JP3838435B2

JP3838435B2 - Hypochlorous acid concentration measuring device

Info

Publication number: JP3838435B2
Application number: JP2003181173A
Authority: JP
Inventors: 明胤秋山; 稔首藤; 保昌原; 寛士渡辺
Original assignee: Individual
Current assignee: Individual
Priority date: 2003-06-25
Filing date: 2003-06-25
Publication date: 2006-10-25
Anticipated expiration: 2023-06-25
Also published as: JP2005017079A

Description

【０００１】
【発明の属する技術分野】
本発明は流水中の次亜塩素酸のみを選択的に分析する装置であって、長期間にわたって精度よく安定した分析が可能で、しかも自動化が容易な次亜塩素酸濃度測定装置に関するものである。
【０００２】
【従来の技術】
塩素系消毒剤は消毒水の形で水道水の滅菌をはじめとして、食品工場、プール、温泉施設、病院などで広く使用されている。現在主に使用されている弱アルカリ性から弱酸性の消毒水中には、次亜塩素酸イオン〔ＣｌＯ^-〕、次亜塩素酸〔ＨＣｌＯ〕、そしてごく微量の溶存塩素〔Ｃｌ₂〕などが存在するが、その殺菌力は、主として次亜塩素酸〔ＨＣｌＯ〕の強力な酸化力に起因すると考えられている。
これらの消毒水、あるいはこれらに由来する塩素系物質が溶存している各種用水や排水においては、工程管理上溶存している塩素系物質の濃度を測定することが重要で、種々の方法が実施されており、また、水溶液中の残留塩素濃度（遊離塩素濃度）を測定する装置も多数市販されている。
【０００３】
次亜塩素酸などの残留塩素濃度の測定方法としては、比色法と電気化学的方法が代表的であるが、装置の自動化の観点から見ると電気化学的分析法が主流である。電気化学的方法を用いる分析法の原理は次のとおりである。
水溶液中に次亜塩素酸が存在するとき、検出電極を適当な電位（基準電極に対する電位：基準電極としては銀／塩化銀電極が一般に用いられている）に設定（以下、電解電位と略）すると、次亜塩素酸〔ＨＣｌＯ〕は、電極表面上で（１）の化学式に示すように電気化学的に還元される。
【化１】
ＨＣｌＯ＋Ｈ⁺＋２ｅ＝Ｃｌ^-＋Ｈ₂Ｏ・・・（１）
このとき、（１）式の電子〔ｅ〕の量を電流値として計測し、次亜塩素酸濃度に換算する。
電解電位をマイナス方向にシフトすると（２）式により次亜塩素酸イオン〔ＣｌＯ^-〕の電解還元が、さらにマイナスにシフトすると（３）式により溶存酸素〔Ｏ₂〕の電解還元による還元電流が加算される。
【化２】
ＣｌＯ^-＋Ｈ₂Ｏ＋２ｅ＝Ｃｌ^-＋２ＯＨ^-・・・（２）
Ｏ₂＋２Ｈ₂Ｏ＋４ｅ＝４ＯＨ^- ・・・（３）
実際の測定における電解電位は、各電気化学反応式の単極電極電位（水素電極基準）を参考にして決定される。前記（１）、（２）及び（３）式の単極電極電位はそれぞれ〔１．４９Ｖ〕、〔０．９４Ｖ〕及び〔０．４０Ｖ〕である。
【０００４】
前記の電流値を計測して次亜塩素酸などの残留塩素濃度を測定する装置として、検出電極と基準電極の２電極を定電圧に保って、流れる電流値を計測する２電極・定電圧方式の装置がある（例えば、特許文献１、２参照）。２電極方式は制御回路が簡素化されることもあって広く採用され、市販品の多くはこの方式である。しかしながら、２電極方式は、基準電位を与える基準電極（銀／塩化銀電極）に電解電流が不可避的に流れ、基準電極値が不安定となり、結果として設定電位が一定しないという大きな欠陥がある。
そのため、電流を流すための補助電極を用いる３電極・定電位電解方式による装置も提案されている（例えば、特許文献３、４参照）。しかしながら、この３電極・定電位電解装置は、２電極の定電圧方式と比べると制御回路が複雑となって大型するという問題がある。
【０００５】
また、電気化学的方法を用いて安定した再現性のある測定結果を得るためには、検出電極表面は、常に一定の状態を保つ必要がある。従来、検出電極としては高価な白金、金等の貴金属が用いられており、適宜、洗浄・活性化を行いながら使用されている。なお、参考文献３、４などには電極材料として白金、金に加えてカーボンも例示されているが、従来、炭素電極を使用した装置は実現されていない。電極の洗浄／活性化方法として、酸素発生の陽極処理と水素発生の陰極処理を交互に行わせる電気化学的方法（例えば、特許文献１参照）と、機械的に研磨する方法（例えば、特許文献２参照）が提案されているが、電気化学的洗浄／活性化は不十分な結果を与える場合が多く、一方、機械的研磨法は特に自動化を視野に入れたとき、装置が複雑化し、従って装置の制作費が上昇してしまうという欠点がある。
【０００６】
【特許文献１】
特開平１０−１８５８７１号公報
【特許文献２】
特開２０００−４６７９４号公報
【特許文献３】
特開２００１−１７４４３１号公報
【特許文献４】
特開２００１−１０８６５２号公報
【０００７】
【発明が解決しようとする課題】
本発明は前記従来技術における問題点を解決し、高価な貴金属電極を使用することがなく、従来に比べてより正確な測定値を長期間にわたって安定して得ることができ、しかもコンパクトで自動化が容易な次亜塩素酸濃度測定装置を提供することを目的とする。
【０００８】
【課題を解決するための手段】
本発明は上記課題を解決する手段として次の（１）〜（４）の構成の装置を提供するものである。
（１）検出電極、補助電極及び基準電極を備え、検出電極を定電位に設定し、該検出電極と基準電極との間に流れる電解電流を計測して流水試料中の次亜塩素酸濃度を電気化学的に測定する３電極方式の次亜塩素酸濃度測定装置であって、検出電極が炭素電極、基準電極が銀／塩化銀電極であり、測定開始に先立って検出電極に該電極を電気化学的に酸化、還元して洗浄／活性化するように電圧を印加する制御回路、及び洗浄／活性化した検出電極を所定時間開放した後、定電位に設定し、所定時間経過後の一定期間内に流れる電解電流を計測し、その積算電気量から次亜塩素酸濃度を算出する制御回路を有する制御部を具備してなることを特徴とする次亜塩素酸濃度測定装置。
（２）補助電極が炭素電極であることを特徴とする前記（１）の次亜塩素酸濃度測定装置。
【０００９】
