JP6036558B2 - Calibration method for redox potential measurement - Google Patents
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本発明は、ガラス電極等を用いて酸化還元電位を測定する際の校正方法と、その校正に用いる校正用標準液に関する。 The present invention relates to a calibration method for measuring an oxidation-reduction potential using a glass electrode or the like, and a calibration standard solution used for the calibration.
水溶液の酸化や還元状態の把握は、化学反応の状態や制御を行うために重要である。酸化還元状態を具体的に測定する方法には、電極を測定対象の水溶液に浸漬し、電極表面と水溶液との間に生じる電位差を電気的に増幅し、指針式もしくはデジタル表示などで可視化し、酸化還元電位（Ｏｘｉｄａｔｉｏｎ−Ｒｅｄｕｃｔｉｏｎ Ｐｏｔｅｎｔｉａｌ：以下、「ＯＲＰ」と称する。）として表示する方法が広く用いられている。 Understanding the oxidation or reduction state of an aqueous solution is important for the state and control of chemical reactions. To measure the oxidation-reduction state specifically, immerse the electrode in the aqueous solution to be measured, electrically amplify the potential difference generated between the electrode surface and the aqueous solution, visualize it with a pointer type or digital display, A method of displaying as an oxidation-reduction potential (hereinafter referred to as “ORP”) is widely used.
上記の測定に用いる電極をＯＲＰ電極と称するが、測定原理は、銀-塩化銀または水銀-塩化水銀(Ｉ)などの比較電極を基準として、被検液の電位差を検出するものである。
このＯＲＰ電極は、電極表面や電極内部の水溶液の汚染、比較電極の劣化・剥離、液絡部の閉塞などにより検出する電位差に誤差を生じてくる。また電極と表示装置との接続部の接触抵抗や表示装置内の増幅精度などによっても誤差を生じることとなる。
An electrode used for the above measurement is referred to as an ORP electrode. The measurement principle is to detect a potential difference of a test solution with reference to a comparison electrode such as silver-silver chloride or mercury-mercury chloride (I).
The ORP electrode causes an error in the potential difference detected due to contamination of the aqueous solution on the electrode surface or inside the electrode, deterioration or peeling of the comparative electrode, blockage of the liquid junction, and the like. An error also occurs depending on the contact resistance of the connection portion between the electrode and the display device, the amplification accuracy in the display device, or the like.
そこで、誤差が少なく精度の高いＯＲＰ測定値を得るためには、定期的にＯＲＰ電極内部液の交換や電極表面の洗浄が必要となる。
また、基準となる電圧を増幅器の電極を接続する端子に印加し、対応するＯＲＰ値を表示するように増幅器での増幅率やオフセット値と呼ばれる電圧の加算・減算を調整し、最終的に電極を基準となる標準液に浸漬し、起電力と表示装置に示される表値との差異の比較、確認を行っている。
Therefore, in order to obtain a highly accurate ORP measurement value with little error, it is necessary to periodically replace the liquid inside the ORP electrode and clean the electrode surface.
In addition, a reference voltage is applied to a terminal connecting the electrodes of the amplifier, and the addition / subtraction of voltage called amplification factor or offset value in the amplifier is adjusted so as to display the corresponding ORP value, and finally the electrode Is immersed in a standard solution, and the difference between the electromotive force and the table value shown on the display device is compared and confirmed.
このような校正作業に用いる標準液としては、特許文献１に記載されているような「キンヒドロン水溶液」がもっぱら使用されている。
この「キンヒドロン」とは、酸化型のキノン（ｐ−ベンゾキノン)と還元型のハイドロキノンの１：１モルの付加物(分子化合物)であり、酸化還元に対して緩衝性を示す。
具体的には、濃度が０．６ｇ／Ｌのキンヒドロン水溶液であるｐＨ４．０１の緩衝液に、銀-塩化銀電極でＫＣｌ飽和水溶液型のＯＲＰ電極を浸漬し、液温を２５℃に維持した場合、２５６ｍＶの電位差を示す。
As the standard solution used for such calibration work, “quinhydrone aqueous solution” as described in Patent Document 1 is exclusively used.
This “quinhydrone” is a 1: 1 molar adduct (molecular compound) of oxidized quinone (p-benzoquinone) and reduced hydroquinone, and exhibits buffering properties against oxidation and reduction.
Specifically, a KCl saturated aqueous ORP electrode was immersed with a silver-silver chloride electrode in a buffer solution of pH 4.01, which is a 0.6 g / L quinhydrone aqueous solution, and the liquid temperature was maintained at 25 ° C. In this case, the potential difference is 256 mV.
