WO2014188166A1 - Détermination électrochimique de la concentration d'un halogénure ou d'un pseudohalogénure - Google Patents

Détermination électrochimique de la concentration d'un halogénure ou d'un pseudohalogénure Download PDF

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WO2014188166A1
WO2014188166A1 PCT/GB2014/051530 GB2014051530W WO2014188166A1 WO 2014188166 A1 WO2014188166 A1 WO 2014188166A1 GB 2014051530 W GB2014051530 W GB 2014051530W WO 2014188166 A1 WO2014188166 A1 WO 2014188166A1
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sample
anion
concentration
electrode
substance
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Her Shuang TOH
Christopher BATCHELOR-MCAULEY
Kristina TSCHULIK
Richard Guy Compton
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Oxford University Innovation Ltd
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Oxford University Innovation Ltd
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
    • G01N27/26—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating electrochemical variables; by using electrolysis or electrophoresis
    • G01N27/416—Systems
    • G01N27/48—Systems using polarography, i.e. measuring changes in current under a slowly-varying voltage
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
    • G01N33/18—Water
    • G01N33/182—Specific anions in water
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
    • G01N33/48—Biological material, e.g. blood, urine; Haemocytometers
    • G01N33/483—Physical analysis of biological material
    • G01N33/487—Physical analysis of biological material of liquid biological material
    • G01N33/48707—Physical analysis of biological material of liquid biological material by electrical means

Definitions

  • the present invention relates to the determination of the concentration of a halide ion or pseudohalide ion in a sample, e.g. a biological sample. It can be used, for example, to determine the concentration of chloride in a sweat sample, as a preliminary screening for cystic fibrosis. Other possible uses are described herein. Background
  • cystic fibrosis is a common disease which has an associated characteristic symptom of high sweat chloride content.
  • Cystic fibrosis (CF) is a common genetic disease caused by an autosomal recessive gene known as the cystic fibrosis transmembrane conductance regulator (CFTR) gene. 1 It affects multiple organs including the lungs and the intestines. The defective gene leads to an expression of a non-functional channel protein, leading to irregular transport of sodium and chloride ions across the epithelial cells.
  • the sweat chloride level is measured and matched against a guideline.
  • the references for sweat chloride levels for adults are categorised into: less than 39 mM (negative), 40 - 59 mM (borderline) and greater than 60 mM (positive).
  • sweat chloride levels are categorised as: less than 29mM (negative), 40 - 59 mM (borderline) and greater than 60 mM (positive).
  • '- '1 The Cystic Fibrosis Foundation from the US recommends a sweat chloride sensor range to be 10 - 160 mM.— The Association of Clinical Biochemistry from the UK states that the maximum level of sweat chloride in human is 160 mM.
  • the excess or deficiency of iodide in the human body can be indicative of a range of health problems, which are often associated with the thyroid.
  • the current method used for determination of iodine in a human body involves a urine sample collection. Patients receive and ingest an iodine tablet and the iodine level in the urine is measured over 24 hours (preferred) or on a single morning. Sandell-Kolthoff reaction is performed on the urine sample before the iodine levels are measured spectrophotometrically or colorimetrically. Sandell-Kolthoff involves a pretreatment of chloric acid digestion or oxidation with ammonium persulphate to remove interference.
  • the main reaction involves reduction of yellow eerie ions by arsenic in presence of iodide to form colourless cerous ions.
  • the disappearance of yellow eerie ions determines the iodine concentration by cross referencing with a determined relationship between known iodine concentration and absorbance.
  • ICP- MS can also be used to determine iodine concentration.
  • Figure 1 shows a schematic diagram for the preparation and use of a silver nanoparticle modified screen printed electrode and the anodic stripping voltammogram of silver nanoparticles, as described in the Examples below.
  • Step 1 Drop casting of silver nanoparticle suspension onto a screen printed electrode with micropipette.
  • Step 2 Dry electrode in a 50°C oven for 12 minutes. Steps 1 and 2 are repeated five times.
  • the modified electrodes are used for anodic stripping voltammetry in two conditions: in the absence of chloride ions and in the presence of chloride ions. In the presence of different concentration of chloride ions, the peak height of the voltammetric signal at the lower potential increases with increasing chloride concentration.
  • FIG. 3 shows scanning electron microscopy image for silver nanoparticles used in the Examples below.
  • Figure 4 shows the oxidative stripping of silver nanoparticles from a glassy carbon electrode in 0.1 M sodium nitrate spiked with different amount of potassium chloride (KCI) at a scan rate of 0.05 V s '
  • KCI potassium chloride
  • Grey dashed line No KCI
  • Black solid line 2mM KCI
  • Black dashed Line 8mM KCI
  • Black dotted line 16mM KCI
  • Grey solid line 32mM KCI.
  • Reference electrode Ag/AgN0 3 (10 mM) & NaN0 3 (90 mM)
  • Counter electrode Platinum mesh
  • Inlay Calibration plot of peak height of peak A against the concentration of chloride ions. Each data point consists of a minimum of 3 repeats.
  • Figure 5 shows the oxidative stripping of silver nanoparticles from a screen printed electrode in 0.1 M sodium nitrate spiked with different amount of potassium chloride at a scan rate of 0.05 V s '
  • the peak height of peak A (see Figure 4) is plotted against concentration of chloride. Each data point consists of a minimum of 3 repeats. The experiment is described in more detail in the Examples below.
