JP5814025B2 - Method and apparatus for electrochemical analysis of cadmium - Google Patents
Method and apparatus for electrochemical analysis of cadmium Download PDFInfo
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この発明は、試料溶液中のカドミウムを電気化学的手法を利用して簡便な操作で、高感度かつ高精度に検出・定量することができる分析方法及び装置に関するものである。 The present invention relates to an analysis method and apparatus capable of detecting and quantifying cadmium in a sample solution with high sensitivity and high accuracy by a simple operation using an electrochemical technique.
カドミウムは、比較的さびにくく美しい金属光沢を放つことより、古くは自動車等のめっき材料として用いられてきた。しかしながら、カドミウムは人体にとって有毒であり、カドミウムが体内に蓄積すると腎臓機能等が侵される。 Cadmium has long been used as a plating material for automobiles and the like because it emits a beautiful metallic luster that is relatively rustless. However, cadmium is toxic to the human body, and when cadmium accumulates in the body, kidney function and the like are affected.
このようなカドミウムの人体への毒性が広く知られるようになってからは、その利用は避けられるようになってきており、例えば、2006年7月より施行されたEUのRoHS規制(欧州有害物質規制)では、電気電子機器における特定有害物質の含有が禁止されたが、カドミウムも規制対象となっている。 Since such cadmium toxicity has become widely known, its use has been avoided. For example, EU RoHS regulations (European hazardous substances) that came into force in July 2006 Regulation) prohibits the inclusion of specific hazardous substances in electrical and electronic equipment, but cadmium is also subject to regulation.
また、米をはじめとする食物にも含有基準が設けられており、食品衛生法上では玄米において1ppm以下と規定され、基準値以上のカドミウムを含む場合は販売することができず、全て焼却処分される。また、食糧庁通達により、玄米中0.4ppm以上の検出がされた米については全て工業用にされる。 In addition, there is a content standard for foods including 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 value, it cannot be sold and all are incinerated. Is done. 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.
従来、カドミウムを分析する方法としては、公定分析法である原子吸光分析法、ICP発光分析法、ICP質量分析法等が知られている。しかし、これらの分析を行う装置は大型で高価であり、その操作も複雑である。 Conventionally, atomic absorption analysis, ICP emission analysis, ICP mass spectrometry, and the like, which are official analysis methods, are known as methods for analyzing cadmium. However, these analysis apparatuses are large and expensive, and their operations are complicated.
一方、電気化学的にカドミウムを分析する試みも行われているが(特許文献1)、試料溶液に含まれる銅の干渉が精度の高い分析を阻んでいる。すなわち、試料溶液中に銅が含まれていると、銅の干渉によりカドミウムに起因する電流ピークが減少し消滅してしまい、カドミウムの分析が阻害される。 On the other hand, attempts have been made to electrochemically analyze cadmium (Patent Document 1). However, the interference of copper contained in the sample solution prevents high-precision analysis. That is, if copper is contained in the sample solution, the current peak due to cadmium decreases and disappears due to the interference of copper, and the analysis of cadmium is hindered.
また、銅だけでなく、鉛、セレン、クロム、ホウ素についても同様の干渉が認められ、カドミウムの分析が阻害される。 Further, not only copper but also lead, selenium, chromium, and boron are observed with the same interference, which inhibits analysis of cadmium.
そこで本発明は、銅や鉛等の干渉による影響を排除して、試料溶液中のカドミウムを電気化学的に高い精度で分析することができる分析方法及び装置を提供すべく図ったものである。 Therefore, the present invention is intended to provide an analysis method and apparatus capable of analyzing cadmium in a sample solution with high electrochemical accuracy by eliminating the influence of interference such as copper and lead.
本発明者らは、鋭意検討を重ねた結果、第11族元素の共存下で試料溶液中のカドミウムを電気化学的に分析すると、カドミウムと第11族元素との複合体に起因する電流ピークが検出され、このピーク電流値はカドミウム濃度と良好に相関することを見出し、本発明を完成させるに至った。 As a result of intensive studies, the present inventors have electrochemically analyzed cadmium in a sample solution in the presence of a group 11 element. As a result, a current peak caused by a complex of cadmium and a group 11 element is found. The peak current value detected was found to correlate well with the cadmium concentration, and the present invention was completed.
なお、このようにカドミウムと第11族元素との複合体に起因する電流ピークが検出されるのは、第11族元素(Me)のアンダーポテンシャル析出(UPD:Under potential deposition)効果により、カドミウムが、カドミウム表面上に析出する電位(カドミウム電着の標準酸化還元電位)よりも高い電位で、Me表面上にCd−Me複合体として析出し、カドミウム単独の酸化還元電位よりも高い電位で溶出するためであると考えられる。 Note that the current peak due to the complex of cadmium and the Group 11 element is detected in this way because of the under potential deposition (UPD) effect of the Group 11 element (Me). , Deposited at a higher potential than the potential deposited on the cadmium surface (standard redox potential for cadmium electrodeposition), and deposited as a Cd-Me complex on the Me surface, and eluted at a potential higher than the redox potential of cadmium alone. This is probably because of this.
