JP2007071721A - Electrode for arsenic detection, sensor using it, and arsenic concentration measuring method - Google Patents
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本発明は、ヒ素の電気化学的検出用電極、これを使用するヒ素用センサー及びヒ素濃度測定方法に関する。 The present invention relates to an arsenic electrochemical detection electrode, an arsenic sensor using the same, and an arsenic concentration measurement method.
ＷＨＯ（世界保健機構）の飲料水ガイドラインではヒ素の許容濃度は0.01ppm（0.13μM）以下であり、厳しい管理を要求されている。土壌に広範に存在するヒ素による地下水汚染が問題となっている国は数多くあり、その除去設備と水質検査が必須となっている。
Ａｓ（III）、Ａｓ（Ｖ）の検出法として、既に多くの分析手法が報告されている。市販試薬による手段としては、亜鉛（還元剤）により発生する水素化ヒ素（アルシン）ガスを指標とするものがあるが、２ppbが測定限界であり、安全な濃度を管理するにはやや感度が劣る。
According to the WHO (World Health Organization) drinking water guidelines, the allowable concentration of arsenic is 0.01 ppm (0.13 μM) or less, and strict management is required. There are many countries where groundwater contamination by arsenic, which is widely present in soil, is a problem, and removal facilities and water quality tests are essential.
Many analytical methods have already been reported as detection methods for As (III) and As (V). Some commercially available reagents use arsenic hydride (arsine) gas generated by zinc (reducing agent) as an index, but 2 ppb is the limit of measurement, and sensitivity is somewhat inferior to manage safe concentrations. .
分析手法については、Talanta, 64, 269-277(2004)に詳細に紹介されている。原子吸光法、ＩＣＰ−ＭＳ（誘導励起発光プラズマ質量分析）などが優れているが、現場において、迅速で簡易かつ低価格な測定手段としては不向きである。
その点では、電気化学的方法が好適といえる。例えば水銀電極は再現性、安定性の点で優れているが、取り扱いが不便であり、最近では固体電極が利用されている。その中で、金はヒ素イオン還元に対して、また、電着したヒ素の酸化においても安定に作動するため、好適である。
しかしながら、ヒ素還元又は酸化に関して選択性の高い電極材料はなく、実用の観点から、安定かつ選択性の高いヒ素還元又は酸化電極の開発が望まれている。
電気化学的手法でヒ素の濃度測定を行う場合、電極材料の選定が重要である。一般に金電極が安定な材料として利用されるが、後述のように、金表面では液中に存在する酸素還元による過酸化水素生成の際に電流が流れ、ヒ素還元の電流と区別できないため、ヒ素濃度を正確に定量できなくなる。
従って実用性の観点から、安定かつ選択性の高い電極の開発が望まれていた。
The analysis method is introduced in detail in Talanta, 64, 269-277 (2004). Atomic absorption, ICP-MS (Inductive Excitation Luminescence Plasma Mass Spectrometry) and the like are excellent, but are not suitable as a quick, simple, and low-cost measuring means in the field.
In that respect, an electrochemical method is preferable. For example, a mercury electrode is excellent in terms of reproducibility and stability, but is inconvenient to handle, and recently a solid electrode has been used. Among them, gold is preferable because it operates stably against arsenic ion reduction and also in the oxidation of electrodeposited arsenic.
However, there is no electrode material with high selectivity for arsenic reduction or oxidation, and development of an arsenic reduction or oxidation electrode with high stability and selectivity is desired from a practical viewpoint.
When measuring the concentration of arsenic by an electrochemical method, the selection of the electrode material is important. Generally, a gold electrode is used as a stable material. However, as will be described later, an electric current flows on the gold surface when hydrogen peroxide is generated by oxygen reduction present in the liquid and cannot be distinguished from an arsenic reduction current. The concentration cannot be accurately determined.
Accordingly, development of a stable and highly selective electrode has been desired from the viewpoint of practicality.