  • Figure 6 shows the oxidative stripping of silver nanoparticles from a screen printed electrode in 0.1 M sodium nitrate with different synthetic sweat samples (diluted by a factor of 4) at a scan rate of 0.05 V s '
  • Black solid line Synthetic sweat sample 1 ;
  • Black dash line Synthetic sweat sample 2.
  • Star Diluted synthetic sweat sample 2.
  • Each data point consists of three repeats.
  • the present invention provides a method of determining the concentration of an anion selected from a halide ion and a pseudohalide ion in a sample of interest, the method involving:
  • a working electrode having a substance in a first oxidation state on a surface thereof, wherein the electrode is in contact with the sample of interest that contains the anion;
  • Electrochemical information may include, but is not limited to, peak current, peak charge and peak potential.
  • the present invention provides an apparatus for determining the concentration of an anion selected from a halide ion and a pseudohalide ion in a sample of interest, the apparatus comprising a working electrode having a substance in a first oxidation state on a surface thereof, the apparatus adapted to carry out a method involving:
  • a voltammetry or chronoamperometry experiment that involves increasing the potential applied to the working electrode to a first potential to oxidise the substance to a second oxidation state, wherein, at the first potential, the electrochemical response of the substance is different when the anion is present in the sample compared to when the anion is absent in the sample, and obtaining electrochemical information during the voltammetry or chronoamperometry experiment; using a determined relationship between the electrochemical information and the concentration of the anion in a reference sample to calculate the concentration of the anion in the sample of interest.
  • the present invention provides a use of an electrode having silver on a surface thereof in an electrochemical test method to determine the concentration of chloride ions in a sweat sample, wherein the electrochemical test method involves oxidation of the silver from Ag (0) to Ag(l) on the electrode in the sweat sample.
  • the electrochemical test method involves oxidation of the silver from Ag (0) to Ag(l) on the electrode in the sweat sample.
  • a finite amount of silver is present on the working electrode, for example in the form of silver nanoparticles, such that peaks of current of a desired height are observed.
  • the present invention provides use of an electrode having silver on a surface thereof in an electrochemical test method to determine the concentration of cyanide ions in a sample, wherein the electrochemical test method involves oxidation of the silver from Ag (0) to Ag(l) on the electrode in the sample.
  • the present inventors have developed an electrochemical method for determining the concentration of a halide or a pseudohalide of interest in a sample, e.g. a biological sample.
  • the method can be cost effective and convenient. They have found that certain substances, e.g. certain metals, give a different electrochemical response in a sample, depending on whether or not a halide ion or pseudohalide ion is present in the sample, and that the response has a relationship with the concentration of the halide or pseudohalide in the sample.
  • the electrochemical oxidation of silver nanoparticles in the absence of chloride ions gives one voltammetric signal related to the oxidation of silver to silver ions (in solution).
  • the present invention provides the first to the fourth aspects described herein. Preferable and optional features are described below. Any of the preferable and optional features are applicable to any aspect of the invention, unless otherwise stated. Any preferable or optional feature may be combined with any other preferable or optional feature.
  • the substance in its first oxidation state contacts the sample of interest.
  • the substance in its second oxidation state forms a species with the anion in which the substance is in a different local environment compared to if it were oxidised to its second oxidation state in the sample in the absence of the anion in question.
  • the substance in its second oxidation state forms a solid compound with the anion on the electrode or forms a complex with the anion; and such a complex may or may not be dissolved in the sample.
  • the substance in its second oxidation state is soluble in the sample. If the complex is formed at the first potential, raising the potential above the first potential to a second potential may involve the dissociation of the substance and the anion.
  • the substance may be silver, and the anion may be chloride.
  • the silver is in an elemental form (i.e. its first oxidation state is 0).
  • the silver on the working electrode is oxidised in the aqueous sample in the absence of chloride ions, a single peak in current is observed; this relates to the formation of silver (I) ions in solution.
  • the method involves a voltammetry or a chronoamperometry experiment.
  • the voltammetry will typically involve monitoring of the current at the working electrode as the potential between the working electrode and a further electrode is changed; the further electrode may be selected from a reference electrode and a counter electrode; in some examples a counter electrode and a reference electrode are both used in the voltammetry, and a potential may be applied between the working electrode and the reference electrode.
  • the voltammetry may involve a voltammetry technique selected from cyclic voltammetry, square wave voltammetry, linear sweep voltammetry, pulse voltammetry, such as normal pulse or differential pulse voltammetry; or an amperometry technique such as chronoamperometry may be used.
  • the voltammetry may be used to obtain electrochemical information, such as the potential, peak current and/or peak charge at which the oxidation of the substance on the working electrode occurs.
  • the voltammetry may involve increasing the potential at the working electrode until a peak in current is observed at a certain potential, and continued until the current has dropped from this peak and then started to rise again.
  • the potential may be raised at a constant rate, for example at a rate of 0.01 to 0.1 Vs “1 , optionally at a rate of from 0.03 Vs "1 to 0.07 Vs “1 , optionally at a rate of 0.04 to 0.06 Vs "1 , optionally about 0.05 Vs "1 .
  • a first peak that may, for example, represent formation on the working electrode of a solid compound of the substance in its second oxidation state with the anion or a complex of the substance in its second oxidation state with the anion
  • the second peak that represents formation of ions of the anion and the substance in its second oxidation state, both of which are in solution in the sample and may be dissociated from one another, e.g. not forming a complex together; optionally the height or area of the first peak may be used as the electrochemical information.
  • the first potential may be a potential in the range of -0.3 V to -0.1 V, optionally in the range of -0.3 to -0.2 V, optionally about -0.25V (vs Ag/AgN0 3 (10 mM) as a reference electrode), for example when using a glassy carbon working electrode having silver nanoparticles thereon, and optionally using other conditions given in the Examples below.