すなわち本発明に係る電気化学的分析方法は、対電極とカーボン電極からなる作用電極とを用いて、試料溶液中のカドミウムを電気化学的に分析する方法であって、前記試料溶液に第11族元素を添加する添加工程と、前記第11族元素が添加された前記試料溶液に前記作用電極と前記対電極とを接触させた状態で、前記作用電極と前記対電極との間に、前記作用電極にカドミウムと前記第11族元素との複合体が電着する電圧を印加し、前記作用電極に前記複合体を電着させる電着工程と、前記作用電極と前記対電極との間に、前記作用電極に電着した前記複合体が溶出する電圧を印加して、前記作用電極から前記複合体を溶出させる溶出工程と、前記複合体の溶出に起因して、前記作用電極と前記対電極との間に生じた電流を検出する検出工程と、を備えていることを特徴とする。 That is, the electrochemical analysis method according to the present invention is a method for electrochemically analyzing cadmium in a sample solution using a counter electrode and a working electrode composed of a carbon electrode, wherein An adding step of adding an element; and the working electrode and the counter electrode between the working electrode and the counter electrode in a state where the working electrode and the counter electrode are in contact with the sample solution to which the Group 11 element has been added. Applying a voltage at which a complex of cadmium and the Group 11 element is electrodeposited to an electrode, electrodepositing the complex onto the working electrode, and between the working electrode and the counter electrode, An elution step of eluting the complex from the working electrode by applying a voltage at which the complex electrodeposited on the working electrode is eluted; and the working electrode and the counter electrode due to the elution of the complex To detect the current generated between Characterized in that it comprises a step.
このようなものであれば、カドミウムをCd−Me複合体(Me:第11族元素)として作用電極に電着させて、これを検出対象とすることができ、当該Cd−Me複合体のピーク電流値はカドミウム濃度と良好に相関するので、試料溶液中に銅や鉛等が混入していても、これらの干渉に影響されずに、カドミウムを電気化学的に高感度かつ高精度に検出・定量することが可能となる。 In such a case, cadmium can be electrodeposited on the working electrode as a Cd-Me complex (Me: Group 11 element), and this can be detected, and the peak of the Cd-Me complex can be detected. The current value correlates well with the cadmium concentration, so even if copper or lead is mixed in the sample solution, cadmium can be detected electrochemically with high sensitivity and high accuracy without being affected by these interferences. It becomes possible to quantify.
本発明において作用電極として機能するカーボン電極としては、導電性ダイヤモンド電極が好適に用いられる。当該導電性ダイヤモンド電極としては、例えば、ホウ素、窒素、リン等がドープされているもの等が挙げられるが、なかでも高濃度でホウ素をドープしたボロンドープダイヤモンド電極が好ましい。ボロンドープダイヤモンド電極は、電位窓が広く(酸化電位及び還元電位が広い)、他の電極材料と比較してバックグラウンド電流が低く、酸化還元種に対して感度が高く、金や白金等に比べて電極表面に物理的吸着が生じにくいため酸素・水素発生以外のピークが出にくい、といった優れた性質を有している。また、ボロンドープダイヤモンド電極は、化学的耐久性、機械的耐久性、電気伝導度、耐腐食性等にも優れている。更に、ボロンドープダイヤモンド電極は、その硬度から、化学的・物理的な洗浄を行いやすく、電極表面を清浄な状態に維持しやすいという利点も有する。 As the carbon electrode functioning as a working electrode in the present invention, a conductive diamond electrode is preferably used. 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.
第11族元素としては、銅、銀、金、レントゲニウムが挙げられるが、なかでも、カドミウムとの複合体に起因する電流値のカドミウム濃度依存性に優れており、また、他の妨害物質共存下においても定量的な分析が可能であることから、銅が好適に用いられる。 Examples of Group 11 elements include copper, silver, gold, and roentgenium. Among them, the cadmium concentration dependency of the current value resulting from the complex with cadmium is excellent, and in the presence of other interfering substances. Since copper can be quantitatively analyzed, copper is preferably used.
銅の前記試料溶液への添加量は、カドミウムとの複合体に起因する電流値のカドミウム濃度依存性の観点からは、0.3〜4mM程度であることが好ましい。 The amount of copper added to the sample solution is preferably about 0.3 to 4 mM from the viewpoint of the cadmium concentration dependence of the current value resulting from the complex with cadmium.
本発明に係るカドミウムの電気化学的分析方法は、例えば以下のような構成を有する分析装置によって実施することができる。すなわち、試料溶液中のカドミウムを電気化学的に分析するための装置であって、対電極とカーボン電極からなる作用電極とを内蔵し、前記試料溶液を収容するためのセルと、前記試料溶液に第11族元素を添加する添加手段と、前記作用電極と前記対電極との間に、前記作用電極にカドミウムと前記第11族元素との複合体が電着する電圧を印加し、次いで、前記作用電極に電着した前記複合体が溶出する電圧を印加する印加手段と、前記作用電極と前記対電極との間に生じた電流を検出する検出手段と、を備えていることを特徴とする。このような電気化学的分析装置もまた、本発明の1つである。 The electrochemical analysis method for cadmium according to the present invention can be carried out by an analyzer having the following configuration, for example. That is, an apparatus for electrochemically analyzing cadmium in a sample solution, including a counter electrode and a working electrode composed of a carbon electrode, a cell for containing the sample solution, and the sample solution A voltage for electrodepositing a complex of cadmium and the Group 11 element is applied to the working electrode between the adding means for adding the Group 11 element and the working electrode and the counter electrode, An application means for applying a voltage at which the complex electrodeposited on the working electrode is eluted; and a detection 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.
本発明は、上述の構成よりなるので、試料溶液中に銅や鉛等が混入していても、これらの干渉による影響を排除して、高感度かつ高精度にカドミウムの検出・定量を行うことが可能となる。 Since the present invention is configured as described above, even if copper, lead, or the like is mixed in the sample solution, the influence of these interferences is eliminated, and cadmium can be detected and quantified with high sensitivity and high accuracy. Is possible.
以下に本発明の一実施形態について図面を参照して説明する。 An embodiment of the present invention will be described below with reference to the drawings.
本実施形態に係る電気化学的分析装置1は、図1に模式的に示すように、電気化学的測定用のバッチセルを用いたものである。 The electrochemical analyzer 1 according to this embodiment uses a batch cell for electrochemical measurement, as schematically shown in FIG.
