Electrochemical analysis of trace metal impurities

Abstract

Electrochemical systems, devices, and methods for quantitative analysis of the concentration of a target analyte ionic species (e.g., arsenic (III) or arsenic (V), lead, cadmium, or copper) in a liquid sample. The system provides a convenient, reliable and accurate target analyte concentration determination method using voltammetry analysis as an analysis technology. An electrochemical instrument and sensor including a working electrode, a reference electrode, and a counter electrode are configured to perform anodic stripping voltammetry (ASV) and determine a target analyte within a large concentration range. The system provides an apparatus and method for normalizing the resulting peak current using the initial plating / pre-enrichment current by applying at least one arithmetical operation to the peak current, the arithmetical operation comprising dividing the peak current by the sum of charges or currents measured during electrodeposition.

Description

Field of the Invention

[0001] The present invention relates to an electrochemical method and apparatus for analyzing a target analyte in a liquid sample, and in particular, but not exclusively, to an electrochemical analysis system for quantitatively determining the concentration of an electrochemically active substance in an aqueous sample. Background Art

[0002] Anodic stripping voltammetry (ASV) and potentiometric stripping analysis (PSA) are widely used for the analysis of trace metals in aqueous samples. ASV typically involves the electrodeposition of the target metal analyte onto a working electrode; this initial stage is known as plating or preconcentration. The deposited metal is then anodically reoxidized (stripped). The resulting Faradaic current is then analyzed as a function of voltage as part of the ASV process.

[0003] Typically, an electrochemical analysis system includes a potentiostat, which produces the desired plating and stripping potential patterns for electrodes immersed in a sample solution containing the target analyte. The potentiostat also measures the current generated by the oxidation of the analyte. The potential-current relationship generated by the potentiostat is then used to determine the analyte concentration. WO 00 / 67011 A1 discloses an electroanalytical potentiostat capable of performing voltammetric analysis.

[0004] US 2006 / 0011474 A1 describes a device for detecting an analyte in a liquid sample. The device comprises a sensor having a plurality of mutually insulated electrodes and a working electrode. The insulated electrodes are located on a non-conductive plate and are immersible in the liquid sample. The working electrode includes an analyte-specific coating. An electrical conductor electrically connects the sensor to a potentiostat.

[0005] Arsenic is a highly toxic substance, especially in its inorganic form, and long-term exposure can cause serious health conditions. Arsenic occurs naturally throughout the world, with contaminated groundwater posing the greatest risk to human health. The current limit for arsenic in drinking water is 10 ppb, as recommended by the World Health Organization (WHO). Despite this, many people around the world only have access to water with arsenic concentrations many times higher than 10 ppb. Consequently, a variety of methods exist for quantifying arsenic in drinking water, varying in speed, accuracy, cost, and portability. Common approaches include:

[0006] Standard Method 3500-As B Silver Diethyldithiocarbamate

[0007] Electrothermal atomic absorption spectrometry

[0008] Hydride generation atomic absorption spectrometry

[0009] Inductively coupled plasma (ICP) optical emission spectroscopy

[0010] Inductively coupled plasma mass spectrometry

[0011] In Method 3500-As B, As(III) (arsenite) is selectively reduced to arsenic gas (AsH3) by sodium borohydride, where the pH of the sodium borohydride solution is 6. The arsenic gas is then carried away from the reduction vessel by a stream of oxygen-free nitrogen and reacts with silver diethyldithiocarbamate. It then exhibits a red color that can be measured at a wavelength of 520 nm. As(V) (arsenate) can be reduced in a similar manner, but the sample must first have its pH lowered to 1 by adding HCl. Since As(III) will also react under these conditions, it must be removed beforehand, otherwise the latter's reaction will generate total inorganic arsenic. Therefore, this method requires the use of cumbersome equipment and produces highly toxic arsenic gas.