  • the electrochemical information may be the height or area of a peak of current at the first potential, and preferably when the substance in its second oxidation state forms a solid compound on the electrode with the anion or forms a complex with the anion.
  • a first peak of current is observed at the first potential, and the method further involves raising the potential above the first potential, so that a second peak in current is observed at a second potential.
  • the difference between the first and second potentials at which there is a peak in current is used to identify the anion and/or used as the electrochemical information to calculate the concentration of the anion in the sample of interest.
  • a ratio of (i) the area under the peak of current at the first potential and (ii) the area under the peak of current at the second potential is used as the electrochemical information to calculate the concentration of the anion in the sample of interest.
  • the method involves using a determined relationship between the electrochemical information and the concentration of the anion in a reference sample to calculate the concentration of the anion in the sample of interest.
  • the determined relationship may have been determined in a reference experiment in which is measured the variation of the electrochemical information, e.g. the height or area or a peak of current at the first potential, over a range of concentrations of the anion in the reference sample.
  • the reference sample can be a sample suitable for calibrating the concentration of the anion in the sample of interest.
  • the reference sample and the sample of interest may be similar to one another, for example in that they contain the same liquid medium, e.g. water, in approximately the same amount, and any other components, aside from the anion, in the same amounts.
  • the sample of interest may be sweat containing a certain concentration of chloride ions
  • the reference sample is a biological or synthetic sweat sample that contains chloride ions; and optionally the reference experiment involves measuring the variation of the electrochemical information, e.g. the height or area of a peak of current at the first potential, over a range of concentrations of the chloride in the reference sample.
  • the electrochemical information is the height of a peak of current at the first potential, and the determined relationship may be represented by formula (a)
  • I C + n[anion] formula (a) wherein I is the height of a peak of current at the first potential, C is a constant, and n is a coefficient, and [anion] is the concentration of the anion in the sample of interest (or in the reference experiment, the concentration of the anion in the reference sample). C and n may be determined in the reference experiment. From determining I in the sample of interest, and using the formula above, i.e. (l-C)/n, the concentration of anion in the sample of interest, [anion], can be determined. The present inventors have found that the variation of peak height at the first potential can vary linearly with anion concentration within useful ranges.
  • higher order polynomials may be used for the determined relationship between the peak of current at the first potential and the concentration of anion in the reference sample.
  • the relationship may be expressed by a second degree polynomial of formula (b)
  • I C + n[anion] + m[anion] 2 formula (b) wherein I, C, n and [anion] are as defined above and m is a further coefficient.
  • C, n and m may be determined in a reference experiment by measuring I over a range of known anion concentrations in the reference sample.
  • Higher degree polynomials relating I and [anion] can also be used, such as third degree polynomials, fourth degree polynomials, and so on.
  • Other functional forms can be used and the most appropriate can be determined by the skilled person. However, in many circumstances, the relationship between I and [anion] has been found to be sufficiently linear that formula (a) can be used and is adequate for determination of the concentration in a sample of interest.
  • the voltammetry or chronoamperometry experiment may be carried out using a suitable electrochemical analytical device, for example a potentiostat.
  • the method typically involves use of a counter electrode.
  • the counter electrode may be made of any suitable material, for example a metal or carbon.
  • the counter electrode may be selected such that it is inert, i.e. not oxidised or reduced under the conditions at which the electrochemical analysis is carried out.
  • the counter electrode may comprise a metal selected from gold, silver, copper and platinum.
  • the counter electrode may comprise a carbon-containing material, which may be selected from edge plane pyrolytic graphite, basal plane pyrolytic graphite, a glassy carbon, boron doped diamond, highly ordered pyrolytic graphite, carbon powder and carbon nanotubes.
  • the method may involve use of a reference electrode.
  • a reference electrode for example a Ag/Ag + (e.g.
  • Ag/AgCI reference electrode or a saturated calomel reference electrode may be connected to the working and/or counter electrodes as is known in the art.
  • a pseudo reference electrode may be used.
  • a pseudo reference electrode may be defined as electrode through which no appreciable current is allowed to flow and is used to observe or control the potential at a working electrode.
  • a pseudo-reference electrode such as a Ag or Pt wire, may be used.
  • a means for applying a potential e.g. a potentiostat, is electrically connected to the working, counter and, if present, (pseudo)reference electrodes.
  • the working electrode forms part of a screen printed electrode, which further comprises one or both of a counter electrode and a reference electrode, which may be as described herein.
  • the working electrode before carrying out the voltammetry experiment, may comprise an electrically conductive or semi-conductive material having on a surface thereof the substance in the first oxidation state; the substance in the first oxidation state may be different from the electrically conductive or semi-conductive material.
  • the substance on the working electrode comprises silver (and the first oxidation state is 0)
  • the electrically conductive or semi-conductive substance is not silver and is inert during the oxidation; for example the electrically conductive or semi-conductive substance is or comprises carbon.
  • the electrically conductive or semi-conductive material is preferably inert.
  • the electrically conductive material may comprise a metal or carbon.
  • the electrically conductive material may comprise a metal selected from gold, silver and platinum.
  • the electrically conductive material comprises indium tin oxide.
  • the electrically conductive material comprises a conductive polymer.
  • the electrically conductive material may comprise a carbon-containing material, which may be selected from glassy carbon, edge plane pyrolytic graphite, basal plane pyrolytic graphite, boron doped diamond, highly ordered pyrolytic graphite, carbon powder and carbon nanotubes.