（３）検出電極、補助電極及び基準電極を備え、検出電極を定電位に設定し、該検出電極と基準電極との間に流れる電解電流を計測して流水試料中の次亜塩素酸濃度を電気化学的に測定する３電極方式の次亜塩素酸濃度測定装置であって、１つの支持体に炭素電極である検出電極及び補助電極、銀／塩化銀電極である基準電極、ｐＨ計測手段及び温度計測手段が集約一体化された構成のセンサー部を有し、測定開始に先立って検出電極に該電極を電気化学的に酸化、還元して洗浄／活性化するように電圧を印加する制御回路と、洗浄／活性化した検出電極を所定時間開放した後、定電位に設定し、所定時間経過後の一定期間内に流れる電解電流を計測し、その積算電気量から次亜塩素酸濃度を算出する制御回路を有する制御部を具備してなることを特徴とする次亜塩素酸濃度測定装置。
（４）測定開始に先立って検出電極に該電極を電気化学的に酸化、還元して洗浄／活性化するように電圧を印加する制御回路と、洗浄／活性化した検出電極を所定時間開放した後、定電位に設定し、所定時間経過後の一定期間内に流れる電解電流を計測し、その積算電気量から次亜塩素酸濃度を算出する制御回路を有する制御部が、ｐＨ、温度及び流水量を測定するアナログ測定機能と周辺機器の動作を制御するデジタル入出力機能を内蔵した制御部であることを特徴とする前記（３）の次亜塩素酸濃度測定装置。
【００１０】
本発明の装置においては、電気化学的洗浄／活性化工程を確実なものにするため、検出電極として炭素電極を使用し、電気化学的活性化及びその後の電極開放時間の時間管理を厳密化する制御回路を組み込んでいる。
電気化学的方法を用いて分析装置を作製するとき、電極材質として採用されてきたのは、白金や金などの貴金属電極であって、現在市販されているすべての装置においてこれら貴金属電極が採用されている。貴金属は化学的に安定な酸化膜で覆われていると考えられ、この酸化膜上に有機物などが付着しやすいという欠点があり、その解決策として機械的研磨が推奨されてきた。しかしながら、機械的研磨行程を共存させた装置は機械的要素を含むため安定性がなく、さらに装置全体が複雑化するなどの問題が発生する。
本発明の装置では、検出電極として炭素電極を採用し、電気化学的活性化工程の時間管理を厳密化することにより効果的な洗浄／活性化が可能になり、正確な測定値を安定して得られるようになった。
【００１１】
炭素電極とすることにより効果的な洗浄／活性化が可能になった理由は、炭素電極上で電気化学的に酸素を発生させる（電解電位をプラス数Ｖに設定する）と、電極表面の数層の炭素原子が酸化され二酸化炭素、あるいは一酸化炭素ガスとして取り除かれ、この反応に伴って表面に付着した汚染物は取り除かれ、同時に活性の高い表面が現出するためと考えられる。従って、炭素電極を検出電極として用い電気化学的活性化手段を採用すると、常に新しい電極を用いたのと同じ分析結果、すなわち再現性、安定性の高い測定結果を得ることができる。電気化学的に洗浄／活性化する工程は、例えば１０ミリ秒から５００ミリ秒間隔でマイナス数Ｖの還元電位、プラス数Ｖの酸化電位、マイナス数Ｖの還元電位、１Ｖ程度の安定化電位の順にパルス分極を行い、電極を開回路して所定の時間開放することによって行えばよい。
【００１２】
電気化学的活性化により検出電極は洗浄／活性化されるが、その後、電極表面の不活性化が急速に進行する。従って、検出電極は分析操作の直前に必ず活性化する必要性があり、また、活性化後電極を解放し、その解放時間を厳密な一定時間に設定しなければならない。この電気化学的活性化工程後の一定解放時間は、（イ）活性化時の影響を取り除くこと、（ロ）活性化後の不活性化を極力小さく押さえること、（ハ）測定時間の短縮、などの点を考慮して決定する。この電極開放時間は（ハ）の点を考慮すれば短い方が好ましいが、（イ）及び（ロ）の点を考慮して決定する（例えば２秒程度）。この開放時間は同一、一定間隔として厳密に管理する必要があるので、洗浄／活性化工程は制御回路によりコンピュータ制御する。
【００１３】
電気化学的手法により次亜塩素酸濃度を測定するためには、設定電解電位を長期間安定に保つ必要があり、そのためには基準電極が長期間安定である必要がある。現在、基準電極として、一般に用いられているのは銀／塩化銀電極であり、本発明の装置においてもこの銀／塩化銀電極を使用する。また、基準電極に電解電流が流れると設定電解電位が不安定になる。そのため本発明の装置では検出電極、基準電極の他に電解電流部分を担う電極（補助電極）を設けた３電極方式の定電位電解方式を採用している。しかし、この３電極・定電位電解方式の装置は、２電極の定電圧方式の装置と比べると制御回路が複雑となって大型するため、市販されている分析装置は２電極方式が主流である。本発明の装置は、定電位電解部をコンピュータ制御部と一体化し、かつ小型化するように回路設計することによって、３電極方式が採用されているにかかわらず、コンパクトな装置とすることができた。
補助電極は化学的に不活性で、毒性のないものであれば特に材質に制限はなく、従来使用されていた金、白金等が使用できるが、検出電極と同様に炭素電極を使用するのが経済的であり好ましい。補助電極は電流を捕捉しやすいよう検出電極に比べて表面積が大きいものを使用し、流水との接触効率がよくなるような形で設置する。
【００１４】
本発明の装置により水溶液中の次亜塩素酸濃度を測定する場合、洗浄／活性化した検出電極を所定時間開放した後、定電位に設定し、検出電極と補助電極間に流れる電解電流を計測する。従来の電気化学的分析装置では、検出電極を電解電位に設定後直ちに電解電流値を測定し、その電流値を濃度に換算して分析値としているが、本発明の装置では、定電位に設定した直後の電解電流の計測値は採用せず、所定の除外期間をおいたあとの一定期間内に流れる電解電流を計測し、その積算電気量から次亜塩素酸濃度を算出する制御回路を設けている。このようにして電解初期に観察される電解電流を測定結果から取り除くことによって、初期の電極近傍に高濃度に存在する物質に起因する不安定電流領域を取り除くことができ、流動によって運ばれる流水検体中の電気化学的活性物質濃度のみを直接分析結果に反映させることができる。また、測定値は所定時間間隔の電流の積分値であることから、測定時に誤差の原因となる周期的ノイズを必然的に取り除くことになる。
本発明の場合、次亜塩素酸濃度測定用の電解電位は５０ｍＶ±１００ｍＶ（銀／塩化銀基準電極基準）の範囲とする。この電解電位は前記の式（１）〜（３）における単極電極電位（水素電極基準）を参考として多数の実験を重ね、思考錯誤により決定したものである。
【００１５】
前記の除外期間の長さは、測定条件等により異なるが、要は電流値がほぼ一定になるまでとすればよく、通常は１５秒程度で十分である。積算電気量を求める期間は長い方が平均したデータが得られるが、長くなればそれだけ分析所要時間が長くなる。本発明の装置によれば十分安定した計測値が得られるので１０秒程度で十分である。制御回路には予め測定した電解電気量と次亜塩素酸濃度との相関データが入力されており、計測した積算電気量から次亜塩素酸の濃度を算出することができる。