本実施形態に係る電気化学的分析装置1は、ボロンドープダイヤモンド電極2、対電極3及び参照電極4と、これら3本の電極が内蔵された測定セル5と、を備えており、ボロンドープダイヤモンド電極2、対電極3及び参照電極4は、情報処理装置8が設けられたポテンショガルバノスタット7に接続されている。また、測定セル5には、試料溶液Sを攪拌する攪拌子6と試料溶液Sに銅を供給する銅供給装置9とが設けられている。 The electrochemical analyzer 1 according to the present embodiment includes a boron-doped diamond electrode 2, a counter electrode 3, a reference electrode 4, and a measurement cell 5 in which these three electrodes are built, and boron-doped diamond. The electrode 2, the counter electrode 3, and the reference electrode 4 are connected to a potentio galvanostat 7 provided with an information processing device 8. The measurement cell 5 is provided with a stirrer 6 for stirring the sample solution S and a copper supply device 9 for supplying copper to the sample solution S.
以下に各部を説明する。
ボロンドープダイヤモンド電極2は、絶縁体であるダイヤモンドにホウ素が混入されることにより導電性が付与されたものであり、電気化学的分析装置1において作用電極として機能するものである。
Each part will be described below.
The boron-doped diamond electrode 2 is provided with conductivity by mixing boron into diamond, which is an insulator, and functions as a working electrode in the electrochemical analyzer 1.
ボロンドープダイヤモンド電極2としては適宜公知のものを使用することができ、その形状としては、棒状又は平面状のいずれであってもよい。 As the boron-doped diamond electrode 2, a known one can be used as appropriate, and the shape thereof may be either a rod shape or a planar shape.
対電極3としては、例えば、白金、炭素、ステンレス、金、ダイヤモンド、SnO2等からなる電極を用いることができる。 As the counter electrode 3, for example, an electrode made of platinum, carbon, stainless steel, gold, diamond, SnO 2 or the like can be used.
参照電極4としては公知のものを利用することができ、例えば、銀塩化銀電極、カロメル電極、標準水素電極、水素パラジウム電極等を用いることができる。 A known electrode can be used as the reference electrode 4, and for example, a silver-silver chloride electrode, a calomel electrode, a standard hydrogen electrode, a hydrogen palladium electrode, or the like can be used.
測定セル5は、その内部に試料溶液Sを収容し、当該試料溶液Sがボロンドープダイヤモンド電極2、対電極3及び参照電極4と接触できるよう構成されているものである。測定セル5は、内部に試料溶液Sを収容することができるものであればその材質は特に限定されないが、例えば、できるだけ不純物の溶出を抑えられるポリテトラフルオロエチレン等のフッ素樹脂製であることが好ましい。 The measurement cell 5 contains a sample solution S therein, and is configured so that the sample solution S can come into contact with the boron-doped diamond electrode 2, the counter electrode 3, and the reference electrode 4. The material of the measurement cell 5 is not particularly limited as long as it can accommodate the sample solution S therein. For example, the measurement cell 5 may be made of a fluororesin such as polytetrafluoroethylene that can suppress the elution of impurities as much as possible. preferable.
撹拌子6は、測定セル5に収容された試料溶液Sを撹拌するものである。撹拌子6が試料溶液Sを攪拌することによって、ボロンドープダイヤモンド電極2にカドミウムを電着させる際の効率が向上する。撹拌子6の羽の形状や材質、羽の動作方法は特に限定されないが、試料溶液Sの充分な攪拌が可能であり、かつ不純物や微粉末等の発生や、電極表面からの気泡発生をできるだけ抑えることができるものが好ましく、例えば、十字型攪拌子が好適に用いられる。 The stirrer 6 stirs the sample solution S accommodated in the measurement cell 5. When the stirrer 6 stirs the sample solution S, the efficiency when electrodepositing cadmium on the boron-doped diamond electrode 2 is improved. The shape and material of the wing of the stirrer 6 and the operation method of the wing are not particularly limited, but the sample solution S can be sufficiently stirred, and as much as possible generation of impurities, fine powder, and generation of bubbles from the electrode surface are possible. What can be suppressed is preferable, for example, a cross-shaped stirrer is preferably used.
ポテンショガルバノスタット7は、ボロンドープダイヤモンド電極2の電位を参照電極4に対して一定にした状態で、ボロンドープダイヤモンド電極2と対電極3との間に発生した電流を検出し、その検出信号を情報処理装置8に伝達するものである。ポテンシオスタット7は、電位を一定に保つ機能のほか、電位を一定速度で走査したり、指定した電位に一定時間ごとにステップしたりする機能を有する。これらの機能は、1台に搭載する必要はなく、例えば電位保持機能と電位走査機能とが別体に設けてあってもよい。 The potentiogalvanostat 7 detects a current generated between the boron-doped diamond electrode 2 and the counter electrode 3 in a state in which the potential of the boron-doped diamond electrode 2 is kept constant with respect to the reference electrode 4, and outputs the detection signal. The information is transmitted to the information processing device 8. In addition to the function of keeping the potential constant, the potentiostat 7 has a function of scanning the potential at a constant speed and stepping to a specified potential at regular intervals. 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.
情報処理装置8は、CPUや、メモリ、入出力チャンネル、キーボード等の入力手段、ディスプレイ等の出力手段、A/D変換器、D/A変換器等を備えた汎用乃至専用のものであり、前記CPU及びその周辺機器が、前記メモリの所定領域に格納されたプログラムにしたがって協働動作することにより、ポテンショガルバノスタット7で検出された信号が解析され、カドミウムの検出・定量が行われる。なお、情報処理装置8は、物理的に一体である必要はなく、有線又は無線により複数の機器に分割されていてもよい。 The information processing apparatus 8 is a general purpose or dedicated device including a CPU, memory, input / output channels, input means such as a keyboard, output means such as a display, A / D converter, D / A converter, etc. The CPU and its peripheral devices cooperate with each other according to a program stored in a predetermined area of the memory, whereby the signal detected by the potentiogalvanostat 7 is analyzed, and cadmium is detected and quantified. The information processing apparatus 8 does not need to be physically integrated, and may be divided into a plurality of devices by wire or wireless.
