JP4207276B2

JP4207276B2 - Acidity measuring device

Info

Publication number: JP4207276B2
Application number: JP36455698A
Authority: JP
Inventors: 毅日下部; 毅西田; 康行花田
Original assignee: Panasonic Corp; Matsushita Electric Industrial Co Ltd
Current assignee: Panasonic Corp; Panasonic Holdings Corp
Priority date: 1998-12-22
Filing date: 1998-12-22
Publication date: 2009-01-14
Anticipated expiration: 2018-12-22
Also published as: JP2000187020A

Description

【０００１】
【発明の属する技術分野】
本発明はキノン誘導体、電解質、有機溶媒を混合した測定溶液に所定の濃度の被測定液を混合し、作用電極、比較電極、対極を用いて電位を掃引して酸度を測定し、温度補正する酸度測定装置に関するものである。
【０００２】
【従来の技術】
近年、食品は健康や安全面から一定の水準以上の品質が要求されるようになってきている。中でも食品中に含有された酸は食品の品質に大きな影響を与えている。この酸について説明すると、食品の酸度としては、食用油、ジュース等の果実飲料、ウィスキーや酒、ワイン等のアルコール飲料、コーヒーなどがあり、その酸の測定として従来は主に中和滴定法を使用していた。この中和測定方法には様々なものがあり、一例を上げると、基準油脂分析法、日本農林規格、ＪＩＳ、日本薬局方油脂試験法、衛生試験法飲食物試験法、上水試験方法などで定められた方法があるが、いずれもその測定の基本はフェノールフタレインを指示薬としたものである。
【０００３】
ところで、このような中和滴定法によらず、ボルタンメトリーによって酸度を測定する方法がある。これは特開平５−２６４５０３号公報で開示されたもので、遊離脂肪酸とナフトキノン誘導体が共存する測定電解液を電位規制法によるボルタンメトリーによって測定するものである。ナフトキノン誘導体の還元前置波の電流値の大きさが、蟻酸のような低級脂肪酸からオレイン酸やリノール酸のような高級脂肪酸まで全ての脂肪酸について、遊離脂肪酸の濃度に比例し、各脂肪酸の電流値を重ね合わせた値が脂肪酸の総濃度に対応することを利用している。すなわち、予め既知の酸度の脂肪酸において後述する図１２に示すようなプレピーク電流値−酸度の関係（検量線）を作成しておけば、未知の酸度の脂肪酸をボルタンメトリーによってプレピーク電流値を検出し、この検量線によってその酸度を導き出すことができるというものである。
【０００４】
【発明が解決しようとする課題】
以上説明したように従来の酸度測定装置は、中和滴定法を用いているため測定者がフェノールフタレイン指示薬による色変化を判断して滴定の終点としており、測定者によってその終点がまちまちとなって、酸度が測定者によって変化する可能性があった。
【０００５】
一方、特開平５−２６４５０３号公報で開示された技術は、ボルタンメトリーで用いるキノン類が光安定性に欠け測定値がばらつくという欠点をナフトキノン誘導体を使うことで解決しているが、溶液中の溶存酸素の影響を受け易く、測定前に不活性ガスで除酸素する必要があり、大規模で面倒な処理が必要なものであった。しかも、電極と測定溶液の関係、電極表面の状態によって、測定したプレピーク電流値が変化し、特に測定温度に関しては前記プレピーク電流値は敏感で、算出する酸度はこれらの変化によりばらついていた。すなわち、温度が変化すると算出する酸度も変化するという問題があるものであった。
【０００６】
そこで、このような問題を解決するために本発明は、簡単な構成で、溶存酸素や光の影響を受けることがなく、測定時の温度が変化するようなことがあっても温度補正して正確な酸度を算出することができる酸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】
上記課題を解決するために本発明の酸度測定装置は、容器内の共存電解液の温度を検出する温度検出手段を備え、前記温度検出手段で検知した温度Ｔから下記の（１）〜（３）式によって前記被測定試料の酸度θを算出する演算部を備えたことを特徴とする。
θ＝Ｋ・Ｉ_P＋ｋ・・・（１）
ここで、
Ｋ＝１／（Ａ₁・Ｔ＋Ｂ₁）・・・（２）
ｋ＝−（Ａ₂・Ｔ＋Ｂ₂）／（Ａ₁・Ｔ＋Ｂ₁）・・・（３）
（但し、θは酸度、Ｉ_Pはプレピーク電流値、Ｔは温度、Ａ₁，Ａ₂，Ｂ₁，Ｂ₂は共存電解液固有の定数）
これにより、測定時の温度が変化するようなことがあっても温度補正して正確な酸度を算出することができる。
【０００９】
【発明の実施の形態】
本発明の請求項１に記載された発明は、オルトベンゾキノン誘導体もしくはパラベンゾキノン誘導体、電解質を有機溶媒で溶解した測定溶液と酸含有の被測定試料を混合した共存電解液を収容する容器と、前記容器に設けられ前記共存電解液に浸漬される作用電極と対極と比較電極と、前記作用電極の電極電位を所定の電位範囲内で掃引するとともに、前記作用電極と前記対極間を流れる電流のプレピーク電流値Ｉ_Pを検出する制御部と、前記容器内の前記共存電解液の温度を検出する温度検出手段を備え、前記温度検出手段で検知した温度Ｔから下記の（１）〜（３）式によって前記被測定試料の酸度θを算出する演算部を備えたことを特徴とする酸度測定装置
θ＝Ｋ・Ｉ_P＋ｋ・・・（１）
ここで、
Ｋ＝１／（Ａ₁・Ｔ＋Ｂ₁）・・・（２）
ｋ＝−（Ａ₂・Ｔ＋Ｂ₂）／（Ａ₁・Ｔ＋Ｂ₁）・・・（３）
（但し、θは酸度、Ｉ_Pはプレピーク電流値、Ｔは温度、Ａ₁，Ａ₂，Ｂ₁，Ｂ₂は共存電解液固有の定数）
であるから、溶存酸素や光、測定温度に影響されず酸度を算出することができる。
【００１０】
請求項２に記載された発明は、温度検出手段が、共存電解液中に浸漬した温度センサーによって直接測定溶液の温度を測ることを特徴とする請求項１記載の酸度測定装置であるから、溶存酸素や光等の影響を受けないだけでなく、測定温度に影響されない正確な酸度を算出することができる。
【００１１】
請求項３に記載された発明は、オルトベンゾキノン誘導体もしくはパラベンゾキノン誘導体、電解質を有機溶媒で溶解した測定溶液と酸含有の被測定試料を混合した共存電解液を収容する容器と、前記容器に設けられ前記共存電解液に浸漬される作用電極と対極と比較電極と、前記作用電極の電極電位を所定の電位範囲内で掃引するとともに、前記作用電極と前記対極間を流れる電流のプレピーク電流値Ｉ_Pとメインピーク電流値Ｉ_Mを検出する制御部を備え、前記制御部が検知したメインピーク電流値Ｉ_Mから下記の（４）式に従って前記被測定溶液の温度Ｔを算出し、下記の（１）〜（３）式によって前記被測定試料の酸度θを算出する演算部を備えたことを特徴とする酸度測定装置
θ＝Ｋ・Ｉ_P＋ｋ・・・（１）
ここで、
Ｋ＝１／（Ａ₁・Ｔ＋Ｂ₁）・・・（２）
ｋ＝−（Ａ₂・Ｔ＋Ｂ₂）／（Ａ₁・Ｔ＋Ｂ₁）・・・（３）
また、
Ｔ＝Ｘ・Ｉ_M ²＋Ｙ・Ｉ_M＋Ｚ・・・（４）
（但し、θは酸度、Ｉ_Pはプレピーク電流値、Ｉ_Mはメインピーク電流値、Ｔは温度、Ａ₁，Ａ₂，Ｂ₁，Ｂ₂，Ｘ，Ｙ，Ｚは共存電解液固有の定数）
であるから、特別な温度検出のためのセンサなどを設けることなく、電流のメインピーク電流値とプレピーク電流値を検出するだけで、測定温度のみならず他の測定環境にも影響されずに酸度を測定することができる。
【００１２】
請求項４に記載された発明は、オルトベンゾキノン誘導体もしくはパラベンゾキノン誘導体、電解質を有機溶媒で溶解した測定溶液と所定酸度の低級酸及び酸含有の被測定試料を混合した共存電解液を収容する容器と、前記容器に設けられ前記共存電解液に浸漬される作用電極と対極と比較電極と、前記作用電極の電極電位を所定の電位範囲内で掃引するとともに、前記作用電極と前記対極間を流れる電流の前記被測定試料由来のプレピーク電流値ＩＰと前記低級酸由来のプレピーク電流値Ｉ_αとを検出する制御部を備え、前記制御部が検知したプレピーク電流値Ｉ_αから下記の（５）式に従って前記被測定溶液の温度Ｔを算出し、下記の（１）〜（３）式によって前記被測定試料の酸度θを算出する演算部を備えたことを特徴とする酸度測定装置。
θ＝Ｋ・Ｉ_P＋ｋ・・・（１）
ここで、
Ｋ＝１／（Ａ₁・Ｔ＋Ｂ₁）・・・（２）
ｋ＝−（Ａ₂・Ｔ＋Ｂ₂）／（Ａ₁・Ｔ＋Ｂ₁）・・・（３）
また、
Ｔ＝ｘ・Ｉ_α ²＋ｙ・Ｉ_α＋ｚ・・・（５）
（但し、θは酸度、Ｉ _P はプレピーク電流値、Ｉ _α は低級酸のプレピーク電流値、Ｔは温度、Ａ₁，Ａ₂，Ｂ₁，Ｂ₂，ｘ，ｙ，ｚは共存電解液固有の定数）であるから、被測定試料由来のプレピーク電流値と既知の低級酸のプレピーク電流値を測定するだけで、溶存酸素や光等の影響を受けないだけでなく、測定温度にも影響されない正確な酸度を測定することができる。
【００１３】
請求項５に記載された発明は、（１）〜（３）式によって被測定試料の酸度を算出する演算部に代え、前記被測定溶液の温度ごとにＫとｋを対応させた換算テーブルを記憶した記憶部を備えて、該記憶部から読み出した温度に対応したＫとｋにより前記演算部が（１）式に従って温度補正を行う請求項１〜４のいずれかに記載の酸度測定装置であるから、演算部によって測定のたびごとに酸度の算出をする必要はなく、記憶部に換算テーブルをもっていれば直ちに正確な酸度の測定をすることができる。
【００１８】
以下、本発明の実施の形態について図１〜図２０を用いて説明する。
（実施の形態１）
まず本発明の一実施の形態の酸度測定装置について、図面に基づいて詳細に説明する。図１は本発明の一実施の形態における酸度測定装置の概略外観図である。図１において１は酸度測定装置本体、２は測定容器である。３は測定容器２を収納する収納部でスライドさせて測定容器２を出し入れすることができる。４は測定酸度を表示するＬＣＤ、５は本装置の電源をＯＮ、ＯＦＦする電源ボタン、６は測定した酸度を記憶させる記憶ボタン、７は測定を開始するためのスタート・ストップボタン、８は校正時に用いる校正ボタンである。次に、図２は本発明の実施の形態１における測定容器の断面図である。ここで、９はオルトベンゾキノン誘導体もしくはパラベンゾキノン誘導体、電解質を有機溶媒で溶解した測定溶液と被測定試料を混合した共存電解液を収容する容器、１０は作用電極、１１は比較電極、１２は対極、１３は温度センサー、１４はセンサーカバー、１５は前記作用電極１０、前記比較電極１１、前記対極１２、前記温度センサー１３、前記センサーカバー１４を取り付けた容器カバーで、容器９と容易に脱着できる構造となっている。温度センサー１３が直接共存電解液に触れると測定系に影響を及ぼすため、センサーカバー１４で絶縁されている。すなわち、センサーカバー１４はガラスなどの熱伝導性のよい絶縁体が望ましい。測定容器２は容器９内に前記共存電解液を収容するとともに、作用電極１０、比較電極１１、対極１２、温度センサー１３、センサーカバー１４を取り付けた容器カバー１５が共存電解液に各電極を浸漬した状態で容器９に装着されている。作用電極１０の材料としては、炭素もしくはグラッシーカーボンと呼ばれるガラス状炭素や、ＰＦＣと呼ばれるプラスチックフォームを１０００℃〜２０００℃で焼結した炭素が適当である。比較電極１１の材料としては、作用電極１０で用いられる材料もしくは銀−塩化銀、飽和カロメル、銀−銀イオン、水銀−飽和硫酸水銀でもよい。対極１２の材料としては共存電解液中でも腐食しないで化学的に安定な白金、黒鉛、金が望ましいが、腐食しないステンレス、アルミニウム及びその合金等であってもよい。
【００１９】
次に、容器９に収容する共存電解液の説明をすると、本実施の形態１では溶媒として、エタノール、イソプロピルアルコール、水をそれぞれ６：２：２に混合したものにオルトベンゾキノン２０ｍＭ、ＮａＣｌ１５０ｍＭを溶解したものであって、共存電解液はこの測定溶液に被測定試料を５０：１の割合で混合して用いている。このようにエタノール、イソプロピルアルコール、水の３元系溶媒を用いると、果汁のみならず、濃縮還元ジュースやインスタントコーヒーまでも溶解させることができ、従来の技術のような攪拌と遠心分離をせずとも十分に溶解し、酸度の測定が非常に簡単になる。
【００２０】
ところで、本発明では共存電解液にはオルトベンゾキノン誘導体もしくはパラベンゾキノン誘導体を混合している。以下、なぜオルトベンゾキノン誘導体もしくはパラベンゾキノン誘導体を混合するのかの説明を行う。図３はオルトベンゾキノン誘導体が共存する測定電解液のボルタンメトリーによる酸度測定の電位−電流関係図である。図３の横軸は、作用電極，比較電極ともにプラスチックフォームカーボンを用いたときの、比較電極に対する作用電極の電位、縦軸はこのとき対極に流れる電流値である。ただ、電流値は作用電極の表面積の大きさや酸の濃度といった条件によって変わるものである。これに対して横軸のピークの現れる電位は酸の濃度によって若干変動はあるものの、その変動は無視できる程度のものである。図３に示すように、ベンゼン環に側鎖をもつオルトベンゾキノン誘導体の還元電流波形（以下、ボルタモグラム）は、溶存酸素の還元波形が出現する領域から正電位側に大きく離れて出現している。実線がオルトベンゾキノン誘導体のボルタモグラムであり、破線が溶存酸素の還元波形を示すものである。図３によれば、プレピークはもとよりメインピークの位置でも溶存酸素の還元の影響はほとんど受けない。このように溶存酸素の影響のない領域でプレピーク電流値、メインピーク電流値を測定できるので、予め溶存酸素を除去しなくても、溶存酸素の影響を受けることなく、従ってバラつきもなく酸度を正確に測ることができるものである。また、パラベンゾキノン誘導体を用いても、プレピーク，メインピークの出現電位に多少の違いがあるが、図３と同様の電位−電流関係図が得られ、溶存酸素の影響のない領域で、プレピーク、メインピーク電流値を測定できる。このように、溶存酸素の影響のない領域で測定できるので、従来技術のような除酸素などは必要なく装置が小型化できる。
【００２１】
ところでベンゼン環に側鎖をもつオルトベンゾキノン誘導体もしくはパラベンゾキノン誘導体は、溶存酸素の還元電位と離れた位置にプレピークをもつという上記の特性以外に、キノン類に多い光分解を起こすことなく安定した測定をすることができる優れた特性をもっている。図４はオルトベンゾキノン誘導体の構造図、図５はパラベンゾキノン誘導体の構造図である。また、図６はオルトベンゾキノンの構造図、図７はパラベンゾキノンの構造図である。図４のオルトベンゾキノン誘導体、図５のパラベンゾキノン誘導体は、図６のオルトベンゾキノン、図７のパラベンゾキノンに対して側鎖であるＲ部分が存在するために、光によって分解のエネルギーを与えられたとしても、側鎖Ｒの分子内伸縮や側鎖Ｒの回転のための運動エネルギーとして光のエネルギーを消費するために光分解を受けにくい。さらに、図８は3,5−ジ−ｔｅｒｔ−ブチル−1,2−ベンゾキノンの構造を示す図、図９は2,6−ジメチル−1,4−ベンゾキノンの構造を示す図である。オルトベンゾキノンの中でも、図８に示す3,5−ジ−ｔｅｒｔ−ブチル−1,2−ベンゾキノンと、パラベンゾキノンの中でも図９に示す2,6−ジメチル−1,4−ベンゾキノンを用いると、構造的に−ｔｅｒｔ−ブチルやメチル基がベンゼン環の中に電子を供与するため、分子構造が共役構造を取り易くなり、さらに光のエネルギーが多く吸収されるため光分解がほとんど起こらず、安定した測定が可能になるものである。
【００２２】
そしてこれらのキノン類の光に対する安定性と、ボルタモグラムのプレピークが溶存酸素の還元波形からどの程度離れているかについては、次に説明するような関係がある。すなわち、光に対する安定性が高いナフトキノン誘導体のようなキノン類は、安定性が向上するに従って、ボルタモグラムのプレピーク位置が次第に負電位側によっていき、溶存酸素の還元波形と重なるような傾向をもつ。また逆に、光に対する安定性が悪いキノン類は、光に対する安定性が悪くなるに従って、溶存酸素の還元波形と重ならない方向へシフトする傾向をもつが、光の影響によって電解液自身に変化を生じ、測定値がバラついて電解液として実用性が悪くなる。そこで、光に対する十分な安定性を備え、同時にボルタモグラムのプレピーク位置が少なくとも溶存酸素の還元波形と重ならないキノン類であれば、溶存酸素の影響によらないため酸度測定装置の電解液として適した特性をもつものである。このようなキノン類として、ベンゼン環の3,5位置に側鎖をもつオルトベンゾキノン誘導体、中でも3,5−ジ−ｔｅｒｔ−ブチル−1,2−ベンゾキノンが優れ、またベンゼン環の2,6位置に側鎖をもつパラベンゾキノン誘導体、中でも2,6−ジメチル−1,4−ベンゾキノンが優れているのである。これらは光分解を起こすことなく安定した測定をすることができ、図３に示すように溶存酸素の還元電位からプレピークが分離しているものである。なお、光に対する安定性が高く、ボルタモグラムのプレピーク位置が溶存酸素の還元波形と重ならないキノン類であれば他のキノン類、材料でも使用することができる。
【００２３】
次に、本実施の形態１の酸度測定装置の制御を行う制御回路について説明する。図１０は本発明の実施の形態１における酸度測定装置の回路図である。図１０において１６は測定時の容器９内の共存電解液の温度を検出する温度検出手段、１７は掃引電圧を制御する電圧制御部、１８は前記電圧掃引で作用電極１０と対極１２間に流れる電流を検知する電流検出部、１９は酸度を算出するためのメモリー機能などを備えた制御部、２０は各種操作ボタンに対応している操作部、２１は算出された酸度を表示する表示部、２２は酸度を算出する演算部である。
【００２４】
さて、本実施の形態１の酸度測定装置を操作するときの装置の動作の説明をする。測定溶液５ｍＬと被測定試料である果汁を０．１ｍＬ容器９に入れ、次いで容器カバー１５を取り付けてた測定容器２を十分撹拌した後、収容部３を開けセットし、再び収容部３を閉じると測定可能状態となる。電源ボタン５を押して電源ＯＮとした後、スタート・ストップボタン７を押して測定開始すると、電圧制御部１７が作用電極１０の電位を比較電極１１の電位に対して所定の範囲で、所定の掃引速度で掃引するように作用電極１０と対極１２間に電圧を印加していく。このような掃引を行うことで図１１に示すような還元電流波形が得られる。図１１において２つのピークが存在するが、Ｐは被測定試料に含まれる酸に由来するプレピーク、Ｍは本測定で使用した共存電解液の主溶媒であるエタノールに由来するメインピークである。この時、プレピークと被測定試料に混入している酸の酸度θは図１２に示すようにプレピーク電流値Ｉ_Pと比例関係にあることが知られている。すなわちプレピーク電流値Ｉ_Pと酸度θには、
θ＝Ｋ・Ｉ_P＋ｋ・・・（１）
の関係がある。ただし、（１）式のＫ、ｋは後述するように共存電解液の温度Ｔの関数であるから、温度Ｔが変れば図１２に示すようにプレピーク電流値Ｉ_Pと酸度θの関係は変化する。従って、共存電解液の温度とＡのプレピーク電流値Ｉ_pを測定することで酸度θを測定することができるものである。
【００２５】
この関係を一例をあげて説明すると、溶媒として、エタノール、イソプロピルアルコール、水を６：２：２に混合したものに3,5−ジ−ｔｅｒｔ−ブチル−1,2−ベンゾキノン２０ｍＭ、ＮａＣｌ１５０ｍＭを溶解したものを測定溶液として用いる。なお、電極は作用電極１０、比較電極１１、対極１２ともにプラスチックフォームカーボンを用いている。
【００２６】
まず、測定溶液５ｍＬと２ｗｔ．％のクエン酸標準液を０．１ｍＬを容器９に収容し、作用電極１０、比較電極１１、対極１２を備えた容器カバー１５を設置し、十分撹拌した後、共存電解液が所定の温度に落ち着くまで待って、作用電極１０の電位を比較電極１１の電位に対して０〜１０００ｍＶの範囲で、１００ｍＶ／秒の掃引速度で掃引するように作用電極１０と対極１２間に電圧を印加していくと、図１１に示すような電位―電流関係図が得られる。これらの操作を５℃から約５℃間隔で３５℃まで繰り返し測定する。次に、測定溶液５ｍＬと４ｗｔ．％のクエン酸標準液を０．１ｍＬを容器９に収容し同様の測定をすると、図１３に示すような共存電解液の温度とプレピーク電流値の関係が得られ、プレピーク電流値Ｉ_Pは次の一次関数で与えられる。図１３は本発明の実施の形態１，２，３における共存電解液の温度−プレピーク電流値関係図、図１４は本発明の実施の形態１，２，３における共存電解液の温度−Ａ(θ）、Ｂ(θ）の関係図、図１５は本発明の実施の形態１，２，３における共存電解液の温度−Ｋ、ｋの関係図である。
Ｉ_P4%＝０．７８０４Ｔ＋３３．９３・・・（６）
Ｉ_P2%＝０．３７９５Ｔ＋１８．９９・・・（７）
ここで、Ｉ_P2%は酸度２ｗｔ．％のクエン酸標準液を加えたときのプレピーク電流値、Ｉ_P4%は酸度４ｗｔ．％のクエン酸標準液を加えたときのプレピーク電流値、Ｔは共存電解液の温度である。
【００２７】
ところで、このプレピーク電流値Ｉ_Pと温度Ｔとの間で成立した一次関数に、酸度θがどのような影響をもつのか検討したところ、図１４に示すように次のような関係が成り立つことが分かった。
Ｉ_P＝Ａ（θ）・Ｔ＋Ｂ（θ）・・・（８）
ここで、Ａ（θ）＝１．９６０×１０^-1・θ−１．４８１×１０^-3・・・（９）
Ｂ（θ）＝７．５３４・θ＋３．９８８・・・（１０）
そして、この関係は基本的に他の共存電解液でも成り立ち、一般的に、
Ａ（θ）＝Ａ₁・θ＋Ａ₂・・・（１１）
Ｂ（θ）＝Ｂ₁・θ＋Ｂ₂・・・（１２）
であり、Ａ₁、Ａ₂、Ｂ₁、Ｂ₂は共存電解液に固有の定数である。
【００２８】
この（１）（１０）（１１）（１２）式から、θ₁，θ₂に対して、
θ₁＝Ｋ・｛Ａ（θ₁）・Ｔ＋Ｂ（θ₁）｝＋ｋ
θ₂＝Ｋ・｛Ａ（θ₂）・Ｔ＋Ｂ（θ₂）｝＋ｋ
従って、

