Measurement of local ion concentrations using glass capillary electrodes

2022 Fiscal Year Final Research Report

• Project/Area Number: 21K18687
• Research Category: Grant-in-Aid for Challenging Research (Exploratory)
• Allocation Type: Multi-year Fund
• Review Section: Medium-sized Section 19:Fluid engineering, thermal engineering, and related fields
• Research Institution: Toyohashi University of Technology
• Principal Investigator: Doi Kentaro 豊橋技術科学大学, 工学(系)研究科(研究院), 教授 (20378798)
• Project Period (FY): 2021-07-09 – 2023-03-31
• Keywords: ガラスキャピラリー電極 / イオン輸送現象 / イオン濃度 / pH / イオンダイオード

Outline of Final Research Achievements

In this study, in order to confirm the measurement accuracy of the glass capillary electrode, a reservoir with an orifice-like test section was filled with an electrolyte solution, and the glass electrode was scanned along the test section to analyze the electrical conductivity. As a result of using KCl solutions, the accuracy of the measurement error of less than 5% was confirmed for the concentrations ranging from 1 to 100 mmol/L. It is a novel measurement method that does not require calibration because it directly measures the local potential difference in the liquid under an ionic current condition. In addition, we fabricated a triple-barrelled glass capillary electrode by bundling three glass tubes together and measured proton concentration using pH standard solutions. The asymmetry of the potential difference with respect to the ionic current was observed, and the pH difference was quantitatively evaluated from the rectification ratio.

Free Research Field

マイクロ・ナノ熱流体工学

Academic Significance and Societal Importance of the Research Achievements

本研究で開発したガラスキャピラリー電極は，ガラス管を伸長してその先端径を数100 nmに絞り込んだものであり，液中を走査することで局所的な電場や濃度場を測ることができる．これまで困難と考えられてきた電極から離れた沖合の電場を直接的に測定することが可能となり，理論的に求められてきた電場の空間分布が実験的にも明らかにされたことは学術的に有意義である．また，寸法が既知の検査体積を走査するため，事前の較正を必要とすることなく，試料液の濃度を直接的に評価することを可能とする新しい測定手法といえる．さらに，3連管の電極を作製することで局所的なpH測定も実現され，各種イオン濃度測定への発展が期待される．