[0012] Compton et al. demonstrated that a glassy carbon electrode modified with AuNPs can detect As(III) using ASV (Anal. Chem. 2004, 76, 19, 5924-5929). Silver electrodes can also be used to detect As(III) (Simm, A., Banks, C. and Compton, R. (2005), The Electrochemical Detection of Arsenic(III) at a SilverElectrode, Electroanalysis, 17: 1727-1733).

[0013] US2020 / 0319131 A1 describes a method for detecting As(III) in water samples. A colloidal solution of AuNPs is deposited onto a carbon electrode, and As(III) is measured using ASV with a limit of quantification (LOQ) of 0.075 ppb.

[0014] However, existing electrochemical methods suffer from a number of shortcomings in terms of ease of use, portability, and the ability to reliably and reproducibly measure target analytes over a wide concentration range. Summary of the Invention

[0015] It is an object of the present invention to provide an electrochemical device and method for conveniently, reliably and reproducibly measuring a wide range of target analyte concentrations in a liquid sample, preferably an aqueous sample. Another specific object of the present invention is to provide an electrochemical device and method for quantitatively analyzing and determining the concentrations of a range of target analytes, including in particular arsenic, lead, cadmium and copper. Another specific object of the present invention is to provide an electrochemical analysis system that is portable and capable of performing analyte concentration analysis over a wide range of analyte concentrations. Another object of the present invention is to provide an electrochemical analysis system that can be configured for use with electrochemical stripping voltammetry for determining the concentration of a target analyte in a sample liquid with high accuracy.

[0016] The objects of the present invention are achieved by an apparatus and method for analyzing metal analytes in a liquid sample using electrochemical stripping voltammetry, wherein the peak current obtained during oxidation of the target analyte is normalized by current data obtained during initial electroplating of the target analyte with the working electrode. Thus, a highly sensitive electrochemical analysis system with improved accuracy in determining the concentration of the target analyte is provided relative to the prior art. The apparatus and method of the present invention are particularly suitable for analyzing target metal analytes comprising any of arsenic, lead, cadmium, and copper.

[0017] According to a first aspect of the present invention, an electrochemical method for analyzing an analyte in a liquid sample is provided, comprising: performing electrochemical stripping voltammetry on the liquid sample using a potentiostat and a cell having a working electrode, a reference electrode, and a counter electrode, comprising subjecting the analyte to electrodeposition and subsequent oxidation at the working electrode, and measuring the current to determine a peak current of the analyte during oxidation of the analyte; measuring the charge or current at the working electrode during electrodeposition of the analyte at the working electrode; and normalizing the peak current determined during oxidation of the analyte by applying at least one mathematical operation to the peak current, comprising dividing the peak current by the charge or current measured during electrodeposition.

[0018] Optionally, the step of performing electrochemical stripping voltammetry includes applying a plating potential to a working electrode and obtaining plating current data measured at the working electrode during the application of the plating potential. Optionally, the method includes storing the plating current data in a data storage utility. Optionally, the method includes applying a stripping potential to the working electrode and obtaining stripping current data measured at the working electrode during the application of the stripping potential. Optionally, the method includes storing the stripping current data in a data storage utility.

[0019] Optionally, the step of applying a mathematical operation comprises dividing the peak current of the analyte oxidation by the charge or current measured during electrodeposition.

[0020] Optionally, the analysis includes performing a quantitative concentration analysis of the analyte in the liquid sample by applying a mathematical function module to the normalized peak current to generate a normalized concentration of the analyte in the sample. Optionally, the mathematical function module is generated by mathematically fitting known analyte concentration data to corresponding reference peak current data measured using electrochemical stripping voltammetry during a temperature-concentration-current calibration process.

[0021] Optionally, the peak current reference data can be normalized, comprising the steps of measuring the charge or current at the working electrode during electrodeposition of the analyte at the working electrode, and normalizing the peak current by dividing the peak current determined during oxidation of the analyte by the charge or current measured during electrodeposition.