さらに還元領域の電位を測定する場合、特許文献２に示すようなキンヒドロンに亜硫酸ナトリウムを添加した標準液が使用される。
特許文献２の方法は、還元側の酸化還元電位に対して電極の性能が正常であるか否かをより確実に検査することを可能とする酸化還元電位測定装置の電極検査方法及び酸化還元装置の電極検査用の標準液を提供するもので、測定電極及び比較電極を被検液に浸漬して被検液の酸化還元電位を測定する酸化還元電位測定装置の電極を検査する方法で、水に亜硫酸塩とキンヒドロンとを添加して調製された容器内の標準液に測定電極及び比較電極を浸漬する工程を有する構成とする。具体的には、例えば、亜硫酸ナトリウム２．１ｇ／Ｌ以下、キンヒドロン８ｇ／Ｌ以下を含む水溶液が使用される。この場合、ＯＲＰ値は−４３０〜−４４０ｍＶを示す。
Further, when measuring the potential of the reduction region, a standard solution in which sodium sulfite is added to quinhydrone as shown in Patent Document 2 is used.
The method of Patent Document 2 discloses an electrode inspection method and an oxidation-reduction device for an oxidation-reduction potential measuring device that can more reliably inspect whether or not the performance of the electrode is normal with respect to the reduction-side oxidation-reduction potential. In this method, the measurement electrode and the reference electrode are immersed in the test solution and the redox potential of the test solution is measured. And a step of immersing the measurement electrode and the comparative electrode in a standard solution in a container prepared by adding sulfite and quinhydrone to the container. Specifically, for example, an aqueous solution containing 2.1 g / L or less of sodium sulfite and 8 g / L or less of quinhydrone is used. In this case, the ORP value indicates −430 to −440 mV.
しかしながら、上記のような標準液では、安定性が欠如するという課題があった。
例えば、「キンヒドロン水溶液」は、製造直後には上記の理論値に近い値を示すが、空気と接触すると急速に酸化が進行し、上述のキノンが増えることにより酸化還元に対する緩衝液としての機能が失われる性質があった。そのため、例えばキンヒドロン水溶液を密栓し冷蔵庫に保管することが行われるが、それでも劣化を食い止めることは困難であった。
However, the standard solution as described above has a problem of lack of stability.
For example, “quinhydrone aqueous solution” shows a value close to the above theoretical value immediately after production, but when it comes into contact with air, the oxidation proceeds rapidly, and the above quinone increases to function as a buffer solution for redox. There was a lost property. Therefore, for example, a quinhydrone aqueous solution is sealed and stored in a refrigerator, but it is still difficult to prevent deterioration.
一方、キンヒドロン水溶液に亜硫酸ナトリウムを添加した場合は、優先的に亜硫酸ナトリウムが酸化されるため、その結果キンヒドロンの酸化が抑制され、安定性は向上する効果がある。
しかし、一般に行われるように標準液の容器を開栓し、開放状態で校正に供する場合、亜硫酸ナトリウムの酸素の吸収速度が速いこともあって、硫酸ナトリウムに変化した時点で上述のキンヒドロンの酸化が開始し誤差が生じるという課題もあった。
On the other hand, when sodium sulfite is added to the quinhydrone aqueous solution, sodium sulfite is preferentially oxidized, and as a result, the oxidation of quinhydrone is suppressed and the stability is improved.
However, when the standard solution container is opened and used for calibration in the open state as is generally done, the absorption rate of sodium sulfite oxygen may be high, and when the quinhydrone changes to sodium sulfate, There is also a problem that an error occurs.
さらに、キンヒドロン自体に発がん性の疑いがあるなど、保管、取扱、廃棄に関して細心の注意を払う必要があるなど実用上の課題もあった。
このように、ＯＲＰ測定における校正に用いる標準液の安定性が劣る課題から、標準液自身の安定性を、酸化還元滴定や水溶液中の化学種の化学分析によって定量的に把握する必要があるなど、容易に電極を校正する用途に用いるのは困難だった。
Furthermore, there were practical problems such as the quinhydrone itself being suspected of having carcinogenicity and careful attention to storage, handling and disposal.
As described above, since the stability of the standard solution used for calibration in the ORP measurement is inferior, it is necessary to quantitatively grasp the stability of the standard solution itself by oxidation-reduction titration or chemical analysis of chemical species in the aqueous solution. It was difficult to use for the purpose of easily calibrating the electrode.