銅供給装置9は、銅含有溶液を収容する供給容器91と、供給管92とを備えたものであり、当該供給管92上にはペリスタルティックポンプ93が設けられている。供給容器91に収容された銅含有溶液は供給管92内をペリスタルティックポンプ93により輸送されて、測定セル5内に供給される。 The copper supply device 9 includes a supply container 91 that stores a copper-containing solution and a supply pipe 92, and a peristaltic pump 93 is provided on the supply pipe 92. The copper-containing solution accommodated in the supply container 91 is transported through the supply pipe 92 by the peristaltic pump 93 and supplied into the measurement cell 5.
次に電気化学的分析装置1を用いてストリッピング法によりカドミウムを分析する方法について説明する。なお、以下に説明する分析方法では第11族元素として銅を用いている。 Next, a method for analyzing cadmium by the stripping method using the electrochemical analyzer 1 will be described. In the analysis method described below, copper is used as the Group 11 element.
まず、分析対象のカドミウムを含有しないキャリア溶液のみを測定セル5に注入し、いわゆるバックグラウンド電流をできるだけ小さくし、かつ安定させる。次いで、試料溶液Sを測定セル5に注入し、試料溶液Sを攪拌しながら、銅イオンの濃度が0.3〜4mM程度になるようにCuCl2等の銅化合物を添加する。 First, only the carrier solution that does not contain cadmium to be analyzed is injected into the measurement cell 5 to minimize and stabilize the so-called background current. Next, the sample solution S is injected into the measurement cell 5 and a copper compound such as CuCl 2 is added while stirring the sample solution S so that the concentration of copper ions is about 0.3 to 4 mM.
その後、試料溶液Sを攪拌しながら、ポテンシオスタット7を用いてボロンドープダイヤモンド電極2の電位を負電位方向に変動させて、電位を−0.8Vにすることにより、カドミウムと銅との複合体をボロンドープダイヤモンド電極2の表面に電着させる。そして、電位を−0.8Vにした後は、しばらくの間ボロンドープダイヤモンド電極2の電位を−0.8Vに保持することによりカドミウムと銅との複合体を濃縮し充分に電着させることができる。 Thereafter, while stirring the sample solution S, the potential of the boron-doped diamond electrode 2 is changed in the negative potential direction by using the potentiostat 7 so that the potential is set to −0.8 V, whereby the composite of cadmium and copper is obtained. The body is electrodeposited on the surface of the boron-doped diamond electrode 2. Then, after the potential is set to −0.8 V, the composite of cadmium and copper can be sufficiently electrodeposited by maintaining the potential of the boron-doped diamond electrode 2 at −0.8 V for a while. it can.
なお、電着電位が−0.8Vより小さい場合(例えば、電着電位が−1.0Vや−0.9Vである場合)は、溶出工程時にカドミウムと銅との複合体に起因する電流ピークに加え、カドミウム単体に起因する電流ピークも観察されるが、分析を容易にするためにはカドミウムに起因する電流ピークは1種類のみが検出されるほうが好ましいので、本実施形態ではカドミウム単体に起因する電流ピークが出現しない電着電位である−0.8Vを採用した。 In addition, when the electrodeposition potential is smaller than −0.8 V (for example, when the electrodeposition potential is −1.0 V or −0.9 V), a current peak caused by a complex of cadmium and copper during the elution process. In addition to this, a current peak due to cadmium alone is also observed, but it is preferable to detect only one type of current peak due to cadmium in order to facilitate analysis. -0.8 V, which is an electrodeposition potential at which no current peak appears, was employed.
ボロンドープダイヤモンド電極2の表面にカドミウムと銅との複合体が電着したら、撹拌子6を停止し、ポテンシオスタット7により、ボロンドープダイヤモンド電極2の電位を−0.8Vから正電位方向に0Vまで掃引して、カドミウムと銅との複合体を試料溶液S中に溶出させる。すると、カドミウムと銅との複合体の溶出に伴い電流が発生する。 When the composite of cadmium and copper is electrodeposited on the surface of the boron-doped diamond electrode 2, the stirrer 6 is stopped and the potential of the boron-doped diamond electrode 2 is changed from −0.8 V to the positive potential direction by the potentiostat 7. Sweep to 0 V to elute the complex of cadmium and copper into the sample solution S. Then, an electric current is generated with the elution of the complex of cadmium and copper.
このような電気化学的反応によって発生した電流値(電気信号)はポテンシオスタット7に伝達され各電極における信号の制御・検出が行われる。ポテンシオスタット7で検出された信号は情報処理装置8に送信され、予め作成されたカドミウムの濃度と電流値との検量線と、得られた電流値とが対比されて、試料溶液中のカドミウム濃度が算出される。 The current value (electric signal) generated by such an electrochemical reaction is transmitted to the potentiostat 7 to control and detect the signal at each electrode. The signal detected by the potentiostat 7 is transmitted to the information processing device 8, and a calibration curve between the cadmium concentration and the current value prepared in advance is compared with the obtained current value, so that the cadmium in the sample solution is compared. The concentration is calculated.