本発明の装置による次亜塩素酸の分析操作は、検出電極を洗浄／活性化した後（開放時間を含む）、定電位に設定して電流の計測を開始し、計測開始初期のデータを除外してその後の所定時間に流れる電解電流を計測し、その積算電気量から次亜塩素酸濃度を算出するものである。この一連の分析操作において各工程の操作条件は常に一定としておくことが必要である。
【００１６】
分析装置の信頼のおける運転には、常に装置の安定動作と分析結果の信頼性を確認する必要性がある。本発明装置は、流水中の物質の分析を目的として構築され、しかも検出電極を定電位に設定し、所定時間経過後の計測値を分析値として採用するようにしている。次亜塩素酸の電気化学的還元反応は速度が大きく、電解電流は拡散律速電流（電解物質の電極への拡散によって電解電流が律速されている）を電流値として測定していると考えられる。本発明において流水中と規定したのは、電解物質である次亜塩素酸の電極表面への拡散速度を大きくするためである。その結果、測定電気量は大きな値をとり、一定時間後、理論的には一定の値となる。一方、理想的静水時の電流測定値は、時間とともに減少し理論的には「ゼロ」に近づく。実験結果からも本発明装置のように一定時間後の電解電気量を測定した場合、静水時の電気量測定値を「ゼロ濃度」の値と推定できることが確認された。これは本発明装置の一つの大きな特徴であって、必要に応じて静水時の状態を作り「ゼロ濃度」を確認することができ、測定結果の信頼性を高めることができた。
【００１７】
本発明の装置の好ましい形態として、センサー部をプラスチックなどの１つの支持体に炭素電極である検出電極及び補助電極、銀／塩化銀電極である基準電極、ｐＨ計測電極及び温度計測手段が集約一体化された構成とすることができる。このように構成したセンサー部は各種パイプ内の流水中に直接設置し次亜塩素酸濃度分析を行うことができる。また、本発明装置にはｐＨや温度の測定、さらには流水量測定などアナログ測定の機能や、ポンプなどの動作を制御するデジタル入出力機能を内蔵させることにより、消毒システムのエンジニアリングにおいて中心的制御装置としても充分に機能する能力を持たせることができる。
【００１８】
なお、本発明装置は流水中に設置して次亜塩素酸濃度を測定する装置として開発されたが、従来の分析装置と比べて、流水時の測定結果が静水時の場合と比較して極端に大きく、また流水速度による測定値の影響が小さいことから、流水量を定量化できないマグネチックスターラーによるサンプル水の攪拌によっても良好な分析結果を与えることが確認された。このことから、適当な攪拌手段を備えれば本発明装置はサンプル水の分析にも応用可能である。
【００１９】
【発明の実施の形態】
以下、図面を参照して本発明の次亜塩素酸濃度測定装置について具体的に説明する。
図１は本発明の次亜塩素酸濃度測定装置の１構成例を模式的に示す説明図である。図１において符号１及び５はそれぞれ測定対象の試験水が流れるパイプ１０内に挿入されたセンサー部と、流水量センサーであり、２はアナログ制御部３とデジタル制御部４を有する制御部である。デジタル制御部４はレコーダ６とパーソナルコンピュータ（又はタッチパネル）７に接続されており、デジタル入力８及びデジタル出力９により周辺器具を制御するように構成されている。制御部２は測定開始に先立ってセンサー部１の検出電極に該電極を電気化学的に酸化、還元して洗浄／活性化するように電圧を印加する制御回路、及び洗浄／活性化した検出電極を所定時間開放した後、定電位に設定し、所定時間経過後の一定期間内に流れる電解電流を計測し、その積算電気量から次亜塩素酸濃度を算出する制御回路を備えている。この例では、制御部２は１枚のプリント板（１０５×２７０ｍｍ）上に、アナログ計測回路とデジタル制御回路が共存している。このプリント基板回路は、パソコンまたはタッチパネルとＲＳ２３２Ｃのシリアル通信を介しての命令によって、センサー部を操作して分析結果を得、各種デジタル機器を制御することができる。
【００２０】
図２はセンサー部１の要部（先端部）を示す説明図であり、図２（ａ）は概略見取り図であり、図２（ｂ）はその側面断面の展開図である。このセンサー部１は複合電極であって、検出電極１１、基準電極１２、補助電極１４、温度センサー１９を入れる温度センサー室１６、オプションで半導体ｐＨ電極１５が塩化ビニル樹脂製の支持体１７（直径１５ｍｍ）により一体化されたものである。この例において、検出電極１１は直径３ミリの炭素棒で、２０ｐｐｍまでの低濃度分析には支持体１７から１５ミリ露出させた炭素棒の円柱側面を電極として使用し、２０００ｐｐｍまでの高濃度分析には支持体１７からの露出部分を少なくしその断面を電極面として使用した。補助電極１４としては、直径１０ミリの炭素棒を使用した。銀／塩化銀電極である基準電極１２を収納した標準電極室１８はマイクロフィルタ１３を隔てて試験水と接触するように支持体１７で支持されており、その標準電極室１８は、飽和塩化カリウム水溶液で満たされ、塩化銀がメッキされた銀線（基準電極１２）が封入されている。
【００２１】
このような構成の装置により内径２０ｍｍのパイプ中の流水中の次亜塩素酸濃度の分析試験を行った。
全ての測定に先立って、検出電極１１を図３に示す標準的なパターンによる電解電位操作で電気化学的に洗浄／活性化した。すなわち、検出電極１１を１０ミリ秒間隔で、マイナス５Ｖの還元電位、５Ｖの酸化電位、マイナス５Ｖの還元電位、１Ｖの安定化電位、の順にパルス分極を行い、その後電極を開回路して２秒間放置した。引き続き直ちに、検出電極の電解電位をプラス５０ｍＶに設定し、１５秒間の電解電流を除外し、その後の１０秒間に消費された電解電気量を計測し次亜塩素酸濃度に換算して分析値とした。なお、図３には電解電位をプラス５０ｍＶに設定した後の１５秒間の除外期間の初めの部分までを示した。このパターンによる分析所要時間は１回当たり約３０秒であった。
【００２２】
図４及び図５はｐＨ６．５、流水量１０リットル／分の条件で所定濃度の次亜塩素酸を含む試験水について測定した電解電気量（クーロンの相対値）と次亜塩素酸濃度（ｐｐｍ）との関係を示すグラフである。図４は低濃度用の検出電極を用いて濃度１０ｐｐｍまでの低濃度溶液について測定した結果であり、図５は高濃度用の検出電極を用いて１０００ｐｐｍまでの高濃度溶液について測定した結果である。いずれの場合も電解電気量と次亜塩素酸濃度とは良好な相関関係を示し、測定の再現性は測定値平均の１％以内であった。なお、図４及び図５において点線は静水状態で測定した結果を示しており、いずれも静水の状態では電気量はほとんどゼロであることがわかる。