  • the electrically conductive comprises a glassy carbon material.
  • the working electrode may form part of a screen printed electrode, and the working electrode may be or comprise a screen printed carbon electrode having on a surface thereof the substance in the first oxidation state (before the voltammetry experiment).
  • the working electrode may be a carbon electrode and form part of a screen printed electrode that further comprises a reference electrode that may comprise, for example, silver.
  • the substance on the working electrode may be selected from silver, gold, platinum, palladium, iron, copper, zinc, mercury, tin, lead, bismuth, gallium and indium, and the first oxidation state is 0.
  • the substance is selected from silver, lead, mercury, copper, and thallium, and the first oxidation state is 0.
  • the substance is silver, the first oxidation state is 0 and the second oxidation state is 1.
  • the substance may be in elemental form. If the substance comprises a metal, e.g. silver, the substance may be present, in the first oxidation state, as a pure metal or an alloy of this metal.
  • Silver for example, can be present as an alloy with a metal selected from copper, gold, platinum, bismuth, and combinations thereof.
  • the substance, in its second oxidation state can form a compound with the anion that is substantially insoluble in water at 25 °C or can form a complex with the anion, which may or not be soluble in water at 25 °C.
  • the substance, in its second oxidation state can form a compound with the anion that has a solubility product constant, K sp ,(at 25 °C in water) of 1 x 10 "4 or less, optionally 1 x 10 "5 or less, optionally 1 x 10 "6 or less, optionally 1 x 10 "7 or less.
  • the substance may be in any suitable form on the working electrode.
  • the substance is in a form selected from nanoparticles and a film.
  • the entirety of the substance is oxidised during the method, and preferably substantially none of the material of the working electrode on which it was disposed is oxidised.
  • the substance is in the form of nanoparticles.
  • the present inventors have found that having a finite amount of oxidisable material on the electrode (i.e. the substance as described herein), such that the entirety of which is oxidised during the method, produces peaks of potential of a desired size.
  • the amount of such substance deposited onto a working electrode can be carefully controlled, such that it is entirely oxidised during the method.
  • the nanoparticles may be or comprise particles having a diameter of from 1 to 500 nm, optionally from 1 to 200 nm, optionally from 10 to 100 nm.
  • the diameter of a nanoparticle, and/or particle size distributions of nanoparticles in a sample can be determined by a technique selected from scanning electron microscope (SEM) imaging, atomic force microscopy, dynamic light scattering techniques, UV-visible spectroscopy, and other suitable techniques, as would be appreciated by the skilled person.
  • the nanoparticle can be any suitable shape, including spherical, and elongated, for example a rod-shaped nanoparticle. If a nanoparticle is non-spherical, the diameter of the nanoparticle as measured herein will be the smallest diameter across the particle.
  • the nanoparticles may comprise, consist essentially of, or consist of, a type of substance, as described herein. If a nanoparticle consists essentially of a material, this indicates that preferably the particle comprises at least 95 % by weight of this material, preferably 98 % by weight, preferably 99 % by weight, of this material.
  • the anion may be a halide and may be selected from chloride, bromide and iodide.
  • the substance is silver, the first oxidation state is 0 and the halide is chloride, and optionally the second oxidation state is 1.
  • a pseudohalide may be defined as the anion of a pseudohalogen.
  • a pseudohalogen may be defined as a monovalent, inorganic group, consisting of two or more electronegative elements, including, but not limited to, C, N, O, S, Se and Te.
  • Pseudohalogens can have similar chemical and physical properties to halogens.
  • the pseudohalides may be selected from CN “ , N 3 " , NCO “ , SCN “ , NCS “ , SeCN “ , NCSe “ , CS 2 N 3 " and TeCN “ .
  • Pseudohalogens are described, for example, in New Pathways in Inorganic Chemistry, edited by E.A.V.
  • the sample of interest and/or the reference sample may be a liquid sample.
  • the sample of interest and/or the reference sample is a biological sample, which may be selected from a sweat sample, a blood sample, saliva and a urine sample.
  • the blood sample may be selected from a whole blood sample, a plasma sample and a serum sample. If the sample of interest is a sweat sample from a human patient, the reference sample may be a biological or synthetic sweat sample.
  • the synthetic sweat sample may be prepared according to a known standard, including, but not limited to, the German industrial standard (DIN-53160-2) or the British Standard (BS EN181 1-1999), adapted as required to alter the concentration of the anion, e.g. chloride, therein, and by the addition of one or more electrolytes, e.g. sodium nitrate, to a desired concentration.
  • a known standard including, but not limited to, the German industrial standard (DIN-53160-2) or the British Standard (BS EN181 1-1999)
  • BS EN181 1-1999 British Standard
  • the sample of interest and/or the reference sample may be selected from sea water, river water, drinking water, waste water and effluent.
  • the sample may be diluted, e.g. with a liquid medium such as water, the diluted sample used in the method, and the dilution is taken into account when calculating the concentration of the anion in the undiluted sample.
  • a liquid medium such as water
  • the liquid medium may comprise an electrolyte, including, but not limited to sodium nitrate.
  • the sample of interest which may be a biological sample, may be diluted so that its concentration is 1/N of its original concentration (e.g. biological concentration), e.g. by the addition of water (that optionally contains an electrolyte), and N may be 2 or more, optionally 3 or more, optionally 4 or more, optionally 2 to 5, optionally about 4.
  • the sample before contacting with the working electrode, may be concentrated, e.g. by allowing liquid, e.g. water, to evaporate from the sample, the concentrated sample used in the method, and the pre-concentration is taken into account when calculating the concentration of the anion in the unconcentrated sample.