前述した通り、電気化学的なヒ素検出方法における金材料の利用は従来から行われており、検出限界は0.2ppb程度まで向上したが、再現性を得るのが困難であった。
最近になってCompton [Anal. Chem., 76, 5924-5929(2004)]らは、陰分極によるヒ素析出後のアノードストリッピング法を提案し、金ナノ粒子を電着させたグラッシーカーボンにより、安定した応答性を報告したが、上記した過酸化水素生成の際の電流の問題は未解決のままであった。
As described above, the use of a gold material in an electrochemical arsenic detection method has been conventionally performed, and the detection limit has been improved to about 0.2 ppb, but it has been difficult to obtain reproducibility.
Recently Compton [Anal. Chem., 76, 5924-5929 (2004)] and others proposed an anodic stripping method after arsenic precipitation by negative polarization, and by glassy carbon electrodeposited with gold nanoparticles, Although stable responsiveness was reported, the problem of current during hydrogen peroxide generation described above remained unresolved.
本発明者らは、ヒ素成分を選択的かつ安定に電着かつ離脱できる電極につき鋭意検討の結果、目的の反応を効率よく行える特殊な電極、及びこれを用いたセンサーを見出したものである。 As a result of intensive studies on electrodes capable of selectively and stably electrodepositing and releasing arsenic components, the present inventors have found a special electrode capable of efficiently performing a desired reaction and a sensor using the same.
本発明は、第１に導電性基体、及び該導電性基体表面全体に被覆された、ハロゲン化物イオンを吸着した金を含んでなることを特徴とするヒ素検出用電極、第２にこのヒ素検出用電極を作用極とし、他に対極及び基準極を含んで成るヒ素検出用センサーであり、第３に、このセンサーを用い、貴の電位から卑の電位に電位を走査し溶液に存在するヒ素成分を還元電着させ、その後卑な電位から貴な電位に走査し該成分を溶解させ、発生する酸化電流或いは電気量から、ヒ素濃度を求めることを特徴とするヒ素濃度検出方法である。 The present invention provides, firstly, an arsenic detection electrode comprising a conductive substrate and gold adsorbed on halide ions coated on the entire surface of the conductive substrate, and secondly, this arsenic detection. A sensor for detecting arsenic comprising a working electrode as a working electrode and a counter electrode and a reference electrode. Third, arsenic present in a solution by scanning the potential from a noble potential to a base potential using this sensor. This is an arsenic concentration detection method characterized in that a component is subjected to reductive electrodeposition, and then scanned from a base potential to a noble potential to dissolve the component, and an arsenic concentration is determined from the generated oxidation current or quantity of electricity.
以下本発明を詳細に説明する。
本発明の電極では、導電性部材の表面全体に、吸着種であるハロゲン化物イオンを吸着した金を被覆する。吸着種の被覆は、好ましくは原子レベルの薄膜状又は単層吸着とし、当該電極はヒ素検出用センサー（ヒ素の濃度測定）に使用できる。
The present invention will be described in detail below.
In the electrode of the present invention, the entire surface of the conductive member is coated with gold adsorbed with halide ions as adsorbing species. The coating of the adsorbed species is preferably an atomic level thin film or single layer adsorption, and the electrode can be used for an arsenic detection sensor (arsenic concentration measurement).
通常の場合、ヒ素濃度の定量にはアノードストリッピング法が使用される。
この方法は、貴の電位から卑の電位に向けて電位を走査し溶液に存在するヒ素成分を電極上に還元電着させ、その後卑な電位から貴な電位に走査し前記ヒ素成分を溶解させ、この再溶解時に発生する酸化電流或いは電気量から、ヒ素濃度を求める方法である。
Usually, the anodic stripping method is used to determine the arsenic concentration.
In this method, the potential is scanned from the noble potential to the base potential, the arsenic component present in the solution is reduced and electrodeposited on the electrode, and then the base potential is scanned to the noble potential to dissolve the arsenic component. This is a method for obtaining the arsenic concentration from the oxidation current or the amount of electricity generated during the remelting.