【００２３】
また、図６は次亜塩素酸濃度が５０ｐｐｍの試験水について、流水量を変えて電気量を測定した結果（高濃度用電極を使用）であり、流水量がゼロ、すなわち静止水の場合、測定値はゼロに近く、また試験水中の次亜塩素酸濃度による変化は小さい。また、５から１５リットル／分における測定電気量の差は、０から５リットル／分における変化分と比べて非常に小さく、５リットル／分以上の流量があれば安定した測定値が得られることがわかる。さらに、静水中では電解電気量がほとんどゼロになることから、流水中での測定時に随時静止状態として測定を行い、測定値がゼロになることを確認することによって、装置が正常に作動していることを確認することができる。
以上の結果を総括すると、この装置は消毒システムのエンジニアリングにおいて中心的制御装置として充分に機能する能力を有する次亜塩素酸濃度分析装置であり、０〜２０００ｐｐｍの測定範囲で、最大測定設定値の±１％という高い精度／感度で、分析所要時間約３０秒という優れた性能を有することがわかる。
【００２４】
【発明の効果】
本発明の次亜塩素酸濃度測定装置は、高価な貴金属電極を使用することがなく、従来の装置に比べてより正確な測定値を長期間にわたって安定して得ることができ、しかもコンパクトで自動化が容易な次亜塩素酸濃度測定装置である。
また、この分析装置は分析試薬などを一切使用しないので、分析による殺菌水などの分析対象水の汚染も皆無であるため、センサー部を消毒水パイプラインの中などに直接組み込むことが可能である。
本発明の装置は、塩素系消毒剤を含む消毒水、あるいはこれらに由来する塩素系物質が溶存している各種用水や排水中の次亜塩素酸の濃度測定装置として極めて優れた性能を有するものである。また、消毒水の流量測定や、薬液注入ポンプ制御などの周辺の機器の制御指令が可能なように制御回路を設計することにより、システムエンジニアリングの中心部を担う装置として活用することができるので、殺菌工程を必要とする産業上での利用分野は無限に広がっている。
【図面の簡単な説明】
【図１】本発明の次亜塩素酸濃度測定装置の１構成例を模式的に示す説明図。
【図２】図１のセンサー１の要部（先端部）を示す説明図。
【図３】電気化学的洗浄／活性化の電解電位操作の１パターンを示す説明図。
【図４】低濃度の次亜塩素酸を含む試験水について測定した電解電気量と次亜塩素酸濃度との関係を示すグラフ。
【図５】高濃度の次亜塩素酸を含む試験水について測定した電解電気量と次亜塩素酸濃度との関係を示すグラフ。
【図６】次亜塩素酸を含む試験水について流水量を変えて電気量を測定した結果を示すグラフ。
【符号の説明】
１センサー部２制御部３アナログ制御部
４デジタル制御部５流水量センサー６レコーダ
７パーソナルコンピュータ（又はタッチパネル）８デジタル入力
９デジタル出力１０パイプ１１検出電極１２基準電極
１３マイクロフィルタ１４補助電極１５半導体ｐＨ電極
１６温度センサー室１７支持体１８標準電極室
１９温度センサー[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an apparatus for selectively analyzing only hypochlorous acid in running water, and relates to a hypochlorous acid concentration measuring apparatus that can perform stable analysis with high accuracy over a long period of time and is easy to automate. .
[0002]
[Prior art]
Chlorine-based disinfectants are widely used in the form of disinfecting water, including sterilization of tap water, food factories, swimming pools, hot spring facilities, and hospitals. There are hypochlorite ions [ClO ⁻ ], hypochlorous acid [HClO], and a very small amount of dissolved chlorine [Cl ₂ ] in the weakly alkaline to weakly acidic disinfecting water mainly used at present. However, the bactericidal power is thought to be mainly due to the strong oxidizing power of hypochlorous acid [HClO].
It is important to measure the concentration of dissolved chlorinated substances for process control in these sterilized water or various irrigation water and wastewater in which chlorinated substances derived from them are dissolved. Many devices for measuring the residual chlorine concentration (free chlorine concentration) in an aqueous solution are also commercially available.
[0003]
Typical methods for measuring the concentration of residual chlorine such as hypochlorous acid are the colorimetric method and the electrochemical method, but from the viewpoint of automation of the apparatus, the electrochemical analysis method is the mainstream. The principle of the analytical method using the electrochemical method is as follows.
