JP5759442B2 - Electrochemical analysis method, electrochemical analyzer and reagent set - Google Patents

Description

  The present invention relates to a method, an apparatus, and a reagent set for electrochemically detecting cadmium contained in a biological sample.

  Cadmium is toxic to the human body, and it is known that kidney function and the like are affected when cadmium accumulates in the body. For this reason, there is a standard for the amount of cadmium contained in foods such as rice. Under the Food Sanitation Law, it is regulated to 1 ppm or less in brown rice, and if it contains cadmium above the standard, it can be sold. Cannot be incinerated. In addition, according to the notification of the Food Agency, all rice that has been detected to have a content of 0.4 ppm or more in brown rice is made industrial.

  Conventionally, as a method for analyzing cadmium, an atomic absorption analysis method, an ICP emission analysis method, an ICP mass spectrometry method, and the like, which are official analysis methods, are known. However, these analysis apparatuses are large and expensive, and their operations are complicated.

  On the other hand, attempts have been made to electrochemically analyze cadmium (Patent Document 1). However, when trying to analyze cadmium contained in food, the organic matter contained in the food becomes an interfering factor and is highly accurate. The realization of is blocked.

JP 2005-49275 A

  Therefore, the present invention is intended to provide an electrochemical analysis method, apparatus, and reagent set capable of detecting and quantifying cadmium contained in a biological sample with high sensitivity and high accuracy.

That is, the electrochemical analysis method according to the present invention is a method for electrochemically analyzing cadmium contained in a biological sample using a counter electrode and a working electrode, and is oxidative with respect to the biological sample. And an acid that does not form a complex with cadmium is added to extract cadmium from the biological sample.

  Thus, by extracting cadmium from a biological sample using an acid that has an oxidizing property and does not form a complex with cadmium, the organic matter contained in the biological sample can be decomposed satisfactorily. Since the acid and cadmium do not form a complex, cadmium can be detected and its concentration can be measured with high accuracy.

  Perchloric acid is preferably used as the acid that has oxidizing properties and does not form a complex with cadmium. In ICP emission spectrometry and ICP mass spectrometry, hydrochloric acid is used for pretreatment of biological samples, but when cadmium is extracted using hydrochloric acid, the current peak when cadmium is eluted from the working electrode is reduced. Highly accurate analysis becomes difficult. This is because hydrochloric acid and sulfuric acid form a complex with cadmium.

  It is preferable to adjust pH of the obtained extract to 3-7. Preferably it is pH 3-6. When the pH is less than 3, the current peak when cadmium is eluted from the working electrode becomes small, and it becomes difficult to perform highly accurate analysis. On the other hand, when pH exceeds 7, cadmium will precipitate.

  When adjusting the pH of the extract to 3 to 7, it is preferable to use a buffer comprising an organic acid and / or a salt thereof. The carboxyl group of organic acid has a chelating action, and it is assumed that interference with cadmium can be prevented by encapsulating metals such as lead, selenium, chromium, boron, etc., which are inhibitors when cadmium is analyzed. Is done. The organic acid is preferably one having one or two carboxyl groups in one molecule, and examples thereof include phthalic acid and acetic acid. When phthalic acid is used, it is appropriate to adjust the pH to about 4, and when acetic acid is used, it is appropriately adjusted to about pH 5.

  In biological sample extracts, cadmium often forms a complex with copper. In that case, electrochemical analysis detects a current peak derived from the complex of cadmium and copper. The For this reason, in order to prevent the measurement result from being affected by the copper content in the biological sample, copper may be added to the biological sample in advance. As an addition amount of copper at this time, for example, copper that is less than a predetermined reference value (for example, the maximum content of copper expected in the target biological sample) may be added, or cadmium. You may add copper so that it may become a density | concentration (large excess) about 3 to 10 times the measured density range. When adding copper, a copper compound such as a copper electrolyte may be used.

  The electrochemical analysis method according to the present invention is an electrode that applies a positive voltage to the working electrode in contact with the solution having the same composition and pH of the extract and acid and buffer after pH adjustment. It is preferable to provide a washing step. By performing the electrode cleaning step, organic substances and heavy metals adhering to the working electrode can be removed in advance, so that highly accurate analysis can be performed.

  Although it does not specifically limit as said working electrode, It is preferable to use a carbon electrode, and a conductive diamond electrode is used suitably especially. Examples of the conductive diamond electrode include those doped with boron, nitrogen, phosphorus, etc. Among them, a boron-doped diamond electrode doped with boron at a high concentration is preferable. The boron-doped diamond electrode has a wide potential window (wide oxidation potential and reduction potential), low background current compared to other electrode materials, high sensitivity to redox species, compared to gold, platinum, etc. In addition, since physical adsorption hardly occurs on the electrode surface, it has an excellent property that peaks other than the generation of oxygen and hydrogen hardly occur. Further, the boron-doped diamond electrode is excellent in chemical durability, mechanical durability, electrical conductivity, corrosion resistance, and the like. Furthermore, the boron-doped diamond electrode also has the advantage that it is easy to perform chemical and physical cleaning due to its hardness, and it is easy to maintain the electrode surface in a clean state.

Further, as the counter electrode, such as platinum, carbon, stainless steel, gold, diamonds, can be used an electrode made of SnO ₂ or the like, further, when using a reference electrode, to utilize those suitable known For example, a silver-silver chloride electrode, a calomel electrode, a standard hydrogen electrode, a hydrogen palladium electrode, or the like can be used.