電位の掃引が終わった後、ボロンドープダイヤモンド電極2の電位を例えば1.0Vで保持することにより、電着したカドミウムや銅は溶出するので、ボロンドープダイヤモンド電極2を測定前の状態に戻して再生することができ、同じ電極を繰り返し使用することが可能となる。なお、ボロンドープダイヤモンド電極2の再生は、一定電位の保持のみだけでなく、広い電位で繰り返し掃引を行うことによっても可能である。 After the potential sweep is completed, the electrodeposited cadmium and copper are eluted by holding the potential of the boron-doped diamond electrode 2 at, for example, 1.0 V. Therefore, the boron-doped diamond electrode 2 is returned to the state before the measurement. The same electrode can be used repeatedly. The boron-doped diamond electrode 2 can be regenerated not only by maintaining a constant potential but also by repeatedly performing sweeping at a wide potential.
したがって、このように構成された本実施形態によれば、試料溶液S中に大過剰の銅を共存させることにより、カドミウムが銅との複合体として電着する。そして、カドミウムと銅との複合体に起因するピーク電流値はカドミウムの濃度と良好に相関するので、試料溶液S中に銅や鉛等が混入していても、これらの干渉の影響を受けずに、カドミウムを高感度かつ高精度に検出・定量することができる。 Therefore, according to the present embodiment configured as described above, cadmium is electrodeposited as a complex with copper by allowing a large excess of copper to coexist in the sample solution S. And since the peak current value resulting from the composite of cadmium and copper correlates well with the concentration of cadmium, even if copper or lead is mixed in the sample solution S, it is not affected by these interferences. In addition, cadmium can be detected and quantified with high sensitivity and high accuracy.
なお、本発明は前記実施形態に限られるものではない。 The present invention is not limited to the above embodiment.
例えば、測定セル5はバッチ型に限定されず、ストップドフロー型のものであってもよい。 For example, the measurement cell 5 is not limited to a batch type, and may be a stopped flow type.
また、前記実施形態に係る電気化学的分析装置1は、ボロンドープダイヤモンド電極2、対電極3及び参照電極4を備えた三電極法による測定を行うものであるが、本発明に係る分析方法を実施するための電気化学的分析装置1としては、ボロンドープダイヤモンド電極2及び対電極3のみを備えた二電極法によるものであってもよい。三電極法の方が、ボロンドープダイヤモンド電極2と対電極3との間に印加する電圧の絶対値を制御することができるので、感度及び精度の高い測定を行うことが可能であるが、二電極法によれば、用いる電極がボロンドープダイヤモンド電極2及び対電極3の2電極ですむので、測定セル5の構造を単純化、小型化することができるので、測定セル5をチップ化し使い捨てとすることも可能となり、より簡便な測定を行いうる。 The electrochemical analysis apparatus 1 according to the embodiment performs measurement by the three-electrode method including the boron-doped diamond electrode 2, the counter electrode 3, and the reference electrode 4, but the analysis method according to the present invention is performed. The electrochemical analyzer 1 for carrying out may be based on the two-electrode method including only the boron-doped diamond electrode 2 and the counter electrode 3. In the three-electrode method, the absolute value of the voltage applied between the boron-doped diamond electrode 2 and the counter electrode 3 can be controlled, so that measurement with higher sensitivity and accuracy can be performed. According to the electrode method, since two electrodes, that is, a boron-doped diamond electrode 2 and a counter electrode 3 are used, the structure of the measurement cell 5 can be simplified and miniaturized. It is also possible to perform simpler measurement.
その他、電気化学的分析装置1は、上述のカドミウムの電気化学的分析が実施可能なものであれば、専用装置であっても汎用装置を組み合わせたものであってもよく、装置の形状や、セル容量、電極サイズ等は特に限定されない。 In addition, the electrochemical analyzer 1 may be a dedicated device or a combination of general-purpose devices as long as the above-described electrochemical analysis of cadmium can be performed. Cell capacity, electrode size, etc. are not particularly limited.
更に、前述した実施形態や変形実施形態の一部又は全部を適宜組み合わせてもよく、本発明の趣旨を逸脱しない範囲で種々の変形が可能であるのは言うまでもない。 Furthermore, it is needless to say that some or all of the above-described embodiments and modified embodiments may be appropriately combined, and various modifications are possible without departing from the spirit of the present invention.
以下に実施例を掲げて本発明を更に詳細に説明するが、本発明はこれら実施例のみに限定されるものではない。 The present invention will be described in more detail with reference to the following examples. However, the present invention is not limited to these examples.
<試験1>Cuの干渉の確認
(1)測定試料の調製
Cd標準液及び0.4M HClO4を用いて、0.4M HClO4を1mL、Cd標準液を1ppmになるように加え、全量が4mLになるよう超純水で調整した。更に、Cu標準液を用い、同様にして、Cu1ppm、及び、Cd1ppm−Cu1ppmになるよう調整した。なお、各標準液は以下のとおりである。
・Cd標準液:Cd(NO3)2 in 0.1mol/L HNO3
・Cu標準液:Cu(NO3)2 in 0.1mol/L HNO3
<Test 1> Confirmation of Cu interference (1) Preparation of measurement sample Using Cd standard solution and 0.4 M HClO 4 , 0.4 M HClO 4 was added to 1 mL and Cd standard solution to 1 ppm, and the total amount was It adjusted with the ultrapure water so that it might be set to 4 mL. Furthermore, using Cu standard solution, it adjusted similarly so that it might become Cu1ppm and Cd1ppm-Cu1ppm. Each standard solution is as follows.
Cd standard solution: Cd (NO 3 ) 2 in 0.1 mol / L HNO 3
Cu standard solution: Cu (NO 3 ) 2 in 0.1 mol / L HNO 3
(2)測定条件
測定は、ボロンドープダイヤモンド電極を作用電極、参照電極にAg/AgCl、対電極にPtを使用し、以下の条件にて、ストリッピング法で行った。
(2) Measurement conditions Measurement was performed by a stripping method using a boron-doped diamond electrode as a working electrode, Ag / AgCl as a reference electrode, and Pt as a counter electrode under the following conditions.