同様に、

となる。上記の共存電解液の場合には、２ｗｔ．％と４ｗｔ．％の酸度を測定して次の値を得たから、
Ａ₁＝１．９６０×１０^-1 Ａ₂＝１．４８１×１０^-3
Ｂ₁＝７．５３４Ｂ₂＝３．９８８
（２）（３）式は、
Ｋ＝１／（１．９６０×１０^-1・Ｔ＋７．５３４）・・・（１３）
ｋ＝−（１．４８１×１０^-3・Ｔ＋３．９８８）／（１．９６０×１０^-1・Ｔ＋７．５３４）・・・（１４）
となることが分かる。図１５に示すように、かなりの精度で（１３）（１４）式でＫ，ｋが予測できることが分かる。
【００２９】
この（１３）、（１４）式から（１）式に従いそれぞれＫ、ｋを計算し、（１）式の一般式を求めると下記のようになることが分かる。
θ＝｛１／（１．９６０×１０^-1・Ｔ＋７．５３４）｝・Ｉ_P−（１．４８１×１０^-3・Ｔ＋３．９８８）／（１．９６０×１０^-1・Ｔ＋７．５３４）（１５）ここで、θは酸度、Ｉ_Pはプレピーク電流値、Ｔは共存電解液の温度である。すなわち、共存電解液の一般的な通性として、酸度θはプレピーク電流値Ｉ_Pと共存電解液の温度Ｔの関数として表すことができるものである。
【００３０】
従って、例えば、溶媒として、エタノール、イソプロピルアルコール、水を６：２：２に混合したものに3,5−ジ−ｔｅｒｔ−ブチル−1,2−ベンゾキノン２０ｍＭ、ＮａＣｌ１５０ｍＭを溶解したものを測定溶液とし、測定試料としてクエン酸を添加して酸度を図る場合には、予め、この（１５）式を制御部１９に記憶させておき、測定時に電流検出部１８でプレピーク電流値Ｉ_Pを検出し、あわせて同時に共存電解液の温度Ｔを温度センサー１３により検知すると、（１５）式から被測定試料の酸度が補正でき、正確に算出できることになる。
【００３１】
【表１】

【００３２】
また、（表１）に示すように（１５）式をもとに予め計算した共存電解液の温度Ｔと温度によるＫ、ｋの値を換算テーブルの形でそれぞれ制御部１９の記憶部へ記憶させておけば、測定時に温度センサー１３により検知した温度におけるＫ、ｋを選択し、電流検出部１８により検出したプレピーク電流値Ｉ_pから被測定試料の酸度θを簡単に算出することができる。例えば、測定時のプレピーク電流値が３０μＡ、共存電解液の温度が２５℃だったとすると、（表１）より酸度θは次式で与えられる。

さらに記憶部に換算テーブルを記憶させるのではなく、共存電解液と温度ごとの検量線の形で酸度測定装置に備え付けておき、ある温度を検出したときにはプレピーク電流値Ｉ_Pと該温度に対応した検量線から酸度読み取れば簡単に酸度を温度補正することができる。なお、Ｋ、ｋの値は基本的に（１３）（１４）で表されるが、一般式（１１）（１２）からもわかるようにＫ、ｋの実測値にわずかながら若干の変動が存在する場合もあるから、この場合には換算テーブルや検量線に実測値を与えておけばより精度が増すものである。
【００３３】
このように、実施の形態１の酸度測定装置と測定方法は、溶存酸素や光等の影響を受けないだけでなく、測定温度に影響されない正確な酸度を算出することができるものである。
【００３４】
（実施の形態２）
実施の形態２の酸度測定装置の概略外観図は実施の形態１で示した図１と同様であるからここでは省略する。次に、図１６は本発明の実施の形態２，３における測定容器２の断面図である。ここで、９’はオルトベンゾキノン誘導体もしくはパラベンゾキノン誘導体、電解質を有機溶媒で溶解した測定溶液と被測定試料を混合した共存電解液を収容する容器、１０’は作用電極、１１’は比較電極、１２’は対極、１５’は前記作用電極１０’、前記比較電極１１’、前記対極１２’を取り付けた容器カバーで、前記容器９’と容易に脱着できる構造となっている。測定容器２は容器９’内に前記共存電解液を収容するとともに、作用電極１０’、比較電極１１’、対極１２’を取り付けた容器カバー１５’が前記共存電解液に各電極を浸漬した状態で容器９’に装着されている。
【００３５】
次に、本実施の形態２の酸度測定装置の制御を行う制御回路について説明する。図１７は本発明の実施の形態２，３における酸度測定装置の回路図である。図１７において１７’は掃引電圧を制御する電圧制御部、１８’は前記電圧掃引で作用電極１０’と対極１２’間に流れる電流を検知する電流検出部、１９’は酸度を算出するためのメモリー機能などを備えた制御部、２０’は各種操作ボタンに対応している操作部、２１’は算出された酸度を表示する表示部、２２’は酸度を算出する演算部である。
【００３６】
さて、本実施の形態２の酸度測定装置を操作するときの装置の動作の説明をする。測定溶媒５ｍＬと被測定試料である果汁を０．１ｍＬ容器９’に入れ、次いで容器カバー１５’を取り付けた測定容器２を十分撹拌した後、収容部３を開けセットし、再び収容部３を閉じると測定可能状態となる。電源ボタン５を押して電源ＯＮとした後、スタート・ストップボタン７を押して測定開始すると、電圧制御部１７’が作用電極１０’の電位を比較電極１１’の電位に対して所定の範囲で所定の掃引速度で掃引するように作用電極１０’と対極１２’間に電圧を印加していく。このような掃引を行うことで図１１に示すような還元電流波形（ボルタモグラム）が得られる。この図１１において、２つのピークが存在するが、Ｐは被測定試料に含まれる酸に由来するプレピーク、Ｍは本測定で使用した共存電解液の主溶媒であるエタノールに由来するメインピークである。すなわち、メインピーク電流値Ｉ_Mは被測定試料の酸濃度によらず常に一定の値を示す。しかしながら、温度Ｔに関してはプレピーク電流値Ｉ_p同様温度変化に対応してメインピーク電流値Ｉ_Mも変化する。メインピーク電流値Ｉ_Mと共存電解液の温度Ｔとの間には図１８に示すような一次関数か、限りなく一次関数に近い二次関数で与えられる。つまり、メインピーク電流値を検出すれば容易に測定時の共存電解液の温度Ｔを計算することができるのである。図１８は本発明の実施の形態２におけるメインピーク電流値−共存電解液の温度関係図である。
【００３７】
一例をあげて説明すると、溶媒として、エタノール、イソプロピルアルコール、水を６：２：２に混合したものに3,5−ジ−ｔｅｒｔ−ブチル−1,2−ベンゾキノン２０ｍＭ、ＮａＣｌ１５０ｍＭを溶解したものを測定溶液として用いる。電極は作用電極１０’、比較電極１１’、対極１２’ともにプラスチックフォームカーボンを用いている。まず、酸度１ｗｔ．％のクエン酸標準液０．１ｍｌと測定溶液５ｍｌを容器９’に収容し、作用電極１０’、比較電極１１’、対極１２’を備えた容器カバー１５’を設置し、十分撹拌した後、測定溶液が所定の温度に落ち着くまで待って、作用電極１０’の電位を比較電極１１’の電位に対して０〜１０００ｍＶの範囲で、１００ｍＶ／秒の掃引速度で掃引するように作用電極１０’と対極１２’間に電圧を印加していくと、図１１に示すようなボルタモグラムが得られる。これらの操作を５℃から約５℃間隔で３５℃まで繰り返し測定し、共存電解液の温度Ｔとメインピーク電流値の関係を求めると、図１８に示すような二次曲線となる。これをメインピークＩＭと共存電解液の温度Ｔとで表すと、
Ｔ＝−７．２８９９×１０^-4・Ｉ_M ²＋５．６２９８×１０^-1・Ｉ_M−３．９６６４×１０・・・（１７）
一般式としては、
Ｔ＝Ｘ・Ｉ_M ²＋Ｙ・Ｉ_M＋Ｚ・・・（４）
（但し、Ｘ，Ｙ，Ｚは共存電解液固有の定数）
そして、Ｉ_M ²の係数は（１７）式においては−７．２８９９×１０^-4であるが、一次関数で表せる場合にはこの値がＸ＝０ということになるものである。
【００３８】
一方、プレピーク電流値Ｉ_pと共存電解液の温度Ｔは実施の形態１と同様の操作によって図１５のように表せる。すなわち、酸度θとプレピーク電流値Ｉ_Pと共存電解液Ｔの温度は（１５）式のようになるから、（１５）式と（１７）式から酸度θとプレピーク電流値ＩＰ、メインピーク電流値ＩＭの関係は次式で表される。
Ｋ＝１／（−１．４２９×１０^-4・Ｉ_M ²＋１．１０３×１０^-1・Ｉ_M−２．４０１×１０^-1）
ｋ＝（−１．０８０×１０^-6・Ｉ_M ²＋８．３３８×１０^-4・Ｉ_M−４．０４７）／（−１．４２９×１０^-4・Ｉ_M ²＋１．１０３×１０^-1・Ｉ_M−２．４０１×１０^-1）
従って、
θ＝｛１／（−１．４２９×１０^-4・Ｉ_M ²＋１．１０３×１０^-1・Ｉ_M−２．４０１×１０^-1）｝・Ｉ_P＋｛（−１．０８０×１０^-6・Ｉ_M ²＋８．３３８×１０^-4・Ｉ_M−４．０４７）／（−１．４２９×１０^-4・Ｉ_M ²＋１．１０３×１０^-1・Ｉ_M−２．４０１×１０^-1）｝・・・（１８）
従って、この（１８）式を予め、制御部１９’に記憶させておけば、被測定試料の測定時に電流検出部１８’によってプレピーク電流値Ｉ_Pとともにメインピーク電流値Ｉ_Mを検出すると、（１８）式から被測定試料の酸度が算出できる。
【００３９】
【表２】

【００４０】
また、（表２）に示すようにメインピーク電流値Ｉ_Mから（１７）式に従ってＴを算出し、さらに（１３）（１４）式に基づいて計算したＫ、ｋの値をそれぞれ制御部１９’の記憶部へ記憶させておけば、測定時に電流検出部１８’によってプレピーク電流値Ｉ_Mとともにメインピーク電流値Ｉ_Mを検出し、制御部１９’で検知したメインピーク電流値Ｉ_MにおけるＫ、ｋを選択し、得られたプレピーク電流値Ｉ_Pから被測定試料の酸度θを算出することができる。なお、共存電解液のメインピーク電流値Ｉ_Mごとに検量線の形で換算関係を備えておき温度補正することもできる。例えば、測定時のプレピーク電流値Ｉ_Pが３０μＡ、メインピーク電流値Ｉ_Mが１５０μＡだったとすると、（表２）より酸度θは次式で与えられる。

