Development of a System for Determining a Small Amount of Acid Based on Electrolysis of Quinone

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An analytical system for determining a small amount of acid with high reliability and feasibility was developed. An acid detector for high-performance liquid chromatography (HPLC) and acid sensors were constructed and applied to various samples. The main contents of the results are as follows :1. High-sensitive detection system for free fatty acids (FFAs)A system with a high-sensitive detector was developed for FFA determination. In order to determine FFAs in human skin lipids and to clarify their distribution on skin surface, HPLC with this detector was carried out using an ODS separation column. This HPLC method was selective and high-sensitive and thus needed only a very simple sampling method. A piece of oil-absorbing paper (5 mm x 5 mm) was put on a sampling point of man's face. This procedure was useful for the research on FFA distribution on patient skin.2. Sensors for juice and wineAcid sensors were developed for the quality control of juice and wine, the taste of which strongly depends on acid content. The sensors were handy-type and functioned by common dry batteries. Several hundred microliters of juice or wine sample were added to a quinone solution in an electrochemical cell, and then the current value corresponded to acid content was measured within 60 s. The range of acid concentration determined by the sensors was from 0.1 to 3%. Acid contents of 20 samples were measured by the present and the conventional methods, and the correlation coefficient of those methods was 0.900. This sensor should thus prove quite useful for monitoring acid content of fruits and their products in fields or wineries.