[0022] Optionally, prior to the step of performing electrochemical stripping voltammetry, metal cation interferants are removed from the sample, comprising contacting the sample with a cation exchange component. Optionally, the liquid sample is passed through a cation exchange unit or membrane. Preferably, the cation exchange component comprises a cation exchange column, and the sample contacting step comprises passing the sample through the cation exchange column and collecting the filtered sample.

[0023] Optionally, the method may further include measuring the temperature of the sample at least during oxidation of the analyte; and applying the measured temperature and peak current to a mathematical function module derived from a mathematical fit of reference peak current data, reference temperature data, and reference analyte concentration data measured and determined during electrochemical stripping voltammetry as part of a temperature-concentration-current calibration process to determine a temperature-calibrated concentration of the analyte in the sample. Optionally, the method may include measuring the temperature of the sample during plating and stripping and determining an average temperature.

[0024] Optionally, the temperature-concentration-current calibration process includes measuring the temperature of a reference sample simultaneously with measuring the charge, the reference sample containing a known concentration of the analyte.

[0025] Optionally, the analyte comprises a metal analyte. Optionally, the metal analyte comprises any one of arsenic, lead, cadmium and copper.

[0026] Optionally, the electrochemical stripping voltammetry includes adsorptive stripping voltammetry and any one of anodic voltammetry and cathodic voltammetry.

[0027] According to a second aspect of the present invention, there is provided a device for electrochemically analyzing an analyte in a sample, comprising: a sensor having a working electrode, a reference electrode, and a counter electrode configured to be at least partially immersed in an electrolyte solution containing the analyte; a potentiostat electrically connectable and configured to apply a potential to the working electrode; and a control utility having a normalization module for receiving charge or current data measured at the working electrode during electrodeposition of the analyte at the working electrode, receiving current data measured during oxidation of the analyte at the working electrode, and calculating a normalized peak current of oxidation of the analyte at the working electrode.

[0028] In this specification, applying a potential to the working electrode includes applying a potential difference between the working electrode and another electrode (eg, a counter electrode, an auxiliary electrode, and / or a reference electrode).

[0029] Optionally, the device further comprises an electrochemical potential module to generate and apply a potential to the working electrode. Optionally, the electrochemical potential module comprises a plating module to generate and apply a plating potential to the working electrode and deposit the analyte on the working electrode. Optionally, the electrochemical potential module comprises a stripping module to generate and apply a pulsed potential to the working electrode and oxidize the analyte at the working electrode.

[0030] Optionally, the apparatus further comprises a data acquisition module for receiving charge or current data during electrodeposition and oxidation of the analyte at the working electrode.

[0031] Optionally, the normalization module is configured to perform a mathematical operation on the peak current data obtained during oxidation of the analyte at the working electrode, the mathematical operation comprising dividing the peak current data by the charge or current data obtained during electrodeposition of the analyte at the working electrode to produce the normalized peak current of oxidation of the analyte at the working electrode.

[0032] Optionally, the device further comprises a mathematical function module configured to process the normalized peak current data and calculate the analyte concentration. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Specific embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0035] Figure 1 is a schematic diagram of the physical and electronic architecture of an electrochemical system configured for voltammetric analysis of a target analyte in an aqueous sample, according to an embodiment of the present inventive concepts;

[0036] Figure 2 yes Figure 1 Schematic diagram of the control utility portion and database forming part of the potentiostat of the electrochemical system;

[0037] Figure 3 is a plan view of an electrochemical sensor according to a specific embodiment, the sensor including a working electrode, a reference electrode, and a counter electrode;

[0038] Figure 4 is a flow chart detailing various operational steps as part of an electrochemical concentration analysis of a target analyte within an aqueous sample;

[0039] Figure 5 is a schematic diagram of potential characteristics as part of differential pulse voltammetry (DPV) to oxidize a target metal analyte at a working electrode;