このように、実施の形態２の酸度測定装置と酸度測定方法は、特別な温度検出のためのセンサなどを設けることなく、電流のメインピーク電流値とプレピーク電流値を検出するだけで、測定温度のみならず他の測定環境にも影響されずに酸度を正確にかつ簡単に測定することができる。
【００４１】
（実施の形態３）
実施の形態３に記載された酸度測定装置の概略外観図は、実施の形態１の図１と同様であり、また、その測定容器の断面図及び回路図は、実施の形態２で示した図１６および図１７の測定容器の断面図及び回路図と同様であるので詳細な説明は省略する。図１９は本発明の実施の形態３における電位−電流関係図、図２０は本発明の実施の形態３におけるピークαの電流値−共存電解液の温度関係図である。
【００４２】
本実施の形態３の酸度測定装置を操作するときの装置の動作の説明をする。測定溶液としてオルトベンゾキノン誘導体もしくはパラベンゾキノン誘導体、電解質を有機溶媒で溶解した実施の形態１、２の測定溶液に予め既知の低級酸を混合したものを測定溶液として用いる。前記測定溶液５ｍＬと被測定試料である果汁を０．１ｍＬ容器９’に入れ、次いで容器カバー１５’を取り付けてた測定容器２を十分撹拌した後、収容部３を開けセットし、再び収容部３を閉じると測定可能状態となる。電源ボタン５を押して電源ＯＮとした後、スタート・ストップボタン７を押して測定開始すると、電圧制御部１７’が作用電極１０’の電位を比較電極１１の電位に対して所定の範囲で所定の掃引速度で掃引するように作用電極１０と対極１２’間に電圧を印加していく。このような掃引を行うことで図１９に示すようなボルタモグラムが得られる。図１９において示すように、この場合３つのピークが形成されるが、Ｐ’は被測定試料に含まれる酸に由来するプレピーク、Ｍ’は本測定で使用した共存電解液の主溶媒であるエタノールに由来するメインピーク、αは予め測定溶液に加えた低級酸に由来するピークである。このピークαは被測定試料の酸濃度によらず常に一定の値を示す。しかしながら、温度に関しては、プレピーク、メインピークと同様に、温度が変化するのに対応して変化する。すなわち、ピークαの電流値と共存電解液の温度との間には図２０に示すように簡単な１次関数か、あるいは１次関数に限りなく近い２次関数で与えられる関係がある。つまり、ピークαの電流値を検出すれば容易に測定時の共存電解液の温度を予測し算出できるのである。
【００４３】
この関係を一例をあげて説明すると、溶媒として、エタノール、イソプロピルアルコール、水を６：２：２に混合したものに3,5−ジ−ｔｅｒｔ−ブチル−1,2−ベンゾキノン２０ｍＭ、ＮａＣｌ１５０ｍＭ、硝酸３．８４ｍＭを溶解したものを測定溶液として用いる。低級酸として本実施の形態３では硝酸を用いているが、図１９に示すようにプレピークより低い電位でピークが観察されるものであればよく、濃度に関してはピークが観察できる程度の濃度であればよい。低級酸の濃度を高くすると被測定試料のプレピークと干渉し、正確な測定ができなくなるおそれがある。実施の形態３の酸度測定装置においては、電極は、作用電極１０’、比較電極１１’、対極１２’の３電極ともにプラスチックフォームカーボンを用いた。
【００４４】
まず、酸度１ｗｔ．％のクエン酸標準液０．１ｍｌと測定溶液５ｍｌを容器９’に収容し、作用電極１０’、比較電極１１’、対極１２’を備えた容器カバー１５’を設置し、十分撹拌した後、測定溶液が所定の温度に落ち着くまで待って、作用電極１０’の電位を比較電極１１’の電位に対して０〜１０００ｍＶの範囲で、１００ｍＶ／秒の掃引速度で掃引するように作用電極１０’と対極１２’間に電圧を印加していくと、図１９に示すようなボルタモグラムが得られる。これらの操作を５℃から約５℃間隔で３５℃まで繰り返し測定し、共存電解液の温度とピークαの電流値の関係を求めると、図２０に示すように２次曲線で示される。このときのピークαの電流値Ｉαと共存電解液の温度Ｔとの関係は次式で表される。
Ｔ＝−８．１５６０×１０^-3・Ｉα²＋１．６１５０・Ｉα−９．４３７０・・・（２０）
次に、測定溶液５ｍＬと４ｗｔ．％のクエン酸標準液を０．１ｍＬを容器９に収容し同様の測定をすると、図１５に示すような共存電解液の温度とプレピーク電流値の関係が得られ、プレピーク電流値Ｉ_Pは上記（６）（７）式で与えられる。というのは、エタノール、イソプロピルアルコール、水、3,5−ジ−ｔｅｒｔ−ブチル−1,2−ベンゾキノン、ＮａＣｌのほかに硝酸を溶解しているが、硝酸は低級酸で通常被測定試料（この場合はクエン酸）のプレピークより正側に還元前置波であるピークαが形成されるため、この場合の共存電解液が示すボルタモグラムは硝酸以外の溶液のボルタモグラムに硝酸由来のピークαが重ね合わさった波形となり、プレピークでの共存電解液の温度とプレピーク電流値の関係はピークαに影響されず、（６）（７）式と同様になると考えられる。従ってＫ、ｋもプレピークでは硝酸の影響を受けず、
Ｋ＝１／（１．９６０×１０^-1・Ｔ＋７．５３４）・・・（１３）
ｋ＝−（１．４８１×１０^-3・Ｔ＋３．９８８）／（１．９６０×１０^-1・Ｔ＋７．５３４）・・・（１４）
で与えられる。そして、温度Ｔは（２０）式で与えられるから、
Ｋ＝１／（−１．５９９×１０^-3・Ｉα²＋３．１６５×１０^-1・Ｉα−５．６８４・・・（２１）
ｋ＝（−１．２０８×１０^-5・Ｉα²＋２．３９２×１０^-3・Ｉα−４．００２）／（−１．５９９×１０^-3・Ｉα²＋３．１６５×１０^-1・Ｉα−５．６８４）・・・（２２）
となる。
【００４５】
この（２１）、（２２）式から（１）式の一般式を求めると下記のようになることが分かる。
θ＝｛１／（−１．５９９×１０^-3・Ｉα²＋３．１６５×１０^-1・Ｉα−５．６８４｝・Ｉ_P＋（−１．２０８×１０^-5・Ｉα²＋２．３９２×１０^-3・Ｉα−４．００２）／（−１．５９９×１０^-3・Ｉα²＋３．１６５×１０^-1・Ｉα−５．６８４）・・・（２３）
従って、この式を予め、制御部１９’に記憶させておけば、被測定試料の測定時に電流検出部１８’によってプレピーク電流値Ｉ_Pとともにピークαのピーク電流値Ｉαを検出すれば（２３）式から被測定試料の酸度θが算出できる。
【００４６】
【表３】

【００４７】
また、（２）（３）式から（表３）に示すようにピークαのピーク電流値Ｉαに対するＫ、ｋの値をそれぞれ制御部１９’へ記憶させておけば、測定時に電流検出部１８’によってプレピーク電流値Ｉ_Pとともにピーク電流値Ｉαを検出し、制御部１９’で検知したピーク電流値ＩαにおけるＫ、ｋを選択し、得られたプレピーク電流値Ｉ_Pから（１）式に基づいて被測定試料の酸度θを算出することができる。なお、ピーク電流値Ｉαごとに検量線を備えて換算するのもよい。例えば、測定時のプレピーク電流値Ｉ_Pが３５μＡ、ピークαの電流値が２０μＡだったとすると、（表３）より酸度θは次式で与えられる。