  When the working electrode used in the present invention is a conductive diamond electrode, a hydrogen termination step of applying a negative voltage to the conductive diamond electrode to hydrogen terminate the electrode surface after the electrode cleaning step. Preferably it is done. Thus, by hydrogen-termination of the surface of the conductive diamond electrode, the sensitivity of the electrode surface is increased and analysis with high accuracy can be performed.

  The electrochemical analysis method according to the present invention can be implemented by an analyzer having the following configuration, for example. That is, an apparatus for electrochemically analyzing cadmium contained in a biological sample, wherein an acid that has an oxidizing property and does not form a complex with cadmium is added to the biological sample. Extraction means for extracting cadmium from a sample derived therefrom, pH adjustment means for adjusting the pH of the obtained extract to 3-7, a counter electrode and a working electrode, and a cell for containing the extract And a voltage at which cadmium or a composite thereof is electrodeposited between the working electrode and the counter electrode, and then a voltage at which the cadmium or the composite electrodeposited on the working electrode is eluted. And a detecting means for detecting a current generated between the working electrode and the counter electrode. Such an electrochemical analyzer is also one aspect of the present invention.

  Further, when carrying out the electrochemical analysis method according to the present invention, cadmium is extracted from the organism-derived sample, and the cadmium is oxidizing in order to adjust the obtained extract for test use. A reagent set that includes an acid that does not form a complex with the acid, a buffer composed of an organic acid and / or a salt thereof, and a copper compound may be used. Such a reagent set is also one aspect of the present invention.

  In the reagent set according to the present invention, an acid (A component) that has an oxidizing property and does not form a complex with cadmium, a buffer (B component) comprising an organic acid and / or a salt thereof, and a copper compound (C component) May be provided as separate reagents, but component A and component C may be included in one reagent, or component B and component C may be included in one reagent. . Moreover, it does not specifically limit as a dosage form of the reagent contained in the said reagent set, Solid (powder form, a tablet, etc.) may be sufficient, and liquid may be sufficient.

  According to the present invention configured as described above, the organic matter contained in the biological sample is satisfactorily decomposed, and since cadmium does not form a complex, it is possible to accurately detect cadmium and measure its concentration. it can.

The schematic diagram which shows the structure of the electrochemical measuring apparatus of this embodiment. The perspective view which shows typically the heavy metal ion measuring apparatus of the embodiment. Sectional drawing which shows the structure of the measurement cell of the embodiment typically. The perspective view of the stirring element of the embodiment. The top view of the stirring bar of the embodiment. The front view of the stirring bar of the embodiment. The right view of the stirring bar of the embodiment. The figure which shows typically the manufacturing method of the stirring element of the embodiment. FIG. 3 is a first schematic diagram showing a specific configuration inside the measurement cell of the embodiment. The 2nd schematic diagram which shows the specific structure inside the measurement cell of the embodiment. Voltammogram when cadmium is extracted from rice using perchloric acid. Voltammogram when cadmium is extracted from rice using hydrochloric acid. The schematic diagram which shows the modification of a holding surface. The schematic diagram which shows the modification of a holding surface.

  Hereinafter, an electrochemical measurement apparatus according to the present invention will be described with reference to the drawings.

  The electrochemical measurement apparatus 100 of the present embodiment analyzes cadmium contained in a biological sample such as rice, for example, using a stripping voltammetry method with a three-electrode system of a counter electrode, a reference electrode, and a working electrode.

<Device configuration>
Specifically, as shown in FIG. 1, the electrochemical measurement apparatus 100 includes a measurement cell 2 that accommodates a liquid sample, a counter electrode 3, a reference electrode 4 and a working electrode 5 provided in contact with the liquid sample, and a working electrode. 5, a potential changing unit 6 that changes the potential of 5, a liquid replacement mechanism 11 that replaces at least a part of the liquid sample accommodated in the measurement cell 2 with an acidic buffer that is a measurement solution, the working electrode 5, and the counter electrode 3. And a concentration calculation unit 8 for calculating the heavy metal ion concentration from the current value detected by the current detection unit 7.

  As shown in FIG. 2, each of the above-described components is housed in a casing C. In the lower part of the front surface of the casing C, a buffer solution tank T1 for storing the acidic buffer solution, a liquid sample, and after use A waste liquid tank T2 is provided for storing a waste liquid such as a buffer solution. Further, an upper part of the front surface of the casing C is provided with an operation button group B such as a power ON / OFF button, a measurement start button, a calibration button, and a washing button, and a display unit 801 for displaying a measurement result (concentration, etc.). . Furthermore, a sample introduction part 21 for injecting a liquid sample into the measurement cell 2 is provided at the upper part of the casing C.

  First, the potential fluctuation unit 6, the current detection unit 7, the liquid replacement mechanism 11, and the concentration calculation unit 8 will be described.

  The potential fluctuation unit 6 and the current detection unit 7 are configured by a potentiostat PS. The potentiostat PS detects a current generated between the working electrode 5 and the counter electrode 3 in a state where the potential of the working electrode 5 is constant with respect to the reference electrode 4, and this detection signal is used as a concentration described later. It outputs to the arithmetic and control unit 8 which has a function as a calculation part.