つまりアノードストリッピング法では、まずヒ素イオンの還元による電極上への析出が式（１）に従って進行する。
Ａｓ(3＋)＋３ｅ = Ａｓ（０） （１）
次いでこのヒ素が析出した電極を陽分極することで、式（２）に従ってヒ素が再溶解する。
Ａｓ(０) = Ａｓ（３＋）＋ ３ｅ （２）
この再溶解時の電流値を測定し、この値を濃度に換算してヒ素濃度を算出する。
That is, in the anode stripping method, first, precipitation on the electrode by reduction of arsenic ions proceeds according to the equation (1).
As (3 +) + 3e = As (0) (1)
Next, the electrode on which the arsenic is deposited is positively polarized, so that arsenic is redissolved according to the formula (2).
As (0) = As (3 +) + 3e (2)
The current value at the time of re-dissolution is measured, and this value is converted into a concentration to calculate the arsenic concentration.
しかしこの再溶解の電流測定時に、酸素が存在すると、目的とする式（１）及び（２）の反応以外に、前記酸素の還元反応が生じてヒ素濃度の算定に誤差を生じると予測できる。
つまり、下記の酸素還元による過酸化水素の生成と酸素の４電子還元による過酸化水素の生成が生じ、この際に生じる電流を、電着ヒ素の還元再溶解による電流と区別できず、この再溶解時の電流を正確に測定できなくなる。
However, when oxygen is present at the time of re-dissolution current measurement, it can be predicted that the oxygen reduction reaction occurs in addition to the intended reactions of equations (1) and (2), resulting in an error in the calculation of the arsenic concentration.
In other words, hydrogen peroxide is generated by the following oxygen reduction and hydrogen peroxide is generated by four-electron reduction of oxygen. The current generated at this time cannot be distinguished from the current due to the re-dissolution of electrodeposited arsenic. The current during melting cannot be measured accurately.
[１]酸素還元による過酸化水素の生成
溶液中に溶存している酸素が、還元しうる電位に電極が保持されている場合、式（３）及び（４）に従って容易に過酸化水素に変換される。
Ｏ２＋２ｅ＋Ｈ２Ｏ ＝ ＯＨ−＋ＨＯ２ − （３）
Ｏ２＋２ｅ＋２Ｈ＋ ＝ Ｈ２Ｏ２ （４）
この電位はヒ素の電着電位より貴であるため、容易に反応が進行し、ヒ素の電着を阻害する。また、過酸化水素は金表面が露出していると触媒的に分解が進行するが、一方で酸化剤として、電着したヒ素を酸化する作用がある。
従って酸素が存在すると、従来の電極を使用するヒ素濃度測定では、電着量が変化し、酸化電流（ストリッピング）から正確なヒ素濃度を算出できない。
[1] Generation of hydrogen peroxide by oxygen reduction When the electrode is maintained at a potential at which oxygen dissolved in the solution can be reduced, it is easily converted to hydrogen peroxide according to equations (3) and (4). Is done.
O 2 + 2e + H 2 O = OH − + HO 2 − (3)
O 2 + 2e + 2H + = H 2 O 2 (4)
Since this potential is more noble than the arsenic electrodeposition potential, the reaction proceeds easily and inhibits arsenic electrodeposition. In addition, hydrogen peroxide decomposes catalytically when the gold surface is exposed, but on the other hand, it acts to oxidize electrodeposited arsenic as an oxidizing agent.
Therefore, when oxygen is present, in the arsenic concentration measurement using a conventional electrode, the amount of electrodeposition is changed, and an accurate arsenic concentration cannot be calculated from the oxidation current (stripping).
[２]酸素の４電子還元
酸素の４電子還元反応も金表面で進行し、例えば金の(１００)面では−０．３５Ｖより貴の電位で式（５）に従って進行することが報告されている。
Ｏ２＋４ｅ−＋２Ｈ２Ｏ＝ ４ＨＯ− （５）
この反応も電着を阻害し、酸素の存在により酸素還元に起因する電流が流れ、正確なヒ素濃度を算出ができなくなる。
[2] Four-electron reduction of oxygen It is reported that the four-electron reduction reaction of oxygen also proceeds on the gold surface, for example, on the (100) plane of gold, proceeding according to formula (5) at a noble potential from -0.35V. Yes.