このような状況に鑑み、本発明は、大気に曝されても安定したＯＲＰ値を示し、かつ、有害性が低く取り扱いやすい酸化還元電気測定における酸化還元電位の校正に適した校正用標準液と、その校正用標準液を用いた酸化還元電位測定の校正方法を提供することを目的とするものである。 In view of such a situation, the present invention provides a calibration standard solution that exhibits a stable ORP value even when exposed to the atmosphere, and is suitable for calibration of the oxidation-reduction potential in oxidation-reduction electric measurement with low toxicity and easy handling. An object of the present invention is to provide a calibration method for redox potential measurement using the calibration standard solution.
上記の課題を解決するための本発明の第１の発明は、０．０２５ｍｏｌ／Ｌの硫酸鉄（ＩＩ）アンモニウムと、硫酸鉄（ＩＩＩ）アンモニウムを含有する水溶液で、その水溶液に含まれる２価の鉄イオンと３価の鉄イオンの割合が、２価鉄イオンのモル数の１倍から２倍の範囲にあり、その水溶液を作製後、水溶液を密栓した状態で９０日間保管前後の酸化還元電位に変化が見られない水溶液を校正用標準液に用い、その校正用標準液の液温を変えて、酸化還元電位測定装置の酸化還元電位の校正を行うことを特徴とする酸化還元電位測定の校正方法である。 The first invention of the present invention for solving the above problems is an aqueous solution containing 0.025 mol / L of iron (II) ammonium sulfate and iron (III) ammonium sulfate, and the divalent contained in the aqueous solution. The ratio of iron ions to trivalent iron ions is in the range of 1 to 2 times the number of moles of divalent iron ions. After preparing the aqueous solution, the redox before and after storage for 90 days with the aqueous solution sealed. An oxidation-reduction potential measurement characterized in that an aqueous solution with no change in potential is used as a calibration standard solution, and the oxidation-reduction potential of the oxidation-reduction potential measuring device is calibrated by changing the temperature of the calibration standard solution. This is the calibration method.
本発明の第２の発明は、０．０２５ｍｏｌ／Ｌのヘキサシアノ鉄（ＩＩ）酸カリウムと、ヘキサシアノ鉄（ＩＩＩ）酸カリウムを含有する水溶液で、その水溶液に含まれる２価の鉄イオンと３価の鉄イオンの割合が、２価鉄イオンのモル数の１倍から２倍の範囲にあり、その水溶液を作製後、水溶液を密栓した状態で９０日間保管前後の酸化還元電位に変化が見られない水溶液を校正用標準液に用い、その校正用標準液の液温を変えて酸化還元電位測定装置の酸化還元電位の校正を行うことを特徴とする酸化還元電位測定の校正方法である。 The second aspect of the present invention, a potassium hexacyanoferrate (II) of 0.025 mol / L, an aqueous solution containing potassium hexacyanoferrate (III), and divalent iron ions contained in the aqueous solution 3 ratio of the valence of the iron ions, divalent iron are two fold range near from 1 times the number of moles of ions, after making the aqueous solution, a change in redox potential before and after 90 days storage while stoppered solution An oxidation-reduction potential measurement calibration method characterized in that an unseen aqueous solution is used as a calibration standard solution, and the oxidation-reduction potential of the oxidation-reduction potential measuring device is calibrated by changing the temperature of the calibration standard solution. .
本発明の第３の発明は、保管時の酸化還元電位の変化が小さい酸化還元電位測定における校正用標準液であって、０．０２５ｍｏｌ／Ｌの硫酸鉄（ＩＩ）アンモニウムと、硫酸鉄（ＩＩＩ）アンモニウムを含有する水溶液で、その水溶液に含まれる２価の鉄イオンと３価の鉄イオンの割合が、２価鉄イオンのモル数の１倍から２倍の範囲にあり、水溶液を作製後、水溶液を密栓した状態で９０日間保管前後の酸化還元電位に変化が見られないことを特徴とする校正用標準液である。 A third aspect of the present invention is a calibration standard solution in the oxidation-reduction potential measuring changes in redox potential is less during storage, and iron (II) sulfate ammonium 0.025 mol / L, iron sulfate (III ) with water solutions containing ammonium, the percentage of divalent iron ions and the trivalent iron ions contained in the aqueous solution, there from 1 times the number of moles of divalent iron ions in the range of 2 times, prepare an aqueous solution Thereafter, the standard solution for calibration is characterized in that no change is observed in the oxidation-reduction potential before and after storage for 90 days with the aqueous solution sealed .
