JP2007309802A - Solution analyzer and analysis method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To perform microanalysis (for example, measurement of a trace amount of metal ions) with high sensitivity and high accuracy of solution such as service water or environmental water, or solution or the like eluting from soil, food, waste or the like. <P>SOLUTION: A working electrode (copper electrode) 2, a counter electrode 3 and a reference electrode 4 are dipped into an analysis object 1a, and while keeping the potential of the working electrode 2 at a prescribed potential (potential keeping process), the potential of the working electrode 2 is swept in a differential pulse mode, to thereby elute a measuring object deposited by the working electrode 2 into the analysis object, and a current change to a voltage change of the working electrode 2 is detected (potential sweeping process). In the potential sweeping process, an electrolytic current is sampled on a sampling position (for example, within 23 ms) except a sufficient attenuation position (namely, on an insufficient attenuation position) wherein attenuation of a charge current is not sufficient. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a solution analyzer and a solution analysis method that can measure (qualitatively and quantitatively) analyze metal ions and the like by voltammetry comprising a working electrode, a counter electrode, and a reference electrode. Related to an apparatus and method capable of measuring and analyzing trace amounts (100 ppt level or more) of lead, cadmium, zinc, etc. contained in solutions such as environmental water and solutions eluted from soil, food, waste, etc. It is.

  Various unintended hazardous substances (for example, toxic metals) are present in solutions such as tap water and environmental water (for example, seawater, rivers, lakes, and groundwater), and solutions that elute from soil, food, waste, etc. It may have been included and has been raised in the past.

  For example, the review of drinking water quality guidelines by the World Health Organization (WHO), the revision of the water supply law by the Ministry of Health, Labor and Welfare (the revised water law has been enforced since April 1, 2004 Effective March 31, 2004), revision of the Soil Contamination Countermeasures Law (enforcement of the Soil Contamination Countermeasures Law from February 15, 2003) is underway.

  Examples of harmful metals include heavy metals such as mercury, zinc, cadmium, and lead, and it has been pointed out that they may affect the human body and the like as the amount increases. For these reasons, it has been pointed out that various substances existing in nature need to be measured (qualitative and quantitative), analyzed, and monitored.

  For example, atomic absorption is an official analytical method for analyzing heavy metals (measurement target) contained in solutions such as tap water and environmental water, and solutions eluted from soil, food, waste, etc. (analysis target) A method for measuring and analyzing a specific substance (measurement target) by an analysis method, an ICP emission analysis method, an ICP mass spectrometry method, or the like is known.

  Although this official analysis method can measure and analyze a very small amount of measurement object in the object to be analyzed (hereinafter referred to as microanalysis), the apparatus to be used is large (for example, in a form that cannot be easily transported by an operator) and Since it is expensive and requires technical skill and effort (such as requiring a long time) in operating the apparatus, it cannot be handled generally (easily). For this reason, compared with the official analysis method, application of a simple analysis method or the like in which an apparatus to be used is small and inexpensive and does not require complicated operations has been attempted.

  In recent years, paying attention to the fact that many of the harmful substances present in the solution have electrochemical activity, an attempt to analyze various harmful substances using electrochemical techniques, such as working electrodes (mercury electrodes, carbon-based electrodes) , Gold electrode, copper electrode, etc.), counter electrode, reference electrode, etc., an attempt has been made to analyze by an anodic (or cathodic) stripping voltammetry method (hereinafter referred to as voltammetry method). This voltammetry method is simpler than the above-mentioned official analysis method (for example, downsizing and cost reduction of the apparatus used), and can be used for trace analysis (for example, determination of trace metal ion concentration) in a short time. There is a possibility that it can be easily performed, and it is also advantageous for analysis of an analyte (for example, seawater) containing a large amount of electrolyte.

  For example, a mercury electrode (such as an electrode using a mercury drop) is used as a working electrode, an amalgam is formed at the mercury electrode and analyzed (an extremely low concentration analysis method; (for example, Non-Patent Document 1)), A method is known in which a copper electrode is used as a working electrode and an object to be measured is deposited (concentrated by reduction or the like) on the surface of the copper electrode (analysis method assuming a relatively low concentration (100 nM level)) (for example, Patent Document 1). In these voltammetry methods, for example, a potential of the working electrode is maintained at a predetermined potential and a measurement object is deposited on the working electrode (hereinafter referred to as a potential holding step), and then the potential of the working electrode is changed in one direction ( By sweeping in the positive or negative direction according to the measurement object, the measurement object deposited on the working electrode is eluted into the object to be analyzed, and the current change with respect to the potential change of the working electrode is detected (sampling) This step is performed (hereinafter referred to as potential sweep step).

  In the potential sweep step, since a charging current (charging current) is applied to the working electrode in addition to the electrolytic current, the differential pulse mode is applied to avoid the influence of the charging current (for example, the S / N ratio). The method of improving is used conventionally.

For example, in the case of differential pulse polarography using a mercury electrode as the working electrode, when the potential of the working electrode is swept in pulses, a charging current is applied in addition to the Faraday current. Since this charging current is sufficiently attenuated after a predetermined time has elapsed, the electrolytic current is sampled at a sampling position (hereinafter referred to as an attenuation sufficient position) after the sufficient attenuation. In general, when analysis of an analysis target of an extremely low concentration is assumed, for example, a mercury electrode is used, and a pulse width is set to 50 ms or more, for example, a sampling position of 40 ms to 50 ms (that is, each pulse period) The electrolysis current is sampled at a time from the leading edge (corresponding to 40 ms to 50 ms), and the current difference between I _f (Faraday current) and I _B (background current) (difference in electrolysis current sampled in each pulse period) ) A polarogram (current change characteristic with respect to potential change) based on ΔI is obtained (for example, Non-Patent Document 2). Since the peak current value of this polarogram changes according to the concentration of the measurement target, the characteristic line of each peak current value (hereinafter referred to as the peak current characteristic line) for various concentrations (concentration of the measurement target) has linearity. When it has, the peak current characteristic line can be applied as a calibration curve.