  The potentiostat PS has the potential of the working electrode 5 to be the potential at which the heavy metal is electrodeposited on the working electrode 5 and the potential at which the heavy metal electrodeposited on the working electrode 5 is eluted. Fluctuate between. Specifically, the potentiostat PS changes the potential of the working electrode 5 in the negative potential direction in a state where the working electrode 5 is in contact with the liquid sample, and sets the potential for electrodepositing the heavy metal to be measured on the surface of the working electrode 5. Then, in a state where the working electrode 5 electrodeposited with the heavy metal on the surface is in contact with the phthalic acid buffer solution which is an acidic buffer solution, the potential of the working electrode 5 is swept in the positive potential direction to the working electrode 5. A potential is applied to elute the electrodeposited heavy metals.

  The potentiostat PS detects the current generated between the working electrode 5 and the counter electrode 3 when the electric potential of the working electrode 5 is swept in the positive potential direction by the electric fluctuation function. To do.

  The potentiostat PS has a function of scanning the potential at a constant speed and stepping to a specified potential at regular intervals in addition to a function of keeping the potential constant. These functions do not need to be mounted on one unit, and for example, the potential holding function and the potential scanning function may be provided separately.

  As shown in FIG. 1, the liquid replacement mechanism 11 has a discharge line 12 for discharging the liquid in the measurement cell 2 to the waste liquid tank T2 and a phthalate buffer solution from the buffer tank T1 to the measurement cell 2. Supply line 13.

  The discharge line 12 includes a discharge pipe 121 connected to the measurement cell 2 and a discharge pump 122 provided in the discharge pipe 121 for discharging the liquid stored in the measurement cell 2 to the outside. The discharge pipe 121 is provided through the bottom wall 2c of the measurement cell 2 so as to open near the surface of the working electrode 5 (not shown). The downstream side of the discharge pipe 121 is connected to the waste liquid tank T2. The operation timing and the like of the discharge pump 122 are controlled by the arithmetic and control unit 8 described later.

  The supply line 13 includes a supply pipe 131 connected to the measurement cell 2 and a supply pump 132 that is provided in the supply pipe 131 and supplies the phthalate buffer solution stored in the buffer solution tank T1 to the measurement cell 2. Have. Similarly to the counter electrode 3 and the reference electrode 4, the supply pipe 131 is inserted and fixed obliquely on the side wall 2 b of the measurement cell 2 so as to face the working electrode 5 (not shown). The upstream side of the supply pipe 131 is connected to the buffer tank T1. The operation timing and the like of the supply pump 132 are controlled by the arithmetic and control unit 8 described later.

  The liquid replacement mechanism 11 is controlled by the arithmetic and control unit 8 so as to replace the liquid sample stored in the measurement cell 2 while maintaining at least the amount of liquid in which the counter electrode 3 and the working electrode 5 are in contact with the liquid sample. . Specifically, the discharge pump 122 and the supply pump 132 of the liquid replacement mechanism 11 divide the liquid sample stored in the measurement cell 2 into a plurality of times and replace it with a phthalate buffer solution that is a measurement solution. Controlled by. For example, the liquid replacement mechanism 11 replaces the liquid sample with a phthalate buffer solution in a plurality of times (for example, about four times), for example, in half. As a replacement method, after the liquid sample accommodated in the measurement cell 2 is half discharged by the discharge line 12, an amount of phthalate buffer corresponding to the discharge amount is supplied by the supply line 13. This is repeated a plurality of times, for example. In addition, the discharge of the liquid sample and the supply of the phthalate buffer solution may be performed simultaneously.

  The arithmetic and control unit 8 acquires a detection signal detected by the potentiostat PS, and performs detection and concentration measurement of heavy metal ions. Specifically, the arithmetic control device 8 is a general purpose or dedicated device including a CPU, output means 801 such as a memory, an input / output channel, a display, an A / D converter, a D / A converter, and the like. And the peripheral device performs a cooperative operation according to a measurement program stored in a predetermined area of the memory, thereby executing a measurement sequence described later. Note that the arithmetic and control unit 8 does not have to be physically integrated, and may be divided into a plurality of devices by wire or wirelessly.

  Next, the measurement cell 2, the electrode groups 3 to 5 provided in the measurement cell 2, and the stirring mechanism 9 provided in the measurement cell 2 will be described.

  As shown in FIG. 3, the measurement cell 2 forms a liquid sample storage space 2S therein, and a sample introduction part 21 for introducing a liquid sample is formed on the upper wall part 2a. Yes.

  Further, the counter electrode 3 and the reference electrode 4 are inserted and fixed to the side wall 2b of the measurement cell 2 from an oblique direction so as to face the lower side (the bottom wall 2c side). Further, the working electrode 5 is fixed to the bottom wall 2c of the measurement cell 2 so as to be exposed to the accommodation space 2S.

  Here, regarding the electrode groups 3 to 5 of the present embodiment, the counter electrode 3 is, for example, a platinum electrode, the reference electrode 4 is, for example, a silver-silver chloride electrode, and the working electrode 5 is doped with boron at a high concentration. This is a boron-doped diamond electrode (conductive diamond electrode).

  As described above, the counter electrode 3 and the reference electrode 4 are inserted and fixed obliquely in the side wall 2b of the measurement cell 2 so as to face the working electrode 5 provided on the bottom wall 2c of the measurement cell 2. Thus, since the counter electrode 3 and the reference electrode 4 are provided obliquely so as to face the working electrode 5 on the side wall 2b of the measurement cell 2, these electrodes 3 and 4 interfere with the surrounding structure. Can be arranged without. The counter electrode 3 and the reference electrode 4 are inserted into an insertion through hole 91H of a stirrer 91 described later, and the tips of the electrodes 3 and 4 are close to the electrode surface 5a of the working electrode 5.