本発明の第４の発明は、保管時の酸化還元電位の変化が小さい酸化還元電位測定における校正用標準液であって、０．０２５ｍｏｌ／Ｌのヘキサシアノ鉄（ＩＩ）酸カリウムと、ヘキサシアノ鉄（ＩＩＩ）酸カリウムを含有する水溶液で、その水溶液に含まれる２価の鉄イオンと３価の鉄イオンの割合が、２価鉄イオンのモル数の１倍から２倍の範囲にあり、その水溶液を作製後、水溶液を密栓した状態で９０日間保管前後の酸化還元電位に変化が見られないことを特徴とする校正用標準液である。 A fourth invention of the present invention is a standard solution for calibration in redox potential measurement with a small change in redox potential during storage, wherein 0.025 mol / L potassium hexacyanoferrate (II) and hexacyanoferrate ( with an aqueous solution containing III) potassium, proportion of bivalent iron ion and trivalent iron ions contained in the water solution, are two fold range near from 1 times the number of moles of divalent iron ions, After preparing the aqueous solution, the standard solution for calibration is characterized in that no change is observed in the oxidation-reduction potential before and after storage for 90 days with the aqueous solution sealed .
本発明の酸化還元電位測定用の校正用標準液は、大気に曝された状態であっても常温で長時間にわたり安定したＯＲＰ値を示す。このため、この標準液を用いて校正することによりＯＲＰ測定値の信頼性が高く維持でき、工業的にＯＲＰ値による液性の定量的な制御、管理を可能とするものである。また、有害性も低いため、保管、取扱、廃棄も容易となり工業上顕著な効果を奏するものである。 The calibration standard solution for measuring the oxidation-reduction potential of the present invention exhibits a stable ORP value at room temperature for a long time even when exposed to the atmosphere. For this reason, by calibrating using this standard solution, the reliability of the ORP measurement value can be maintained high, and the liquid property can be quantitatively controlled and managed by the ORP value industrially. Further, since it is low in toxicity, it is easy to store, handle and dispose of it, and has a remarkable industrial effect.
本発明は、ＯＲＰ測定における校正用標準液として、水溶性の鉄（ＩＩ）化合物と鉄（ＩＩＩ）化合物との混合物の水溶液を用いて校正する方法である。
具体的な混合物として、下記（１）、（２）に示す２種の水溶性の鉄（ＩＩ）化合物と鉄（ＩＩＩ）化合物との混合物のいずれかを用いる。
The present invention is a method of calibrating by using an aqueous solution of a mixture of a water-soluble iron (II) compound and an iron (III) compound as a standard solution for calibration in ORP measurement.
As a specific mixture, any one of a mixture of two water-soluble iron (II) compounds and iron (III) compounds shown in the following (1) and (2) is used.
（１）硫酸鉄（ＩＩ）アンモニウムおよび硫酸鉄（ＩＩＩ）アンモニウムの混合物。
（２）ヘキサシアノ鉄（ＩＩ）酸カリウムおよびヘキサシアノ鉄（ＩＩＩ）酸カリウムの混合物。
(1) A mixture of iron (II) ammonium sulfate and iron (III) ammonium sulfate.
(2) A mixture of potassium hexacyanoferrate (II) and potassium hexacyanoferrate (III).
鉄（ＩＩ）化合物と鉄（ＩＩＩ）化合物の量は、鉄（ＩＩ）イオンと鉄（ＩＩＩ）イオンのモル比が、１：１〜１：２となる割合で混合された場合が望ましい。 The amount of the iron (II) compound and the iron (III) compound is desirably mixed in such a ratio that the molar ratio of iron (II) ion to iron (III) ion is 1: 1 to 1: 2.
次に、本発明に係る標準液を用いた酸化還元電位の測定原理を説明する。
酸化還元電位：Ｅは、下記式（１）に示すネルンストの式で表現される。
Next, the measurement principle of the oxidation-reduction potential using the standard solution according to the present invention will be described.
The oxidation-reduction potential: E is expressed by the Nernst equation shown in the following equation (1).
上記式（１）において、［Ｏｘ］と［Ｒｅｄ］の比が１に近くなるほど、対数項が０に近づき、［Ｏｘ］や［Ｒｅｄ］が若干変動してもＥの値の変動が小さくなる。
すなわち、原理的にはどのような酸化剤、還元剤の組み合わせでも［Ｏｘ］と［Ｒｅｄ］とを、１に近づければ、ＯＲＰ標準液として使用可能な緩衝液となる。
In the above formula (1), the closer the ratio of [Ox] and [Red] is to 1, the closer the logarithmic term is to 0, and even if [Ox] and [Red] slightly change, the fluctuation of the value of E becomes smaller. .