However, even when the above voltammetry method is used, for example, when a mercury electrode is used, the mercury electrode itself is a dangerous substance, and its handling method and environmental pollution (contamination due to elution or disposal etc. at a fixed time) Is concerned. Even when electrodes other than mercury electrodes (carbon electrodes such as copper electrodes and glassy carbon electrodes) are used, trace analysis with higher sensitivity and higher accuracy, for example, due to recent environmental issues, etc. There is a need for the emergence of analytical methods that can be used.
JP 2004-294422 A Daniel F. Tibbetts, James Davis, Richard G. Compton, “Sonoelectroanalytical detection of lead at a bare copper electrode” (Germany), Fresenius' Journal Analytical Chemistry, Springer-Verlag. 2000. 412-414. Suzuki Shigeaki and Yoshimori Takayoshi, “Electrolysis-Electrolytic Analysis / Voltammetry”, first edition, Kyoritsu Publishing Co., Ltd., July 20, 1987, p. 105-108.

  As described above, the apparatus and method are simplified (for example, downsizing and cost reduction of the apparatus to be used) compared to the official analysis method described above, and more sensitive and accurate microanalysis ( For example, trace metal ions can be easily measured (for example, it can be done in a short time without the need for cumbersome work like official analysis methods), and there is no need to consider the handling of hazardous materials or environmental pollution. The advent of instruments and analytical methods has been desired.

  The present invention is based on a voltammetry method in which a potential holding step and a potential sweep step are performed in order to solve the above-described problems, and a copper electrode is used as a working electrode, and the potential sweep step is performed in a new differential pulse mode. In this way, it is possible to measure a very low concentration measuring object in the object to be analyzed, and to analyze the object to be analyzed with higher sensitivity and higher accuracy.

  Specifically, the invention described in claim 1 is composed of at least a working electrode, a counter electrode (for example, a platinum electrode in the embodiments described later), a reference electrode (Ag / AgCl reference electrode), and includes a measurement object. Each of the above electrodes is placed in a subject to be analyzed (for example, a solution such as tap water or environmental water, or a solution eluted from soil, food, waste, etc.), and the potential of the working electrode is being analyzed. Can be held at a potential at which the measurement object can be deposited, and can be swept in a differential pulse mode in a direction in which the measurement object deposited by the held potential can be eluted, and a current change with respect to a potential change at the working electrode can be detected. In the solution analyzer capable of analyzing the analyte to be analyzed at the above level, the working electrode is a copper electrode.

  According to the second aspect of the present invention, after the working electrode, the counter electrode, and the reference electrode are arranged in the analysis target, the potential of the working electrode is maintained at a potential at which the measurement target in the analysis target can be deposited. Detects current change in response to potential change at the working electrode while sweeping the potential of the held working electrode in the differential pulse mode in the direction in which the measurement object deposited in the potential holding step can elute. And a potential sweeping step to analyze an object to be analyzed at a level of several hundreds of ppt or more, wherein the working electrode is a copper electrode.

  The invention described in claim 3 is characterized in that, in the invention described in claim 2, chloride ions are contained in the analyte.

  According to a fourth aspect of the present invention, in the third aspect of the present invention, before the potential to be measured can be deposited in the potential maintaining step, the potential is more positive than −100 mV (vs. Ag / AgCl). A potential application before potential deposition is performed on the working electrode.

  According to a fifth aspect of the present invention, in the fourth aspect of the invention, the potential of the pre-deposition potential application is more positive than ± 0 V (vs. Ag / AgCl).

  The invention according to claim 6 is the invention according to claims 2 to 5, characterized in that the object to be analyzed contains at least one of lead, cadmium, and zinc.

  The invention according to claim 7 is the invention according to claim 6, wherein at least lead is included in the object to be analyzed as an object to be measured, and within 23 ms after pulse application by the differential pulse mode in the potential holding step (that is, The electrolytic current is sampled at an attenuation insufficient position).

  The invention according to claim 8 is the invention according to claim 7, wherein when the object to be analyzed does not contain lead and the object to be measured is cadmium, lead is added to the object to be analyzed. It is characterized by that.

  In the first and second aspects of the invention, the working electrode is a copper electrode, and a measuring object of 100 ppt level or more can be measured by sweeping in a direction in which the measuring object deposited on the working electrode can be eluted. .

  In the third aspect of the invention, since the potential holding step is performed in the presence of chloride ions (for example, in an analysis target containing a potassium chloride solution), the chloride ions are specifically adsorbed on the copper electrode surface, that is, 1 Since valent copper chloride is formed, an alloy of the measurement object (lead, cadmium, zinc, etc.) and copper as an electrode is easily formed. Further, due to the specific adsorption of chloride ions, the reduction reaction of dissolved oxygen in the analyte is suppressed and the generation of hydrogen is suppressed, the potential window is widened, and the detection sensitivity is improved.

  In the invention according to claim 4, since the chloride ion in the analyte is easily adsorbed to the copper electrode surface during the potential holding step by applying the potential before deposition, the measurement object (lead, cadmium, zinc) Etc.) and copper as an electrode are more easily formed. In addition, since the reduction reaction of dissolved oxygen and the generation of hydrogen in the analysis target are further suppressed, the potential window (negative potential side potential window) becomes wider, and the detection sensitivity is further improved.

  In the invention according to claim 5, the working electrode surface itself is oxidized and eluted at the molecular level.

  According to the seventh aspect of the present invention, a peak current that increases with an increase in the concentration to be measured can be obtained under conditions where the sampling position in the potential sweep step is not sufficiently attenuated, and sufficiently good linearity is obtained in the peak current characteristic line. Is obtained.