  The working electrode 5 is a flat plate provided so that the electrode surface 5a is exposed to the accommodation space 2S in the bottom wall 2c of the measurement cell 2. The working electrode 5 is provided so as to close the opening formed in the bottom wall portion 2c, whereby the electrode surface 5a is exposed to the accommodation space 2S. A liquid sample accommodated in the measurement cell 2 is provided between the bottom wall 2c and the working electrode 5 or a holding member (not shown) for holding the working electrode 5, for example, a sealing member such as an O-ring. Is prevented from leaking outside through these gaps.

  As shown in FIG. 1, the stirring mechanism 9 provided in the measurement cell 2 includes a stirrer 91 housed in the housing space 2S of the measurement cell 2, and a magnetic actuator for rotating the stirrer 91 by magnetic force. 92. The magnetic actuator 92 is provided below the bottom wall portion 2 c of the measurement cell 2, specifically, below the working electrode 5.

  As shown in FIGS. 4 to 7, the stirrer 91 is made of, for example, a fluorine-based resin such as PTFE, and has a cylindrical main body 911 and one open end 911 p in the axial direction of the main body 911. It has a plurality of blade portions 912 formed continuously and extending along the axial direction. In addition, the stirrer 91 is made of a fluorine-based resin so that it is difficult to get dirty. In addition, although not shown, in the stirrer 91, the radially outer corner of the other opening end 911q of the main body 911 and the corner of the tip of the blade 912 are chamfered into a rounded shape. (R chamfering) is performed. Thereby, the stirrer 91 is configured to rotate easily.

  The other open end 911 q in the axial direction of the main body 911 has a facing surface 911 a that faces the electrode surface 5 a of the working electrode 5 in the state of being accommodated in the measurement cell 2. The facing surface 911a is an annular surface formed by the opening end surface of the other opening end portion 911q of the main body portion 911.

  Since the main body 911 is thus cylindrical, an insertion through hole 91H for inserting the counter electrode 3 and the reference electrode 4 is formed in the rotation center of the stirrer 91 (see FIG. 5). . The insertion through hole 91H has a circular cross section. Since the cross-section is circular, the insertion space into which the counter electrode 3 and the reference electrode 4 are inserted can be made as large as possible while the stirrer 91 is rotated.

  The plurality of blade portions 912 are formed at equal intervals in the circumferential direction at one opening end portion 911 p of the main body portion 911. In the present embodiment, two blade portions 912 are formed, and are provided in one opening end portion 911p of the main body portion 911 so as to face each other in the radial direction. The plurality of blade portions 912 have the same shape. The end surface 912x facing the circumferential direction of each blade portion 912 functions as an agitation surface for agitating the liquid sample accommodated in the accommodation space 2S (see FIGS. 4 and 5). Further, the outer surface 912m of the blade portion 912 is the same surface as the outer peripheral surface 911m of the main body portion 911.

The main body 911 of the stirrer 91 has a plurality of magnets 913 built therein. The plurality of magnets 913 are provided symmetrically with respect to the weight of the stirrer 91 as a whole in a portion where the blade portion 912 is not formed in the circumferential direction of the main body portion 911 (see FIG. 5). Specifically, a plurality of bar-shaped magnets 913 are provided on each of the opposing walls 911s and 911t of the main body portion 911 (three in each of the opposing walls 911s and 911t in FIG. 5). The bar magnets 913 built in the opposing walls 911s and 911t are provided along the axial direction of the main body 911 (see FIGS. 6 and 7). The plurality of rod-shaped magnets 913 provided on one opposing wall 911s have an N pole on one side in the axial direction (blade portion 912 side) and an S pole on the other axial side (the opposing surface 911a side). It is configured. The plurality of rod-shaped magnets 913 provided on the other facing wall 911t have an S pole on one side in the axial direction (blade portion 912 side) and an N pole on the other axial side (the facing surface 911a side). It is configured as follows.

  With respect to the stirrer 91 configured as described above, the rotating body of the magnetic actuator 92 is provided with a magnet having the north pole on the stirrer 91 side at a portion corresponding to the one opposing wall 911s, and the other A magnet having an S pole on the stirrer 91 side is provided at a portion corresponding to the opposite wall 911t. When the stirrer 91 is rotated by the magnetic actuator 92 configured as described above, the magnet 913 of the stirrer 91 is attracted to the magnet of the rotating body (that is, the opposing surface 911a of the stirrer 91 will be described later). It rotates in a state of being pressed against the contact surface 2P. Thus, since the stirring bar 91 is attracted to the rotating body and rotates so that the opposing surface 911a slides on the contact surface 2P, the rotation of the stirring bar 91 can be stabilized.

  Further, one or a plurality of concave portions 914 for allowing bubbles to escape upward are formed on the facing surface 911a of the stir bar 91, that is, the other opening end portion 911q in the axial direction of the main body portion 911. The concave portion 914 opens to the inner peripheral surface and the outer peripheral surface at the other opening end portion 911q of the main body portion 911. In the present embodiment, the other opening end portion 911q of the main body portion 911 is formed at equal intervals in the circumferential direction, and is formed below the blade portion 912 in consideration of the weight balance of the stirrer 91 ( (See FIG. 6).