That is, in principle, any combination of oxidizing agent and reducing agent can be used as an ORP standard solution by bringing [Ox] and [Red] close to 1.
しかしながら、酸化還元に関するイオンの活量は、濃度と比例する場合は極めて限定される。これは、多くの化合物において、酸化還元反応に関する活性化エネルギーが高いためである。
例えば、酸化剤、還元剤の組み合わせとして、硫酸イオン／亜硫酸イオン、リン酸イオン／亜リン酸イオン、硝酸イオン／亜硝酸イオンにおいては、酸化に対しては緩衝されるものの、酸化型化合物(硫酸イオン、リン酸イオン、硝酸イオン)の還元に対する活性化エネルギーが高く、還元に対する緩衝性は少ないため、緩衝液としては使用できない。
However, the ion activity related to redox is extremely limited when it is proportional to the concentration. This is because many compounds have high activation energy for redox reaction.
For example, as a combination of an oxidizing agent and a reducing agent, sulfate ion / sulfite ion, phosphate ion / phosphite ion, and nitrate ion / nitrite ion are buffered against oxidation, but oxidized compounds (sulfuric acid Ions, phosphate ions, nitrate ions) are high in activation energy for reduction and have little buffering property for reduction, and therefore cannot be used as a buffer solution.
また、実用面から、酸化剤、還元剤が反応して、中間化合物に変化する物質も標準液の組成物としては適さない。例えば、Ｍｎ（ＩＩ）化合物とＭｎ（ＶＩＩ）化合物は、いずれも酸化還元の活性化エネルギーが低く反応速度が高いが、混合するとＭｎＯ２やＭｎ２Ｏ３の沈殿が生成するため不適切である。塩素系化合物も活量が高い状態で混合すると塩素ガスが発生する。 In terms of practical use, a substance that changes into an intermediate compound through reaction of an oxidizing agent and a reducing agent is not suitable as a composition of a standard solution. For example, the Mn (II) compound and the Mn (VII) compound both have a low redox activation energy and a high reaction rate, but are inappropriate because they cause precipitation of MnO 2 and Mn 2 O 3 when mixed. . Chlorine gas is generated when chlorine compounds are also mixed in a high activity state.
さらにＨｇ化合物は、活性化エネルギーが低い化合物が多いが、その有毒性から不適切である。Ａｓ（ＩＩＩ）は、酸化に対する活性化エネルギーが高く、Ｓｅ（ＶＩ）は、還元に対する活性化エネルギーが高いという点で不利である。 Further, many Hg compounds have low activation energy, but are inappropriate due to their toxicity. As (III) is disadvantageous in that it has a high activation energy for oxidation, and Se (VI) has a high activation energy for reduction.
また、酸化剤、還元剤自体の安定性も重要である。
目安として、酸化剤が水素／水素ガス間の比較電極（標準水素電極：Ｎｏｒｍａｌ Ｈｙｄｒｏｇｅｎ Ｅｌｅｃｔｒｏｄｅ；ＮＨＥ）に対するＯＲＰ値として、１０００ｍＶ以上の領域では自己分解しやすく、また、２００ｍＶ以下では容易に空気酸化を受ける。
したがって極力この中間付近の値であることが望ましい。
Also, the stability of the oxidizing agent and reducing agent itself is important.
As a guideline, the ORP value for the reference electrode (standard hydrogen electrode: NHE) between the hydrogen and hydrogen gas as the oxidizer is easy to self-decompose in the region of 1000 mV or more, and easily oxidize in the air below 200 mV. receive.
Therefore, it is desirable that the value be in the vicinity of this middle as much as possible.
本発明者は、種々の試薬で前記条件を満たす酸化型化合物、還元型化合物の組み合わせについて、１:１となるモル比の混合水溶液を製造し、一週間以上の長期安定性や、酸化剤・還元剤を添加した場合のＯＲＰ測定値の安定性、温度の上下によるＯＲＰ測定値の変化などを調査した。
この結果、水溶液中で２価の鉄イオンとなる化合物すなわち鉄（ＩＩ）化合物、および３価の鉄イオンとなる化合物すなわち鉄（ＩＩＩ）化合物の組み合わせがこれらの要求事項を最も効果的に満たすことを見出し、本発明の完成に至ったものである。
The present inventor manufactured a mixed aqueous solution having a molar ratio of 1: 1 for various combinations of oxidized compounds and reduced compounds satisfying the above conditions with long-term stability of one week or more, The stability of the ORP measurement value when a reducing agent was added, and the change in the ORP measurement value due to the rise and fall of temperature were investigated.