O 2 + 4e − + 2H 2 O = 4HO − (5)
This reaction also inhibits electrodeposition, and current due to oxygen reduction flows due to the presence of oxygen, making it impossible to calculate an accurate arsenic concentration.
本発明者らは、電極上での過酸化水素や酸素の応答性を鋭意検討し、酸素や過酸化水素が被測定溶液中に存在しても、ヒ素濃度を正確に測定できる電極について種々検討した結果、ハロゲン化物イオンを吸着（原子単層レベル）させた電極は、酸素、過酸化水素に関して不活性な表面となる一方、ヒ素イオンの還元析出に関しては選択的に進行する特徴を見出した。この吸着された電極により、広範囲の濃度に応じた電流が検出できることを確認した。
つまり、吸着種の原子配列による遮蔽効果により、酸素の過酸化水素への還元が阻害されるため、バックグラウンド電流が非常に小さく、電流値はより正確にヒ素濃度に対応することを見出したのである。
The present inventors diligently investigated the responsiveness of hydrogen peroxide and oxygen on the electrode, and variously examined electrodes that can accurately measure the arsenic concentration even when oxygen or hydrogen peroxide is present in the solution to be measured. As a result, it has been found that the electrode on which halide ions are adsorbed (at the atomic monolayer level) has an inactive surface with respect to oxygen and hydrogen peroxide, while selective reduction of arsenic ions proceeds. It was confirmed that a current corresponding to a wide range of concentrations could be detected by the adsorbed electrode.
In other words, because the shielding effect by the atomic arrangement of adsorbed species hinders the reduction of oxygen to hydrogen peroxide, the background current is very small, and the current value more accurately corresponds to the arsenic concentration. is there.
本発明の電極は、ヒ素濃度測定時に電流を正しく選択的に測定してヒ素濃度を正確に算出できる優れた電極であると云える。これは電極表面に被覆形成した吸着種であるハロゲン化物イオンが酸素、過酸化水素に関して不活性な表面となる一方、ヒ素イオンの還元析出に関しては選択的に進行させるからである。
更に吸着種の固定操作が容易であるため、消耗した場合でも原料溶液に浸漬するだけで容易に再活性化される。広い濃度範囲(0.1mM〜100mM)において利用可能であり、センサー価格の低減、測定時間の短縮が達成されるため、実用上の効果は顕著である。
The electrode of the present invention can be said to be an excellent electrode that can accurately calculate the arsenic concentration by correctly and selectively measuring the current when measuring the arsenic concentration. This is because halide ions, which are adsorbed species formed on the electrode surface, become an inactive surface with respect to oxygen and hydrogen peroxide, while selective reduction of arsenic ions proceeds.
Furthermore, since the adsorbing species can be easily fixed, even if it is consumed, it can be easily reactivated simply by immersing it in the raw material solution. Since it can be used in a wide concentration range (0.1 mM to 100 mM) and the sensor price can be reduced and the measurement time can be shortened, the practical effect is remarkable.
次に、本発明のヒ素検出用電極、これを用いるセンサー及びヒ素濃度測定方法の詳細を説明する。
導電性基体の形状は、板や棒のみならず、メッシュ加工や打ち抜きによる穴明き板などが可能である。その材質は、通常の電極で使用されている任意の材料の使用が可能であるが、特に金属、又はカーボン材料が好ましく使用でき、金や銀を被覆した金属でも良い。
金、銀を被覆する場合は、熱分解法、樹脂による固着法、蒸着法、電気めっき、無電解めっきなどにより全面が被覆されていることが好ましい。これらの被覆金属の厚さは、0.1μm〜１mmが好ましい。
Next, details of the arsenic detection electrode of the present invention, a sensor using the same, and an arsenic concentration measurement method will be described.