  • liquid e.g. water
  • the anion, e.g. chloride, concentration in the sample of interest, as tested in the voltammetry experiement, and after any dilution or concentration of the sample of interest is within the range of 1 mM to 160 mM, optionally in the range of 10 mM to 160 rtiM.
  • the anion, e.g. chloride, concentration in the sample of interest, as tested in the voltammetry experiement, and after any dilution or concentration is within the range of 2 mM to 40 mM.
  • the anion is chloride
  • the sample of interest is a sweat sample from a human subject
  • the method gives an indication of whether the concentration of the chloride ion in the sweat sample is above a threshold value, and, optionally, if above a threshold value, further tests are carried out to determine if the subject has cystic fibrosis.
  • the further tests may involve, for example, genetic tests, e.g. CFTR-related genetic tests.
  • the threshold value may be, for example, a value of 40 mM or more, optionally a value of 50 mM or more, optionally a value of 60 mM or more. If the sample of interest has been previously diluted or concentrated before contacting with the working electrode, the threshold value may be the value in the undiluted or non-concentrated sample of interest.
  • the method may be used to determine if a subject, e.g. a human subject, is sufficiently hydrated.
  • the sample may be a sample from a human subject, e.g. a sweat sample, the anion is chloride, and if the sample contains 40 mM or more chloride ion, optionally 60 mM or more chloride ion, this may indicate dehydration in the subject, particularly if the subject is not found to (e.g. in a subsequent test) or known not to have cystic fibrosis.
  • the method can be used to determine the concentration of a halide ion or pseudohalide ion in a very small amount of sample.
  • the amount of the sample of interest in contact with the working electrode is 1 ml or less, optionally 500 ⁇ _ or less, optionally 200 ⁇ _ or less, optionally 100 ⁇ _ or less, optionally 75 ⁇ _ or less, optionally 60 ⁇ _ or less.
  • the amount of sample of interest in contact with the working electrode is at least 1 ⁇ _, optionally at least 5 ⁇ _, optionally at least 10 ⁇ _, optionally at least 20 ⁇ _.
  • the method may be used to determine the amount of iodide in a sample, including, but not limited to, a urine sample from a human subject.
  • a sample including, but not limited to, a urine sample from a human subject.
  • An excess or deficiency of iodide in a human subject can indicate and/or cause certain health problems.
  • a urinary iodine concentration of 100 - 199 ⁇ g/L is adequate.
  • a urinary iodine concentration of 150-249 ⁇ g/L is adequate.
  • a urinary iodine concentration of less than 20 ⁇ g/L can be insufficient and indicate a severe iodine deficiency.
  • a urinary iodine concentration of 20 ⁇ g/L to 49 ⁇ g/L can be insufficient and indicate a moderate iodine deficiency.
  • a urinary iodine concentration of 50 ⁇ g/L to 99 ⁇ g/L can be insufficient and indicate a moderate iodine deficiency.
  • a urinary iodine concentration of 200 ⁇ g/L to 299 ⁇ g/L can be more than adequate and indicate a risk of iodine-induced hyperthyroidism within 5-10 years.
  • a urinary iodine concentration of 300 ⁇ g/L or more can indicate an excessive risk of adverse health consequences (iodine induced hyperthyroidism, autoimmune thyroid diseases). More information on iodine levels in a human subject can be found in a publication by M.Andersson, entitled Iodine Deficiency in Europe: A continuing public health problem, World Health Organisation, 2007.
  • the method may be used to detect whether the iodide/iodine level in a biological sample, e.g. urine, is above or below a threshold value, e.g. the values given above.
  • the present invention provides an apparatus for determining the concentration of an anion selected from a halide ion and a pseudohalide ion in a sample of interest, the apparatus comprising a working electrode having a substance in a first oxidation state on a surface thereof, the apparatus adapted to carry out a method involving:
  • a voltammetry or chronoamperometry experiment that involves increasing the potential applied to the working electrode to a first potential to oxidise the substance to a second oxidation state, wherein, at the first potential, the electrochemical response of the substance is different when the anion is present in the sample compared to when the anion is absent in the sample, and obtaining electrochemical information during the voltammetry or chronoamperometry experiment; using a determined relationship between the electrochemical information and the concentration of the anion in a reference sample to calculate the concentration of the anion in the sample of interest.
  • the apparatus may be adapted to carry out at least part of the method as described herein in an automated way.
  • the apparatus may be adapted to carrying out the voltammetry or chronoamperometry experiment and using the determined relationship to the calculate the concentration of the anion in the sample of interest in an automated way; optionally the device may be adapted to contact the working electrode with the sample of interest in an automated way. All features as described above in relation to the method are equally applicable to the device.
  • the apparatus may be programmed to carry out at least part of the method, e.g. carrying out the voltammetry or chronoamperometry experiment and using the determined relationship to the calculate the concentration of the anion in the sample of interest; and optionally contact the working electrode with the sample of interest.
  • the apparatus may be a portable apparatus.
  • the present invention provides a use of an electrode having silver on a surface thereof in an electrochemical test method to determine the concentration of chloride ions in a sweat sample, wherein the electrochemical test method involves oxidation of the silver from Ag (0) to Ag(l) on the electrode in the sweat sample.
  • the present invention provides use of an electrode having silver on a surface thereof in an electrochemical test method to determine the concentration of cyanide ions in a sample, wherein the electrochemical test method involves oxidation of the silver from Ag (0) to Ag(l) on the electrode in the sample.