As a result, the combination of a compound that becomes a divalent iron ion in an aqueous solution, that is, an iron (II) compound, and a compound that becomes a trivalent iron ion, that is, an iron (III) compound, satisfies these requirements most effectively. And the present invention has been completed.
鉄（ＩＩ）化合物は、陰イオンの形態により空気酸化の影響が異なるが、硫酸塩が比較的安定であり、特にアンモニウムイオンとの複塩（いわゆる「モール塩」）が、１年以上の長期間保管しても酸化が非常にわずかにとどまり適していることが分かった。
一方、鉄（ＩＩＩ）化合物には、硫酸塩が加水分解に対して安定であり、やはりアンモニウムイオンとの複塩（通称「鉄明礬」）が最も安定であることを見出した。
Iron (II) compounds have different effects of air oxidation depending on the form of anions, but sulfates are relatively stable, and in particular, double salts with ammonium ions (so-called “mole salts”) have been long for more than one year. It has been found that oxidation is very small and suitable even after storage for a period of time.
On the other hand, for iron (III) compounds, it was found that sulfates are stable against hydrolysis, and double salts with ammonium ions (commonly called “iron alum”) are also most stable.
なお、上記の鉄明礬液は、容器を開放したまま数年の単位で長期間使用すると、徐々に黄色の沈殿物が析出する。この沈澱物の成分は、鉄明礬石（Ｊａｒｏｓｉｔｅ：ジャロサイト−ＮＨ４；ＮＨ４Ｆｅ（ＩＩＩ）３（ＯＨ）６（ＳＯ４）２）であり、ジャロサイトの生成により水溶液中のＦｅ（ＩＩＩ）／Ｆｅ（ＩＩ）比の増加が防止され、ＯＲＰが長期に安定状態に維持されると考えられる。
なお、沈殿生成を防止するためには硫酸を添加すると効果があるが、酸の添加でＯＲＰ値が上昇してしまうので好ましくない。
In addition, when said iron alum liquid is used for a long time in the unit of several years with the container opened, a yellow precipitate gradually precipitates. The component of this precipitate is iron aurite (Jarosite: Jarosite-NH 4 ; NH 4 Fe (III) 3 (OH) 6 (SO 4 ) 2 ), and Fe (III) in an aqueous solution is formed by the formation of jarosite. ) / Fe (II) ratio is prevented, and ORP is considered to be maintained in a stable state for a long time.
In addition, although it is effective to add sulfuric acid in order to prevent precipitation, it is not preferable because the ORP value is increased by the addition of acid.
他の鉄化合物としては、シアン化物が配位子となった錯体であるヘキサシアノ鉄（ＩＩ）酸塩、ヘキサシアノ鉄（ＩＩＩ）酸塩も同様に使用可能であり、上記のジャロサイトよりさらに長期安定性が高くなる。
ヘキサシアノ鉄酸塩としてはカリウム塩が代表的であるが、水に溶解する塩であれば他の化合物も使用可能である。ヘキサシアノ鉄酸塩は、シアン化物を配位子とするが、極めて安定な錯体であって、生物に対する有害性が低い。
As other iron compounds, hexacyanoiron (II) and hexacyanoiron (III), which are complexes in which cyanide is a ligand, can be used as well, and are more stable than the above jarosite. Increases nature.
The hexacyanoferrate is typically a potassium salt, but other compounds can be used as long as they are soluble in water. Hexacyanoferrate uses cyanide as a ligand, but is a very stable complex and has low harmfulness to living things.
上記のヘキサシアノ鉄（ＩＩＩ）酸塩の標準液は、前記の硫酸鉄アンモニウム系の標準液よりも還元性の液を測定する場合に適している。
また、他にもクエン酸塩など有機酸塩で安定な鉄化合物も利用できるが、価格の点で工業的に不利である。
The above standard solution of hexacyanoferrate (III) is more suitable for measuring a reducing solution than the above-described ammonium sulfate-based standard solution.
In addition, iron compounds that are stable in organic acid salts such as citrate can be used, but this is industrially disadvantageous in terms of price.