  In the invention described in claim 8, when cadmium in an analyte to be analyzed that does not contain lead is measured, if lead is added (used as an additive) to the analyte, the background current can be attenuated and stabilized. (S / B ratio increases).

  According to the inventions described in claims 1 to 8, unlike analysis that requires a large, expensive, and complicated operation such as official analysis, etc. (this is a simplified analysis), It is an analysis that does not require consideration of environmental pollution and the like, and a highly sensitive and highly accurate microanalysis can be performed on an analysis target including a measurement target having an extremely low concentration (for example, several hundreds of ppt level or more).

  According to the invention described in claim 3, for example, even if the object to be analyzed includes a plurality of objects to be measured or a large amount of impurities, an alloy is selectively formed with copper as an electrode at the time of deposition. In addition, the measurement can be performed selectively while avoiding (at least suppressing) the interaction between the measurement objects, and higher sensitivity (in particular, detection sensitivity) and high-accuracy microanalysis can be performed with high reproducibility. In addition, since the potential window becomes wider, the range in which trace analysis can be performed becomes wider.

  Furthermore, according to the invention described in claim 4, it becomes easier to selectively measure a plurality of measurement objects in the analysis target, and a highly sensitive and highly accurate trace analysis can be performed with higher reproducibility and a trace analysis can be performed. The range becomes wider.

  Furthermore, according to the invention described in claim 5, the surface of the working electrode is cleaned (regenerated).

  In addition, according to the seventh aspect of the present invention, it is possible to carry out the analysis with extremely high sensitivity and high accuracy especially in the trace analysis of lead with extremely low concentration (for example, several hundreds of ppt level or more).

  In addition, according to the invention described in claim 8, the reproducibility of the microanalysis is further improved.

  Hereinafter, the solution analyzer and the solution analysis method in the present embodiment will be described with reference to the drawings.

  This embodiment uses a working electrode, a counter electrode, and a reference electrode, a solution such as tap water and environmental water (for example, seawater, rivers, lakes, and groundwater), a solution that elutes from soil, food, waste, etc. Analysis apparatus and analysis method by a voltammetric method for analyzing a target analyte (for example, a solution containing a measurement target such as lead, zinc, cadmium, etc.), wherein a copper electrode is used as the working electrode, and a potential sweep step The differential pulse mode is applied. By using the copper electrode and applying the differential pulse mode in the potential sweep process as in the present embodiment, analysis at a level of 100 ppt or more becomes possible.

  In the analysis using a copper electrode, it was known that 100 nM level of lead can be measured by a conventional method such as Patent Document 1, but there was no attempt to apply it to an analysis of 100 ppt level or more as in this embodiment. . That is, when an analysis at a level of 100 ppt or more is performed by a conventional method, an electrode other than a copper electrode, such as a mercury electrode, is applied.

In the present embodiment, it is preferable to adjust the differential pulse condition particularly when lead is a measurement target. That is, unlike the above-described conventional method such as Non-Patent Document 2, the sampling position (for example, within 23 ms) other than the sufficient attenuation position where charging current is not sufficiently attenuated (that is, within the insufficient attenuation position), that is, in the conventional method, Electrolytic currents were sampled at sampling positions that were not assumed at all, and based on the current difference between I _f (Faraday current) and I _B (background current) (difference in electrolytic current sampled during each pulse period) ΔI A polarogram (current change characteristic with respect to potential change) is obtained.

  As described above, the differential pulse mode in which the electrolytic current is sampled at the sampling position where the attenuation is insufficient in each pulse period is insufficient in the attenuation of the charging current at the time of sampling. However, when the differential pulse mode is applied in the potential sweep process using a copper electrode as the working electrode as in the present embodiment, the measurement target in the analysis target is not considered. Even with a very small amount (for example, several hundreds of ppt level or more), a highly accurate and highly sensitive minute amount analysis can be performed. Further, since the sampling position is an insufficiently attenuated position, it is not necessary to set the pulse width to 50 ms or more as in the conventional method (that is, the pulse width is not limited).

[Example of equipment applied to analysis method]
FIG. 1 is a schematic diagram showing an example of an apparatus applied to the analysis method in the present embodiment. In FIG. 1, reference numeral 1 indicates a measurement container (cell), and the measurement container 1 is eluted from an object to be analyzed (for example, a solution such as tap water or environmental water, soil, food, waste, etc.). Solution 1a) is contained and is sealed by the sealing member 1b. Reference numeral 2 is a working electrode made of a copper electrode (for example, a substantially cylindrical or substantially flat electrode), reference numeral 3 is a counter electrode (for example, a coiled electrode made of platinum or carbon), and reference numeral 4 is a reference electrode (a reference electrode). For example, an Ag / AgCl electrode (saturated potassium chloride) or a saturated calomel electrode), and the working electrode 2, the counter electrode 3, and the reference electrode 4 are separated from each other by a certain distance, It arrange | positions so that it may be immersed in the to-be-analyzed object 1a in the said measurement container 1. FIG.

  Reference numeral 5 denotes a potentiostat, and the working electrode 2, the counter electrode 3, and the reference electrode 4 are connected to the potentiostat 5 through, for example, wirings 2a, 3a, 4a and the like. Further, the potentiostat 5 includes a computer (for example, a personal computer) 6 capable of performing calculations related to measurement data obtained through the potentiostat 5 and the like, and a recorder, a potential sweeper as necessary. Etc. are connected. Reference numeral 7 denotes a stirrer, and the stirrer 7 a located at the bottom of the measurement container 1 is operated by the stirrer 7 to stir the object 1 a to be analyzed in the measurement container 1.