  • the electrode in the use, the electrode may be the working electrode described in the method; and the silver in the use is the substance in the first oxidation state, which in the use is 0.
  • the electrochemical test method may be the voltammetry or chronoamperometry experiment described herein.
  • the sweat sample in the use of the third or fourth aspect may be the sample of interest in the method. Determining the concentration of chloride ions in a sweat sample may be as described for the method using the determined relationship described herein. Determining the concentration of cyanide ions in a sample may be as described for the method using the determined relationship described herein, and in an analogous manner to that exemplified for chloride ions.
  • the sample may comprise a liquid, e.g. water
  • the sample in the fourth aspect may, for example, be selected from sea water, river water, drinking water, waste water and effluent.
  • the sample in the third and fourth aspects may be a biological sample, which may be selected from a sweat sample, a blood sample, saliva and a urine sample.
  • the present inventors use silver nanoparticle modified screen printed electrodes to detect chloride levels in sweat, artificial sweat and in other liquids demonstrating the possibility of using the method for a cystic fibrosis screening system.
  • the basis of such a procedure is depicted in Figure 1 ; layers of silver nanoparticles are deposited onto the working electrode of a screen printed electrode or glassy carbon electrode and anodically stripped off to generate silver cations.
  • the anodic stripping voltammetry of silver nanoparticles yields a single silver oxidation peak.
  • the favourable conditions of formation of silver chloride causes two stripping peaks to be voltammetrically recorded, one for formation of silver chloride and another for the oxidation of silver to silver ions.
  • the silver chloride peak may be used for the quantitative determination of chloride concentration in the target sample.
  • Silver nanoparticles are chosen for the experiments as they provide a facile method for producing a finite surface coverage on carbon electrodes which is needed to give the peaked responses. The usage of silver nanoparticles further ensures that the signal for the formation of silver chloride from silver is not dominated by the signal for silver oxidation to silver cations.
  • TM ' 22 In the following sections, chloride ion quantification is performed using a silver nanoparticle modified screen printed electrode.
  • Sodium nitrate >99.5%, NaN0 3
  • Trisodium citrate >99%, Na 3 C 6 H 5 0 7
  • BDH Laboratory Supplies Poole, UK.
  • Potassium chloride >99.5%, KCI
  • silver nitrate >99%, AgN0 3
  • urea >99%, CH 4 N 2 0
  • lactic acid solution in water, >85%, C 3 H 6 0 3
  • nitric acid 7.0%, HN0 3
  • hexaamineruthenium(lll) chloride 98%, Ru(NH 3 ) 6 CI 3
  • sodium chloride >99%, NaCI
  • Synthetic sweat sample 1 was obtained from Synthetic Urine e.k., Eberdingen, Germany (DIN 53160-2). The solid given was dissolved in water. The solution was tuned to the required pH of 6.5 ⁇ 0.1 with the given ammonia hydroxide solution and 0.1 M nitric acid. The final volume was ensured to be 100 ml_. Synthetic sweat sample 1 had a sodium chloride concentration of 5 g/L, which equates to 85.5 mM of chloride ions in the sample. Synthetic sweat sample 2 was prepared following British Standard (BS EN 1811-1999). However, a reduced sodium chloride concentration (10% of original value) was used.
  • Silver nanoparticles capped with citrate were synthesised based on a method devised by Lee and Miesel. 22
  • 25 mL of silver nitrate (0.1 M) solution was added to a flask containing 25 mL of ultrapure water.
  • the solution mixture was heated in an 110°C oil bath with violent magnetic stirring.
  • 1 g of trisodium citrate was dissolved in 100 mL ultrapure water.
  • 5 mL of the trisodium citrate solution was added into the boiling silver nitrate solution.
  • the solution was left to boil for an hour before it was cooled in a cold water bath.
  • the resulting solution of silver nanoparticle obtained was washed with ultrapure water twice and the supernatant was removed each time.
  • Figure 3 illustrates scanning electron microscopy image for silver nanoparticles.
  • the washed silver nanoparticle suspension was characterised by UV-vis spectroscopy (U-2001 , Hitachi, Mannheim, Germany).
  • UV-vis spectroscopy U-2001 , Hitachi, Mannheim, Germany
  • the washed nanoparticle suspension was diluted by a factor of 30 with ultrapure water.
  • Both tungsten iodide and deuterium light source were used to run a wavelength scan from 600 nm to 250 nm with a scan rate of 400 nm min "1 .
  • a broad surface plasmon peak at 419 nm was observed and indicated the presence of silver nanoparticles.
  • Nanoparticle tracking analysis (LM 10, NanoSight Ltd, Wiltshire, UK) were performed to size the silver nanoparticles in solution-phase.
  • Figure 2 shows the nanoparticle tracking analysis for the sample.
  • the mean diameter of the nanoparticles was 35 nm.
  • Scanning electron microscopy (LEO Gemini 1530, Zeiss, Oberkochen, Germany) was used to confirm that the synthesized nanoparticles were about 40 nm in diameter, see Figure 3.
  • the redox peaks were found to differ by +0.45 V compared to an experiment with a standard calomel electrode (SCE, +0.24 V vs NHE).
  • SCE standard calomel electrode
  • the Ag/Ag(10 mM) & NaN0 3 (90 mM) reference had a potential of +0.69 V vs NHE.
  • the reference electrode consists of a silver wire submerged in a solution of 10 mM silver nitrate and 90 mM sodium nitrate. The silver nitrate/sodium nitrate solution was changed regularly to maintain electrode stability. A platinum mesh functioned as the counter electrode. All experiments were generally performed under a nitrogen atmosphere and all solutions were degassed thoroughly with nitrogen. Screen printed electrodes were manufactured by Dropsens, S.