[0040] Figure 6 is a graph of the current response during initial electroplating of the working electrode with As(III);

[0041] Figure 7 is a graph of the current response during the oxidation or stripping phase, where As(0) is oxidized at the working electrode;

[0042] Figure 8 is a graph showing the relationship between differential current and potential for a series of relatively low concentrations of As(III) at 20°C;

[0043] Figure 9 yes Figure 8 The relationship between the peak current and the As(III) concentration at 20℃ is shown in the graph;

[0044] Figure 10 is a graph showing the relationship between differential current and potential for a series of relatively high concentrations of As(III) at 20°C;

[0045] Figure 11 yes Figure 10 The relationship between the peak current and the As(III) concentration at 20℃ is shown in the graph;

[0046] Figure 12 is a graph of the relationship between the differential current and the potential of total arsenic measured during differential pulse voltammetry (DPV) at 20 ppb at three different temperatures;

[0047] Figure 13 It is a 3D calibration curve of peak current, temperature and arsenic concentration, suitable for temperature calibration / compensation of electrochemical concentration analysis of target analytes;

[0048] Figure 14 is a diagram illustrating the effect of cation exchange pretreatment of an aqueous sample containing target analytes prior to DPV;

[0049] Figure 15 is a schematic diagram of the stripping voltammetry stage for concentration determination analysis of As(III) and total As (III plus V) according to a specific embodiment of the present invention. DETAILED DESCRIPTION

[0050] The electrochemical system of the present invention includes an apparatus and method for conveniently, reliably and accurately measuring the concentration of a target analyte over a wide concentration range. Figure 1 , the electrochemical device 10 generally includes an electrochemical instrument 11 and an electrically connectable sensor 19. The instrument 11 includes a central processor 12 for performing calculations and firmware-driven operations; a potentiostat 13 for performing electrochemical tests, particularly anodic stripping voltammetry (ASV) tests, in which a desired potential is maintained between a working electrode and a reference electrode; a user interface 14; a sample container 15 for placing and testing test samples; a data storage 16 for storing test data and other data; and a database 17 including sensor calibration information loaded for obtaining accurate sensor responses.

[0051] like Figure 3 As shown, the electrochemical sensor 19 includes a screen-printed carbon working electrode 20, which is equipped with appropriate reagents for the specific electrochemical test; a screen-printed silver electrode 21 for maintaining a stable reference potential; and a screen-printed counter electrode 22 for providing a current path between itself and the working electrode 20 and ensuring that no significant current flows through the reference electrode 21.

[0052] Figure 2 Schematically illustrated is selected firmware 23 for the potentiostat 13, which includes a control utility 24 comprising an electrochemical potential module 25 (which has an electroplating module 26 and a dissolution module 27); a data acquisition module 28; a mathematical function module 29; and a normalization module 30. Specifically, the database 17 includes a concentration-current reference library 32 comprising data and coefficients derived / generated from a mathematical function that relates a range of target analyte concentrations to observed dissolution peak currents generated by the ASV.

[0053] Reference Figure 3Sensor 19 includes an electrically inert plastic substrate 31 having a thickness of approximately 500 μm. Sensor 19 also includes a carbon electrical contact 33 positioned toward a first end 37 of the generally elongated sensor 19 to provide an electrical connection to potentiostat 13. An insulating layer 34 covers a conductive track 35 to enable immersion of sensor 19 in a liquid sample. Track 35 comprises silver or a silver-based material to provide a low-resistance current path connecting electrical contact 33 to an electrode array disposed at a second end 36 of sensor 19. Specifically, sensor 19 includes a carbon counter electrode 22 to allow current to pass between itself and working electrode 20 while ensuring that substantially no current flows into reference electrode 21. Reference electrode 21 comprises silver or a silver-based material to provide a stable electrical potential for application of the other potential. Working electrode 20 comprises carbon reinforced / coated with gold nanoparticles. Working electrode 20 provides a working / functional electrode at which reduction and subsequent oxidation of the target metal analyte occurs to provide a resultant electrochemical current that is measured and analyzed to determine the concentration of the target species in the liquid sample.