The shape of the conductive substrate can be not only a plate or a bar but also a perforated plate by mesh processing or punching. As the material, any material used in ordinary electrodes can be used, but a metal or a carbon material can be preferably used, and a metal coated with gold or silver may be used.
When gold or silver is coated, the entire surface is preferably coated by a thermal decomposition method, a resin fixing method, a vapor deposition method, electroplating, electroless plating, or the like. The thickness of these coated metals is preferably 0.1 μm to 1 mm.
この導電性基体上に金粒子、特に金ナノ粒子を被覆する。当該金ナノ粒子上にハロゲン化物イオンを吸着させることで、より優れた濃度応答性を示す。ハロゲン化物イオンの吸着が必須であり、金ナノ粒子のみでは、溶存酸素、吸着酸素の還元反応が同時に進行するため、バックグランド電流が大きく、濃度の算定における誤差となる。
前記ナノ粒子を形成させる方法としては、電気化学的手法が好適であることが知られている。例として、0.1mMの塩化金イオンを溶解した溶液中にカーボン製導電性基材を浸漬し、0.5Mの硫酸中で、+1.1V（vs.Ag/AgCl）から０V付近まで電位をステップさせ、数秒程度保持することにより、金粒子が形成される。液濃度が高く、また、電析時間が長すぎると、粒子が成長しすぎて不均一化し、かえって感度が低下する。
The conductive substrate is coated with gold particles, particularly gold nanoparticles. By adsorbing halide ions on the gold nanoparticles, better concentration responsiveness is exhibited. Adsorption of halide ions is essential, and with gold nanoparticles alone, the reduction reaction of dissolved oxygen and adsorbed oxygen proceeds at the same time, so the background current is large and an error in calculating the concentration.
It is known that an electrochemical method is suitable as a method for forming the nanoparticles. As an example, a carbon conductive substrate is immersed in a solution of 0.1 mM gold chloride ion, and the potential is stepped from +1.1 V (vs. Ag / AgCl) to around 0 V in 0.5 M sulfuric acid. By holding for about several seconds, gold particles are formed. If the liquid concentration is high and the electrodeposition time is too long, the particles grow too much and become non-uniform, and the sensitivity is lowered.
次に、ハロゲン化物イオンを溶かした水或いは有機溶媒（メタノール、アセトンなど）に前記導電性基体を浸漬すると、金粒子表面に選択的にハロゲン化物イオンが吸着される。吸着種は特別な保存方法を行わなくても、大気中に安定に保存できる。固着されなかった分は有機溶媒のみの溶液に浸漬すると簡単に除去でき、水洗してから電極として用いる。
ハロゲン化物イオンとしては、ヨウ素、塩素、臭素、フッ素化合物が使用でき、安定性に優れるヨウ素、臭素化合物が特に好ましい。これらの化合物は塩でもよく、また酸の形態でもよい。
Next, when the conductive substrate is immersed in water or an organic solvent (methanol, acetone, etc.) in which halide ions are dissolved, the halide ions are selectively adsorbed on the gold particle surfaces. Adsorbed species can be stably stored in the atmosphere without any special storage method. The part that has not been fixed can be easily removed by immersing it in a solution containing only an organic solvent.
As the halide ion, iodine, chlorine, bromine and fluorine compounds can be used, and iodine and bromine compounds having excellent stability are particularly preferred. These compounds may be a salt or an acid form.