  • Nanoparticle modification of the glassy carbon electrode involved drop casting of 3 ⁇ _ of washed silver nanoparticle sample onto the electrode surface and drying the electrode in an oven at 50°C for 10 minutes. Five coatings of silver nanoparticles were applied to the glassy carbon electrode. Screen printed electrodes were modified in a similar manner with 5.3 ⁇ _ of washed silver nanoparticle sample to compensate for the difference in working electrode area. Each coat was dried for 12 minutes in a 50°C oven. Three repeats were done for each experiment performed.
  • section (i) the experiments performed on glassy carbon electrodes are summarised. Silver nanoparticles were coated onto the glassy carbon electrode and anodic stripping voltammetry were undertaken in sodium nitrate solutions spiked with different concentration of potassium chloride. A linear correlation of the voltammetric peak height and chloride ion concentration is found. In section (ii), experiments similar to the first section were performed on screen printed electrodes and similar correlation between peak height and chloride ion concentration was observed. In section (iii), repeat measurements and calculations of the sweat chloride levels for two synthetic sweat samples using the calibration plot obtained from the linear correlation of peak height and chloride ion concentration obtained from section (ii).
  • Figure 4 illustrates the oxidative stripping of silver nanoparticles from a glassy carbon electrode in 0.1 M sodium nitrate spiked with different amount of potassium chloride (KCI) at a scan rate of 0.05 V s ' Grey dashed line: No KCI; Black solid line: 2mM KCI; Black dashed Line: 8mM KCI; Black dotted line: 16mM KCI; Grey solid line: 32mM KCI.
  • Counter electrode Platinum mesh;
  • Inlay Calibration plot of peak height of peak A against the concentration of chloride ions. Each data point consists of a minimum of 3 repeats.
  • Sweat chloride levels are crucial to the diagnosis of cystic fibrosis.
  • a set of experiments in an electrochemical cell with a silver nanoparticle modified glassy carbon electrode was performed to determine if chloride detection is possible in an electrochemical system.
  • the anodic stripping of silver nanoparticles was performed in a 0.1 M sodium nitrate solution with varied chloride ions concentration to observe silver nanoparticles' behaviour in the presence and absence of chloride ions.
  • Silver nanoparticles were drop cast onto a glassy carbon electrode through five coatings of 3.0 ⁇ _ of washed silver nanoparticle aliquot. Each of the coatings was dried in an oven at 50°C for 10 minutes.
  • the modified electrodes were used in cyclic voltammetric experiment, which started at -0.7 V, swept towards +0.4 V before returning back to -0.7 V in a cell filled with 0.1 M sodium nitrate and varying concentration of potassium chloride (2 mM - 40 rtiM). For every new scan, the electrodes were polished to a mirror finish before silver nanoparticles were drop cast on. Each experiment was repeated for three times.
  • Sodium nitrate was chosen as the electrolye as the nitrate ion is a weakly co-ordinating anion. Hence, it does not affect the peak positions as it does not form a strong ionic pair or precipitate with the silver ions.
  • the nitrate ion is also not expected to alter the diffusion coefficient of silver ion or the rate constant of silver oxidation.
  • the formal potential of the redox couple of Ag/AgCI (equation (2)) corrected for the concentration of chloride ions at 20 mM is +0.32 V vs NHE.
  • formal potential of Ag/Ag + redox couple (equation (1)) is +0.80 V vs NHE
  • peak A and B should have a theoretical potential difference of -0.48 V; which is close to the experimentally measured difference of 0.45 V. 2 - 4
  • peak A increases in height, the height of peak B decreases. This indicates that the process at peak A has consumed some of the silver nanoparticles attached to the working electrode, causing less charge to be passed under peak B.
  • the linear range of the glassy carbon electrode system is between 2 mM and 40 mM of potassium chloride in the system.
  • Figure 5 illustrates the oxidative stripping of silver nanoparticles from a screen printed electrode in 0.1 M sodium nitrate spiked with different amount of potassium chloride at a scan rate of 0.05 V s '
  • the peak height of peak A (see Figure 4) is plotted against concentration of chloride. Each data point consists of a minimum of 3 repeats.
  • the disposable screen printed electrode has a 4.0 mm diameter carbon working electrode, a silver pseudo reference electrode and a carbon counter electrode.
  • each coat was changed from 3.0 ⁇ _ to 5.3 ⁇ _ of washed silver nanoparticle suspension.
  • the five coatings of silver nanoparticles were dried in a 50°C oven for 12 minutes each.
  • 50 ⁇ _ of analyte solution was used to cover the entire screen printed electrode.
  • the analyte consisted of 0.1 M sodium nitrate and varying concentrations of potassium chloride from 2 mM to 40 mM. Each experiment was repeated for three times. The same trend for peak A and peak B was observed for the measurements done on the screen printed electrodes. The voltammetric signal height of peak A forms a direct linear correlation with concentration of chloride for up to 40 mM and the calibration graph has been plotted in Figure 5.
  • Figure 6 shows the oxidative stripping of silver nanoparticles from a screen printed electrode in 0.1 M sodium nitrate with different synthetic sweat samples (diluted by a factor of 4) at a scan rate of 0.05 V s '
  • Black solid line Synthetic sweat sample 1 ;
  • Black dash line Synthetic sweat sample 2.
  • Star Diluted synthetic sweat sample 2.
  • Each data point consists of three repeats.