このように、被測定試料由来のプレピーク電流値と既知の低級酸のプレピーク電流値を測定するだけで、溶存酸素や光等の影響を受けないだけでなく、測定温度にも影響されない正確な酸度を測定することができる。
【００４８】
【発明の効果】
本発明の酸度測定装置は、簡単な構成で、溶存酸素や光の影響を受けることがなく、測定時の温度が変化するようなことがあっても温度補正して正確な酸度を算出することができるものである。温度センサーにより直接共存電解液の温度を測定すれば正確に温度補正ができるし、メインピークを用いて温度の予測ができるから、特別に検出器を設けることなく温度補正を行うことができる。さらに低級酸を添加して別のピークを形成すれば、このピークから温度が換算でき、特別に検出器を用意しないでも温度補正ができる。
【図面の簡単な説明】
【図１】本発明の実施の形態１における酸度測定装置の概略外観図
【図２】本発明の実施の形態１における測定容器の断面図
【図３】オルトベンゾキノン誘導体を用いた場合の電位―電流関係図（ボルタンメトリー）
【図４】オルトベンゾキノン誘導体の構造図
【図５】パラベンゾキノン誘導体の構造図
【図６】オルトベンゾキノンの構造図
【図７】パラベンゾキノンの構造図
【図８】 3,5−ジ−ｔｅｒｔ−ブチル−1,2−ベンゾキノンの構造図
【図９】 2,6−ジメチル−1,4−ベンゾキノンの構造図
【図１０】本発明の実施の形態１における酸度測定装置の回路図
【図１１】本発明の実施の形態１および２における電位−電流関係図
【図１２】本発明の実施の形態１におけるプレピーク電流−酸度関係図
【図１３】本発明の実施の形態１，２，３における共存電解液の温度−プレピーク電流値関係図
【図１４】本発明の実施の形態１，２，３における共存電解液の温度−Ａ（θ）、Ｂ（θ）の関係図
【図１５】本発明の実施の形態１，２，３における共存電解液の温度−Ｋ、ｋの関係図
【図１６】本発明の実施の形態２，３における測定容器の断面図
【図１７】本発明の実施の形態２，３における酸度測定装置の回路図
【図１８】本発明の実施の形態２におけるメインピーク電流値−共存電解液の温度関係図
【図１９】本発明の実施の形態３における電位−電流関係図
【図２０】本発明の実施の形態３におけるピークαの電流値−共存電解液の温度関係図
【符号の説明】
１酸度測定装置本体
２測定容器
３収容部
４ＬＣＤ
５電源ボタン
６記憶ボタン
７スタート・ストップボタン
８校正ボタン
９容器
１０作用電極
１１比較電極
１２対極
１３温度センサー
１４センサーカバー
１５容器カバー
１６温度検出手段
１７電圧制御部
１８電流検出部
１９制御部
２０操作部
２１表示部
２２演算部[0001]
BACKGROUND OF THE INVENTION
  In the present invention, a liquid to be measured having a predetermined concentration is mixed into a measurement solution in which a quinone derivative, an electrolyte, and an organic solvent are mixed, and the acidity is measured by sweeping the potential using a working electrode, a reference electrode, and a counter electrode,The present invention relates to an acidity measuring device for temperature correction.
[0002]
[Prior art]
In recent years, food products have been required to have a certain level of quality in terms of health and safety. Above all, the acid contained in the food has a great influence on the quality of the food. The acidity of foods includes edible oils, fruit drinks such as juices, alcoholic drinks such as whiskey, liquor, wine, coffee, etc. I was using it. There are various neutralization measurement methods. For example, the standard oil and fat analysis method, Japanese agricultural and forestry standard, JIS, Japanese Pharmacopoeia oil and fat test method, hygiene test method food and drink test method, water test method, etc. Although there are defined methods, the basis of the measurement of all is phenolphthalein as an indicator.
[0003]
By the way, there is a method of measuring acidity by voltammetry irrespective of such neutralization titration method. This is disclosed in Japanese Patent Application Laid-Open No. 5-264503, and a measurement electrolyte solution in which a free fatty acid and a naphthoquinone derivative coexist is measured by a voltammetry by a potential regulating method. The current value of the pre-reduction wave of the naphthoquinone derivative is proportional to the free fatty acid concentration for all fatty acids from lower fatty acids such as formic acid to higher fatty acids such as oleic acid and linoleic acid. It is used that the value obtained by superimposing the values corresponds to the total concentration of fatty acids. That is, if a relationship (calibration curve) of pre-peak current value-acidity as shown in FIG. 12 to be described later in a fatty acid having a known acidity is prepared, a pre-peak current value is detected by voltammetry for a fatty acid having an unknown acidity, The acidity can be derived from this calibration curve.
[0004]
[Problems to be solved by the invention]
As described above, since the conventional acidity measuring apparatus uses the neutralization titration method, the measurer determines the color change caused by the phenolphthalein indicator and determines the end point of the titration, and the end point varies depending on the measurer. Therefore, the acidity may vary depending on the measurer.
[0005]
On the other hand, the technique disclosed in Japanese Patent Application Laid-Open No. 5-264503 solves the disadvantage that the quinones used in voltammetry lack light stability and the measured values vary, but the naphthoquinone derivative is used. It was easily affected by oxygen, and it was necessary to remove oxygen with an inert gas before measurement, which required a large-scale and troublesome treatment. In addition, the measured pre-peak current value varies depending on the relationship between the electrode and the measurement solution and the state of the electrode surface. Particularly, the pre-peak current value is sensitive with respect to the measurement temperature, and the calculated acidity varies depending on these changes. That is, there is a problem that the calculated acidity also changes when the temperature changes.
[0006]
Therefore, in order to solve such problems, the present invention has a simple configuration, is not affected by dissolved oxygen and light, and corrects the temperature even when the temperature during measurement changes. An object of the present invention is to provide an acidity measuring apparatus capable of calculating an accurate acidity.
[0008]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the acidity measuring device of the present invention comprises temperature detection means for detecting the temperature of the coexisting electrolyte in the container, and the following (1) to (3) from the temperature T detected by the temperature detection means. ), An arithmetic unit for calculating the acidity θ of the sample to be measured is provided.
θ = KI_P+ K (1)
here,
K = 1 / (A₁・ T + B₁) ... (2)
k =-(A₂・ T + B₂) / (A₁・ T + B₁(3)
(Where θ is acidity, I_PIs pre-peak current value, T is temperature, A₁, A₂, B₁, B₂Is a constant specific to the coexisting electrolyte)
Thereby, even if the temperature at the time of measurement changes, the temperature can be corrected and an accurate acidity can be calculated.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
The invention described in claim 1 of the present invention includes an orthobenzoquinone derivative or a parabenzoquinone derivative, a container containing a coexisting electrolyte solution in which a measurement solution in which an electrolyte is dissolved in an organic solvent and an acid-containing sample to be measured are mixed, A working electrode, a counter electrode, a reference electrode, and a working electrode immersed in the coexisting electrolyte are swept within a predetermined potential range, and a pre-peak of current flowing between the working electrode and the counter electrode is provided. Current value I_PAnd a temperature detection means for detecting the temperature of the coexisting electrolyte in the container, and the temperature to be measured according to the following equations (1) to (3) from the temperature T detected by the temperature detection means: An acidity measuring apparatus comprising an arithmetic unit for calculating the acidity θ of a sample
θ = KI_P+ K (1)
here,
K = 1 / (A₁・ T + B₁) ... (2)
k =-(A₂・ T + B₂) / (A₁・ T + B₁(3)
(Where θ is acidity, I_PIs pre-peak current value, T is temperature, A₁, A₂, B₁, B₂Is a constant specific to the coexisting electrolyte)
Therefore, the acidity can be calculated without being affected by dissolved oxygen, light, and measurement temperature.
[0010]
The invention described in claim 2 is the acidity measuring apparatus according to claim 1, wherein the temperature detecting means directly measures the temperature of the measurement solution by a temperature sensor immersed in the coexisting electrolyte. It is possible to calculate an accurate acidity that is not affected by oxygen, light, or the like but is not affected by the measurement temperature.
[0011]
The invention described in claim 3 includes an orthobenzoquinone derivative or a parabenzoquinone derivative, a container for storing a coexisting electrolyte solution in which an electrolyte is dissolved in an organic solvent and an acid-containing sample to be measured, and the container is provided in the container. The working electrode, the counter electrode, the reference electrode, and the working electrode immersed in the coexisting electrolyte are swept within a predetermined potential range, and the pre-peak current value I of the current flowing between the working electrode and the counter electrode_PAnd main peak current value I_MA main peak current value I detected by the control unit._MThe temperature T of the solution to be measured is calculated according to the following equation (4), and an arithmetic unit for calculating the acidity θ of the sample to be measured by the following equations (1) to (3) is provided. Acidity measuring device
θ = KI_P+ K (1)
here,
K = 1 / (A₁・ T + B₁) ... (2)
k =-(A₂・ T + B₂) / (A₁・ T + B₁(3)
Also,
T = X · I_M ²+ Y ・ I_M+ Z (4)
(Where θ is acidity, I_PIs the pre-peak current value, I_MIs the main peak current value, T is the temperature, A₁, A₂, B₁, B₂, X, Y, and Z are constants unique to the coexisting electrolyte)
Therefore, it is possible to detect the main peak current value and pre-peak current value of the current without providing a special temperature detection sensor, and so on, without affecting the measurement temperature and other measurement environments. Can be measured.
[0012]
  The invention described in claim 4 is a container for storing a coexisting electrolytic solution in which an orthobenzoquinone derivative or a parabenzoquinone derivative, a measurement solution in which an electrolyte is dissolved in an organic solvent, a lower acid having a predetermined acidity and a sample to be measured containing acid are mixed. And a working electrode, a counter electrode, a reference electrode, and a working electrode, which are provided in the container and are immersed in the coexisting electrolyte, sweep the electrode potential of the working electrode within a predetermined potential range and flow between the working electrode and the counter electrode. Pre-peak current value IP derived from the sample to be measured and pre-peak current value I derived from the lower acid_αAnd a pre-peak current value I detected by the control unit._αThe temperature T of the solution to be measured is calculated according to the following equation (5), and an arithmetic unit for calculating the acidity θ of the sample to be measured by the following equations (1) to (3) is provided. Acidity measuring device.
θ = KI_P+ K (1)
  here,
K = 1 / (A₁・ T + B₁) ... (2)
k =-(A₂・ T + B₂) / (A₁・ T + B₁(3)
  Also,
T = x · I_α ²+ Y · I_α+ Z (5)
(Where θ is acidity,I _P Is the pre-peak current value, I _α Is the pre-peak current value of the lower acid,T is temperature, A₁, A₂, B₁, B₂, X, y, and z are constants unique to the coexisting electrolyte), and only by measuring the pre-peak current value derived from the sample to be measured and the pre-peak current value of a known lower acid, it is affected by dissolved oxygen and light. In addition, it is possible to measure an accurate acidity that is not affected by the measurement temperature.
[0013]
The invention described in claim 5 is a conversion table that associates K and k for each temperature of the solution to be measured, instead of the arithmetic unit that calculates the acidity of the sample to be measured by the equations (1) to (3). The acidity measuring device according to any one of claims 1 to 4, further comprising: a storage unit that stores therein, wherein the calculation unit performs temperature correction according to the equation (1) using K and k corresponding to the temperature read from the storage unit. Therefore, it is not necessary to calculate the acidity for each measurement by the calculation unit, and if the storage unit has a conversion table, the acidity can be accurately measured immediately.
[0018]
Hereinafter, embodiments of the present invention will be described with reference to FIGS.
(Embodiment 1)
First, an acidity measuring apparatus according to an embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic external view of an acidity measuring apparatus according to an embodiment of the present invention. In FIG. 1, 1 is an acidity measuring apparatus main body, and 2 is a measuring container. 3 can slide the measurement container 2 in and out of the storage unit for storing the measurement container 2. 4 is an LCD for displaying the measured acidity, 5 is a power button for turning the apparatus on and off, 6 is a memory button for storing the measured acidity, 7 is a start / stop button for starting the measurement, and 8 is calibration. It is a calibration button used sometimes. Next, FIG. 2 is a cross-sectional view of the measurement container according to Embodiment 1 of the present invention. Here, 9 is an orthobenzoquinone derivative or parabenzoquinone derivative, a container for storing a coexisting electrolyte obtained by mixing a measurement solution in which an electrolyte is dissolved in an organic solvent and a sample to be measured, 10 is a working electrode, 11 is a reference electrode, and 12 is a counter electrode. , 13 is a temperature sensor, 14 is a sensor cover, 15 is a container cover to which the working electrode 10, the comparison electrode 11, the counter electrode 12, the temperature sensor 13, and the sensor cover 14 are attached. It has a structure. When the temperature sensor 13 directly touches the coexisting electrolyte, the measurement system is affected, so that it is insulated by the sensor cover 14. In other words, the sensor cover 14 is preferably an insulator with good thermal conductivity such as glass. The measuring container 2 accommodates the coexisting electrolyte in a container 9 and a container cover 15 equipped with a working electrode 10, a reference electrode 11, a counter electrode 12, a temperature sensor 13 and a sensor cover 14 immerses each electrode in the coexisting electrolyte. In this state, the container 9 is mounted. As the material of the working electrode 10, glassy carbon called carbon or glassy carbon, or carbon obtained by sintering a plastic foam called PFC at 1000 ° C. to 2000 ° C. is suitable. The material of the reference electrode 11 may be the material used for the working electrode 10 or silver-silver chloride, saturated calomel, silver-silver ion, or mercury-saturated mercury sulfate. As the material of the counter electrode 12, platinum, graphite, and gold that are chemically stable without being corroded even in the coexisting electrolyte are preferable, but stainless steel, aluminum, an alloy thereof, and the like that do not corrode may be used.