測定(リニアスイープボルタンメトリ(LSV))
・電着時間:60秒(55秒攪拌、5秒停止)
・電着電位:−1.4V
・走査速度:300mV/s
・走査範囲:−1.4〜1.0V
測定結果は図2に示す。
Measurement (Linear sweep voltammetry (LSV))
・ Electrodeposition time: 60 seconds (55 seconds stirring, 5 seconds stop)
・ Electrodeposition potential: -1.4V
・ Scanning speed: 300mV / s
・ Scanning range: -1.4 to 1.0V
The measurement results are shown in FIG.
図2に示すように、Cd単体に起因するピークはCuの干渉により減少(消失)することが確認された。また、0.1V(vs.Ag/AgCl)付近のピークがCuに起因することから、Cuに起因するピークはCdの干渉により増加することも確認された。 As shown in FIG. 2, it was confirmed that the peak caused by Cd alone decreased (disappeared) due to Cu interference. Further, since the peak near 0.1 V (vs. Ag / AgCl) is attributed to Cu, it was also confirmed that the peak attributed to Cu increases due to the interference of Cd.
<試験2>Au共存下でのCdの電気化学的分析
(1)測定試料の調製
0.4M HClO4を1mL、Au標準液を100ppmになるように加え、更に、Cd標準液又はCu標準液を、Cd1ppm又はCu1ppmになるように加え、全量が4mLになるよう超純水で調整した。なお、Au標準液は以下のとおりである
・Au標準液:HAuCl4 in 1mol/L HCl
<Test 2> Electrochemical analysis of Cd in the presence of Au (1) Preparation of measurement sample 0.4 M HClO 4 was added to 1 mL and Au standard solution to 100 ppm, and Cd standard solution or Cu standard solution was further added. Was added so that it might become Cd1ppm or Cu1ppm, and it adjusted with the ultrapure water so that the whole quantity might be set to 4 mL. In addition, Au standard solution is as follows: Au standard solution: HAuCl 4 in 1 mol / L HCl
測定は、ボロンドープダイヤモンド電極を作用電極、参照電極にAg/AgCl、対電極にPtを使用し、以下の条件にて、ストリッピング法で行った。 The measurement was performed by a stripping method using a boron-doped diamond electrode as a working electrode, Ag / AgCl as a reference electrode, and Pt as a counter electrode under the following conditions.
測定(リニアスイープボルタンメトリ(LSV))
・電着電位:−0.4V
・電着時間:60秒(55秒攪拌、5秒停止)
・走査速度:300mV/s
・走査範囲:−0.4〜0.8V
Measurement (Linear sweep voltammetry (LSV))
・ Electrodeposition potential: -0.4V
・ Electrodeposition time: 60 seconds (55 seconds stirring, 5 seconds stop)
・ Scanning speed: 300mV / s
・ Scanning range: -0.4 to 0.8V
後電解(サイクリックボルタンメトリ(CV))
・電解溶液:0.1M HCl
・走査範囲:−0.4〜1.4V、5サイクル
測定結果は図3に示す。
Post-electrolysis (cyclic voltammetry (CV))
Electrolyte solution: 0.1M HCl
Scanning range: -0.4 to 1.4V, 5 cycles The measurement results are shown in FIG.
図3に示すように、Cd又はCuを含む試料について測定を行ったところ、−0.15〜0V(vs.Ag/AgCl)付近にCdに起因するピークが確認され、0.35V(vs.Ag/AgCl)付近にCuに起因するピークが確認された。 As shown in FIG. 3, when a sample containing Cd or Cu was measured, a peak caused by Cd was confirmed in the vicinity of −0.15 to 0 V (vs. Ag / AgCl), and 0.35 V (vs. In the vicinity of (Ag / AgCl), a peak due to Cu was confirmed.
なお、通常−0.4Vでは電着しないCdのピークが本試験で観察されたのは、AuによるUPD効果によるものと考えられ、CdはCd表面上に析出する電位よりも高い電位で、Au表面上にCd−Au複合体として析出し、Cd単独の酸化還元電位よりも高い電位で溶出するためであると思われる。このため、−0.15〜0V(vs.Ag/AgCl)付近のCdに起因するピークは、Cd−Au複合体に起因するピークに相当すると思われる。 Note that the Cd peak, which is not electrodeposited at −0.4 V, is observed in this test because of the UPD effect due to Au, and Cd is higher than the potential deposited on the Cd surface. This is presumably because it precipitates as a Cd—Au complex on the surface and elutes at a higher potential than the redox potential of Cd alone. For this reason, the peak attributed to Cd in the vicinity of −0.15 to 0 V (vs. Ag / AgCl) seems to correspond to the peak attributed to the Cd—Au complex.
<試験3>Cd−Au複合体ピーク電流値のCd濃度依存性
Au100ppm共存下で、Cu濃度を1ppmに固定し、Cd濃度を変えて、−0.15〜0V(vs.Ag/AgCl)付近のピーク電流値のCd濃度依存性の検討を行った。得られた結果(検量線)を図4に示す。
<Test 3> Cd concentration dependence of Cd-Au composite peak current value In the presence of 100 ppm of Au, the Cu concentration is fixed at 1 ppm, the Cd concentration is changed, and is around -0.15 to 0 V (vs. Ag / AgCl) The Cd concentration dependence of the peak current value was examined. The obtained results (calibration curve) are shown in FIG.
図4に示すように、−0.15〜0V(vs.Ag/AgCl)付近のピーク電流値にはCd濃度との高い相関性が確認された。 As shown in FIG. 4, the peak current value near −0.15 to 0 V (vs. Ag / AgCl) was confirmed to be highly correlated with the Cd concentration.
