Ultrapure water quality monitoring by a silicon-based potentiometric sensor

A solid state silicon-based potentiometric sensor and a resistivity sensor were employed to monitor the water quality from an ultra-pure water production unit. A minute ionic impurity increase (at the low ppt level), which was not detectable by the conventional water resistivity sensor, can be sensitively detected by the silicon-based sensor. This slight degradation of water purity, independently confirmed by inductively coupled plasma mass spectrometry and atomic force microscopy, was attributed to early boil-off from the saturated water purification cartridge. The silicon-based sensor can potentially function as an ultra-sensitive monitoring sensor in conjunction with the conventional resistivity sensor to ensure water purity at parts per trillion level.