When hypochlorous acid is present in the aqueous solution, the detection electrode is set to an appropriate potential (potential with respect to the reference electrode: a silver / silver chloride electrode is generally used as the reference electrode) (hereinafter abbreviated as electrolytic potential) Then, hypochlorous acid [HClO] is electrochemically reduced on the electrode surface as shown by the chemical formula (1).
[Chemical 1]
HClO + H ⁺ + 2e = Cl ⁻ + H ₂ O (1)
At this time, the amount of the electron [e] in the formula (1) is measured as a current value and converted to a hypochlorous acid concentration.
When the electrolytic potential is shifted in the negative direction, the reduction of hypochlorite ion [ClO ⁻ ] is reduced according to the formula (2), and when the potential is further shifted down, the reduction current due to the electrolytic reduction of dissolved oxygen [O ₂ ] is calculated according to the formula (3). Is added.
[Chemical 2]
ClO ⁻ + H ₂ O + 2e = Cl ⁻ + 2OH ⁻ (2)
O ₂ + 2H ₂ O + 4e = 4OH ⁻ (3)
The electrolytic potential in actual measurement is determined with reference to the monopolar electrode potential (hydrogen electrode standard) of each electrochemical reaction formula. The monopolar electrode potentials of the equations (1), (2) and (3) are [1.49 V], [0.94 V] and [0.40 V], respectively.
[0004]
As a device that measures the current value and measures the residual chlorine concentration such as hypochlorous acid, it keeps the two electrodes of the detection electrode and the reference electrode at a constant voltage and measures the flowing current value. (For example, refer to Patent Documents 1 and 2). The two-electrode system is widely adopted because the control circuit is simplified, and many commercially available products are this system. However, the two-electrode method has a major defect that an electrolytic current inevitably flows through a reference electrode (silver / silver chloride electrode) that provides a reference potential, the reference electrode value becomes unstable, and as a result, the set potential is not constant.
Therefore, an apparatus using a three-electrode / constant-potential electrolysis method using an auxiliary electrode for flowing current has also been proposed (see, for example, Patent Documents 3 and 4). However, this three-electrode / constant-potential electrolyzer has a problem that the control circuit is complicated and large as compared with the two-electrode constant voltage system.
[0005]
In addition, in order to obtain a stable and reproducible measurement result using an electrochemical method, the detection electrode surface must always be kept in a certain state. Conventionally, expensive noble metals such as platinum and gold are used as detection electrodes, and they are used while being appropriately cleaned and activated. In addition, in References 3 and 4 and the like, carbon is exemplified as an electrode material in addition to platinum and gold, but conventionally, an apparatus using a carbon electrode has not been realized. As an electrode cleaning / activation method, an electrochemical method (for example, see Patent Document 1) in which oxygen generation anodization and hydrogen generation cathode treatment are alternately performed, and mechanical polishing method (for example, Patent Document 1) 2) have been proposed, but electrochemical cleaning / activation often gives inadequate results, while mechanical polishing methods, especially when looking at automation, complicate the equipment and therefore There is a drawback that the production cost of the device increases.
[0006]
[Patent Document 1]
JP-A-10-185871 [Patent Document 2]
JP 2000-46794 A [Patent Document 3]
JP 2001-174431 A [Patent Document 4]
JP 2001-108652 A
[Problems to be solved by the invention]
The present invention solves the above-described problems in the prior art, does not use expensive noble metal electrodes, can stably obtain more accurate measurement values over a long period of time, and is compact and automated. An object is to provide an apparatus for easily measuring hypochlorous acid concentration.
[0008]
[Means for Solving the Problems]
The present invention provides an apparatus having the following configurations (1) to ( 4 ) as means for solving the above problems.
(1) A detection electrode, an auxiliary electrode, and a reference electrode are provided, the detection electrode is set to a constant potential, the electrolytic current flowing between the detection electrode and the reference electrode is measured, and the hypochlorous acid concentration in the flowing water sample is determined. A three-electrode type hypochlorous acid concentration measuring apparatus for electrochemical measurement, wherein the detection electrode is a carbon electrode, the reference electrode is a silver / silver chloride electrode, and the electrode is electrically connected to the detection electrode prior to the start of measurement. A control circuit that applies voltage to chemically oxidize, reduce , and wash / activate , and the washed / activated detection electrode is opened for a predetermined time, then set to a constant potential, and after a predetermined time has elapsed the electrolytic current is measured flowing through the inside, the integrated amount of electricity hypochlorite concentration measuring apparatus characterized by being provided with a control unit having a control circuit for calculating the concentration of hypochlorous acid from.
( 2 ) The hypochlorous acid concentration measuring device according to (1 ), wherein the auxiliary electrode is a carbon electrode.
[0009]
( 3 ) A detection electrode, an auxiliary electrode, and a reference electrode are provided, the detection electrode is set to a constant potential, the electrolytic current flowing between the detection electrode and the reference electrode is measured, and the hypochlorous acid concentration in the flowing water sample is determined. A three-electrode type hypochlorous acid concentration measuring apparatus for electrochemical measurement, comprising a detection electrode and auxiliary electrode which are carbon electrodes, a reference electrode which is a silver / silver chloride electrode, a pH measuring means, A control circuit having a sensor unit with a configuration in which temperature measuring means is integrated and integrated, and prior to starting measurement, a voltage is applied to the detection electrode so that the electrode is electrochemically oxidized, reduced and cleaned / activated. Then, after opening the cleaned / activated sensing electrode for a predetermined time, set it to a constant potential, measure the electrolytic current flowing within a certain period after the predetermined time has elapsed, and calculate the hypochlorous acid concentration from the accumulated amount of electricity A control unit having a control circuit for Hypochlorous acid concentration measuring apparatus characterized by.
( 4 ) Prior to the start of measurement, a control circuit for applying a voltage to electrochemically oxidize and reduce the electrode to the detection electrode to be cleaned / activated, and the cleaned / activated detection electrode are opened for a predetermined time. Thereafter, a control unit having a control circuit that sets a constant potential, measures an electrolytic current flowing within a predetermined period after a predetermined period of time, and calculates a hypochlorous acid concentration from the accumulated amount of electricity is used for pH, temperature, and flowing water. The hypochlorous acid concentration measuring apparatus according to ( 3 ), wherein the apparatus is a control unit having a built-in analog measurement function for measuring the amount and a digital input / output function for controlling the operation of the peripheral device.
