light reflected 10 by the optode 1. A processing unit, connected or not to the measuring device, is arranged and / or configured to process the measured data.The measuring device 7 comprises two light-emitting diodes 8 of model YJ-VTC-5730-G01-65 sold by the company YUJILEDS® which are arranged to illuminate the active layer 2 of the optode 1 with a white light D65 CRI 98. The light beam reflected 10 by the active layer 2 is measured by the multispectral sensor 9. Preferably, the optical measuring device 7 comprises a cover 11 intended to be brought into contact with the black layer 4 of chemically inert material of the optode 1 which constitutes the external or upper layer of the optode 1. The multispectral sensor 9 is placed facing the optode 1 when the latter is coupled with the optical measuring device 7. The light coming from the LEDs 8 is “guided” at 45° in channels 12 arranged in the cover 11 to illuminate an individual well 6 of optode 1.The data from the multispectral measurement are then converted, by the processing unit, into a three-dimensional color space and then a lithium concentration value is determined. The step of converting the measured characteristics of the light wave coming from the active layer 2, or the multispectral values, is a step well known to those skilled in the art.

[0100] A person skilled in the art will therefore deduce directly from the preceding paragraph that the method comprises, according to the non-limiting embodiment, a step of converting the measured characteristics of the light wave coming from the active layer 2 into a three-dimensional colorimetric space.

[0101] The measurement of at least one characteristic of at least one light wave coming from the active layer 2 of the optode 1 corresponds to the multispectral measurement.

[0102] The measurements or results presented in the remainder of the description were obtained by implementing the method described above and, in particular, by using the discriminating solution according to the invention.

[0103] With reference to FIGURE 2, the variations in the hue of the active layer 2 of the optode 1 are illustrated as acquired by photography of the optode 1 and as observable with the naked eye for Lithium concentrations of 0 (a), 1 (b), 2 (c), 3 (d) and 4 (e) mM in deionized water. The lithium level influences the hue of the active layer 2 of the optode 1. These results are obtained from an optode 1 not comprising a well 6. A drop of each Lithium solution of different concentration was deposited on the active layer 2. This optode 1 is preferably dedicated to experimental studies or to obtaining calibration data. The optode 1 intended to be used by a user will preferably comprise a single well 6 constituting a consumable intended to be replaced. These results show that it is possible to detect variations in the color of active layer 2 with the naked eye.Of course, it is also possible to detect very small variations in the hue of active layer 2, which are undetectable to the naked eye, by digitally analyzing the hue values ​​converted from the spectral measurements taken.

[0104] However, the variation in hue of the active layer 2 of the optode 1 in the therapeutic window is small and is hardly perceptible to the naked eye. In addition, other factors can modify the hue such as the variation in thickness of the active layer 2 of the optode 1, the photobleaching of the chromophore of the active layer 2 and the aging of the optode 1. The variations in hue, even slight, disturb and distort the measurement. It has been observed by the inventors that the other components of the color space also vary with these disturbances. Also, the invention also consists of exploiting the information contained in all the components of the XYZ color space to compensate for the measurement error.

[0105] Also, another embodiment is presented offering greater detection sensitivity and better measurement reproducibility. The chromaticity diagram, providing information on the hue, corresponds to the xy components of the CIE xyY color space. The chromaticity diagram is a two-dimensional representation of the CIE XYZ color space without luminance information. Measurements were carried out on optode 1 from aqueous solutions of deionized water comprising 0.25, 0.5, 1 and 1.5 mM of Lithium. In order to evaluate the stability of the light emission by the active layer 2 of optode 1, these measurements were carried out on the same optode 1 on the first day of its manufacture and then on the seventh and fourteenth days after its manufacture. In addition, these measurements were carried out on several distinct optodes 1 whose active layers 2 were deposited at two distinct deposition rates.A first deposition speed of the active layer 2 by dip-coating is 50 mm / s, called fast deposition speed, and a second deposition speed of the active layer 2 by dip-coating is 10 mm / s. The multispectral measurements carried out in each case were converted into the three-dimensional CIE XYZ color space. With reference to FIGURES 3a and 3b, the chromaticity diagram is shown, corresponding to the colorimetric values ​​of the two xy dimensions of the CIE xyY color space. The chromaticity diagram provides information on the hue of the active layer 2.

[0106] In this CIE xyY color space, it is possible to apply a linear regression on the different lithium measurements despite the variations in parasitic hues. However, since these regressions are not parallel, it is not possible to calculate a reliable color-dependent metric corresponding to a lithium concentration.

[0107] Also, a change of reference is first made, within the CIE XYZ color space, on the two XY dimensions. This change of reference can be, for example, a principal component analysis or a rotation of the components in the CIE XYZ color space. Depending on the embodiment, a rotation of between 45 and 47° is made within the CIE XYZ space. This range of values ​​is not limiting and will be adapted according to the experimental conditions used, such as, for example, the composition of the discriminating solution, in particular the salt concentration in the buffer solution, the type of buffer, the pH of the solution or the type of counter-ion accompanying the oxalate, the targeted biological fluid or the composition of the active layer 2 used. The rotation angle will mainly be between 35° and 60°.Following the change of reference, a projection of the XY colorimetric components onto the Y axis of the CIE XYZ color space is carried out. The result of the projection is illustrated in FIGURE 4. Following this change of reference and this projection, it can be observed that the colorimetric values ​​projected onto the Y axis are a function of and vary linearly with respect to the lithium concentration on the abscissa. The data thus obtained can be used as calibration data when implementing the method to determine the lithium level in a biological fluid.