[0019]
Next, the coexisting electrolyte contained in the container 9 will be described. In the first embodiment, 20 mM orthobenzoquinone and 150 mM NaCl are dissolved in a 6: 2: 2 mixture of ethanol, isopropyl alcohol, and water. In this case, the coexisting electrolyte is used by mixing the sample to be measured at a ratio of 50: 1 to this measuring solution. In this way, using ternary solvents of ethanol, isopropyl alcohol and water can dissolve not only fruit juice, but also concentrated reduced juice and instant coffee, without stirring and centrifuging as in the prior art. Both are sufficiently soluble and the acidity can be measured very easily.
[0020]
By the way, in the present invention, an orthobenzoquinone derivative or a parabenzoquinone derivative is mixed in the coexisting electrolyte. Hereinafter, why the orthobenzoquinone derivative or parabenzoquinone derivative is mixed will be described. FIG. 3 is a potential-current relationship diagram of acidity measurement by voltammetry of a measurement electrolyte solution in which an orthobenzoquinone derivative coexists. In FIG. 3, the horizontal axis represents the potential of the working electrode relative to the comparative electrode when plastic foam carbon is used for both the working electrode and the comparative electrode, and the vertical axis represents the current value flowing to the counter electrode. However, the current value varies depending on conditions such as the surface area of the working electrode and the acid concentration. In contrast, the potential at which the horizontal axis appears varies slightly depending on the acid concentration, but the variation is negligible. As shown in FIG. 3, the reduction current waveform (hereinafter, voltammogram) of an orthobenzoquinone derivative having a side chain on the benzene ring appears far away from the region where the reduction waveform of dissolved oxygen appears on the positive potential side. The solid line is the voltammogram of the orthobenzoquinone derivative, and the broken line shows the reduced waveform of dissolved oxygen. According to FIG. 3, there is almost no influence of the reduction of dissolved oxygen at the position of the main peak as well as the pre-peak. In this way, the pre-peak current value and the main peak current value can be measured in a region where there is no influence of dissolved oxygen, so even if the dissolved oxygen is not removed in advance, it will not be affected by the dissolved oxygen, and therefore the acidity can be accurately measured without variation. It can be measured. Moreover, even if the parabenzoquinone derivative is used, there are some differences in the appearance potentials of the pre-peak and the main peak, but the same potential-current relationship diagram as in FIG. 3 is obtained, and the pre-peak, The main peak current value can be measured. Thus, since it can measure in the area | region which does not have the influence of dissolved oxygen, oxygen removal etc. like a prior art are unnecessary, and an apparatus can be reduced in size.
[0021]
By the way, ortho-benzoquinone derivatives or parabenzoquinone derivatives with side chains on the benzene ring have a pre-peak at a position away from the reduction potential of dissolved oxygen, and in addition to the above characteristics, stable measurement without causing much photolysis in quinones. It has excellent characteristics that can be used. 4 is a structural diagram of an orthobenzoquinone derivative, and FIG. 5 is a structural diagram of a parabenzoquinone derivative. FIG. 6 is a structural diagram of orthobenzoquinone, and FIG. 7 is a structural diagram of parabenzoquinone. The orthobenzoquinone derivative in FIG. 4 and the parabenzoquinone derivative in FIG. 5 were given the energy of decomposition by light because the R part which is a side chain exists with respect to the orthobenzoquinone in FIG. 6 and the parabenzoquinone in FIG. Even so, light energy is consumed as kinetic energy for intramolecular expansion and contraction of the side chain R and rotation of the side chain R, so that it is difficult to undergo photolysis. FIG. 8 is a diagram showing the structure of 3,5-di-tert-butyl-1,2-benzoquinone, and FIG. 9 is a diagram showing the structure of 2,6-dimethyl-1,4-benzoquinone. Among the orthobenzoquinones, when 3,5-di-tert-butyl-1,2-benzoquinone shown in FIG. 8 and 2,6-dimethyl-1,4-benzoquinone shown in FIG. 9 among parabenzoquinones are used, the structure In particular, since -tert-butyl and methyl groups donate electrons into the benzene ring, the molecular structure is easy to take a conjugated structure, and more light energy is absorbed, so that photolysis hardly occurs and is stable. Measurement is possible.
[0022]
The relationship between the stability of these quinones to light and how far the pre-peak of the voltammogram is from the reduced waveform of dissolved oxygen has the following relationship. That is, quinones such as a naphthoquinone derivative having high stability to light have a tendency that the pre-peak position of the voltammogram gradually moves toward the negative potential side and overlaps with the reduced waveform of dissolved oxygen as the stability improves. Conversely, quinones with poor stability to light tend to shift in a direction that does not overlap with the reduction waveform of dissolved oxygen as the stability to light deteriorates. As a result, the measured value varies and the practicality as an electrolytic solution deteriorates. Therefore, if the quinones have sufficient stability against light and at the same time the pre-peak position of the voltammogram does not overlap with the reduced waveform of dissolved oxygen, it is not affected by the dissolved oxygen, so it is suitable as an electrolyte for the acidity measuring device. It has something. As such quinones, orthobenzoquinone derivatives having a side chain at the 3,5 position of the benzene ring, among them, 3,5-di-tert-butyl-1,2-benzoquinone are excellent, and the 2,6 position of the benzene ring. A parabenzoquinone derivative having a side chain at the end, particularly 2,6-dimethyl-1,4-benzoquinone, is excellent. These can be measured stably without causing photolysis, and the pre-peak is separated from the reduction potential of dissolved oxygen as shown in FIG. Other quinones and materials can be used as long as they are quinones that have high stability to light and whose pre-peak position of the voltammogram does not overlap with the reduced waveform of dissolved oxygen.
[0023]
Next, a control circuit that controls the acidity measuring apparatus according to the first embodiment will be described. FIG. 10 is a circuit diagram of the acidity measuring apparatus according to Embodiment 1 of the present invention. In FIG. 10, 16 is a temperature detecting means for detecting the temperature of the coexisting electrolyte in the container 9 at the time of measurement, 17 is a voltage control unit for controlling the sweep voltage, and 18 is a voltage sweep that flows between the working electrode 10 and the counter electrode 12. A current detection unit for detecting current; 19 a control unit having a memory function for calculating acidity; 20 an operation unit corresponding to various operation buttons; 21 a display unit displaying the calculated acidity; Reference numeral 22 denotes an arithmetic unit for calculating acidity.
[0024]
Now, the operation of the apparatus when operating the acidity measuring apparatus according to the first embodiment will be described. After 5 mL of the measurement solution and fruit juice as the sample to be measured are put into a 0.1 mL container 9, the measurement container 2 to which the container cover 15 is attached is sufficiently stirred, and then the container 3 is opened and set, and the container 3 is closed again. It becomes a measurable state. When the power is turned on by pressing the power button 5 and the start / stop button 7 is pressed to start the measurement, the voltage control unit 17 sets the potential of the working electrode 10 to a predetermined range with respect to the potential of the comparison electrode 11 and a predetermined sweep speed. A voltage is applied between the working electrode 10 and the counter electrode 12 so as to sweep. By performing such sweeping, a reduction current waveform as shown in FIG. 11 is obtained. In FIG. 11, there are two peaks, P is a pre-peak derived from the acid contained in the sample to be measured, and M is a main peak derived from ethanol which is the main solvent of the coexisting electrolyte used in this measurement. At this time, the acidity θ of the acid mixed in the pre-peak and the sample to be measured is the pre-peak current value I as shown in FIG._PIt is known that there is a proportional relationship. That is, the pre-peak current value I_PAnd acidity θ
θ = KI_P+ K (1)
There is a relationship. However, since K and k in the equation (1) are functions of the temperature T of the coexisting electrolyte as described later, if the temperature T changes, the pre-peak current value I as shown in FIG._PAnd the acidity θ change. Therefore, the temperature of the coexisting electrolyte and the pre-peak current value I of A_pThe acidity θ can be measured by measuring.
[0025]
Explaining this relationship with an example, as a solvent, ethanol, isopropyl alcohol and water mixed in 6: 2: 2 dissolve 3,5-di-tert-butyl-1,2-benzoquinone 20 mM and NaCl 150 mM. The solution used is used as the measurement solution. In addition, the plastic electrode carbon is used for the working electrode 10, the comparison electrode 11, and the counter electrode 12 as an electrode.
[0026]
First, 5 mL of measurement solution and 2 wt. Of 0.1% citric acid standard solution in a container 9, and a container cover 15 provided with a working electrode 10, a reference electrode 11, and a counter electrode 12 is placed and stirred sufficiently, and then the coexisting electrolyte is brought to a predetermined temperature. After waiting until it settles, a voltage is applied between the working electrode 10 and the counter electrode 12 so that the potential of the working electrode 10 is swept at a sweep rate of 100 mV / sec in the range of 0 to 1000 mV with respect to the potential of the reference electrode 11. Then, a potential-current relationship diagram as shown in FIG. 11 is obtained. These operations are repeatedly measured from 5 ° C. to 35 ° C. at intervals of about 5 ° C. Next, 5 mL and 4 wt. When 0.1 mL of 0.1% citric acid standard solution was placed in the container 9 and the same measurement was performed, the relationship between the temperature of the coexisting electrolyte and the pre-peak current value as shown in FIG._PIs given by the linear function FIG. 13 is a temperature-pre-peak current value relationship diagram of the coexisting electrolytes in the first, second, and third embodiments of the present invention, and FIG. θ), B (θ), FIG. 15 is a relationship diagram of coexisting electrolyte temperatures −K, k in the first, second, and third embodiments of the present invention.
I_P4%= 0.7804T + 33.93 (6)
I_P2%= 0.3795T + 18.9 (7)
Where I_P2%Has an acidity of 2 wt. % Of pre-peak current when I% citric acid standard solution is added_P4%Has an acidity of 4 wt. The pre-peak current value when T% citric acid standard solution is added, and T is the temperature of the coexisting electrolyte.
[0027]
By the way, this pre-peak current value I_PWhen the influence of the acidity θ on the linear function established between the temperature T and the temperature T was examined, it was found that the following relationship was established as shown in FIG.
I_P= A (θ) · T + B (θ) (8)
Here, A (θ) = 1.960 × 10^-1・ Θ-1.481 × 10^-3... (9)
B (θ) = 7.534 · θ + 3.988 (10)
And this relationship basically holds true for other coexisting electrolytes.
A (θ) = A₁・ Θ + A₂(11)
B (θ) = B₁・ Θ + B₂(12)
And A₁, A₂, B₁, B₂Is a constant inherent to the coexisting electrolyte.
[0028]
From the equations (1), (10), (11), and (12), θ₁, Θ₂Against
θ₁= K · {A (θ₁) ・ T + B (θ₁)} + K
θ₂= K · {A (θ₂) ・ T + B (θ₂)} + K
Therefore,