  Next, an outline of an analysis method using the apparatus shown in FIG. 1 will be described. First, in order to promote the movement of the measurement object to the surface of the working electrode 2, the substance movement in the analysis object 1a is performed by stirring (turbulent flow) the analysis object 1a via the stirrer 7 and the stirring bar 7a. Desiring the potential of the working electrode 2 (potential regulated by the reference electrode 4) by the potentiostat 5 while promoting the mass transfer of the electrochemically active substance, that is, the deposition efficiency (concentration efficiency) of the deposited substance described later) (At least the potential at which the measurement target can precipitate) and hold for a predetermined time, and the measurement target in the analyte 1a is deposited on the surface of the working electrode 2 (forming a simple substance or forming an alloy with the copper electrode) A concentrated material is formed). Thereafter, the potential held by the working electrode 2 by the potentiostat 5 is set to a predetermined differential pulse condition in a direction (positive direction or negative direction) in which the deposited substance (single concentrated substance or alloy concentrated substance) can be eluted. And the precipitated substance is eluted (stripped) into the analyte 1a.

  Since each of the deposited substances is eluted at a predetermined potential, when the potential of the working electrode 2 is swept (the deposited substance is eluted into the analyte 1a), the current with respect to the potential change of the working electrode 2 The change is detected (the electrolytic current flowing between the working electrode 2 and the counter electrode 3 is sampled). Then, by comparing the electric quantity (coulomb quantity) or peak current value obtained by integrating the change in current with a calibration curve, the measurement object is measured (quantitative, qualitative), and the analysis of the object 1a to be analyzed (measurement) Analysis by measurement of the target concentration and the like.

  Next, in the analysis as shown in the schematic explanatory diagram of FIG. 1 (the same reference numerals are used for the same components as in FIG. 1 and detailed description is omitted), the decay behavior of the charging current is verified by the chronoamperometry method. Then, according to Examples 1 to 7, various samples S1 to S7 (corresponding to the analysis target 1a) were analyzed.

In the analyzer shown in FIG. 1, the working electrode 2, the counter electrode 3 and the reference electrode 4 are each made of an electrode (covered electrode) manufactured by Hokuto Denko Co., Ltd. formed by embedding a copper electrode in a contracted Teflon (registered trademark) tube. An area in contact with the analysis target was 0.07 cm ² ), a Φ0.5 mm coiled platinum wire, and a saturated potassium chloride Ag / AgCl electrode (HX-R6 manufactured by Hokuto Denko) was used. The measuring vessel 1 was a 50 mL glass beaker, and the potentiostat 5 was a HOE series manufactured by Hokuto Denko. The working electrode 2 was used after the surface was polished with sandpaper (# 1200).

(Verification example)
In this verification example, first, a formulation in which a 10 mM acetate buffer solution (pH 4.5) at a concentration of 10 mM (concentration necessary for exhibiting a buffering effect) was added to a solution of potassium chloride (KCl) (0.2 M solution). The measurement container 1 was sealed with the sealing member 1b so that the working electrode 2, the counter electrode 3, and the reference electrode 4 were immersed in the liquid mixture.

  Thereafter, the potential of the working electrode 2 with respect to the reference electrode 4 is stepped from −200 mV to −150 mV by chronoamperometry, and a change in the charging current applied to the working electrode 2 immediately after the potential step is detected for a predetermined time. Thus, a charge current change characteristic diagram with respect to time change as shown in FIG. 1 was obtained.

  As shown in FIG. 2, it can be seen that a charging current of about 150 μA is applied immediately after the potential step and decays with time. For example, it can be seen that the charging current is sufficiently attenuated after about 40 ms to 50 ms and converges to about 1/75 or less immediately after the potential step (the charging current value becomes substantially flat).

  Therefore, from the viewpoint of the conventional method, when the analysis is performed in the differential pulse mode using the analyzer as shown in FIG. 1, for example, the pulse width is set to about 50 ms or more, and about 40 ms which is a sufficient attenuation position in each pulse period. The electrolytic current is sampled at a sampling position after ˜50 ms.

Example 1
In Example 1, each target was analyzed using various analytes containing various concentrations of lead ions, and differential pulse conditions for the potential sweep process were set in various ways. First, 10 mM acetate buffer solution (pH 4.5), 0 to 0.060 mg / l (0, 0.006, 0.012, 0.018, 0.024, 0) with respect to 0.2 M potassium chloride solution. Sample S1 was obtained by blending 0.030, 0.036, 0.042, 0.048, 0.054, 0.060 mg / l (concentration of several ppb level)) lead ions. Next, it sealed with the sealing member 1b so that the working electrode 2, the counter electrode 3, and the reference electrode 4 might be immersed in sample S1 in the measurement container 1. FIG.

  Thereafter, the potential of the working electrode 2 with respect to the reference electrode 4 is maintained at −500 mV for 180 seconds while maintaining a mass transfer promoting atmosphere via the stirrer 7 and the stirrer 7a. Precipitation (reduction concentration) was performed on the surface of 2 (potential holding step).

  Then, after the stirrer 7 and the stirring bar 7a are stopped, the potential of the working electrode 2 with respect to the reference electrode 4 is changed to a differential pulse mode (differential pulse condition: pulse period 100 ms, pulse interval 50 ms, pulse height 50 mV, sampling position. 8 ms to 35 ms), by sweeping in the positive direction from −500 mV (oxidizing and eluting the deposited substance), the current change with respect to the potential change of the working electrode 2 is detected, and the detection result is shown in FIG. 3A for each sampling position. It was shown in the peak current characteristic diagram of FIG.

  From the results shown in FIGS. 3A to 4D, the linearity is low in the case of a peak current characteristic line with a sampling position of 26 ms or more, and the peak current value at a lead ion concentration of 0.02 ppm or more deviates from the line of the calibration curve. Can be read. On the other hand, when the sampling position is a peak current characteristic line within 23 ms, the linearity is good, and it can be read that the peak current value with a lead ion concentration of 0.02 ppm or more is located on the calibration curve line.