  A method for manufacturing the stirrer 91 will be briefly described. As shown in FIG. 8, the side wall portions 901 and 902 facing each other on one end side in the axial direction of the pre-processing part 900 having a cylindrical shape are substantially L-shaped in an axially symmetrical manner when viewed from the direction orthogonal to the axial direction. Sharpen it like a notch. Thereby, the main-body part 911 and the blade | wing part 912 are formed. Further, by forming a recess at the opening end on the other end side in the axial direction of the pre-processing component 900, a bubble removal recess 914 is formed. Further, an embedding hole for embedding the magnet 913 in the main body 911 is cut by an end mill or the like. Then, the magnet 913 is fitted into the buried hole. After such processing is performed, the stirrer 91 is formed by performing the above-described R chamfering processing on the processed component. An R chamfering process may be performed before embedding the magnet 913.

  Then, as shown in FIGS. 9 and 10, the measurement cell 2 of the present embodiment contacts the facing surface 911a of the stir bar 91 facing the electrode surface 5a, and separates the facing surface 911a from the electrode surface 5a. The stirrer contact surface 2P (hereinafter referred to as contact surface 2P) is formed at a position different from the contact surface 2P, and a surface different from the facing surface 911a of the stirrer 91 rotates along the stirrer 91. And a holding surface 2Q for holding the rotation posture.

  The contact surface 2P supports the electrode surface 5a so that the opposed surface 911a of the stirrer 91 does not contact the electrode surface 5a. The contact surface 2P is an annular plane formed so as to be separated from the electrode surface 5a of the working electrode 5 in the direction (upward direction) toward the electrode surface 5a, and the stirrer 91 is placed thereon. Specifically, the contact surface 2 </ b> P is formed on a projecting portion 22 that forms an annular shape and projects radially inward from the inner peripheral surface 2 x of the measurement cell 2 at the upper portion of the electrode surface 5 a of the working electrode 5. Specifically, the protrusion 22 is formed by a plane (upper surface) opposite to the working electrode 5.

  As described above, on such a contact surface 2P, the stirrer 91 is attracted to the magnetic actuator 92, and the opposing surface 911a of the stirrer 91 rotates while being pressed against the contact surface 2P. Thereby, since the opposing surface 911a rotates so as to slide on the contact surface 2P, the rotation of the stirrer 91 can be stabilized, and the convection of the liquid sample generated on the electrode surface 5a by the stirrer 91 can be made constant. Can do.

  The holding surface 2Q holds the rotating posture of the stirrer 91 with the rotation axis of the stirrer 91 being substantially constant with respect to the electrode surface 5a. The holding surface 2Q is a cylindrical surface formed on the upper side of the contact surface 2P (projecting portion 22) inside the measurement cell 2. The central axis of the holding surface 2Q substantially coincides with the rotation central axis of the stirring bar. Specifically, the holding surface 2Q is formed by the inner peripheral surface 2x that forms the cylindrical shape of the measurement cell 2. The holding surface 2Q is formed to face substantially the entire outer peripheral surface 911m of the main body 911 of the stirrer 91 with a slight gap therebetween. The gap between the outer peripheral surface 911m of the main body 911 and the holding surface 2Q is desirably as small as possible so that the rotation of the stirrer 91 can be ensured, for example, about 0.5 mm. The holding surface 2Q prevents the stirrer 91 from being turned upside down at the start of rotation or during rotation, suppresses vibration of the rotating shaft of the stirrer 91, or reduces the amplitude of vibration of the rotating shaft. The rotation posture of the child 91 can be kept substantially constant. Therefore, the rotation of the stirrer 91 can be stabilized, and the convection of the liquid sample generated on the electrode surface 5a by the stirrer 91 can be made substantially constant.

  In the present embodiment, the outer peripheral surface 911m of the main body portion 911 and the outer surface 912m of the blade portion 912 are the same surface, and the holding surface 2Q is configured to face the outer surface 912m of the blade portion 912. (See FIG. 10). Thereby, when the stirrer 91 rotates, the outer surface 912m of the blade portion 912 also rotates along the holding surface 2Q (the inner peripheral surface 2x of the measurement cell 2), so that the rotation posture of the stirrer 91 becomes substantially constant. Can be held.

<Cadmium analysis method>
Next, a method for analyzing cadmium by the stripping method using the electrochemical analyzer 100 will be described.

1. Extraction liquid preparation process Hereinafter, a case where rice is used as a biological sample will be described as an example. First, rice is pulverized to obtain rice flour. Next, the obtained rice flour is dissolved in perchloric acid to extract cadmium while decomposing organic matter. The residue is removed by subjecting the obtained extract to suction filtration. Further, potassium hydrogen phthalate and sodium hydroxide are added to the extract after suction filtration to adjust the pH to around 4.0 to obtain an extract for cadmium measurement.

In rice extract, cadmium often forms a complex with copper. When cadmium forms a complex with copper, in addition to the current peak due to the cadmium-copper complex during the elution process, a current peak due to cadmium alone may be observed, but analysis is easy. In order to achieve this, it is preferable that only one type of current peak due to cadmium is detected. Moreover, the detection sensitivity in an electrochemical analysis differs in the cadmium simple substance and the composite_body | complex of cadmium and copper. Therefore, to detect cadmium as a complex with copper in order to align detection sensitivity and facilitate analysis of analysis results, the copper concentration in the rice extract is the reference concentration (for example, the highest expected concentration). 4ppm), the copper may be supplemented by adding a deficient amount of copper to the extract, or a large excess of copper so that the concentration is about 3 to 10 times the expected cadmium concentration. (For example, when the cadmium concentration is 50 ppb, copper is added so that the concentration becomes 200 to 400 ppb), and cadmium may be detected as a complex with copper. Incidentally, when adding copper to the extract can be used a copper compound such as CuCl _2. The copper compound may be added to the extract alone, but may be added together with perchloric acid or added together with potassium hydrogen phthalate.