Similarly,

It becomes. In the case of the above coexisting electrolyte, 2 wt. % And 4 wt. % Acidity was measured and the following values were obtained:
A₁= 1.960 × 10^-1 A₂= 1.481 × 10^-3
B₁= 7.534 B₂= 3.988
(2) Equation (3) is
K = 1 / (1.960 × 10^-1・ T + 7.534) (13)
k = − (1.481 × 10^-3T + 3.988) / (1.960 × 10^-1・ T + 7.534) (14)
It turns out that it becomes. As shown in FIG. 15, it can be seen that K and k can be predicted by Equations (13) and (14) with considerable accuracy.
[0029]
From the equations (13) and (14), K and k are calculated according to the equation (1), and the general equation of the equation (1) is obtained.
θ = {1 / (1.960 × 10^-1・ T + 7.534)} ・ I_P− (1.481 × 10^-3T + 3.988) / (1.960 × 10^-1T + 7.534) (15) where θ is acidity, I_PIs the pre-peak current value, and T is the temperature of the coexisting electrolyte. That is, as a general characteristic of the coexisting electrolyte, the acidity θ is a pre-peak current value I_PAnd can be expressed as a function of the temperature T of the coexisting electrolyte.
[0030]
Therefore, for example, a solution in which ethanol, isopropyl alcohol, and water are mixed at a ratio of 6: 2: 2 in which 3,5-di-tert-butyl-1,2-benzoquinone 20 mM and NaCl 150 mM are dissolved is used as the measurement solution. When citric acid is added as a measurement sample to achieve acidity, the equation (15) is stored in the control unit 19 in advance, and the pre-peak current value I is measured by the current detection unit 18 during measurement._PWhen the temperature T of the coexisting electrolyte is detected by the temperature sensor 13 at the same time, the acidity of the sample to be measured can be corrected from the equation (15) and can be accurately calculated.
[0031]
[Table 1]

[0032]
Further, as shown in Table 1, the temperature T of the coexisting electrolyte calculated in advance based on the equation (15) and the values of K and k depending on the temperature are stored in the storage unit of the control unit 19 in the form of a conversion table. In this case, K and k at the temperature detected by the temperature sensor 13 at the time of measurement are selected, and the pre-peak current value I detected by the current detection unit 18 is selected._pThus, the acidity θ of the sample to be measured can be easily calculated. For example, if the pre-peak current value at the time of measurement is 30 μA and the temperature of the coexisting electrolyte is 25 ° C., the acidity θ is given by the following equation from (Table 1).