[0054] Example 1

[0055] Anodic stripping voltammetry (ASV) was used in combination with a gold nanoparticle (AuNP) modified screen printed carbon electrode (SPCE) 20. The potentiostat 13 was a Kemio TM (Palintest Ltd.) The sensor 19 was fabricated by drop-casting a solution of citrate-coated AuNPs (average diameter approximately 10 nm) onto the working electrode 20, followed by drying in an oven.

[0056] To perform anodic stripping voltammetry (ASV), a potential is first applied between a working electrode (WE) 20 and a reference electrode (RE) 21 to reduce As(III) to As(0), thereby depositing elemental arsenic onto the AuNPs at the WE 20. This provides initial plating or pre-concentration, with different plating times allowing for different sensitivity levels. After a predetermined period of time, DPV is used to oxidize the elemental arsenic (previously plated onto the gold-coated working electrode 20 during the pre-concentration stage). After oxidation, the arsenic redissolves, enabling measurement with high sensitivity.

[0057] Reference Figure 4 In an initial stage 38, the potentiostat 13 maintains a constant potential difference between the working electrode 20 and the reference electrode 21 for a predetermined time. In stage 39, the current flowing between the working electrode 20 and the counter electrode 22 is measured. In stage 40, the currents are summed over a specified time, and the total current is recorded and stored in the data memory 16 at the instrument 11.

[0058] Then, in stage 41, DPV is performed by the potentiostat 13, wherein the potential difference between the working electrode 20 and the reference electrode 21 is varied in a controlled manner, e.g. Figure 5 As shown. Specifically, a starting potential 45 is applied, which has typical parameters (scan rate, pulse amplitude, step size, starting potential, ending potential, pulse width). Specifically and for the sake of completeness, a pulse amplitude 46 is introduced, the pulse width 47 is maintained for a predetermined time, and then the amplitude is reduced and maintained for a period of time (period) 48. Then, the amplitude is increased again 49 and maintained for a predetermined pulse width 50, and then the amplitude is reduced again and maintained for a predetermined step size 51. It should be noted that Figure 5 The values ​​(50mV, 5ms) are "typical" for this technology, but are not necessarily the values ​​used.

[0059] Reference again Figure 4 At stage 42, the instrument 11 records the differential current and stores it as a data array in the memory / data storage 16. At stage 43, the data set is baseline corrected and the associated peak current value is obtained and stored in the data storage 16. According to a final normalization stage 44, the peak current value obtained at stage 43 is divided by the plating current measured at stage 40, and the resulting normalized value is stored in the instrument memory / data storage 16.

[0060] Figure 6 and 7 The current responses during the plating and stripping stages are illustrated respectively, where the potential is expressed relative to the silver reference electrode 21 .

[0061] Reference Figure 15 The procedure used to measure total arsenic (the sum of As(III) and As(V)) was similar to that used in the reference Figure 4 The procedure is similar to that described above, but there are two differences: the applied potential and the solution pH. Since As(III) can be electrochemically reduced to As(0) on the AuNP surface, As(V) must first be reduced to As(III) and then further reduced to As(0). This is achieved by utilizing a significantly higher reduction potential (about -1.2V relative to Ag RE) and a lower solution pH (typically about 1). This creates conditions on the surface of WE 20 that allow As(V) to be reduced to As(III) and then electrochemically reduced to As(0). Since As(III) can also be electrochemically reduced under these conditions, this test is used to measure the total arsenic concentration. The concentration of As(III) is subtracted from the total arsenic concentration to calculate the concentration of As(V).