  • Table 1 gives a summary of the expected chloride concentration and the measured chloride concentration of various synthetic sweat samples.
  • Synthetic sweat sample 1 was prepared in accordance to the German industrial standard (DIN-53160- 2).
  • Synthetic sweat sample 2 was prepared from a recipe from the British Standard (BS EN 181 1-1999) but the amount of sodium chloride used was 10% of its original value. This is because the original chloride amount was beyond the 160 mM recommended by authorities and beyond the sensing range of 2 mM to 40 mM.— ⁇ — ⁇ — Each sweat sample was diluted with sodium nitrate solution by a factor of four with final concentration of chloride ion being a quarter of the original and concentration of sodium nitrate being 0.1 M.
  • the dilution of sweat sample by a factor of four ensures that the sensing range of 2 mM to 40 mM of chloride ions complies with the recommended range of 10mM to 160 mM of chloride ions.
  • Dilution with sodium nitrate solution also brings about advantages of lowering the amount of sweat sample required to 12.5 ⁇ _ and providing the electrochemical system the essential supporting electrolyte.
  • 50 ⁇ _ of the diluted synthetic sweat sample is dropped onto the silver nanoparticles modified screen printed electrode. Cyclic voltammogram was recorded from -0.2 V to +0.8 V before sweeping back to -0.2 V. Each experiment was repeated for three times.
  • Figure 6 shows the voltammograms recorded from the synthetic sweat samples.
  • the measured concentration of chloride ion in the diluted sweat samples was calculated.
  • the experimentally measured value was 18.9 ⁇ 1.3 mM and 3.9 ⁇ 0.6 mM for diluted synthetic sweat samples 1 and 2 respectively.
  • the expected chloride ion concentrations for diluted synthetic sweat samples 1 and 2 are 21.4 mM and 4.6 mM respectively.
  • Table 1 summarises the values of the expected and measured chloride ion concentration.
  • the inlay in Figure 6 also displayed the synthetic sweat samples at the expected chloride concentration. As seen in Figure 6 inlay and Table 1 , the synthetic sweat samples had a slightly lower measured concentration compared to the expected chloride ion concentration.
  • cystic fibrosis is an important and common disease which can be diagnosed with sweat chloride levels.
  • the present inventors have shown the sensitivity of oxidised silver nanoparticles towards chloride ions in anodic stripping experiments, the chloride content can be qualified from the analysis of voltammetry peaks. The experiments involving synthetic sweat samples indicated that sweat chloride content determination is possible on a screen printed electrode.

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Abstract

La présente invention concerne un procédé de détermination de la concentration d'un anion choisi parmi un ion halogénure et un ion pseudohalogénure dans un échantillon d'intérêt, le procédé impliquant : la fourniture d'une électrode de travail possédant une substance dans un premier état d'oxydation sur une surface de celle-ci, l'électrode étant en contact avec l'échantillon d'intérêt qui contient l'anion ; l'exécution d'une expérience de voltamétrie ou de chronoampérométrie qui implique une augmentation du potentiel appliqué à l'électrode de travail à un premier potentiel pour oxyder la substance à un second état d'oxydation, caractérisé en ce que, au premier potentiel, la réponse électrochimique de la substance est différente lorsque l'anion est présent dans l'échantillon par comparaison avec lorsque l'anion est absent de l'échantillon, et l'obtention d'informations électrochimiques pendant l'expérience de voltamétrie ou de chronoampérométrie ; l'utilisation d'une relation déterminée entre les informations électrochimiques et la concentration de l'anion dans un échantillon de référence pour calculer la concentration de l'anion dans l'échantillon d'intérêt. L'invention concerne également un appareil pour effectuer le procédé et l'utilisation d'une électrode comportant de l'argent sur sa surface.
PCT/GB2014/051530 2013-05-20 2014-05-19 Détermination électrochimique de la concentration d'un halogénure ou d'un pseudohalogénure Ceased WO2014188166A1 (fr)

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Cited By (10)

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Publication number Priority date Publication date Assignee Title
ES2725248A1 (es) * 2018-03-20 2019-09-20 Univ Burgos Sensor de deteccion de ion cloruro en muestras liquidas y procedimiento para la determinacion del mismo
WO2020054018A1 (fr) * 2018-09-13 2020-03-19 株式会社 東芝 Procédé d'évaluation de la perméabilité aux anions d'un film contenant du graphène et élément de conversion photoélectrique
JPWO2020054018A1 (ja) * 2018-09-13 2020-12-17 株式会社東芝 グラフェン含有膜の陰イオン透過性評価方法および光電変換素子
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JP7022200B2 (ja) 2018-09-13 2022-02-17 株式会社東芝 グラフェン含有膜の陰イオン透過性評価方法および光電変換素子
US11682740B2 (en) 2018-09-13 2023-06-20 Kabushiki Kaisha Toshiba Evaluation method on anion permeability of graphene-containing membrane and photoelectric conversion device
CN111781254A (zh) * 2020-07-06 2020-10-16 安徽大学 一种区分卤素阴离子F-、Br-的方法
CN112858429A (zh) * 2021-03-18 2021-05-28 上海健康医学院 用于检测氯离子的电化学传感器电极及其制备方法和应用
CN112858429B (zh) * 2021-03-18 2023-01-17 上海健康医学院 用于检测氯离子的电化学传感器电极及其制备方法和应用
WO2023018422A1 (fr) * 2021-08-13 2023-02-16 Oceanit Laboratories, Inc. Matériaux de construction ayant des propriétés modifiées d'atténuation du son et procédés associés

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