Further, instead of storing the conversion table in the storage unit, the acidity measuring device is provided in the form of a coexisting electrolyte and a calibration curve for each temperature, and when a certain temperature is detected, the pre-peak current value I_PIf the acidity is read from a calibration curve corresponding to the temperature, the acidity can be easily corrected for temperature. The values of K and k are basically expressed by (13) and (14). As can be seen from the general formulas (11) and (12), there are slight variations in the measured values of K and k. In this case, if an actual measurement value is given to the conversion table or the calibration curve, the accuracy is further increased.
[0033]
As described above, the acidity measuring apparatus and the measuring method according to Embodiment 1 are capable of calculating an accurate acidity that is not affected by dissolved oxygen, light, or the like but is not affected by the measurement temperature.
[0034]
(Embodiment 2)
The schematic external view of the acidity measuring apparatus according to the second embodiment is the same as that shown in FIG. Next, FIG. 16 is a cross-sectional view of the measurement container 2 in the second and third embodiments of the present invention. Here, 9 ′ is an orthobenzoquinone derivative or parabenzoquinone derivative, a container for storing a coexisting electrolyte obtained by mixing a measurement solution in which an electrolyte is dissolved in an organic solvent and a sample to be measured, 10 ′ is a working electrode, 11 ′ is a reference electrode, 12 ′ is a counter electrode, 15 ′ is a container cover to which the working electrode 10 ′, the comparison electrode 11 ′, and the counter electrode 12 ′ are attached. The container cover can be easily detached from the container 9 ′. The measurement container 2 accommodates the coexisting electrolyte in a container 9 ′, and a container cover 15 ′ to which a working electrode 10 ′, a comparison electrode 11 ′, and a counter electrode 12 ′ are attached has each electrode immersed in the coexisting electrolyte. Is attached to the container 9 '.
[0035]
Next, a control circuit that controls the acidity measuring apparatus according to the second embodiment will be described. FIG. 17 is a circuit diagram of the acidity measuring device according to the second and third embodiments of the present invention. In FIG. 17, 17 ′ is a voltage control unit for controlling the sweep voltage, 18 ′ is a current detection unit for detecting a current flowing between the working electrode 10 ′ and the counter electrode 12 ′ by the voltage sweep, and 19 ′ is for calculating the acidity. A control unit having a memory function, 20 ′ is an operation unit corresponding to various operation buttons, 21 ′ is a display unit that displays the calculated acidity, and 22 ′ is a calculation unit that calculates the acidity.
[0036]
Now, the operation of the apparatus when operating the acidity measuring apparatus according to the second embodiment will be described. After 5 mL of measurement solvent and fruit juice as a sample to be measured are placed in a 0.1 mL container 9 ′, the measurement container 2 with a container cover 15 ′ is sufficiently stirred, and then the container 3 is opened and set. When closed, measurement is possible. When the power button 5 is pressed to turn on the power and then the start / stop button 7 is pressed to start the measurement, the voltage control unit 17 ′ sets the potential of the working electrode 10 ′ within a predetermined range with respect to the potential of the comparison electrode 11 ′. A voltage is applied between the working electrode 10 ′ and the counter electrode 12 ′ so as to sweep at the sweep speed. By performing such sweeping, a reduction current waveform (voltammogram) as shown in FIG. 11 is obtained. In FIG. 11, there are two peaks, P is a pre-peak derived from the acid contained in the sample to be measured, and M is a main peak derived from ethanol which is the main solvent of the coexisting electrolyte used in this measurement. . That is, the main peak current value I_MIndicates a constant value regardless of the acid concentration of the sample to be measured. However, for the temperature T, the pre-peak current value I_pSimilarly, the main peak current value I corresponding to the temperature change_MAlso changes. Main peak current value I_MAnd the temperature T of the coexisting electrolyte are given by a linear function as shown in FIG. That is, if the main peak current value is detected, the temperature T of the coexisting electrolyte at the time of measurement can be easily calculated. FIG. 18 is a graph showing the relationship between the main peak current value and the coexisting electrolyte temperature in Embodiment 2 of the present invention.
[0037]
As an example, a solvent in which ethanol, isopropyl alcohol, and water are mixed at a ratio of 6: 2: 2 with 3,5-di-tert-butyl-1,2-benzoquinone 20 mM and NaCl 150 mM dissolved therein. Used as measurement solution. As the electrodes, plastic foam carbon is used for the working electrode 10 ', the reference electrode 11', and the counter electrode 12 '. First, the acidity is 1 wt. Of 0.1% citric acid standard solution and 5 ml of the measurement solution were placed in a container 9 ′, and a container cover 15 ′ equipped with a working electrode 10 ′, a comparison electrode 11 ′, and a counter electrode 12 ′ was placed and stirred sufficiently. After the measurement solution settles down to a predetermined temperature, the working electrode 10 ′ is swept so that the potential of the working electrode 10 ′ is in the range of 0 to 1000 mV with respect to the potential of the comparison electrode 11 ′ at a sweep rate of 100 mV / sec. When a voltage is applied across the counter electrode 12 ', a voltammogram as shown in FIG. 11 is obtained. When these operations are repeatedly measured from 5 ° C. to 35 ° C. at intervals of about 5 ° C., and the relationship between the temperature T of the coexisting electrolyte and the main peak current value is obtained, a quadratic curve as shown in FIG. 18 is obtained. When this is expressed by the main peak IM and the temperature T of the coexisting electrolyte,
T = −7.2899 × 10^-Four・ I_M ²+ 5.6298 × 10^-1・ I_M-3.9664 × 10 (17)
As a general formula,
T = X · I_M ²+ Y ・ I_M+ Z (4)
(However, X, Y, and Z are constants specific to the coexisting electrolyte)
And I_M ²Is a coefficient of -7.2899 × 10 in the equation (17).^-FourHowever, when it can be expressed by a linear function, this value is X = 0.
[0038]
On the other hand, the pre-peak current value I_pThe temperature T of the coexisting electrolyte can be expressed as shown in FIG. 15 by the same operation as in the first embodiment. That is, the acidity θ and the pre-peak current value I_PSince the temperature of the coexisting electrolyte T is as shown in the equation (15), the relationship between the acidity θ, the pre-peak current value IP, and the main peak current value IM is expressed by the following equation from the equations (15) and (17). .
K = 1 / (− 1.429 × 10^-Four・ I_M ²+ 1.103 × 10^-1・ I_M-2.401 × 10^-1)
k = (− 1.080 × 10^-6・ I_M ²+ 8.338 × 10^-Four・ I_M−4.047) / (− 1.429 × 10^-Four・ I_M ²+ 1.103 × 10^-1・ I_M-2.401 × 10^-1)
Therefore,
θ = {1 / (− 1.429 × 10^-Four・ I_M ²+ 1.103 × 10^-1・ I_M-2.401 × 10^-1)} ・ I_P+ {(− 1.080 × 10^-6・ I_M ²+ 8.338 × 10^-Four・ I_M−4.047) / (− 1.429 × 10^-Four・ I_M ²+ 1.103 × 10^-1・ I_M-2.401 × 10^-1)} ... (18)
Therefore, if this equation (18) is stored in the control unit 19 'in advance, the pre-peak current value I is measured by the current detection unit 18' when measuring the sample to be measured._PAnd main peak current value I_MIs detected, the acidity of the sample to be measured can be calculated from the equation (18).
[0039]
[Table 2]

[0040]
Further, as shown in Table 2, the main peak current value I_MT is calculated according to the equation (17), and the values of K and k calculated based on the equations (13) and (14) are stored in the storage unit of the control unit 19 ′. 18 ′, pre-peak current value I_MAnd main peak current value I_MThe main peak current value I detected by the control unit 19 '_MK and k at, and the obtained pre-peak current value I_PFrom this, the acidity θ of the sample to be measured can be calculated. The main peak current value I of the coexisting electrolyte_MIt is also possible to correct the temperature by providing a conversion relationship in the form of a calibration curve for each. For example, pre-peak current value I at the time of measurement_P30μA, main peak current value I_MIs 150 μA, the acidity θ is given by the following equation from (Table 2).

As described above, the acidity measuring apparatus and the acidity measuring method according to the second embodiment can measure the measurement temperature only by detecting the main peak current value and the pre-peak current value of the current without providing a sensor or the like for special temperature detection. In addition, the acidity can be measured accurately and easily without being affected by other measurement environments.
[0041]
(Embodiment 3)
A schematic external view of the acidity measuring apparatus described in the third embodiment is the same as that in FIG. 1 of the first embodiment, and a cross-sectional view and a circuit diagram of the measurement container are those shown in the second embodiment. Since it is the same as the cross-sectional view and circuit diagram of the measurement container of FIGS. 16 and 17, detailed description thereof will be omitted. FIG. 19 is a potential-current relationship diagram in Embodiment 3 of the present invention, and FIG. 20 is a current relationship value of peak α and temperature of the coexisting electrolyte in Embodiment 3 of the present invention.
[0042]
The operation of the apparatus when operating the acidity measuring apparatus according to the third embodiment will be described. As a measurement solution, an orthobenzoquinone derivative or parabenzoquinone derivative, or a solution obtained by mixing a known lower acid in advance with the measurement solution of

