Abstract
The pH values of aqueous solutions are conventionally measured with pH-sensitive electrodes such as glass electrodes or ion-sensitive field-effect transistors (ISFETs) used in conjunction with Ag/AgCl reference electrodes and KCl solutions. The speed of pH measurement with these systems can be deficient, however, as the glass electrode responds slowly during measurements of sample solutions with low buffering capacities. Our group has constructed a new pH measurement system using a microfluidic device and ISFET sensors. The device has a channel with two inlets and one outlet, with a junction connected to a Y-shaped channel on the same plane. Two ISFET sensors and an Ag/AgCl pseudo reference electrode are fitted into the channel to construct a differential measurement device. A sample solution and baseline solution supplied into the inlets by gravity-driven pumps form a flowing liquid junction during measurement. The small size and fast response of the ISFET sensors enable measurement of about 2.0 mL of sample solution over a measurement period of 120 s. The 90% response time is within 2 s. The calibrated sensor signal exhibits a wide range (pH 1.68–10.0) of linearity with a correlation factor of 0.9997. The measurement error for all solutions tested, including diluted solutions, was 0.0343 ± 0.0974 pH (average error ± standard deviation (S.D.), n = 42). The new device developed in this research will serve as an innovative technology in the field of potentiometry.
Highlights
The pH scale is a numeric index used to specify the acidity and alkalinity of aqueous solutions.One of the domains in which it is frequently applied is environmental science
Precise pH values can be obtained by taking potentiometric measurements with devices such as glass electrodes [1] or ion-sensitive field-effect transistors (ISFETs) [2,3] used in conjunction with reference electrodes [4]
The pH-sensitive field-effect transistor (pH-FET) used in this work is a catheter-tip type [21] with a gate region covered with a pH-sensitive
Summary
The pH scale is a numeric index used to specify the acidity and alkalinity of aqueous solutions.One of the domains in which it is frequently applied is environmental science. The most commonly applied pH electrode is a glass type used together with an Ag/AgCl reference electrode and KCl solution [4]. The glass electrode method still has shortcomings. The long response time of the glass electrode precludes a shortened measurement time and leads to large measurement error and low reproducibility [4,5,6]. These shortcomings become especially problematic in the measurement of sample solutions with low buffering capacities [4,5,6]
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