  Therefore, in the analysis as shown in FIG. 1, when the sampling position of the potential sweep process is a position where attenuation is insufficient in each pulse period (for example, within 23 ms as in the first embodiment), Of lead ions at a very low concentration (for example, several ppb levels as in Example 1), and the peak current characteristic line with respect to the lead ion concentration has good linearity over a high concentration, and is reliable. Since it can be applied as a high calibration curve, it has been found that even if the measurement target is an extremely low concentration, a high-sensitivity and high-accuracy trace analysis is possible in a wide concentration range.

(Example 2)
In the second embodiment, an object to be analyzed containing lead ions of various concentrations is used, and the sampling position in the differential pulse condition of the potential sweep process is set as the attenuation sufficient position (within the range of the conventional method) in each pulse period. Each analysis was carried out by setting it to an insufficient position (within the range of the present embodiment). First, 10 mM acetate buffer solution (pH 4.5), 0 to 0.01 mg / l (0, 0.01, 0.02, 0.03, 0.04, 0) with respect to 0.2 M potassium chloride solution. Sample S2 was obtained by blending 0.05, 0.06, 0.07, 0.08, 0.09, 0.10 mg / l (concentration of several 10 ppb level)) lead ions.

  And about the sample S2, it is the same electric potential holding | maintenance process and electric potential sweep process as Example 1, Comprising: Sampling position is set to 10-15 ms (10, 11, 12, 13, 14, etc.) among the differential pulse conditions of this electric potential sweep process. An analysis operation set to 15 ms) was performed to detect current change characteristics with respect to potential changes, and the detection results obtained for each sampling position are shown in the peak current characteristic diagram of FIG. 5A. Similarly, when the sampling position of the potential sweep step is set to 45 to 50 ms (integration of 45, 46, 47, 48, 49, and 50 ms), the current change characteristic with respect to the potential change is similarly detected for the sample S2. The detection results obtained for each sampling position are shown in the peak current characteristic diagram of FIG. 5B.

  As shown in FIG. 5B, in the case of a peak current characteristic line with a sampling position of 45 to 50 ms, the linearity is low, and the peak current value at a lead ion concentration of 0.03 mg / l or more deviates from the line of the calibration curve. Can be read. On the other hand, as shown in FIG. 5A, the linearity is good when the sampling position is a peak current characteristic line of 10 to 15 ms, and even if the peak current value of the lead ion concentration is 0.03 mg / l or more, Can be read.

  Therefore, in the analysis as shown in FIG. 1, the sampling position of the potential sweep process is a position where attenuation is insufficient in each pulse period (for example, 10 to 15 ms as in the second embodiment). Lead ions at an extremely low concentration (several tens of ppb level in this embodiment) in the analyte 1a can be sufficiently measured, and the peak current characteristic line with respect to the lead ion concentration has good linearity over a high concentration, and is reliable. Since it can be applied as a high calibration curve, it has been found that even if the measurement target is an extremely low concentration, a high-sensitivity and high-accuracy trace analysis is possible in a wide concentration range.

(Example 3)
In Example 3, the sample S2 of Example 2 (lead ion concentration of 0 to 0.01 mg / l (concentration of several tens of ppb level)) was used, and various differential pulse conditions for the potential sweep process were set. Analysis was performed.

  First, for the sample S2, the same potential holding step and potential sweeping step as in Example 2 (accumulation of sampling positions 10, 11, 12, 13, 14, and 15 ms), and among the differential pulse conditions of the potential sweeping step, An analysis operation is performed with the pulse width set to 25, 50, and 100 ms (pulse period is 50, 100, and 200 ms, respectively), current change characteristics with respect to potential changes are detected, and the detection results obtained for each sampling position are respectively shown. 6A and 6B (when the pulse width is 25 ms), 6B (when the pulse width is 50 ms), and 6C (when the pulse width is 100 ms).

  As shown in each of the peak current characteristic lines 6A to 6C in FIG. 6, each peak current similarly increases as the lead ion concentration to be measured increases (the slope of each peak current characteristic line is substantially the same), and the peak It can be seen that the linearity of the current characteristic line is also good.

  Therefore, the analysis as shown in FIG. 1 is different even when the sampling position of the potential sweep process is set to a position where attenuation is insufficient in each pulse period (for example, 10 to 15 ms as in the third embodiment). Even if the pulse width is 50 ms or less (in the third embodiment, the pulse width is 25 to 100 ms), lead ions having an extremely low concentration (for example, several tens of ppb level as in the third embodiment) in the analysis target 1a The peak current characteristic line for the lead ion concentration has good linearity over a high concentration and can be applied as a highly reliable calibration curve. It was found that high-sensitivity and high-accuracy microanalysis was possible in the range.

Example 4
When lead ions and other heavy metal ions are contained in the analysis target, it is considered preferable to avoid the interaction between the lead ions and heavy metal ions. For example, in the case where a mercury electrode is used in the conventional method, in order to form mercury as an electrode and an amalgam to be measured in the potential holding step, even if the object to be analyzed contains contaminants, The interaction can be avoided without being affected and the desired analysis can be performed.

  When a glassy carbon electrode or the like is used, the lead ion can be measured sufficiently, but since the measurement object is deposited as a single substance during the potential holding process, a large amount of contaminants are contained in the analysis target. The interaction may occur due to the influence of the contaminants. For this reason, the analysis target may be pre-processed (removal of impurities, etc.) as necessary.