なお、上述の鉄（ＩＩ）、鉄（ＩＩＩ）化合物の比率は、緩衝性の点では、上記式（１）で説明したように１：１に近いほど好ましい。
一方、硫酸アンモニウム複塩の場合、鉄（ＩＩ）：鉄（ＩＩＩ）比が１：２付近になると長期安定性が向上する特徴がある。
これは、標準液のＯＲＰ値が、硫酸鉄（ＩＩ）が単独で存在する水溶液を空気で酸化した際の平衡ＯＲＰ値にほぼ匹敵するためと考えられる。
The ratio of the iron (II) and iron (III) compounds described above is preferably closer to 1: 1 as described in the above formula (1) in terms of buffering properties.
On the other hand, ammonium sulfate double salt is characterized in that long-term stability is improved when the iron (II): iron (III) ratio is around 1: 2.
This is considered because the ORP value of the standard solution is almost comparable to the equilibrium ORP value when an aqueous solution containing iron (II) sulfate alone is oxidized with air.
また、化合物の水溶液中の濃度としては、濃厚すぎると有効成分が結晶して［Ｏｘ］／［Ｒｅｄ］比が変動し、低すぎると緩衝性が損なわれるなど好ましくない。
したがって、ほぼ０．０２５ｍｏｌ／Ｌ付近の濃度とすることが好ましい。
In addition, when the concentration of the compound in the aqueous solution is too thick, the active ingredient is crystallized to change the [Ox] / [Red] ratio, and when it is too low, the buffering property is impaired.
Therefore, the concentration is preferably about 0.025 mol / L.
これらの上述の標準液は、それぞれの種類が単一のＯＲＰ値しか示さないので、その標準液に電極を浸漬し、ＯＲＰ測定装置が表示した数値が液温度に対して所定のＯＲＰ値となるように、測定装置のオフセット値や増幅率などの微調整を行って数値を合わせる校正操作を行えば、電極を実測定液に浸漬した際に正しいＯＲＰ値が表示できる。 Since the above-mentioned standard solutions each show only a single ORP value, an electrode is immersed in the standard solution, and the numerical value displayed by the ORP measurement device becomes a predetermined ORP value with respect to the liquid temperature. As described above, if the calibration operation for adjusting the numerical values by performing fine adjustments such as the offset value and the amplification factor of the measuring apparatus is performed, the correct ORP value can be displayed when the electrode is immersed in the actual measurement liquid.
なお、本発明の標準液は、１つだけでは２点校正とならない。ＯＲＰ測定値の直線性をより厳密に確認する場合は、一点の標準液で校正し、もう一点の標準液での数値の差を確認することにより、ＯＲＰ測定値が直線的に正しい値を示すか検証し、前述のオフセット値や増幅率を微調整することでさらに精度良く校正できる。 It should be noted that a single standard solution of the present invention is not a two-point calibration. In order to confirm the linearity of the ORP measurement value more strictly, the ORP measurement value shows a linearly correct value by calibrating with one standard solution and confirming the difference in the value with the other standard solution. This can be calibrated with higher accuracy by finely adjusting the offset value and amplification factor.
以下、実施例を用いて本発明を詳細に説明する。 Hereinafter, the present invention will be described in detail using examples.
特級試薬の硫酸鉄(ＩＩ)アンモニウム・６水和物（和光純薬工業株式会社製）を９．８ｇ（０．０２５ｍｏｌ）と、同じく特級試薬の硫酸鉄（ＩＩＩ）アンモニウム・１２水和物（和光純薬工業株式会社製）を２４．１ｇ（０．０５０ｍｏｌ）とを秤量し、脱イオン水に溶解して１０００ｍｌに調整して水溶液とした。 9.8 g (0.025 mol) of the special grade reagent iron (II) sulfate ammonium hexahydrate (manufactured by Wako Pure Chemical Industries, Ltd.) and the same special grade reagent iron (III) ammonium sulfate dodecahydrate (0.025 mol) 24.1 g (0.050 mol) of Wako Pure Chemical Industries, Ltd. was weighed and dissolved in deionized water to adjust to 1000 ml to obtain an aqueous solution.
作製した水溶液を、ウォーターバスを用いて、８℃〜３０℃にわたって液温を変化させた。
市販のＯＲＰ電極（ＰＴＳ−５０１１Ｃ型；東亜ＤＫＫ株式会社製）と、当該電極に対応した同社製の計測・表示機器（ＣＭ−４０Ｓ型）を用いてＯＲＰ値を測定した。
その結果を表１に示す。
The liquid temperature of the prepared aqueous solution was changed from 8 ° C. to 30 ° C. using a water bath.