<試験4>大過剰Cu共存下でのCdの電気化学的分析
(1)測定試料の調製
塩化カドミウム(CdCl2)、塩化銅(CuCl2)及び0.4M HClO4を用いて、0.4M HClO4を1mLに対して、Cd0.01.0mM(約1ppm相当)、Cu0.05mM(約3ppm相当)になるように加え、全量が4mLになるよう超純水で調整した。
<Test 4> Electrochemical analysis of Cd in the presence of a large excess of Cu (1) Preparation of measurement sample 0.4 M using cadmium chloride (CdCl 2 ), copper chloride (CuCl 2 ) and 0.4 M HClO 4 HClO 4 was added to 1 mL of Cd to be 0.01.0 mM (equivalent to about 1 ppm) and Cu 0.05 mM (equivalent to about 3 ppm), and the total amount was adjusted to 4 mL with ultrapure water.
(2)測定条件
測定は、ボロンドープダイヤモンド電極を作用電極、参照電極にAg/AgCl、対電極にPtを使用し、以下の条件にて、ストリッピング法で行った。
(2) Measurement conditions Measurement was performed by a stripping method using a boron-doped diamond electrode as a working electrode, Ag / AgCl as a reference electrode, and Pt as a counter electrode under the following conditions.
測定(リニアスイープボルタンメトリ(LSV))
・電着電位:−1.0V、−0.9V、−0.8V
・電着時間:60秒(55秒攪拌、5秒停止)、
・走査速度:300mV/s、
・走査範囲:〜0V
Measurement (Linear sweep voltammetry (LSV))
Electrodeposition potential: -1.0V, -0.9V, -0.8V
-Electrodeposition time: 60 seconds (55 seconds stirring, 5 seconds stop),
・ Scanning speed: 300 mV / s
・ Scanning range: ~ 0V
後電解(リニアスイープボルタンメトリ(LSV))
・電解溶液:0.1M HClO4 aq
・初期電位:−1.0V
・保持時間:1秒
・走査範囲:−1.0〜1.4V
・後処理:PS30秒
測定結果は図5に示す。
Post-electrolysis (Linear sweep voltammetry (LSV))
Electrolyte solution: 0.1M HClO 4 aq
・ Initial potential: -1.0V
-Holding time: 1 second-Scanning range: -1.0 to 1.4V
-Post-processing: PS 30 seconds The measurement results are shown in FIG.
図5に示すように、電着電位が−1.0V及び−0.9Vのときは、−0.6V(vs.Ag/AgCl)付近のCd単体に起因するピークに加えて、−0.45V(vs.Ag/AgCl)付近にCd−Cu複合体に起因するピークが観察された。また、電着電位が−0.8Vであると、Cd−Cu複合体に起因するピークのみが観察され、Cd単体に起因するピークは観察されなかった。これは、Au同様、CuのUPD効果によってCdがCd−Cu複合体となり、標準酸化還元電位よりも高い電位で電着することによるものと考えられる。更に、Cuに起因する過大電流が0Vで生じることも確認された。 As shown in FIG. 5, when the electrodeposition potential is −1.0 V and −0.9 V, in addition to the peak due to Cd alone in the vicinity of −0.6 V (vs. Ag / AgCl), −0. A peak attributed to the Cd—Cu complex was observed near 45 V (vs. Ag / AgCl). Moreover, when the electrodeposition potential was −0.8 V, only the peak attributed to the Cd—Cu composite was observed, and the peak attributed to the Cd simple substance was not observed. This is thought to be due to the fact that Cd becomes a Cd—Cu composite due to the UPD effect of Cu, as with Au, and is electrodeposited at a potential higher than the standard oxidation-reduction potential. Furthermore, it was confirmed that an excessive current caused by Cu was generated at 0V.
<試験5>Cd−Cu複合体ピーク電流値のCd濃度依存性
Cu1.0mM共存下で、Cd濃度を変えて、−0.45V(vs.Ag/AgCl)付近のCd−Cu複合体に起因するピーク電流値のCd濃度依存性の検討を行った。得られた結果(検量線)を図6に示す。
<Test 5> Cd concentration dependency of Cd-Cu complex peak current value Caused by Cd-Cu complex near -0.45 V (vs. Ag / AgCl) by changing Cd concentration in the presence of Cu 1.0 mM The Cd concentration dependence of the peak current value was examined. The obtained results (calibration curve) are shown in FIG.
図6に示すように、Cu1.0mM共存下において、Cd−Cu複合体に起因するピーク電流値にはCd濃度との高い相関性が確認された。なお、Cu0.5mM、Cu1.5mM共存下においても同様なCd濃度依存性が確認された(データ省略)。 As shown in FIG. 6, a high correlation with the Cd concentration was confirmed in the peak current value caused by the Cd—Cu composite in the presence of Cu 1.0 mM. The same Cd concentration dependency was confirmed even in the presence of Cu 0.5 mM and Cu 1.5 mM (data not shown).
<試験6>Cd−Cu複合体ピーク電流値のCd濃度依存性(微量Cu混在下)
水質汚濁防止法の排水基準が3ppmであることに鑑み、Cu1.0mM共存下に、更に±3ppmのCuを加えた状態で、Cd濃度を変えて、−0.45V(vs.Ag/AgCl)付近のCd−Cu複合体に起因するピーク電流値のCd濃度依存性の検討を行った。得られた結果(検量線)を図7に示す。
<Test 6> Dependence of Cd-Cu composite peak current value on Cd concentration (under trace Cu mixing)
In view of the fact that the water pollution standard of the Water Pollution Control Law is 3 ppm, in the coexistence of Cu 1.0 mM, with the addition of ± 3 ppm of Cu, the Cd concentration is changed to −0.45 V (vs. Ag / AgCl) The Cd concentration dependence of the peak current value caused by the nearby Cd—Cu composite was examined. The obtained results (calibration curve) are shown in FIG.
