Routine analysis of ultra pure water by ICP-MS in the low- and sub-ng/L level.

The chemical analysis with inductively coupled plasma-mass spectrometry (ICP-MS) can help to examine the purity of ultra pure water (UPW) down to 10 part per trillion (ng/L) and lower. For a proper determination of a high number of samples per week the analysis must be divided into two parts: the routine analysis and the reference water analysis. The routine analysis is done by direct measurement of the ultra pure water samples. Applying a standard addition method under particular clean conditions, the reference water analysis leads to the definition of the accurate zero. A quick evaluation scheme is also presented for the reference water analysis. The method is tested for its fitness for application by examining LOD (for relevant element < 2 ng/L), reproducibility and linearity of calibration. The ICP-MS was optimized according to the methodology of G. Taguchi to improve reproducibility and LOD.