Construction of a precision capacitance sensing apparatus consisting of interdigital electrode and capacitance-to-digital converter for determination of trace water contents in organic solvents

Abstract

This paper presents a detailed description of the precision of capacitance sensing apparatus constructed using interdigital electrode(IDE) and micro-capacitive technique and application of it for determination of trace water contents in almost all organic solvents having permittivities in the range of 2-8. In order to choose appropriate IDE gap so as to achieve the high sensitivity for water detection, by changing the gap of IDE, we measured capacitance versus water content in various organic solvents with different permittivities. As a result of experiments, the IDE with 20 µm gap had the excellent linear correlation and large slope in the water content‒capacitance curve of selected organic solvents. The developed precision capacitance sensing apparatus exhibits high sensitivity with a detection limit as 0.003, 0.003, 0.004, 0.004, 0.005, 0.006, 0.007, 0.009 v/v% for water in 1,4-dioxane (1,4-Diox), diethyl carbonate (DCE), diethylamine (DEA), methyl tert butyl ether (MTBE), piperidine, methyl acetate (MA), 1,2-dimethoxyethane(1,2-DME), tetrahydrofuran(THF), respectively and the linear relationships with water content within the range 0.01~0.40v/v%. The measuring results of trace water in organic solvents with permittivity below 8 using developed equipment a well consistent with those of the Karl Fischer method. Consequently, it can be employed to real-time monitor trace water during the drying process for almost all organic solvents with low permittivity conveniently.