[0010]
In the apparatus of the present invention, in order to ensure the electrochemical cleaning / activation process, a carbon electrode is used as a detection electrode, and the time management of electrochemical activation and subsequent electrode opening time is tightened. A control circuit is incorporated.
When producing an analytical device using an electrochemical method, the precious metal electrodes such as platinum and gold have been adopted as electrode materials, and these precious metal electrodes are adopted in all devices currently on the market. ing. The precious metal is considered to be covered with a chemically stable oxide film, and has a drawback that organic substances and the like are likely to adhere to the oxide film, and mechanical polishing has been recommended as a solution. However, the apparatus in which the mechanical polishing process coexists has mechanical elements and is not stable, and problems such as complication of the entire apparatus occur.
In the apparatus of the present invention, a carbon electrode is used as a detection electrode, and by strict time management of the electrochemical activation process, effective cleaning / activation is possible, and accurate measurement values can be stably obtained. It came to be obtained.
[0011]
The reason why effective cleaning / activation was made possible by using a carbon electrode is that oxygen is generated electrochemically on the carbon electrode (the electrolytic potential is set to a plus number V) and the number of electrode surfaces is increased. It is thought that carbon atoms in the layer are oxidized and removed as carbon dioxide or carbon monoxide gas, and contaminants attached to the surface are removed along with this reaction, and at the same time, a highly active surface appears. Therefore, when the electrochemical activation means is employed using the carbon electrode as the detection electrode, the same analysis result as that using the new electrode, that is, the measurement result with high reproducibility and stability can be obtained. The step of electrochemical cleaning / activation includes, for example, a reduction potential of minus number V, an oxidation potential of plus number V, a reduction potential of minus number V, and a stabilization potential of about 1 V at intervals of 10 to 500 milliseconds. Pulse polarization may be performed in order, and the electrodes may be opened and opened for a predetermined time.
[0012]
Although the detection electrode is washed / activated by electrochemical activation, the deactivation of the electrode surface proceeds rapidly thereafter. Therefore, it is necessary to activate the detection electrode immediately before the analysis operation, and it is necessary to release the electrode after activation and set the release time to a strict constant time. The constant release time after this electrochemical activation step is (a) removing the influence at the time of activation, (b) minimizing inactivation after activation, (c) reducing the measurement time, Determine in consideration of such points. The electrode open time is preferably shorter in consideration of the point (c), but is determined in consideration of the points (a) and (b) (for example, about 2 seconds). Since the opening times must be strictly managed as the same and constant intervals, the cleaning / activation process is computer-controlled by a control circuit.
[0013]
In order to measure hypochlorous acid concentration by an electrochemical method, it is necessary to keep the set electrolytic potential stable for a long period of time, and for this purpose, the reference electrode needs to be stable for a long period of time. Currently, a silver / silver chloride electrode is generally used as a reference electrode, and this silver / silver chloride electrode is also used in the apparatus of the present invention. Moreover, when an electrolysis current flows through the reference electrode, the set electrolysis potential becomes unstable. For this reason, the apparatus of the present invention employs a three-electrode constant-potential electrolysis system in which an electrode (auxiliary electrode) that carries an electrolytic current portion is provided in addition to the detection electrode and the reference electrode. However, this three-electrode / constant-potential electrolysis type apparatus is more complicated and has a larger control circuit than the two-electrode constant-voltage type apparatus, so the two-electrode type is the mainstream of commercially available analyzers. . The apparatus of the present invention can be made compact by integrating the constant potential electrolysis unit with the computer control unit and designing the circuit so as to be miniaturized, regardless of whether the three-electrode system is adopted. It was.
In auxiliary electrode chemically inert, particularly limited in material as long as no toxicity rather than gold has been conventionally used, but platinum may be used, to use the detection electrodes as well as the carbon electrode Is economical and preferable. The auxiliary electrode has a surface area larger than that of the detection electrode so that current can be easily captured, and is installed in such a way that the contact efficiency with running water is improved.
[0014]
When measuring the concentration of hypochlorous acid in an aqueous solution using the device of the present invention, after opening the cleaned / activated detection electrode for a predetermined time, set it to a constant potential and measure the electrolytic current flowing between the detection electrode and the auxiliary electrode. To do. In the conventional electrochemical analyzer, the electrolytic current value is measured immediately after setting the detection electrode to the electrolytic potential, and the current value is converted into the concentration to obtain the analytical value. In the apparatus of the present invention, the constant potential is set. A control circuit is provided to measure the electrolytic current flowing within a certain period after a predetermined exclusion period and calculate the hypochlorous acid concentration from the accumulated electric quantity without adopting the measured value of the electrolytic current immediately after ing. In this way, by removing the electrolysis current observed in the early stage of electrolysis from the measurement results, the unstable current region caused by the substance present at a high concentration in the vicinity of the initial electrode can be removed, and the flowing water sample carried by flow Only the concentration of the electrochemically active substance can be directly reflected in the analysis result. Further, since the measured value is an integral value of the current at a predetermined time interval, periodic noise that causes an error during measurement is inevitably removed.
In the case of the present invention, the electrolytic potential for measuring hypochlorous acid concentration is in the range of 50 mV ± 100 mV (based on silver / silver chloride reference electrode). This electrolytic potential is determined by thought and error by repeating a number of experiments with reference to the monopolar electrode potential (hydrogen electrode reference) in the above formulas (1) to (3).
[0015]
Although the length of the exclusion period varies depending on the measurement conditions and the like, in short, it is sufficient that the current value becomes substantially constant, and about 15 seconds is usually sufficient. The longer the period for obtaining the integrated amount of electricity, the longer the averaged data can be obtained, but the longer the period, the longer the time required for analysis. According to the apparatus of the present invention, a sufficiently stable measurement value can be obtained, so about 10 seconds is sufficient. Correlation data between the amount of electrolytic electricity measured in advance and the concentration of hypochlorous acid is input to the control circuit, and the concentration of hypochlorous acid can be calculated from the measured accumulated amount of electricity.
In the hypochlorous acid analysis operation using the apparatus of the present invention, after the detection electrode is washed / activated (including the open time), the current measurement is started with a constant potential, and the data at the beginning of measurement is excluded. Then, the electrolytic current flowing for a predetermined time thereafter is measured, and the hypochlorous acid concentration is calculated from the accumulated electric quantity. In this series of analysis operations, it is necessary to keep the operation conditions of each step constant.