2. Electrode treatment process When the user operates the power ON / OFF button, the arithmetic and control unit 8 turns on the main power of the electrochemical analyzer 100. Thereafter, when the user presses the electrode treatment button, the arithmetic and control unit 8 controls the electrode treatment process in the measurement device, specifically, the measurement cell 2. In this electrode treatment process, first, using the supply line 13 of the liquid replacement mechanism 11, the concentration and pH of the liquid used for extraction of cadmium, for example, perchloric acid, potassium hydrogen phthalate, and sodium hydroxide are the same as the extraction liquid. A positive voltage is applied to the conductive diamond electrode 5 for a predetermined time while the phthalate buffer solution is supplied into the measurement cell 2 and the phthalate buffer solution supplied by the magnetic stirring mechanism 9 is stirred (for example, +3. 5V is applied for 60 seconds), and an electrode cleaning process for removing organic substances and heavy metals adhering to the conductive diamond electrode 5 is performed. Next, a negative voltage is applied to the conductive diamond electrode 5 for a predetermined time (for example, a voltage of −3.5 V is applied for 5 seconds) to perform hydrogen termination treatment on the surface of the conductive diamond electrode 5. Then, the electrode treatment process is completed by discharging the phthalate buffer solution from the discharge line 12 of the liquid replacement mechanism 11.

3. Extract Liquid Injection Process After the electrode treatment process is completed, the user moves the open / close lid of the sample introduction part 21 provided on the upper part of the casing C to the open position, and injects the extraction liquid from the sample introduction part 21. Thereafter, when the user presses the measurement start button, the arithmetic and control unit 8 receives a measurement start signal and starts cadmium measurement. At this time, the arithmetic control device 8 obtains a detection signal by a liquid sensor (not shown) that detects whether the counter electrode 3, the conductive diamond electrode 5, and the reference electrode 4 are in contact with the extraction liquid. It is determined whether or not the electrode groups 3 to 5 are in contact with the extract. If it is determined that it is in contact, the process proceeds to the following measurement operation. If it is not in contact, an error display or the like is notified.

4). Electrodeposition process The arithmetic and control unit 8 outputs an electrodeposition start signal to the potentiostat PS. Then, the potentiostat PS changes the potential of the conductive diamond electrode 5 in the negative potential direction so that the potential of the conductive diamond electrode 5 is lower than the reduction potential of cadmium (for example, −1.0 V). Cadmium is electrodeposited on the surface 5 a of the conductive diamond electrode 5. In the case where cadmium forms a composite with copper, the composite of cadmium and copper may be electrodeposited on the surface 5 a of the conductive diamond electrode 5. In this case, the electrodeposition potential may be about −0.8V. This electrodeposition step ends after maintaining the state in which the potential of the conductive diamond electrode 5 is lower than the reduction potential for a predetermined time (for example, 10 minutes).

5. Liquid Replacement Step After the electrodeposition step, the potentiostat PS keeps the potential of the conductive diamond electrode 5 constant at a potential lower than the reduction potential. In this state, the arithmetic control device 8 controls the liquid replacement mechanism 11 to replace the extract in the measurement cell 2 with the phthalate buffer in a plurality of times. In this embodiment, after the extraction liquid accommodated in the measurement cell 2 is half discharged by the discharge line 12, an amount of phthalate buffer corresponding to the discharge amount is supplied by the supply line 13. By performing this operation a plurality of times (for example, about 4 times), the extract is replaced with a phthalate buffer. Thus, in the liquid replacement step, the cadmium electrodeposited on the electrode 5 is eluted in the liquid replacement step by keeping the potential of the conductive diamond electrode 5 constant at a potential lower than the reduction potential. To prevent that. In addition, the discharge amount of the extract and the supply amount of the phthalate buffer may be defined based on the discharge time and the supply time, respectively.

6). Elution process (current detection process)
After substituting the inside of the measuring cell 2 with the phthalate buffer solution in the liquid replacement step, the arithmetic and control unit 8 outputs an elution start signal to the potentiostat PS. Then, the potentiostat PS sweeps the potential of the conductive diamond electrode 5 in the positive potential direction, specifically, to a potential higher than the reduction potential of cadmium (for example, +1.0 V), and thereby a composite of cadmium and copper. Is eluted in phthalate buffer.

  When the composite of cadmium and copper is eluted, a current is generated between the conductive diamond electrode 5 and the counter electrode 3. In the present reaction system, a current resulting from the composite of cadmium and copper is generated in the vicinity of +0.35 V, and this current (electrical signal) is transmitted to the potentiostat PS to control and detect the signal at each electrode. . Here, the signal detected by the potentiostat PS is transmitted to the arithmetic and control unit 8. Then, the elution step is completed by discharging the phthalate buffer solution from the discharge line 12 of the liquid replacement mechanism 11.

  An example of a voltammograph obtained by the elution step is shown in FIG. In the voltammograph shown in FIG. 11, the current peak seen in the vicinity of −0.35 V is derived from a complex of cadmium and copper, and the current peak seen in the vicinity of 0.25 V is derived from copper alone. . Further, in the voltammograph shown in FIG. 11, it can be seen that the current peak increases as the concentration of cadmium increases.

