Methods for Verification of Low Parts-per-Trillion Sodium Determination by On-Line ISE-Based Sodium Monitors

摘要

As needs and capabilities for the production of ultra-pure water advance,the analysis technology for determining contaminant levels is continuously challenged to keep pace.In water used for steam generation,maintaining the lowest possible levels of sodium ion is of great importance for the prevention of damage to turbine blades.Today,sodium levels in water and steam are being pushed lower and lower,making validation of readings from on-line analyzers increasingly difficult.In this paper,we compare two methods of validating on-line,ion-selective electrode-based analyzer performance at low ng centre dot kg~(-1)(low parts-per-trillion,ppt)sodium concentrations.Dynamic dilution and recovery and grab sample analysis by inductively coupled plasma mass spectrometry are applied to analyses by a recently introduced sodium monitor and to an existing monitor provided by another manufacturer.Verification studies in the range of 1 000 ng centre dot kg~(-1)down to less than 10 ng centre dot kg~(-1)are described.Results of this study and discussion of analyzer design features that enable such low-level analysis are presented,and techniques available to plant operators for on-site verification of low-level chemical analyzers are discussed.