[0016]
For reliable operation of the analyzer, it is necessary to always confirm the stable operation of the analyzer and the reliability of the analysis result. The device of the present invention is constructed for the purpose of analyzing substances in running water, and the detection electrode is set to a constant potential, and the measured value after a predetermined time has elapsed is adopted as the analysis value. It is considered that the electrochemical reduction reaction of hypochlorous acid has a high speed, and the electrolysis current is measured by using a diffusion-controlled current (the electrolysis current is controlled by diffusion of the electrolytic substance to the electrode) as a current value. In the present invention, it is defined as flowing water in order to increase the diffusion rate of hypochlorous acid, which is an electrolytic substance, to the electrode surface. As a result, the measured electric quantity takes a large value, and after a certain time, theoretically becomes a constant value. On the other hand, the measured current value during ideal still water decreases with time and theoretically approaches “zero”. From the experimental results, it was confirmed that when the amount of electrolysis after a certain period of time was measured as in the apparatus of the present invention, the measured value of electricity at the time of still water can be estimated as the value of “zero concentration”. This is one major feature of the device of the present invention. If necessary, the state at the time of still water can be created to check "zero concentration", and the reliability of the measurement result can be improved.
[0017]
As a preferred form of the apparatus of the present invention, the sensor part is integrated on one support such as plastic with a detection electrode and auxiliary electrode as a carbon electrode, a reference electrode as a silver / silver chloride electrode, a pH measurement electrode and a temperature measurement means. It can be set as a structured. The sensor unit configured as described above can be directly installed in running water in various pipes to perform hypochlorous acid concentration analysis. In addition, the device according to the present invention incorporates analog measurement functions such as pH and temperature measurement, water flow measurement, and digital input / output functions to control the operation of pumps, etc., thereby providing central control in disinfection system engineering. The ability to function sufficiently as a device can also be provided.
[0018]
The device of the present invention was developed as a device for measuring hypochlorous acid concentration by installing it in running water, but compared with the conventional analysis device, the measurement result during running water is much more extreme than in the case of still water. In addition, since the influence of the measured value due to the flowing water speed is small, it was confirmed that good analysis results can be obtained even by stirring the sample water with a magnetic stirrer that cannot quantify the amount of flowing water. Therefore, the apparatus of the present invention can be applied to the analysis of sample water if an appropriate stirring means is provided.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the hypochlorous acid concentration measuring apparatus of the present invention will be specifically described with reference to the drawings.
FIG. 1 is an explanatory view schematically showing one structural example of a hypochlorous acid concentration measuring apparatus of the present invention. In FIG. 1, reference numerals 1 and 5 are a sensor unit inserted into a pipe 10 through which test water to be measured flows and a flow rate sensor, respectively, and 2 is a control unit having an analog control unit 3 and a digital control unit 4. . The digital control unit 4 is connected to a recorder 6 and a personal computer (or touch panel) 7, and is configured to control peripheral devices by a digital input 8 and a digital output 9. Prior to the start of measurement, the control unit 2 applies a voltage to the detection electrode of the sensor unit 1 so that the electrode is electrochemically oxidized and reduced to be cleaned / activated, and the cleaned / activated detection electrode. Is set to a constant potential after being opened for a predetermined time, and a control circuit is provided for measuring the electrolytic current flowing within a predetermined period after the predetermined time has elapsed and calculating the hypochlorous acid concentration from the accumulated electric quantity. In this example, the control unit 2 includes an analog measurement circuit and a digital control circuit on a single printed board (105 × 270 mm). This printed circuit board circuit can control various digital devices by operating the sensor unit and obtaining analysis results according to commands via a personal computer or a touch panel and RS232C serial communication.
[0020]
FIG. 2 is an explanatory view showing a main part (tip portion) of the sensor unit 1, FIG. 2 (a) is a schematic sketch, and FIG. 2 (b) is a developed view of a side cross section thereof. The sensor unit 1 is a composite electrode, and includes a detection electrode 11, a reference electrode 12, an auxiliary electrode 14, a temperature sensor chamber 16 in which a temperature sensor 19 is placed, and an optional semiconductor pH electrode 15 having a support 17 (diameter made of vinyl chloride resin). 15 mm). In this example, the detection electrode 11 is a carbon rod having a diameter of 3 mm. For low concentration analysis up to 20 ppm, the cylindrical side surface of the carbon rod exposed 15 mm from the support 17 is used as an electrode, and high concentration analysis up to 2000 ppm is used. The number of exposed portions from the support 17 was reduced, and the cross section was used as an electrode surface. As the auxiliary electrode 14, a carbon rod having a diameter of 10 mm was used. A standard electrode chamber 18 containing a reference electrode 12 which is a silver / silver chloride electrode is supported by a support 17 so as to be in contact with test water across a microfilter 13, and the standard electrode chamber 18 is saturated potassium chloride. A silver wire (reference electrode 12) filled with an aqueous solution and plated with silver chloride is enclosed.
[0021]
An analytical test of the concentration of hypochlorous acid in running water in a pipe having an inner diameter of 20 mm was performed using the apparatus having such a configuration.
Prior to all measurements, the sensing electrode 11 was electrochemically cleaned / activated by the electrolytic potential operation according to the standard pattern shown in FIG. In other words, the detection electrode 11 is pulse-polarized in the order of minus 5V reduction potential, 5V oxidation potential, minus 5V reduction potential, 1V stabilization potential at intervals of 10 milliseconds, and then the electrode is opened to open 2 Left for a second. Immediately thereafter, the electrolytic potential of the detection electrode was set to +50 mV, the electrolytic current for 15 seconds was excluded, the amount of electrolytic electricity consumed for the subsequent 10 seconds was measured, converted into hypochlorous acid concentration, and the analytical value. did. FIG. 3 shows up to the beginning of the 15-second exclusion period after setting the electrolytic potential to plus 50 mV. The time required for analysis by this pattern was about 30 seconds per time.