The ORP value was measured using a commercially available ORP electrode (PTS-5011C type; manufactured by Toa DKK Co., Ltd.) and a measuring / display device (CM-40S type) manufactured by the company corresponding to the electrode.
The results are shown in Table 1.
また、密栓した状態に維持し、室温で９０日間保管し、その後２５℃に維持してＯＲＰ値を測定したが、４４８ｍＶで表１の場合と全く変化がなかった。 Further, the container was kept sealed and stored at room temperature for 90 days, and then maintained at 25 ° C., and the ORP value was measured. At 448 mV, there was no change from the case of Table 1.
試薬特級のヘキサシアノ鉄（ＩＩ）酸カリウム・３水和物（和光純薬工業株式会社製）を１０．６ｇ（０．０２５ｍｏｌ）と、試薬特級のヘキサシアノ鉄（ＩＩＩ）酸カリウム・無水塩（和光純薬工業株式会社製）を８．２ｇ（０．０２５ｍｏｌ）とを脱イオン水１０００ｍｌに溶解して水溶液とした。 10.6 g (0.025 mol) of reagent-grade potassium hexacyanoferrate (II) trihydrate (manufactured by Wako Pure Chemical Industries, Ltd.) and reagent-grade potassium hexacyanoferrate (III), anhydrous salt (sum 8.2 g (0.025 mol) of Kojun Pharmaceutical Co., Ltd. was dissolved in 1000 ml of deionized water to obtain an aqueous solution.
この水溶液を実施例１と同じＯＲＰ電極と表示機器を用いて２５℃に維持した場合のＯＲＰ値を測定した。
その結果、２３２ｍＶを示した。
この溶液を密栓して室温で９０日保管し、ＯＲＰ値を再度２５℃で測定したが、２３２ｍＶで全く変化がなかった。
The ORP value was measured when this aqueous solution was maintained at 25 ° C. using the same ORP electrode and display device as in Example 1.
As a result, 232 mV was indicated.
The solution was sealed and stored at room temperature for 90 days, and the ORP value was measured again at 25 ° C., but there was no change at 232 mV.
以上のように、本発明の校正用標準液は酸化還元電位測定における校正用の標準液として安定して用いることが確認でき、酸化還元電位測定機器の校正に適用できる。 As described above, it can be confirmed that the calibration standard solution of the present invention is stably used as a calibration standard solution in the oxidation-reduction potential measurement, and can be applied to the calibration of the oxidation-reduction potential measuring instrument.
Claims (2)
前記水溶液に含まれる２価の鉄イオンと３価の鉄イオンの割合が、２価鉄イオンのモル数の１倍から２倍の範囲にあり、
前記水溶液を作製後、前記水溶液を密栓した状態で９０日間保管前後の酸化還元電位に変化が見られない水溶液を校正用標準液に用い、
前記校正用標準液の液温を変えて、酸化還元電位測定装置の酸化還元電位の校正を行うことを特徴とする酸化還元電位測定の校正方法。 An aqueous solution containing 0.025 mol / L of iron (II) ammonium sulfate and iron (III) ammonium sulfate,
The ratio of divalent iron ions and trivalent iron ions contained in the aqueous solution is in the range of 1 to 2 times the number of moles of divalent iron ions,
After preparing the aqueous solution, an aqueous solution in which the redox potential before and after storage for 90 days is not changed in a state where the aqueous solution is sealed is used as a calibration standard solution.
A calibration method for redox potential measurement, wherein the redox potential of the redox potential measuring device is calibrated by changing the temperature of the calibration standard solution.
前記水溶液に含まれる２価の鉄イオンと３価の鉄イオンの割合が、２価鉄イオンのモル数の１倍から２倍の範囲にあり、
前記水溶液を作製後、前記水溶液を密栓した状態で９０日間保管前後の酸化還元電位に変化が見られない水溶液を校正用標準液に用い、
前記校正用標準液の液温を変えて酸化還元電位測定装置の酸化還元電位の校正を行うことを特徴とする酸化還元電位測定の校正方法。 An aqueous solution containing 0.025 mol / L potassium hexacyanoferrate (II) and potassium hexacyanoferrate (III),
The ratio of divalent iron ions and trivalent iron ions contained in the aqueous solution is in the range of 1 to 2 times the number of moles of divalent iron ions,
After preparing the aqueous solution, an aqueous solution in which the redox potential before and after storage for 90 days is not changed in a state where the aqueous solution is sealed is used as a calibration standard solution.
A calibration method for redox potential measurement, wherein the redox potential of the redox potential measuring device is calibrated by changing the temperature of the calibration standard solution.
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