[0062] In order to handle the arsenic concentration range (about 2-125ppb), the proposed method adopts a dual plating / stripping method. Initially, a relatively short plating time of about 30 seconds is performed by applying an appropriate potential between the working electrode 20 and the reference electrode 21. Then DPV is performed and the stripping current is recorded. Using this value, the instrument 11 (through firmware and reference library 17) determines whether the test sample belongs to the "high" concentration range or the "low" concentration range. For the former, the current value returns the concentration through an appropriate calibration curve. For the latter, another plating step is performed at the same potential as before, but for a longer time of about 300 seconds. After this second plating step, another stripping step is performed, and the concentration is subsequently calculated by an appropriate calibration curve. Based on predetermined calibration information, the "high" and "low" ranges are determined by comparing the initial stripping current with a threshold value. According to further embodiments and for simplicity, regardless of the first result, two plating steps (short and long) can be performed.

[0063] Specifically, refer to Figure 15 To calculate the concentration of As(III), in stage 56, the aqueous sample is passed through an ion exchange column (if necessary to remove interfering substances or other metal ions). In stage 57, a suitable supporting electrolyte and buffer of appropriate pH are added to the sample. In stage 58, a potential is applied to reduce the As(III) at the coated working electrode 20 for a relatively short time. In stage 59, differential pulse voltammetry is performed, whereby As(O) is reoxidized back into solution. In stage 60, if the measured signal (current) is less than a predetermined value, stages 58 and 59 are repeated for a longer pre-enrichment / plating time. In stage 61, the As(III) concentration is calculated using an appropriate calibration curve.

[0064] To measure the total arsenic concentration (As(III)+As(V)), in stage 62, the aqueous sample is passed through an ion exchange column to remove interfering substances (as needed). In stage 63, a supporting electrolyte and a buffer of appropriate pH are added to the aqueous sample. In stage 64, a potential is applied at the gold-coated working electrode 20 to produce appropriate conditions for reducing As(V) to As(III) for a relatively short period of time. In stage 65, differential pulse voltammetry is performed, in which As(O) is reoxidized back into solution. In stage 66, if the observed current is less than a predetermined value, stages 64 and 65 are repeated for a longer plating / pre-concentration time. Then, in stage 67, the concentration of As(III)+As(V) is calculated from a calibration curve. In stage 68, the As(V) concentration is calculated as the difference between the concentrations obtained in stage 67 and stage 61 as a final stage 68.

[0065] Temperature compensation calibration

[0066] When performing ASV measurements with the mentioned sensors, a calibration curve needs to be drawn up in order to relate the actual arsenic concentration to the received signal. Figure 8 and Figure 9 The responses of typical sensors to increasing As(III) concentrations in the low arsenic range and the relationship between the measured DPV peak height and concentration are shown in FIG. Figure 10 and Figure 11 The data for the high arsenic range are shown in FIG.

[0067] Methods used to quantify analyte concentrations may be subject to temperature variations, i.e., different signal amplitudes are measured at different temperatures, which requires compensation. This can be achieved using lookup tables, etc. Electrochemical methods are similarly sensitive to temperature, which affects various factors such as diffusion coefficients and electrochemical rate constants. Figure 12 The effect of temperature on the sensor's response to a total arsenic concentration of 20 ppb is shown in Figure 2. It can be seen that the peak amplitude and peak position vary with temperature.

[0068] The device and method of the present invention is combined with the temperature measuring element on the sensor instrument at the sample container 15 and works with the three-dimensional calibration curve. TM (Palintest Ltd.)), a typical curve produced for this type of calibration is shown in detail in Figure 13 This calibration curve enables the sensor 19 to correctly correlate the current measured at different temperatures with the arsenic concentration. To generate this curve, systematic measurements are taken over a range of arsenic concentrations and solution temperatures, and numerical methods are used to fit the data to a mathematical function. The function's generation coefficients are then used to calculate the concentration from a given temperature and current, i.e., when the user is testing a sample with an unknown arsenic concentration. Separate calibration curves can be obtained for both As(III) and total arsenic concentrations.