前記吸着種の吸着に際しては、導電性基体表面全体に吸着種が存在するように吸着させることが必要で、吸着種が存在しない表面があると、その表面で前記した酸素の還元反応等（[１]〜[２]）が進行してしまい、正確なヒ素濃度の測定ができなくなる。しかし、吸着種を２層以上存在させる必要はなく、吸着種は単層吸着（吸着種の被覆率が１）とすることが望ましく、実際には被覆率が１を僅かに上回るように吸着させることが好ましい。
なお導電性基体表面への金被覆と金粒子への吸着種の吸着を同時に行っても良い。
When adsorbing the adsorbed species, it is necessary to adsorb so that the adsorbed species exist on the entire surface of the conductive substrate. If there is a surface on which no adsorbed species exists, the oxygen reduction reaction described above ([ 1] to [2]) proceed and accurate measurement of the arsenic concentration becomes impossible. However, it is not necessary for two or more layers of adsorbed species to exist, and it is desirable that the adsorbed species be single-layer adsorbed (adsorbed species coverage is 1). In fact, adsorption is performed so that the coverage is slightly higher than 1. It is preferable.
The gold coating on the surface of the conductive substrate and the adsorption of the adsorbed species on the gold particles may be performed simultaneously.
本発明のヒ素検出用電極を使用してセンサーを構成する場合は、基準電極を前記ヒ素検出用電極近傍に設置したセルとすることが好ましい。被測定液と前記過酸化水素還元電極は直接接触させるが、対極、基準電極は隔膜などで区画した別室に配置することが可能である。
被測定液の溶液抵抗が大きい場合には、微小電極、ＭＤＡ（マイクロディスクアレイ）電極の形態が好ましく、イオン伝導性が不足するような系では固体電解質成分を付与する構造であってもよい。通常、被測定液を電極系を設置した容器内に入れ、攪拌のない静置状態で測定することが望ましい。
なお卑な電位では吸着種が脱離して吸着率が低くなり、金などの導電性基体本来の過酸化水素分解特性や酸素還元特性が発現するため、一旦吸着種がなくなれば、センサーとしての精度は低下する。定常的に流れる試料を連続的に測定するには吸着種を補給することが望ましい。従って吸着種を溶解した溶液を準備しておき、測定毎に吸着種を導電性基体表面に吸着させる操作を行うことが望ましい。
When the sensor is configured using the arsenic detection electrode of the present invention, it is preferable that the reference electrode is a cell installed in the vicinity of the arsenic detection electrode. The liquid to be measured and the hydrogen peroxide reduction electrode are in direct contact with each other, but the counter electrode and the reference electrode can be arranged in separate chambers partitioned by a diaphragm or the like.
When the solution resistance of the liquid to be measured is large, a form of a microelectrode or an MDA (microdisk array) electrode is preferable, and a structure in which a solid electrolyte component is imparted may be used in a system in which ion conductivity is insufficient. Usually, it is desirable to place the liquid to be measured in a container provided with an electrode system and perform the measurement in a stationary state without stirring.
At low potential, the adsorbed species are desorbed and the adsorption rate is lowered, and the original hydrogen peroxide decomposition characteristics and oxygen reduction characteristics of conductive substrates such as gold are developed. Will decline. It is desirable to replenish the adsorbed species in order to continuously measure a constantly flowing sample. Therefore, it is desirable to prepare a solution in which the adsorbed species is dissolved and perform an operation of adsorbing the adsorbed species on the surface of the conductive substrate every measurement.
実際の測定操作では、ヒ素が電析する電位から酸化溶解する電位まで走査する。ステップかスィープで電位を走査することが好ましい。感度を向上するために微分電位、電流パルスを加えて、電極界面の容量電流成分や、ＩＲ抵抗を補正する電気制御部に付加しても好ましい。
ヒ素の電析時間を長くすれば、ヒ素付着量が増大するため、測定感度を上げることが可能である。
In the actual measurement operation, scanning is performed from the potential at which arsenic is electrodeposited to the potential at which it is oxidized and dissolved. It is preferable to scan the potential in steps or sweeps. In order to improve the sensitivity, it is preferable to add a differential potential and a current pulse and add them to the electric control unit for correcting the capacitive current component at the electrode interface and the IR resistance.
If the electrodeposition time of arsenic is lengthened, the amount of arsenic adhesion increases, so that measurement sensitivity can be increased.