  On the other hand, when a copper electrode is used as the working electrode, there is a possibility that the current change characteristic with respect to the potential change can be detected only in the alloy by the alloy reaction between the lead ion and the copper electrode in the potential holding step, Even if impurities are included in the target, the interaction can be avoided and the desired analysis can be performed without being affected by the impurities as in the case of using the mercury electrode (described above). It can be analyzed directly without pre-processing).

  Therefore, in this Example 4, each analysis was performed using the analytes including the supporting electrolytes with various concentrations of lead ions and various anionic species. First, a sample S3 was obtained by blending a 0.2 M potassium chloride solution with a 10 mM acetate buffer solution (pH 4.5) and 0 to 5 μM lead ions. Moreover, it was the same mixing | blending as sample S3, Comprising: The potassium nitrate solution was mix | blended instead of the potassium chloride solution, and sample S4 was obtained.

  Samples S3 and S4 are subjected to an analysis operation in the same potential holding step and potential sweeping step (accumulation of sampling positions 10, 11, 12, 13, 14, and 15 ms) as in Example 2 to perform current change characteristics with respect to potential changes. Was detected respectively. As a result, as shown in FIGS. 7A (in the case of sample S3) and B (in the case of sample S4), in each sample S3 and S4, the peak current characteristic line due to the precipitation of a single lead ion, the lead ion and the copper electrode The peak current characteristic line was obtained for the alloy of

  From the results shown in FIG. 7B, when nitrate ions are included as the anion species in the analyte, the peak current (in the precipitation of simple lead ions) increases as the lead ion concentration rises from about 2.5 μM. It can be read that the peak current due to the alloy is hardly detected although the accompanying peak current is increased.

  On the other hand, from the results shown in FIG. 7A, when chloride ions (chlorides) are contained as the anion species in the analyte, the lead ion concentration increases (especially in the range of about 2 μM or less). Although the peak current due to the alloy increases and the peak current characteristic line also has good linearity, the peak current (peak current associated with the precipitation of lead ions alone) must have a lead ion concentration of more than about 1.5 μM. It can be read that almost no detection occurs.

  When chloride ions are contained as in the sample S3, the chloride ions are specifically adsorbed on the surface of the copper electrode during the potential holding step, that is, monovalent copper chloride is formed. It seems that is likely to be formed. Moreover, the specific adsorption of chloride ions described above makes it possible to suppress the reduction reaction of dissolved oxygen in the analyte and to suppress the generation of hydrogen, and the potential window seems to be widened.

  Therefore, in the analysis as shown in FIG. 1, if chloride ions coexist as anion species in the analyte, for example, lead ions (for example, about 1.5 μM or less as in the present Example 4) Even when lead ions) and other heavy metal ions are included, the current change characteristics with respect to potential changes can be detected only with the lead ions and the alloy of the copper electrodes without receiving any interaction with other heavy metals. That is, even when a plurality of measurement objects (for example, lead ions, cadmium ions, and zinc ions) are included in the analysis target, the interaction between these measurement objects is avoided. It was found that it can be selectively measured, enables high sensitivity and high accuracy microanalysis, and has good reproducibility. Further, it has been found that the range in which trace analysis can be performed becomes wider as the potential window becomes wider.

(Example 5)
As in Example 4 described above, by utilizing the alloy reaction between lead ions and copper electrodes (alloy reaction according to the lead ion concentration) during the potential holding step, a plurality of measurement objects in the analysis target are obtained. Although it can be measured sufficiently selectively, it is considered that it is preferable that the range of the lead ion concentration in which only the alloy reaction occurs (the range in which the peak current due to precipitation of the single substance to be measured is not detected) is wider. In this copper electrode, it is a method for the purpose of simply cleaning dirt on the surface of the copper electrode (oxidizing and eluting the working electrode surface at the molecular level and regenerating), but for each analysis (for example, every time repeated analysis is performed) It is known that a positive potential (that is, a potential in a positive direction with respect to a potential at which a measurement target can be deposited) slightly exceeding about ± 0 V (vs. Ag / AgCl) is applied to a copper electrode for a predetermined time.

  Therefore, in Example 5, before using the sample S3 of Example 4 (lead ion concentration of 0 to 5 μM) to deposit the measurement object in the potential holding step, the potential of the measurement object can be precipitated. A positive potential was applied to the working electrode and each analysis was performed.

  First, the sample S3 is subjected to an analysis operation by the same potential holding step and potential sweeping step (sampling positions 10, 11, 12, 13, 14, 15 ms integration) as in Example 4 to detect current change characteristics with respect to potential changes. The detection results obtained for each sampling position are shown in the peak current characteristic diagram of FIG. In each potential holding step of Example 5, a potential of +300 mV was applied to the working electrode immersed in the subject to be analyzed for 10 seconds (hereinafter referred to as pre-deposition potential application) before performing the deposition of the measurement target. did.

  As shown in FIG. 8, a peak current characteristic line due to the precipitation of lead ions and a peak current characteristic line due to the alloy of the lead ions and the copper electrode are obtained. Since it is almost not detected unless the value is more than about 2.5 μM, the lead ion concentration range in which only the alloy reaction occurs is compared with the result of FIG. 7A (that is, the result when the positive potential is not applied before precipitation). However, it can be seen that it is wider.

  This is because the pre-deposition potential application facilitates specific adsorption of chloride ions (chloride ions in the analyte) to the copper electrode surface during the potential holding step (that is, monovalent chloride). It seems that copper is easily formed) and lead ions and copper electrode alloys are easily formed. In addition, it is considered that the reduction reaction of dissolved oxygen and hydrogen generation in the analysis target are further suppressed, and the potential window becomes wider.