  On the other hand, FIG. 12 shows an example of a voltammograph obtained when hydrochloric acid is used as the acid used when preparing the extract. When hydrochloric acid is used during the preparation of the extract, residual organic matter that has not been decomposed becomes an interfering factor, and cadmium forms a complex with hydrochloric acid. Therefore, as shown in FIG. 12, a current peak derived from cadmium (−0 .About 6 V) was unclear and could not be detected with high sensitivity.

7). In this embodiment, in order to analyze the cadmium concentration using the standard addition method, a cadmium standard sample with a known concentration is further added to the extract solution subjected to the above-described electrodeposition step to elution step (for example, 50 ppb). ), The electrodeposition step to the elution step are performed in the same manner as described above, and a relationship line between the cadmium concentration and the current value or the charge amount is created.

8). Cadmium Concentration Calculation Step The arithmetic and control unit 8 calculates the cadmium concentration of the extract by comparing the created relationship line between the cadmium concentration and the current value or charge amount with the obtained current value or charge amount. . At this time, the cadmium concentration is calculated by using the difference current value or the difference charge amount obtained by subtracting the base current value or the charge amount measured using only the phthalate buffer solution from the actual measurement current value or the charge amount. By doing so, it becomes possible to calculate the cadmium concentration with higher accuracy. The cadmium concentration thus calculated is displayed on the display unit 801 provided on the front surface of the casing C.

9. Post-electrolysis step After the potential sweep is completed, the electrodeposited cadmium and copper are completely eluted by holding the potential of the conductive diamond electrode 5 at +1.0 V for a while, and the conductive diamond electrode 5 is removed. It can be played back to the state before the measurement. By regenerating the conductive diamond electrode 5 in this way, the same electrode can be used repeatedly. Note that the conductive diamond electrode 5 can be regenerated not only by maintaining a constant potential but also by repeatedly performing sweeping at a wide potential.

10. Waste Liquid Process After the post-electrolysis process, the arithmetic control device 8 controls the discharge pump 122 of the discharge line 12 of the liquid replacement mechanism 11 to discharge the measured solution in the measurement cell 2 to the waste liquid tank T2. After this waste liquid process is completed, the measurement cell is cleaned and the power is turned off.

<Effect of this embodiment>
According to the electrochemical measuring apparatus 100 according to the present embodiment configured as described above, since the contact surface 2P that separates the electrode surface 5a of the working electrode 5 and the facing surface 911a of the stirrer 91 is provided, the stirrer The working electrode 5 can be configured not to contact the working electrode 5, the working electrode 5 is not damaged by the stirrer 91, and the electric double layer formed on the electrode surface 5a of the working electrode 5 is not disturbed. Thereby, the stability of electrochemical measurement can be improved.
In addition, since the holding surface 2Q for holding the rotation posture of the stirrer 91 is provided, rotation obstacles such as the stirrer 91 breaking the posture during rotation and contacting the working electrode 5 or being unable to rotate are caused. There is no concern about the occurrence, the rotation speed and rotation position of the stirrer 91 can be stabilized, and the rotation of the stirrer 91 can be stabilized. Thus, by stabilizing the rotation of the stirrer 91, the convection of the liquid sample on the electrode surface 5a of the working electrode 5 can be made substantially constant, and the stability of the electrochemical measurement can be improved.

Furthermore, according to the cadmium analysis method of the present embodiment, by extracting cadmium from a biological sample such as rice using perchloric acid, the organic matter contained in the biological sample without forming a cadmium complex is obtained. Since it can be decomposed, cadmium can be detected and its concentration can be measured with high accuracy.
Further, in the present embodiment, by using potassium hydrogen phthalate as a buffering agent, metals such as lead, selenium, chromium, and boron, which are inhibitors when cadmium is measured, are encapsulated with a carboxyl group, and as a result, cadmium It is presumed that interference with is prevented.
Furthermore, in this embodiment, by performing an electrode treatment process including an electrode cleaning process and a hydrogen termination process, organic substances and heavy metals adhering to the working electrode are removed in advance, and then the surface of the conductive diamond electrode is prepared. Thus, the analysis accuracy can be further increased. In particular, in this embodiment, since the electrode cleaning treatment is performed in the phthalate buffer solution, CO radicals are generated by the Corbi reaction, which seems to work effectively for the decomposition and removal of organic substances.

The present invention is not limited to the above embodiment.
For example, in a stirrer, a blade part may be formed inside a cylindrical main body part. In this case, the opening size of the insertion through hole 91H may be reduced, but the axial dimension of the stirrer 91 can be reduced.

Further, the holding surface 2Q of the embodiment is formed by the inner peripheral surface 2x of the measurement cell 2, but as shown in FIG. 13, the inner peripheral surface 2x of the measurement cell 2 and the outer peripheral surface 911m of the stirrer 91. A spacer member 10 may be provided between which the inner peripheral surface 10x serves as the holding surface 2Q. The spacer member 10 has a cylindrical shape whose cross section perpendicular to the axial direction has an equal cross section. Incidentally, by forming the protruding portions of the annular projecting from the inner circumferential surface 10 x of the spacer member 10 radially inward, or as having a contact surface 2P.