図１は、本発明によるヒ素用センサーの一例を示す正面図である。
図示の通り、ヒ素用センサー１は、作用極２及び対極３が隔膜４を介して水平方向に位置するよう設置することにより構成されている。前記作用極２は、金や銀あるいはカーボン等の導電性基体表面に被覆された金粒子にハロゲン化物イオン吸着種を単層吸着して成り、当該作用極２表面では前記吸着種により酸素還元による過酸化水素生成が防止される。対極３のやや上方には内部液５を介して基準電極６が設置されている。
このような構成からなるセンサー１をヒ素含有液（被測定液）７に浸漬すると、前述の式（２）に従って電着ヒ素が再溶解し、この溶解で生じる電流を測定することにより被測定液７中のヒ素濃度を正確に測定できる。
FIG. 1 is a front view showing an example of an arsenic sensor according to the present invention.
As shown in the figure, the arsenic sensor 1 is configured by installing the working
When the sensor 1 having such a structure is immersed in the arsenic-containing liquid (measuring liquid) 7, the electrodeposited arsenic is re-dissolved according to the above-described equation (2), and the current generated by this dissolution is measured to measure the liquid to be measured. The arsenic concentration in 7 can be measured accurately.
次に本発明に係るヒ素検出用電極を使用するヒ素の濃度測定に関する実施例及び比較例を記載するが、本発明はこれらに限定されるものではない。 Next, examples and comparative examples relating to arsenic concentration measurement using the arsenic detection electrode according to the present invention will be described, but the present invention is not limited thereto.
[実施例１]
電極面積が0.0078cm2であるグラッシーカーボンを、0.1mM NaAuCl4 + 0.1mM KI +0.5M H2SO4のめっき浴に浸漬し表面を金めっきし、同時に当該金にヨウ化物イオンを吸着させた。対極として、大面積の白金板、基準電極として、Ag/AgClを用い、１Ｍ塩酸溶液で得られた矩形波ボルタモグラム（周波数15Hz、幅25mV）を図２に示した。ヒ素電着時間は１分間とした（-0.3Vに維持）。ヒ素濃度は4.1 μM 〜 98 μM（高濃度領域）までの16種類とした。
更にこの実験で得られたヒ素濃度[Ａｓ（III）]と検出電流の関係を図３に示した。図３から分かる通り、40μM以下のヒ素濃度では、濃度と電流間で良好な直線性が得られた。
[Example 1]
Glassy carbon having an electrode area of 0.0078 cm 2 was dipped in a plating bath of 0.1 mM NaAuCl 4 +0.1 mM KI + 0.5MH 2 SO 4 and gold-plated on the surface, and at the same time, iodide ions were adsorbed on the gold. A rectangular wave voltammogram (frequency 15 Hz, width 25 mV) obtained with a 1 M hydrochloric acid solution using a large-area platinum plate as a counter electrode and Ag / AgCl as a reference electrode is shown in FIG. The arsenic electrodeposition time was 1 minute (maintained at -0.3 V). The arsenic concentration was 16 types from 4.1 μM to 98 μM (high concentration region).
Furthermore, the relationship between the arsenic concentration [As (III)] obtained in this experiment and the detected current is shown in FIG. As can be seen from FIG. 3, at the arsenic concentration of 40 μM or less, good linearity was obtained between the concentration and the current.
[実施例２]
実施例１と同様の条件で、ヒ素濃度が0.05μM 〜 0.4μM（低濃度領域）での矩形波ボルタモグラム（周波数15Hz、幅25mV）の電流ピークと濃度の関係を図４（黒抜き）に示したが、安全基準レベルの低濃度において良好な直線性を得た。
[Example 2]
FIG. 4 (black) shows the relationship between the current peak and the concentration of a rectangular wave voltammogram (frequency 15 Hz, width 25 mV) when the arsenic concentration is 0.05 μM to 0.4 μM (low concentration region) under the same conditions as in Example 1. However, good linearity was obtained at a low concentration of the safety standard level.