図7に示すように、実サンプルに近い3ppmのCuを含有する測定試料においても、Cd−Cu複合体に起因するピーク電流値にはCd濃度との高い相関性が確認された。 As shown in FIG. 7, even in the measurement sample containing 3 ppm of Cu close to the actual sample, the peak current value caused by the Cd—Cu composite was confirmed to have a high correlation with the Cd concentration.
<試験7>Cd−Cu複合体ピーク電流値のCd濃度依存性(微量Pb混在下)
他の妨害成分共存化におけるCd−Cu複合体に起因するピーク電流値のCd濃度依存性の検討を行うために、Cu3.0mM共存下で、0.0025mM(500ppb相当)及び0.005mM(1ppm相当)の塩化鉛(PbCl2)を添加して、Cd濃度を0.002mM(約200ppb)〜0.01.0mM(約1ppm)の間で変化させて、−0.45V(vs.Ag/AgCl)付近のCd−Cu複合体に起因するピーク電流値のCd濃度依存性の検討を行った。得られた結果(検量線)を図8に示す。
<Test 7> Dependence of Cd-Cu composite peak current value on Cd concentration (under mixed Pb)
In order to investigate the Cd concentration dependency of the peak current value caused by the Cd-Cu complex in the coexistence of other interfering components, 0.0025 mM (equivalent to 500 ppb) and 0.005 mM (1 ppm) in the presence of Cu 3.0 mM. Equivalent) of lead chloride (PbCl 2 ) and the Cd concentration is varied between 0.002 mM (about 200 ppb) to 0.01.0 mM (about 1 ppm) to obtain −0.45 V (vs. Ag / The Cd concentration dependence of the peak current value attributed to the Cd—Cu complex near (AgCl) was examined. The obtained results (calibration curve) are shown in FIG.
図8に示すように、微量のPb混在下においても、Cuを3.0mM添加することにより、Cd−Cu複合体に起因するピーク電流値にはCd濃度との高い相関性が確認された。 As shown in FIG. 8, even in the presence of a small amount of Pb, a high correlation with the Cd concentration was confirmed in the peak current value caused by the Cd—Cu complex by adding 3.0 mM of Cu.
1・・・電気化学的分析装置
2・・・ボロンドープダイヤモンド電極
3・・・対電極
4・・・参照電極
5・・・測定セル
6・・・撹拌子
7・・・ポテンシオスタット
8・・・情報処理装置
9・・・銅供給装置
S・・・試料溶液
DESCRIPTION OF SYMBOLS 1 ... Electrochemical analyzer 2 ... Boron dope diamond electrode 3 ... Counter electrode 4 ... Reference electrode 5 ... Measurement cell 6 ... Stirrer 7 ... Potentiostat 8 ..Information processing device 9 ... Copper supply device S ... Sample solution
Claims (8)
前記試料溶液に、銅、銀又は金のいずれかの金属元素を添加する添加工程と、
前記銅、銀又は金のいずれかの金属元素が添加された前記試料溶液に前記作用電極と前記対電極とを接触させた状態で、前記作用電極と前記対電極との間に、前記作用電極にカドミウムと前記銅、銀又は金のいずれかの金属元素との複合体が電着する電圧を印加し、前記作用電極に前記複合体を電着させる電着工程と、
前記作用電極と前記対電極との間に、前記作用電極に電着した前記複合体が溶出する電圧を印加して、前記作用電極から前記複合体を溶出させる溶出工程と、
前記複合体の溶出に起因して、前記作用電極と前記対電極との間に生じた電流を検出する検出工程と、を備えていることを特徴とする電気化学的分析方法。 A method for electrochemically analyzing cadmium in a sample solution using a counter electrode and a working electrode comprising a carbon electrode,
An addition step of adding any one of copper, silver or gold metal element to the sample solution;
The working electrode is placed between the working electrode and the counter electrode in a state where the working electrode and the counter electrode are brought into contact with the sample solution to which the metal element of copper, silver, or gold is added. Applying a voltage at which a composite of cadmium and the metal element of any one of copper, silver or gold is electrodeposited, and electrodepositing the composite onto the working electrode;
An elution step of eluting the complex from the working electrode by applying a voltage at which the complex electrodeposited on the working electrode is eluted between the working electrode and the counter electrode;
And a detection step of detecting a current generated between the working electrode and the counter electrode due to elution of the complex.
対電極とカーボン電極からなる作用電極とを内蔵し、前記試料溶液を収容するためのセルと、
前記試料溶液に銅、銀又は金のいずれかの金属元素を添加する添加手段と、
前記作用電極と前記対電極との間に、前記作用電極にカドミウムと前記銅、銀又は金のいずれかの金属元素との複合体が電着する電圧を印加し、次いで、前記作用電極に電着した前記複合体が溶出する電圧を印加する印加手段と、
前記作用電極と前記対電極との間に生じた電流を検出する検出手段と、を備えていることを特徴とする電気化学的分析装置。 An apparatus for electrochemically analyzing cadmium in a sample solution,
A cell containing a counter electrode and a working electrode composed of a carbon electrode, and containing the sample solution;
An adding means for adding a metal element of copper, silver or gold to the sample solution;
Between the working electrode and the counter electrode, a voltage at which a complex of cadmium and the metal element of any one of copper, silver, and gold is electrodeposited is applied to the working electrode, and then the electrode is applied to the working electrode. Applying means for applying a voltage at which the worn composite is eluted;
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 5, 6 or 7 , wherein the adding means adds copper to the sample solution .
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