  In the analysis shown in FIG. 8, the potential is set to +300 mV and the application time is 10 seconds in the potential application before deposition. However, as long as the specific adsorption of chloride ions occurs as described above, the potential may be changed as appropriate. it is conceivable that. For example, in the potential application before deposition, the potential is set to a positive direction from −100 mV for 3 seconds or more, and the same analysis as in FIG. 8 is performed. At least the result of FIG. However, it was confirmed that it became wider. In addition, it can be seen that when the potential before deposition is applied in the positive direction from the potential ± 0 V, the working electrode surface itself is oxidized and eluted at the molecular level and the surface is cleaned (regenerated). Furthermore, even when the potential is set to more than +300 mV or the application time is set to be long (for example, more than 10 seconds), specific adsorption of chloride ions may occur, but for example, the copper electrode surface is largely oxidized and eluted. The surface area and the like may change greatly.

  Therefore, in the analysis as shown in FIG. 1, before performing the deposition of the measurement object in each potential holding step, the potential before deposition is applied to the working electrode (for example, the potential −100 mV to +300 mV as in Example 5). , By applying a pre-detection potential application time of 3 to 10 seconds), compared to the analysis of the sample 3 in Example 4, a plurality of measurement objects (for example, as in Example 5) It has been found that it is easier to selectively measure (when about 2.5 μM or less of lead ions are contained in the sample), more sensitive and highly accurate microanalysis is possible, and better reproducibility is achieved. In addition, since the potential window becomes wider, it was found that the range in which trace analysis can be performed becomes wider.

(Example 6)
In the present Example 6, each analysis was implemented using the to-be-analyzed object containing cadmium ion and the to-be-analyzed object containing lead ion and cadmium ion. First, a sample S5 was obtained by blending 0.2 M potassium chloride solution with 10 mM acetate buffer solution (pH 4.5) and 0.04 ppm (concentration of several tens of ppb level) cadmium ions. Further, a sample S6 was obtained by further blending 0.05 ppm (concentration of several tens of ppb level) of lead ions to the same composition as the sample S5.

For samples S5 and S6, the same potential holding step as in Example 5 (potential +300 mV, after applying a potential before deposition of 10 seconds for application time, and then holding at -650 mV for 180 seconds), potential sweep step (sampling positions 10, 11) , 12, 13, 14, and 15 ms integration) to detect current change characteristics with respect to potential changes, and the detection results obtained for each sampling position are shown as current change characteristic lines with respect to potential changes in FIGS. 9A and 9B. 9A ₁ (in the case of sample S5), 9B ₁ (in the case of sample S6). Further, for each of the samples S5 and S6, the current change characteristic with respect to the potential change in the case of not containing cadmium ions, that is, the background current characteristic is similarly detected, and the background current characteristic line 9A _{2 in} FIGS. 9A and 9B is detected. (In the case of sample S5) and 9B ₂ (in the case of sample S6).

  In the result shown in FIG. 9A, it can be seen that the background current is unstable and it is difficult to accurately calculate the peak current value according to the cadmium ion concentration. On the other hand, in the result shown in FIG. 9B, it can be read that the peak current value can be calculated according to the cadmium ion concentration because the background current decreases and is stable.

  Therefore, in the analysis as shown in FIG. 1, it was found that even if the measurement object is cadmium ion, a trace analysis by the same measurement as in Examples 1 to 5 can be performed. Further, for example, when measuring cadmium ions in an analysis target that does not contain lead ions, lead ions (for example, lead ions of several tens of ppb level as in Example 6) are added to the analysis target (additive) As a result, it was found that the background current can be attenuated and stabilized, and the reproducibility of trace analysis becomes better.

(Example 7)
In this Example 7, samples obtained by adding various concentrations of lead ions and cadmium ions to the background solution were repeatedly analyzed (N = 10) for the samples to confirm the level of analysis possible. It was. First, a 10 mM acetate buffer solution (pH 4.5) was blended with a 0.2 M potassium chloride solution to obtain a background solution. Samples S7a, S7b, S7c, S7d, S7e, and S7f were obtained by adding 0, 0.01, 0.02, 0.03, 0.04, and 0.05 ppm lead ions to the background solution. Moreover, it is the same mixing | blending as sample S7a-S7f, Comprising: Instead of lead ion, 0.00.01.0.02, 0.03,0.04, 0.05 ppm cadmium ion is mix | blended, and sample S8a , S8b, S8c, S8d, S8e, S8f were obtained.

  Thereafter, with respect to the samples S7a to S7f and S8a to S8f, the same potential holding step as in Examples 5 and 6 (the potential held at the time of deposition after applying the potential before deposition is −500 mV in the case of samples S7a to S7f, the sample For S8a to S8f, -650 mV), potential sweep process (for samples S7a to S7f, sampling positions 10, 11, 12, 13, 14, 15 ms integration, for samples S8a to S8f, sampling positions 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, and 49 ms integration) to detect current change characteristics with respect to potential changes, respectively. The peak current value characteristics with respect to the lead ion or cadmium ion concentration) calibration curve (hereinafter referred to as the lead calibration curve and cadmium calibration curve, respectively) It was determined as referred to).

  Next, with respect to the background solution, the analysis operation by the potential holding process and the potential sweep process similar to the case of the lead calibration curve and the cadmium calibration curve, respectively, is repeated a total of 10 times to obtain the current change characteristics with respect to the potential change. Asked. Then, the peak current value at each 10 times is collated with the lead calibration curve and cadmium calibration curve to perform concentration conversion, calculate the standard deviation (σ), and detect the lower limit of detection (3σ), the lower limit of quantification (10σ ) And the results are shown in Table 1 below.

  From the results shown in Table 1, it can be read that each S7a to S7f and S8a to S8f can be measured at a level of several hundreds of ppt. Therefore, in the analysis as shown in FIG. 1, it was confirmed that the measurement object (lead ion, cadmium ion, etc. as in Example 7) included in the analysis object can be measured and analyzed. .

