Hirokazu Hara

Dynamic response of a Ta2O5-gate pH-sensitive field-effect transistor

Abstract The dynamic response of a Ta 2 O 5 -gate pH-sensitive field-effect transistor (pH-ISFET) has been investigated using an activity step method. The measurement set-up can produce the activity step of pH within time-frames of several tens of milliseconds. The response time, t 95% , is found to be 0.25-0.30 s, which is almost independent of various factors including the flow rate and the direction of the pH change. The measured response times are slower than those previously reported. The applicability of the existing theories to interpret the dynamic response curves is discussed.

Buffer composition suitable for determining very low fluoride concentrations using a fluoride ion-selective electrode and its application to the continuous analysis of rain water☆

Abstract In order to continuously analyze rain water with a fluoride ion-selective electrode (F− ISE), various buffer systems were examined in terms of the sensitivity enhancement. On the basis of the result that the sensitivity could be maximized at around pH 2.8 using the conventional acetate buffer, we proposed Sorensens buffer (a mixture of glycine and hydrochloric acid, pH 2.8) to be most suitable for rain water analysis. The limit of linear response was 1 × 10−7 mol dm−3 and the detection limit was 1 × 10−8 mol dm−3 by optimizing the sample to buffer dilution rate as 10: 1. A good correlation was found between the results from the rain water analysis using this method and those of ion chromatography. A continuous analysis of rain water during a rainfall event was successfully carried out.

Continous-flow determination of phosphate using a lead ion-selective electrode

Abstract The continous-flow determination of phosphate is described with emphasis on theoretical calcualations to explain the exprimental calibration data. In the determination system, phosphate standards are introduced into a reagent stream containing Pb2+, resulting in the formation of Pb3(PO4)2. The associated decrease in free lead ion concentration is measured by a lead ion-selective electrode. The detection limit is 10−6 M phosphate. The result of a theoretical calculation suggests that at phosphate concentration above 2 × 10−4, the potential response may not significant interferents among inorganic ions for river water analysis, whereas hydrogencarbonate, sulphate and magnesium have much less effect.

Continuous flow determination of chloride in the non-linear response region with a tubular chloride ion-selective electrode

A microcomputer-aided continuous-flow system was constructed for the determination of chloride in the non-linear electrode-response region from 10 to 0.1 mg/l. Interpolation by spline function was used to calculate the concentration from the measured potential. As few as four points were enough to obtain a practical calibration curve, plotted as Evs. log c. The interferences of bromide and iodide (at weight ratios <0.1 to chloride) could be removed by adding colloidal silver chloride continuously in the flow stream. Analysis of rain and snow containing 0.07-8.8 mg/l. chloride showed fairly good agreement with that by ion-chromatography.

High speed potentiometric analyzer equipped with an ion-selective electrode detector

Abstract A new type of microcomputer-controlled potentiometric flow-analysis system has been developed. It utilizes the very fast response of an ion-selective electrode when standard and sample solutions alternately flow past the electrode surface at high flow-rates (ca. 2.0 m s −1 ). The switchover of the solenoid valves for a solution change and the data acquisition are performed by the microcomputer. Regardless of the concentration, it was possible to reduce the analysis time for one sample to 1.2–1.3 s as demonstrated with a solid-state chloride ISE. The repeatability for ten samples of a concentration was within 2% in the concentration range of 10 −2 mol dm −3 to 10 −4 mol dm −3 . This system was applied to the determination of chloride in beverages.

Continuous-flow determination system based on null-point potentiometry using a nitrate ion-selective membrane

Abstract A new automated potentiometric analysis system for nitrate was developed. This system is based on the principle of null-point potentiometry. On either side of a nitrate ion-selective PVC membrane were the flowing sample and standard nitrate solutions. The concentration of the latter was automatically matched with that of the sample solution by controlling the dilution rate of a basic standard solution so that the membrane potential reached the `null-point. The determination without using a calibration graph was possible. The precision of five independent determinations was within 8% in the concentration range above 1xa0×xa010−5xa0molxa0dm−3. This system was applied to rain water analysis.

Nitrate ion-sensitive field effect transistor based on bis(bathocuproin)-copper(I) nitrate dissolved in solid solvents

Abstract Nitrate-selective ion-sensitive field effect transistors (ISFETs) were prepared by dip-coating the silica gate insulator surface with an ion exchanger based on bis(bathocuproin)-copper(I) nitrate in a molten mixture of docosan 1-ol and Triphenylphosphate. This sensor showed a linear response from 10−1 mol dm−3 to at least 10−5 mol dm−3 and maintained its response characteristics for as long as 5 weeks. The selectivity sequence for common anions such as Cl0−4 and Cl− followed the conventional Hofmeister series. This sensor was applied to rain water analysis.