[0022]
4 and 5 show the amount of electrolysis (relative value of Coulomb) and hypochlorous acid concentration (ppm) measured for test water containing hypochlorous acid at a predetermined concentration under conditions of pH 6.5 and flowing water volume of 10 liters / min. ). FIG. 4 shows the result of measurement for a low concentration solution up to a concentration of 10 ppm using a detection electrode for low concentration, and FIG. 5 shows the result of measurement for a high concentration solution up to 1000 ppm using a detection electrode for high concentration. . In any case, the amount of electrolytic electricity and the concentration of hypochlorous acid showed a good correlation, and the reproducibility of the measurement was within 1% of the measured value average. In FIGS. 4 and 5, the dotted line indicates the result of measurement in the still water state, and it can be seen that the amount of electricity is almost zero in the still water state.
[0023]
FIG. 6 shows the result of measuring the amount of electricity by changing the amount of flowing water (using a high concentration electrode) for the test water having a hypochlorous acid concentration of 50 ppm. The measured value is close to zero, and the change due to the hypochlorous acid concentration in the test water is small. Also, the difference in measured electricity from 5 to 15 liters / minute is very small compared to the change from 0 to 5 liters / minute, and a stable measurement value can be obtained with a flow rate of 5 liters / minute or more. I understand. In addition, since the amount of electrolysis is almost zero in still water, the measurement can be performed at any time during measurement in running water, and by confirming that the measured value is zero, the device operates normally. Can be confirmed.
Summarizing the above results, this device is a hypochlorous acid concentration analyzer having the ability to sufficiently function as a central control device in the engineering of disinfection systems, and has a maximum measurement setting value within a measuring range of 0 to 2000 ppm. It can be seen that the high accuracy / sensitivity of ± 1% has an excellent performance of about 30 seconds required for analysis.
[0024]
【The invention's effect】
The hypochlorous acid concentration measuring device of the present invention does not use an expensive noble metal electrode, can stably obtain a more accurate measurement value over a long period of time compared to conventional devices, and is compact and automated. Is a hypochlorous acid concentration measuring device that is easy to use.
In addition, since this analyzer does not use any analysis reagents, there is no contamination of water to be analyzed such as sterilized water by analysis, so it is possible to incorporate the sensor unit directly into the disinfecting water pipeline. .
The apparatus of the present invention has extremely excellent performance as an apparatus for measuring the concentration of hypochlorous acid in disinfecting water containing a chlorine-based disinfectant, or in various effluents and effluents in which chlorine-based substances derived therefrom are dissolved. It is. In addition, by designing the control circuit so that peripheral devices such as disinfection water flow measurement and chemical injection pump control can be controlled, it can be used as a device that plays a central role in system engineering. There are an infinite number of industrial applications that require a sterilization process.
[Brief description of the drawings]
FIG. 1 is an explanatory view schematically showing one configuration example of a hypochlorous acid concentration measuring apparatus of the present invention.
FIG. 2 is an explanatory view showing a main part (tip portion) of the sensor 1 of FIG.
FIG. 3 is an explanatory diagram showing one pattern of electrolytic potential operation for electrochemical cleaning / activation.
FIG. 4 is a graph showing the relationship between the amount of electrolytic electricity measured for test water containing hypochlorous acid at a low concentration and the concentration of hypochlorous acid.
FIG. 5 is a graph showing the relationship between the amount of electrolysis and hypochlorous acid concentration measured for test water containing high concentration hypochlorous acid.
FIG. 6 is a graph showing the results of measuring the amount of electricity by changing the amount of flowing water for test water containing hypochlorous acid.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Sensor part 2 Control part 3 Analog control part 4 Digital control part 5 Flow rate sensor 6 Recorder 7 Personal computer (or touch panel) 8 Digital input 9 Digital output 10 Pipe 11 Detection electrode 12 Reference electrode 13 Micro filter 14 Auxiliary electrode 15 Semiconductor pH Electrode 16 Temperature sensor chamber 17 Support 18 Standard electrode chamber 19 Temperature sensor

Claims

A detection electrode, an auxiliary electrode, and a reference electrode are provided, the detection electrode is set to a constant potential, the electrolytic current flowing between the detection electrode and the reference electrode is measured, and the concentration of hypochlorous acid in the flowing water sample is electrochemical A three-electrode type hypochlorous acid concentration measuring device, wherein the detection electrode is a carbon electrode, the reference electrode is a silver / silver chloride electrode, and the electrode is electrochemically connected to the detection electrode prior to the start of measurement. A control circuit that applies a voltage so as to be cleaned / activated by oxidation and reduction , and a detection electrode that has been cleaned / activated are opened for a predetermined time, set to a constant potential, and flow within a predetermined period after the predetermined time has elapsed. An apparatus for measuring hypochlorous acid concentration , comprising a control unit having a control circuit for measuring an electrolytic current and calculating a hypochlorous acid concentration from the accumulated amount of electricity .

The hypochlorous acid concentration measuring apparatus according to claim 1, wherein the auxiliary electrode is a carbon electrode.

A detection electrode, an auxiliary electrode, and a reference electrode are provided, the detection electrode is set to a constant potential, the electrolytic current flowing between the detection electrode and the reference electrode is measured, and the concentration of hypochlorous acid in the flowing water sample is electrochemical Is a three-electrode type hypochlorous acid concentration measuring device for measuring a single electrode, a detection electrode as a carbon electrode and an auxiliary electrode, a reference electrode as a silver / silver chloride electrode, a pH measurement electrode and a temperature measurement means And a control circuit that applies a voltage so that the electrode is electrochemically oxidized, reduced, and cleaned / activated prior to the start of measurement / A control circuit that sets the constant detection potential after opening the activated detection electrode for a predetermined time, measures the electrolytic current flowing within a certain period after the predetermined time has elapsed, and calculates the hypochlorous acid concentration from the accumulated amount of electricity Comprising a control unit having Hypochlorous acid concentration measuring device according to symptoms.

Prior to the start of measurement, a control circuit that applies a voltage to the detection electrode to electrochemically oxidize, reduce, and wash / activate the electrode, and the cleaned / activated detection electrode is opened for a predetermined time, and then fixed. A control unit with a control circuit that sets the potential, measures the electrolysis current flowing within a certain period of time after a predetermined time, and calculates the hypochlorous acid concentration from the accumulated electric quantity, measures the pH, temperature, and flowing water amount 4. The hypochlorous acid concentration measuring device according to claim 3 , wherein the control unit has a built-in analog measurement function and a digital input / output function for controlling operation of peripheral devices.