Embodiments

1 and 2, in which an electrolyte is dissolved in an organic solvent, is used as the measurement solution. 5 mL of the measurement solution and fruit juice as a sample to be measured are put into a 0.1 mL container 9 ′, and after the measurement container 2 with the container cover 15 ′ attached is sufficiently stirred, the container 3 is opened and set, and the container is again formed. When 3 is closed, measurement is possible. When the power is turned on by pressing the power button 5 and the start / stop button 7 is pressed to start the measurement, the voltage controller 17 ′ sweeps the potential of the working electrode 10 ′ within a predetermined range with respect to the potential of the comparison electrode 11. A voltage is applied between the working electrode 10 and the counter electrode 12 'so as to sweep at a speed. By performing such a sweep, a voltammogram as shown in FIG. 19 is obtained. As shown in FIG. 19, in this case, three peaks are formed. P ′ is a pre-peak derived from the acid contained in the sample to be measured, and M ′ is ethanol which is the main solvent of the coexisting electrolyte used in this measurement. The main peak derived from, α is a peak derived from the lower acid previously added to the measurement solution. This peak α always shows a constant value regardless of the acid concentration of the sample to be measured. However, the temperature changes corresponding to the temperature change, similar to the pre-peak and the main peak. That is, the relationship between the current value of the peak α and the temperature of the coexisting electrolyte is given by a simple linear function or a quadratic function that is as close as possible to the linear function as shown in FIG. That is, if the current value of the peak α is detected, the temperature of the coexisting electrolyte at the time of measurement can be easily predicted and calculated.
[0043]
To explain this relationship with an example, the solvent is ethanol, isopropyl alcohol, water mixed in 6: 2: 2, and 3,5-di-tert-butyl-1,2-benzoquinone 20 mM, NaCl 150 mM, nitric acid. A solution in which 3.84 mM is dissolved is used as a measurement solution. In this Embodiment 3, nitric acid is used as the lower acid. However, as long as the peak can be observed at a potential lower than the pre-peak as shown in FIG. 19, the concentration may be such that the peak can be observed. That's fine. If the concentration of the lower acid is increased, it may interfere with the pre-peak of the sample to be measured, and accurate measurement may not be possible. In the acidity measuring apparatus according to the third embodiment, plastic foam carbon is used for the three electrodes of the working electrode 10 ′, the comparison electrode 11 ′, and the counter electrode 12 ′.
[0044]
First, the acidity is 1 wt. Of 0.1% citric acid standard solution and 5 ml of the measurement solution were placed in a container 9 ′, and a container cover 15 ′ equipped with a working electrode 10 ′, a comparison electrode 11 ′, and a counter electrode 12 ′ was placed and stirred sufficiently. After the measurement solution settles down to a predetermined temperature, the working electrode 10 ′ is swept so that the potential of the working electrode 10 ′ is in the range of 0 to 1000 mV with respect to the potential of the comparison electrode 11 ′ at a sweep rate of 100 mV / sec. When a voltage is applied across the counter electrode 12 ', a voltammogram as shown in FIG. 19 is obtained. When these operations are repeatedly measured from 5 ° C. to about 35 ° C. at intervals of about 5 ° C., and the relationship between the temperature of the coexisting electrolyte and the current value of the peak α is obtained, a quadratic curve is shown as shown in FIG. At this time, the relationship between the current value Iα of the peak α and the temperature T of the coexisting electrolyte is expressed by the following equation.
T = −8.1560 × 10^-3・ Iα²+ 1.6150 · Iα-9.4370 (20)
Next, 5 mL and 4 wt. When 0.1 mL of 0.1% citric acid standard solution was placed in the container 9 and the same measurement was performed, the relationship between the temperature of the coexisting electrolyte and the pre-peak current value as shown in FIG._PIs given by the above equations (6) and (7). This is because, in addition to ethanol, isopropyl alcohol, water, 3,5-di-tert-butyl-1,2-benzoquinone, and NaCl, nitric acid is dissolved. In this case, a peak α, which is a reduction pre-wave, is formed on the positive side of the pre-peak of citric acid). It is considered that the relationship between the temperature of the coexisting electrolyte at the pre-peak and the pre-peak current value is not affected by the peak α, and is the same as the equations (6) and (7). Therefore, K and k are not affected by nitric acid in the pre-peak,
K = 1 / (1.960 × 10^-1・ T + 7.534) (13)
k = − (1.481 × 10^-3T + 3.988) / (1.960 × 10^-1・ T + 7.534) (14)
Given in. And since the temperature T is given by the equation (20),
K = 1 / (− 1.599 × 10^-3・ Iα²+ 3.165 × 10^-1・ Iα-5.684 (21)
k = (− 1.208 × 10^-Five・ Iα²+ 2.392 × 10^-3・ Iα-4.002) / (− 1.599 × 10^-3・ Iα²+ 3.165 × 10^-1・ Iα-5.684) (22)
It becomes.
[0045]
From the equations (21) and (22), it can be seen that the following general equation (1) is obtained.
θ = {1 / (− 1.599 × 10^-3・ Iα²+ 3.165 × 10^-1・ Iα-5.684} ・ I_P+ (− 1.208 × 10^-Five・ Iα²+ 2.392 × 10^-3・ Iα-4.002) / (− 1.599 × 10^-3・ Iα²+ 3.165 × 10^-1・ Iα-5.684) (23)
Therefore, if this equation is stored in the control unit 19 'in advance, the pre-peak current value I is measured by the current detection unit 18' when measuring the sample to be measured._PIf the peak current value Iα of the peak α is detected, the acidity θ of the sample to be measured can be calculated from the equation (23).
[0046]
[Table 3]

[0047]
Further, as shown in (2) and (3), as shown in (Table 3), if the values of K and k with respect to the peak current value Iα of the peak α are stored in the control unit 19 ′, the current detection unit 18 at the time of measurement. 'Pre-peak current value I_PIn addition, the peak current value Iα is detected, K and k in the peak current value Iα detected by the control unit 19 ′ are selected, and the obtained pre-peak current value I_PFrom the equation (1), the acidity θ of the sample to be measured can be calculated. A calibration curve may be provided for each peak current value Iα for conversion. For example, pre-peak current value I at the time of measurement_PIs 35 μA, and the current value of the peak α is 20 μA, the acidity θ is given by the following equation from (Table 3).

In this way, it is possible to measure the pre-peak current value derived from the sample to be measured and the pre-peak current value of a known lower acid. Can be measured.
[0048]
【The invention's effect】
The acidity measuring apparatus of the present invention has a simple configuration, is not affected by dissolved oxygen or light, and calculates an accurate acidity by correcting the temperature even if the temperature at the time of measurement changes. It is something that can be done. If the temperature of the coexisting electrolyte is directly measured by the temperature sensor, the temperature can be accurately corrected, and the temperature can be predicted using the main peak. Therefore, the temperature can be corrected without providing a special detector. Further, if another acid is added to form another peak, the temperature can be converted from this peak, and the temperature can be corrected without preparing a special detector.
[Brief description of the drawings]
FIG. 1 is a schematic external view of an acidity measuring apparatus according to Embodiment 1 of the present invention.
FIG. 2 is a cross-sectional view of a measurement container according to Embodiment 1 of the present invention.
[Fig. 3] Potential-current relationship diagram (Voltammetry) when ortho-benzoquinone derivative is used.
FIG. 4 is a structural diagram of an orthobenzoquinone derivative.
FIG. 5 is a structural diagram of a parabenzoquinone derivative.
FIG. 6 is a structural diagram of orthobenzoquinone.
FIG. 7 is a structural diagram of parabenzoquinone.
FIG. 8 is a structural diagram of 3,5-di-tert-butyl-1,2-benzoquinone.
FIG. 9 is a structural diagram of 2,6-dimethyl-1,4-benzoquinone.
FIG. 10 is a circuit diagram of the acidity measuring apparatus according to Embodiment 1 of the present invention.
FIG. 11 is a potential-current relationship diagram according to the first and second embodiments of the present invention.
FIG. 12 is a pre-peak current-acidity relationship diagram according to Embodiment 1 of the present invention.
FIG. 13 is a graph showing the relationship between the temperature and the pre-peak current value of the coexisting electrolyte in the first, second, and third embodiments of the present invention.
14 is a relationship diagram of coexisting electrolyte temperatures −A (θ) and B (θ) according to

Embodiments

1, 2, and 3 of the present invention. FIG.
FIG. 15 is a graph showing the relationship between coexisting electrolyte temperatures -K, k in

Embodiments

1, 2, and 3 of the present invention.
FIG. 16 is a cross-sectional view of a measurement container according to

Embodiments

2 and 3 of the present invention.
FIG. 17 is a circuit diagram of an acidity measuring apparatus according to

Embodiments

2 and 3 of the present invention.
FIG. 18 is a diagram showing the relationship between main peak current value and coexisting electrolyte temperature in Embodiment 2 of the present invention.
FIG. 19 is a potential-current relationship diagram according to Embodiment 3 of the present invention;
FIG. 20 is a relationship diagram of peak α current value and coexisting electrolyte temperature in Embodiment 3 of the present invention.
[Explanation of symbols]
1 Acidity measuring device
2 measuring containers
3 accommodation section
4 LCD
5 Power button
6 Memory button
7 Start / Stop button
8 Calibration button
9 containers
10 Working electrode
11 Reference electrode
12 Counter electrode
13 Temperature sensor
14 Sensor cover
15 Container cover
16 Temperature detection means
17 Voltage controller
18 Current detector
19 Control unit
20 Operation unit
21 Display
22 Calculation unit

Claims

An orthobenzobenzoquinone derivative or parabenzoquinone derivative, a container for storing a coexisting electrolyte obtained by mixing a measurement solution in which an electrolyte is dissolved in an organic solvent and an acid-containing sample to be measured, and an action provided in the container and immersed in the coexisting electrolyte a reference electrode and the electrode and the counter electrode, as well as sweeping the electrode potential of the working electrode within a predetermined potential range, and a control unit for detecting a pre-peak current value I _P of the current flowing between the said working electrode the counter electrode, the container A temperature detecting means for detecting the temperature of the coexisting electrolyte solution, and calculating the acidity θ of the sample to be measured from the temperature T detected by the temperature detecting means by the following equations (1) to (3) An acidity measuring apparatus comprising:
θ = K · I _P + k (1)
here,
K = 1 / (A ₁ · T + B ₁ ) (2)
k = − (A ₂ · T + B ₂ ) / (A ₁ · T + B ₁ ) (3)
(However, θ is acidity, I _P is pre-peak current value, T is temperature, and A ₁ , A ₂ , B ₁ , and B ₂ are constants specific to the coexisting electrolyte)

2. The acidity measuring apparatus according to claim 1, wherein the temperature detection means directly measures the temperature of the measurement solution with a temperature sensor immersed in the coexisting electrolyte.

An orthobenzobenzoquinone derivative or parabenzoquinone derivative, a container for storing a coexisting electrolyte obtained by mixing a measurement solution in which an electrolyte is dissolved in an organic solvent and an acid-containing sample to be measured, and an action provided in the container and immersed in the coexisting electrolyte The electrode potential of the electrode, the counter electrode, the reference electrode, and the working electrode are swept within a predetermined potential range, and the pre-peak current value I _P and the main peak current value I _M of the current flowing between the working electrode and the counter electrode are detected. And a temperature T of the solution to be measured is calculated from the main peak current value IM detected by the control unit according to the following equation (4), and the device to be measured is expressed by the following equations (1) to (3): An acidity measuring apparatus comprising an arithmetic unit for calculating the acidity θ of a sample.
θ = K · I _P + k (1)
here,
K = 1 / (A ₁ · T + B ₁ ) (2)
k = − (A ₂ · T + B ₂ ) / (A ₁ · T + B ₁ ) (3)
Also,
T = X · I _M ² + Y · I _M + Z (4)
(However, θ is acidity, I _P is a pre-peak current value, I _M is a main peak current value, T is a temperature, A ₁ , A ₂ , B ₁ , B ₂ , X, Y, and Z are constants unique to the coexisting electrolyte. )

An orthobenzoquinone derivative or parabenzoquinone derivative, a container containing a coexisting electrolytic solution in which a measurement solution obtained by dissolving an electrolyte in an organic solvent, a lower acid having a predetermined acidity and an acid-containing sample to be measured, and the coexisting electrolysis provided in the container A pre-peak current derived from the sample to be measured of a working electrode, a counter electrode, a reference electrode, a current flowing between the working electrode and the counter electrode, while sweeping the electrode potential of the working electrode within a predetermined potential range; a control unit for detecting a pre-peak current value I _alpha of the derived lower acid value I _P, the temperature T of the measured solution in accordance with (5) below the pre-peak current value I _alpha which the control unit has detected An acidity measuring apparatus comprising an arithmetic unit that calculates and calculates the acidity θ of the sample to be measured by the following equations (1) to (3).
θ = K · I _P + k (1)
here,
K = 1 / (A ₁ · T + B ₁ ) (2)
k = − (A ₂ · T + B ₂ ) / (A ₁ · T + B ₁ ) (3)
Also,
T = x · I _α ² + y · I _α + z (5)
(However, θ is the acidity, I _P is the pre-peak current value, I _α is the pre-peak current value of the lower acid, T is the temperature, and A ₁ , A ₂ , B ₁ , B ₂ , x, y, z are specific to the coexisting electrolyte. Constant)

In place of the calculation unit that calculates the acidity of the sample to be measured by the equations (1) to (3), a storage unit that stores a conversion table that associates K and k for each temperature of the solution to be measured is provided. The acidity measuring apparatus according to any one of claims 1 to 4, wherein the calculation unit performs temperature correction according to the equation (1) using K and k corresponding to the temperature read from the unit.