  Furthermore, in the embodiment, the stirrer 91 has the insertion through hole 91H, but may not have the insertion through hole 91H. In this case, the counter electrode 3 and the reference electrode 4 cannot be inserted from the upper part of the stirrer 91 to the working electrode 5 side. For example, the distance between the contact surface 2P (protrusion 22) and the working electrode 5 is set as described above. The counter electrode 3 and the reference electrode 4 are inserted into the accommodating space 2S from the side wall between the protruding portion 22 and the working electrode 5, and the counter electrode 3 and the reference electrode 4 are placed on the electrode surface of the working electrode 5. You may comprise so that it may be located in the vicinity of 5a.

  In addition, the holding surface 2Q of the above embodiment is a cylindrical surface formed so as to surround the rotation center axis C of the stirrer 91. However, as shown in FIG. 14, the holding surface 2Q faces the contact surface 2P. The stirrer 91 may be rotatably sandwiched between the contact surface 2P and the contact surface 2P. As the holding surface 2Q, for example, it is conceivable that the holding surface 2Q is an annular plane that contacts the upper surface of the stirrer 91. Similar to the contact surface 2P, the holding surface 2Q is formed by a lower surface of an annular projecting portion 23 formed to project radially inward from the inner peripheral surface 2x of the measurement cell 2. Although FIG. 14 shows the case where a rod-like stirrer 91 is used, it may have an insertion through hole 91H as in the above embodiment.

  In addition, in the above embodiment, the measurement is performed by the three-electrode method including the working electrode 5, the counter electrode 3, and the reference electrode 4, but the two-electrode method including only the working electrode 5 and the counter electrode 3 is used. It may be. In the three-electrode method, the absolute value of the voltage applied between the working electrode 5 and the counter electrode 3 can be controlled, so that measurement with higher accuracy and sensitivity can be performed. Therefore, since the electrode to be used is only two electrodes, the working electrode 5 and the counter electrode 3, the structure of the measurement cell 2 can be simplified and miniaturized.

  In the cadmium analysis method of the above embodiment, the method of creating the relationship line for calculating the cadmium concentration is not limited to the standard addition method, and when the copper concentration in the extract is low, the calibration curve method is used to calculate the cadmium concentration. A relationship line with the current value or the charge amount may be created in advance.

  In addition, the electrochemical measurement device of the above embodiment may be applied to a device that measures any one or more components of heavy metal ions such as Cu, As, Cd, and Zn contained in a liquid sample. .

  In the cadmium analysis method of the above embodiment, a signal with less noise can be obtained by performing the liquid replacement step, but heavy metal ions such as cadmium can be measured without performing the liquid replacement step.

  In addition, it goes without saying that the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention.

DESCRIPTION OF SYMBOLS 100 ... Electrochemical measuring device 2 ... Measurement cell 2P ... Contact surface 2Q ... Holding surface 2x ... Inner peripheral surface 3 ... Counter electrode 4 ... Reference electrode 5 ... Action Electrode 91 ... Stirrer 911a ... Opposing surface 91b ... Outer peripheral surface 91H ... Insertion through-hole 911 ... Main part 912 ... Blade part

Claims (12)

A method of electrochemically analyzing cadmium contained in a biological sample using a counter electrode and a working electrode,
An electrochemical analysis method comprising an extraction step of adding perchloric acid to a biological sample to extract cadmium from the biological sample.   The electrochemical analysis method of Claim 1 provided with the pH adjustment process of adjusting the pH of the extract obtained at the said extraction process to 3-7. The electrochemical analysis method according to claim 2, wherein a buffer comprising an organic acid and / or a salt thereof is added to the extract in the pH adjustment step. The electrochemical analysis method according to claim 1, 2, or 3, further comprising a copper addition step of adding copper to the biological sample. in a state in which the composition and pH of the extract and the acid and buffer after pH adjustment is brought into contact with the solution is the same, according to claim 2, characterized in that an electrode cleaning step of applying a positive voltage to the working electrode Electrochemical analysis method. The working electrode is a conductive diamond electrode;
6. The electrochemical analysis method according to claim 5 , further comprising a hydrogen termination step of applying a negative voltage to the conductive diamond electrode to hydrogen terminate the electrode surface after the electrode cleaning step. An apparatus for electrochemically analyzing cadmium contained in a biological sample,
An extraction means for adding perchloric acid to a biological sample and extracting cadmium from the biological sample;
PH adjusting means for adjusting the pH of the obtained extract to 3-7,
A cell containing a counter electrode and a working electrode and containing the extract;
Between the working electrode and the counter electrode, a voltage at which cadmium or a complex thereof is electrodeposited is applied to the working electrode, and then a voltage at which the electrodeposited cadmium or a complex is eluted is applied to the working electrode Applying means for
An electrochemical analyzer comprising: detection means for detecting a current generated between the working electrode and the counter electrode. The electrochemical analyzer according to claim 7, further comprising a copper addition unit that adds copper to the biological sample. The electrochemical analyzer according to claim 7 or 8 , wherein the working electrode is a conductive diamond electrode. When cadmium contained in a biological sample is electrochemically analyzed using a counter electrode and a working electrode, cadmium is extracted from the biological sample and the resulting extract is prepared for testing. A reagent set for
A reagent set comprising an acid which has an oxidizing property and does not form a complex with cadmium, a buffer comprising an organic acid and / or a salt thereof, and a copper compound. The reagent set according to claim 10 , wherein the acid having an oxidizing property and not forming a complex with cadmium is perchloric acid. The reagent set according to claim 11 , wherein the organic acid is phthalic acid or acetic acid.