[0108] With reference to FIGURE 5, a preferred embodiment of the optode 1 according to the invention intended to be used by a user is illustrated. The optode 1 described below is the one that was used during the implementation of the method described above. The optode 1 comprises a white support 3 made of chemically inert material. According to the embodiment, the material used is a polymer, in particular PMMA. It has been observed that PMMA significantly extends the lifetime of the active layer 2 and reduces the variations in light emission of the active layer 2 over time. The optode 1 can be used for at least fourteen days without significant variations in the chromophore being observed.As comparative examples, it has been observed that the use of polyethylene as support 3 gives a lifetime or use of one day to the active layer 2 and that the use of poly(vinyl chloride) as support 3 makes the optode 1 unusable because it is non-functional. However, it is also possible to use other polymers such as, for example, Teflon, polyetheretherketone or polyurethane or other materials such as, for example, ceramic.

[0109] According to the non-limiting embodiment, the active layer 2 resting on the support 3 comprises poly(vinyl chloride), DOS (Bis(2-ethylhexyl) sebacate), Lithium ionophore VIII, Chromoionophore 1 (ETH 5294) and Potassium tetrakis(4-chlorophenyl)borate (K-TCPB). In practice, the active layer 2 is deposited by dip-coating on the support 3 from a solution obtained by dissolving in 25 ml of tetrahydrofuran 417 mg of PVC, 911 μl of DOS (Bis(2-ethylhexyl) sebacate), 23.7 mg Lithium ionophore VIII, 11.1 mg of Chromoionophore 1 (ETH 5294) and 12.6 mg of Potassium tetrakis(4-chlorophenyl)borate (K-TCPB). The thickness of the active layer 2 obtained after dip-coating is, for example, between 1 and 3 μm. In practice and in a non-limiting manner, the support 3 in white PMMA, in the form of a tab according to the embodiment, is dipped into the solution at a speed of 10 mm / s, then is left for 0.5 s in the solution, then is raised at a speed of 10 mm / s.The support can be dried for approximately 30 min so that the solvent, THF depending on the method, evaporates.

[0110] According to the non-limiting embodiment, the optode 1 also comprises a black layer 4 made of chemically inert material, PMMA according to the embodiment, comprising at least one opening forming a well arranged to receive the solution to be analyzed intended to be in contact with the active layer 2. By way of example, a circular well 6 may have a diameter of 4.5 mm and a height, from the active layer 2 to the top of the well 6, of 3 mm.

[0111] The black layer 4 made of chemically inert material includes a through opening 5. The black layer 4 made of PMMA rests on the active layer 2. The black color of the chemically inert material including the through opening 5 makes it possible to limit the influence of light reflections and ambient light on the multispectral measurement.

[0112] Of course, the invention is not limited to the examples which have just been described and numerous adjustments can be made to these examples without departing from the scope of the invention.

[0113] Thus, in variants of the previously described embodiments which can be combined with each other, the aqueous solution, and / or its use for determining the quantity of Lithium contained in a biological fluid, comprises oxalate ions at a concentration greater than 5 mM and has a pH greater than or equal to 6.

[0114] In addition, the various features, forms, variations and embodiments of the invention may be combined with each other in various combinations to the extent that they are not incompatible or mutually exclusive.

Claims

CLAIMS 1. Method for determining a quantity of Lithium contained in a biological fluid, said method comprises the steps of: - add, to a sample of biological fluid of known volume, a given volume of a discriminating solution having the effect of: • to obtain a solution of biological fluid buffered to a pH between 6 and 8, and • to cause precipitation of at least some of the cations contained in the biological fluid sample with the exception of Lithium ions, - depositing a given volume of biological fluid solution on an active layer (2) of an optode (1); said active layer comprises a chemical transducer of which at least one optical property is modified in the presence of Lithium ions in the biological fluid solution, - measure at least one characteristic of at least one light wave emitted or reflected by the active layer of the optode, - determine, from at least one measured characteristic and from calibration data, a quantity of Lithium contained in the biological fluid.

2. Method according to claim 1, comprising, prior to the step of adding the discriminating solution, a step of filtering the biological fluid solution on a porous membrane having a cut-off threshold less than or equal to 50 pm.

3. Method according to claim 1 or 2, in which the discriminating solution is a buffer solution not comprising Magnesium and Calcium and / or Sodium and Potassium cations.

4. Method according to claim 1 or 2, in which the discriminating solution is a buffer solution not comprising di-cations and / or mono-cations with the exception of Hydronium ions.

5. A method according to any one of the preceding claims, wherein the buffer solution is a pH 7 buffer solution of tris(hydroxymethyl)aminomethane: HCl.

6. Method according to any one of the preceding claims, in which the discriminating solution is an aqueous solution comprising oxalate ions at a concentration greater than ImM.

7. Method according to any one of the preceding claims, in which the at least one characteristic of the at least one light wave emitted or reflected by the active layer (2) of the optode (1) comprises a tint value of the active layer.

8. Method according to any one of the preceding claims, comprising a step of processing the at least one measured characteristic of the at least one light wave emitted or reflected by the active layer (2) of the optode (1): - in which the at least one measured characteristic comprises a set of colorimetric values ​​in a color space, - including: • a change of reference, within the color space, carried out on two dimensions of the color space, noted XY, then • a projection on the Y axis of the color space of the measured colorimetric values.

9. Optode (1) for implementing the method according to any one of claims 1 to 8, said optode comprises: - a white support (3) made of chemically inert material, - an active layer (2) resting on the support, said active layer comprises a chemical transducer arranged so that at least one optical property is modified in the presence of a specific ionic species, - a black layer (4) made of chemically inert material comprising at least one opening (5) forming a well (6) arranged to receive a solution to be analyzed intended to be in contact with the active layer.

10. Optode (1) according to the preceding claim, in which: - the active layer (2) comprises an ionophore and a chromophore, - the chemically inert material is poly(methyl methacrylate) (PMMA).

Images