Anion Analysis of High Purity Water

Abstract

The semiconductor, power and pharmaceutical industries all require ultra high purity water for process control. While the type of demineralizer system used and the specific contaminants of concern may differ, the problems associated with maintaining and monitoring process water quality are similar. The power industry has become increasingly concerned over the levels and transport of trace impurities in steam cycle systems as a result of corrosion problems experienced at supercritical generating units. On-line sodium analysis and continuous conductivity and acid conductivity measurements, used to monitor the high purity water in steam cycle systems, had not prevented the turbine and reheater corrosion in supercritical units. In order to identify the contaminants responsible, ion chromatographic (IC) techniques were developed for analysis of chloride, fluoride, sulfate, formate, acetate, and glycolate at the ppb and ppt levels (parts per billion and parts per trillion). In addition to a discussion of the 1C procedures developed, the paper provides a summary of sample collection and conditioning methods and identifies potential interferences. The paper also examines the relationships between conductivity (or its reciprocal, resistivity), acid conductivity and the level of ionic contamination and presents evidence demonstrating that specific analytical techniques such as 1C need to be used in conjunction with conductivity or resistivity monitoring of ultra pure water.