[0069] Interference removal

[0070] Certain substances are known to interfere with the methods mentioned, such as Pb 2+ 、Cu 2+ 、Cd 2+ and Fe 2+ / Fe 3+. When the interferent in question is present at or sufficiently close to the dissolution potential of arsenic, positive interference occurs, giving an erroneously high reading because the signal cannot be deconvoluted. Arsenic does not normally form cationic species (Determination of arsenic species: A critical review of methods and applications, 2000-2003, Kevin A. Francesconi and Doris Kuehnelt), so interferents present as cations can be removed via ion exchange without reducing the concentration of the arsenic compound. Typically, a cation exchange resin is used, which comprises a cross-linked polymer with appropriate functional groups for chelation. Examples include Puromet MTS9300 and Puromet MTS9500 from Purolite, DIAION CR11 from Mitsubishi Chemical Corporation and Dionex from Thermo Scientific. TM OnGuard TM II M. Arsenic usually exists in the form of arsenide (AsIII) and arsenate (AsV), which are anions and therefore do not bind to cation exchange columns. Figure 14 The effect of ion exchange on the removal of cations is shown in FIG. The lowest dashed line 55 is just the blank solution, i.e., the supporting electrolyte and buffer. The solid line 53 shows the solution containing 2000 ppb Cu 2+ 、50ppb Pb 2+ and 20 ppb Cd 2+ 5. The upper dashed line 54 represents the same solution after treatment with a cation exchange column. Before treatment with the ion exchange material, there is a significant peak at approximately -180 mV. This is close enough to the expected peak position for arsenic (-100 mV) to cause an erroneous high reading. In addition, a larger feature is observed at the more positive potential, which continues to rise. After the addition of the ion exchange beads, this feature is greatly reduced, as shown by the dashed line 54.

[0071] Signal normalization

[0072] The proposed sensor comprises an AuNP-enhanced SPCE electrode 20 for detecting different forms of arsenic in water samples. The signal generated by the sensor is not only a function of the arsenic concentration and the solution temperature, but also a function of the AuNPs loaded onto the carbon substrate. As with any manufacturing process, there are small deviations between sensors manufactured using drip casting, resulting in different signal efficiencies. Sensors with a higher number of AuNPs return a higher signal on average, while the opposite is true for sensors with a lower number of AuNPs. To compensate for this, the present method utilizes signal normalization, whereby the signal obtained during the arsenic dissolution phase is divided by the signal obtained during the electroplating phase. When the sensor has a higher number of AuNPs, a higher-than-average electroplating current (at a given concentration and temperature) is observed. This additional signal is effectively used to cancel the additional signal generated during the dissolution phase. Tables 1 and 2 show the reduction in relative standard deviation (RSD) of two different sensor batches after signal normalization for total arsenic concentration.

[0073] Table 1:

[0074]

[0075]

[0076] Table 2:

[0077]

Claims

1. An electrochemical method for analyzing an analyte in a liquid sample, comprising: performing electrochemical stripping voltammetry on a liquid sample using a potentiostat and a cell having a working electrode, a reference electrode, and a counter electrode, comprising electrodepositing and subsequently oxidizing the analyte at the working electrode and measuring the current to determine a peak analyte current during oxidation of the analyte; measuring the charge or current at the working electrode during electrodeposition of the analyte at the working electrode; as well as The peak current is normalized by applying at least one mathematical operation to the peak current determined during oxidation of the analyte, including dividing the peak current by the charge or current measured during electrodeposition.

2. The method of claim 1, wherein the step of performing electrochemical stripping voltammetry comprises applying a plating potential to the working electrode and acquiring plating current data measured at the working electrode during the application of the plating potential.

3. The method of claim 2, further comprising storing the plating current data in a data storage utility.

4. The method of claim 2 or 3, comprising applying a stripping potential to the working electrode and acquiring stripping current data measured at the working electrode during the application of the stripping potential.