(Example 8)
In the present Example 8, each analysis was carried out using analytes containing various concentrations of lead ions, cadmium ions, and zinc ions. First, 0.2 mM potassium chloride solution, 10 mM acetate buffer solution (pH 5.0), 0 to 0.24 ppm (concentration of several tens of ppb level) lead ion, 0 to 0.12 ppm (concentration of several tens of ppb level) ) And cadmium ions of 0 to 0.084 ppm (concentration of several ppb level) were blended to obtain a sample S9.

  The sample S9 was subjected to the same potential holding step as that of Example 6 (after pre-deposition potential application, held at -950 mV for 180 seconds), and the potential sweep step (sampling position 5 to 19 ms) to perform an analysis operation to cope with the potential change. The current change characteristics were detected, and the detection results obtained for each sampling position are shown in current change characteristic lines 10A to 10L with respect to the potential change in FIG. Further, the current change characteristic with respect to the potential change in the case of not containing lead ion, cadmium ion and zinc ion in the sample S9, that is, the background current characteristic was also detected in the same manner, and is shown by the background current characteristic line 10M in FIG. . Table 1 below shows the concentrations of lead ions, cadmium ions, and zinc ions corresponding to the characteristic lines 10A to 10M in the sample S7.

  As shown in FIG. 10, the background current is relatively low and stable, and the peak currents corresponding to the concentrations of lead ions, cadmium ions, and zinc ions are the same as in the case of the lead ion measurement in Examples 1 to 5 described above. It can be read that is sufficiently detected.

  Therefore, in the analysis as shown in FIG. 1, even if the object to be measured is other than lead ion or cadmium ion (for example, zinc ion), trace analysis by the same measurement as in Examples 1 to 5 is possible. Turned out to be. In addition, even if a plurality of measurement objects (for example, lead ions, cadmium ions, and zinc ions at a level of several ppb to several tens of ppb as in the eighth embodiment) are contained in the analysis target, It was proved that a microanalysis by the same measurement as that of No. 5 was possible.

  Although the present invention has been described in detail only for the specific examples described above, it is obvious to those skilled in the art that various changes and modifications can be made within the scope of the technical idea of the present invention. Such variations and modifications are naturally within the scope of the claims.

  For example, it is composed of at least a working electrode (working electrode made of a gold electrode), a counter electrode, and a reference electrode, and each of the electrodes is arranged in an analysis target, and the potential of the working electrode is held at a predetermined potential by a potential holding step. If the current change with respect to the potential change in the working electrode can be detected while sweeping the potential of the working electrode in the potential sweep step, the design can be changed as appropriate within the scope of common technical knowledge (for example, It is clear that the same effects as in the present embodiment can be obtained even if the configuration of each electrode is changed).

Schematic explanatory drawing of the apparatus applicable to the solution analysis method in this Embodiment. The charging current change characteristic view with respect to the time change by the chronoamperometry method of the verification example. The peak current characteristic diagram of Example 1 (sampling position 8-23 ms). The peak current characteristic diagram of Example 1 (sampling position 26-35 ms). The peak current characteristic diagram of Example 2 (FIG. 5A is sampling position 10-15 ms, FIG. 5B is sampling position 45-50 ms). The peak current characteristic diagram of Example 3. FIG. The peak current characteristic diagram of Example 4 (FIG. 7A is sample S3, FIG. 7B is sample S4). The peak current characteristic diagram of Example 5. FIG. 9A is a current change characteristic diagram with respect to a potential change in Example 6 (FIG. 9A is a sample S5, and FIG. 9B is a sample S6). FIG. 10 is a current change characteristic diagram with respect to potential change in Example 8.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Container 1a ... Analyte 2 ... Working electrode 3 ... Counter electrode 4 ... Reference electrode 5 ... Potentiostat 6 ... Computer 7 ... Stirrer

Claims (8)

It consists of at least a working electrode, a counter electrode, and a reference electrode,
Each electrode described above is placed in an analysis target including the measurement target, and the potential of the working electrode can be held at a potential at which the measurement target in the analysis target can be deposited, and the measurement deposited by the held potential In a solution analyzer that can sweep in a differential pulse mode in a direction in which an object can be eluted, can detect a current change with respect to a potential change in the working electrode, and can analyze an analyte to be analyzed at a level of 100 ppt or more.
The solution analyzer according to claim 1, wherein the working electrode is a copper electrode. After placing the working electrode, counter electrode, and reference electrode in the analyte,
A potential holding step of holding the potential of the working electrode at a potential at which a measurement target in the analysis target can be deposited;
A potential sweep step for detecting a current change with respect to a potential change in the working electrode while sweeping the held potential of the working electrode in a differential pulse mode in a direction in which the measurement object deposited in the potential holding step can be eluted. And a method capable of analyzing an object to be analyzed at a level of several hundreds of ppt or more by performing an analysis operation according to
A solution analysis method, wherein a copper electrode is used as the working electrode.   The solution analysis method according to claim 2, wherein chloride ions are contained in the analysis target.   4. The solution analysis method according to claim 3, wherein the pre-deposition potential is applied to the working electrode at a potential in the positive direction from −100 mV before the potential to be deposited is maintained at the potential at which the measurement object can be deposited in the potential holding step. .   5. The solution analysis method according to claim 4, wherein the potential of the pre-deposition potential application is more positive than ± 0V.   The solution analysis method according to any one of claims 2 to 5, wherein the object to be analyzed contains at least one of lead, cadmium, and zinc.   7. The solution analysis method according to claim 6, wherein at least lead is contained in the analyte as an object to be measured, and the electrolytic current is sampled within 23 ms after pulse application in the differential pulse mode in the potential holding step. .   The solution analysis method according to claim 7, wherein when the object to be analyzed does not contain lead and the object to be measured is cadmium, lead is added to the object to be analyzed.

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