[比較例１]
ヨウ化物イオンの吸着を行わなかったこと以外は実施例２と同様の測定を行い、電流ピークと濃度の関係を図４（白抜き）に示した。図示の通り、原点を通る直線性が得られなかった。
[Comparative Example 1]
Except that no iodide ion was adsorbed, the same measurement as in Example 2 was performed, and the relationship between the current peak and the concentration is shown in FIG. 4 (outlined). As shown in the figure, linearity passing through the origin was not obtained.
[実施例３]
電極として、金粒子を熱分解法によりカーボンペーパー（投影面積0.09cm2）に50mg/cm2となるように被覆形成したものを用い、同面積の白金網を対極として用い、イオン交換膜（NAFION350）を電極間に挟み込み、図１の接合体を作製した。基準電極は陰極と同じ側に設置した。対極の溶液として塩化カリウムの飽和溶液を満たした。ヨウ化カリウムを溶解した水溶液中に金被覆電極を入れ、ヨウ化物イオンを吸着させた後、純水に0.05μM〜0.4μMのヒ素を溶解させた被測定液に該接合体を入れ、実施例１と同様の電気化学的操作を実施し、図５（黒抜き）にピーク電流値と濃度の関係を示した。図示の通り、両者間には良好な直線関係が得られた。
[Example 3]
As an electrode, the gold particles used after coating formation so that 50 mg / cm 2 carbon paper (projected area 0.09 cm 2) by the thermal decomposition method, using a platinum gauze having the same area as the counter electrode, an ion-exchange membrane (NAFION350 ) Was sandwiched between the electrodes to produce the joined body of FIG. The reference electrode was placed on the same side as the cathode. A saturated solution of potassium chloride was filled as the counter electrode solution. An example in which a gold-coated electrode is placed in an aqueous solution in which potassium iodide is dissolved, and after iodide ions are adsorbed, the joined body is placed in a solution to be measured in which 0.05 μM to 0.4 μM arsenic is dissolved in pure water. The same electrochemical operation as in No. 1 was performed, and the relationship between the peak current value and the concentration was shown in FIG. As shown in the figure, a good linear relationship was obtained between the two.
[比較例２]
ヨウ化物イオンの吸着を行わなかったこと以外は実施例３と同様の測定を行い、図５（白抜き）にピーク電流値と濃度の関係を示した。図示の通り、原点を通る直線性が得られなかった。
[Comparative Example 2]
The same measurement as in Example 3 was performed except that no iodide ion was adsorbed, and the relationship between the peak current value and the concentration was shown in FIG. 5 (outlined). As shown in the figure, linearity passing through the origin was not obtained.
１ ヒ素用センサー
２ 作用極
３ 対極
４ 隔膜
５ 内部液
６ 基準電極
７ ヒ素含有液（被測定液）
DESCRIPTION OF SYMBOLS 1 Sensor for
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN101893594A (en) * | 2009-05-22 | 2010-11-24 | 东北电力株式会社 | The electrochemical determination method of arsenic and device thereof |
| CN102520039A (en) * | 2011-12-29 | 2012-06-27 | 济南大学 | Preparation method of aptamer-based molecularly imprinted membrane electrode for detecting organic arsenide in marine products and application |
| CN115479984A (en) * | 2021-05-31 | 2022-12-16 | 武汉中科志康生物科技有限公司 | Detection method of inorganic arsenic |
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| CN101893594A (en) * | 2009-05-22 | 2010-11-24 | 东北电力株式会社 | The electrochemical determination method of arsenic and device thereof |
| JP2010271236A (en) * | 2009-05-22 | 2010-12-02 | Keio Gijuku | Electrochemical measuring method and device for arsenic |
| CN102520039A (en) * | 2011-12-29 | 2012-06-27 | 济南大学 | Preparation method of aptamer-based molecularly imprinted membrane electrode for detecting organic arsenide in marine products and application |
| CN115479984A (en) * | 2021-05-31 | 2022-12-16 | 武汉中科志康生物科技有限公司 | Detection method of inorganic arsenic |
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