5. The method of claim 4, further comprising storing the stripping current data in a data storage utility.

6. A method as claimed in any preceding claim, wherein the step of applying the mathematical operation comprises dividing the peak current of the analyte oxidation by the charge or current measured during electrodeposition.

7. The method of any preceding claim, wherein the analyzing comprises performing a quantitative concentration analysis of the analyte in the sample by applying a mathematical function module to the normalized peak current to produce a normalized concentration of the analyte in the sample.

8. The method of claim 7, wherein the mathematical function module is generated from a mathematical fit of known analyte concentration data and corresponding reference peak current data measured using electrochemical stripping voltammetry during a concentration-current calibration process.

9. The method of claim 8, wherein the peak current reference data is normalized, comprising the steps of: During electrodeposition of the analyte at the working electrode, the charge or current at the working electrode is measured, and the peak current is normalized by dividing the peak current determined during oxidation of the analyte by the charge or current measured during electrodeposition.

10. The method of claim 1, wherein prior to performing the electrochemical stripping voltammetry step, removing metal cation interfering substances from the sample comprises contacting the sample with a cation exchange component.

11. The method of claim 10, wherein the cation exchange component comprises a cation exchange column, and the sample contacting step comprises passing the sample through the cation exchange column and collecting the filtered sample.

12. The method of any preceding claim, wherein the method further comprises: measuring a temperature of the sample at least during oxidation of the analyte; and The measured temperature and the peak current are applied to a mathematical function module derived from a mathematical fit of reference peak current data, reference temperature data, and reference analyte concentration data measured and determined during electrochemical stripping voltammetry as part of a temperature-concentration-current calibration process to determine a temperature-calibrated concentration of the analyte in the sample.

13. The method of claim 12, wherein the temperature-concentration-current calibration process comprises measuring the temperature of a reference sample simultaneously with measuring the charge, the reference sample containing a known concentration of the analyte.

14. The method of any preceding claim, wherein the analyte comprises a metal analyte, and optionally wherein the metal analyte comprises any one of arsenic, lead, cadmium and copper.

15. The method of any preceding claim, wherein the electrochemical stripping voltammetry comprises any one of anodic stripping voltammetry, cathodic stripping voltammetry, and adsorptive stripping voltammetry.

16. A device for electrochemical analysis of an analyte in a liquid sample, comprising: a sensor having a working electrode, a reference electrode, and a counter electrode configured to be at least partially immersed in an electrolyte solution containing an analyte; a potentiostat electrically connectable and configured to apply a potential to the working electrode; and A control utility having a normalization module for receiving charge or current data measured at the working electrode during electrodeposition of the analyte at the working electrode, receiving current data measured during oxidation of the analyte at the working electrode, and calculating a normalized peak current for oxidation of the analyte at the working electrode.

17. The apparatus of claim 16, further comprising an electrochemical potential module for generating and applying a potential difference between the working electrode and the reference electrode.

18. The apparatus of claim 17, wherein the electrochemical potential module comprises an electroplating module for generating and applying a potential difference between the working electrode and the reference electrode and depositing the analyte at the working electrode.

19. The apparatus of claims 17 and 18, wherein the electrochemical potential module comprises a stripping module for generating and applying a pulsed potential to the working electrode and oxidizing the analyte at the working electrode.

20. The apparatus of any one of claims 16 to 19, further comprising a data acquisition module for receiving charge or current data during electrodeposition and oxidation of the analyte at the working electrode.

21. An apparatus as described in any one of claims 16 to 20, wherein the normalization module is configured to perform a mathematical operation on the peak current data obtained during oxidation of the analyte at the working electrode, the mathematical operation comprising dividing the peak current data by the charge or current data obtained during electrodeposition of the analyte at the working electrode to produce the normalized peak current of oxidation of the analyte at the working electrode.

22. The apparatus of claim 21, further comprising a mathematical function module configured to process the normalized peak current data and generate an analyte concentration.

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