Ultrapure Water for Elemental Analysis Down to ppt Levels

Abstract

Recent enhancements in modern analytical instrumentation have dramatically improved the sensitivity of analysis. Trace elements are now measured at ppt and sub-ppt levels. These levels can be achieved if careful control of the analytical protocol is maintained. Contamination can result from anything that comes into contact with the sample; the laboratory environment, the air, and anything used during sample preparation. Limits of detection down to ppt levels can be achieved if special care is taken with the experimental environment as well as with the quality of the reagents. This includes the ultrapure water used to run blanks, dilute samples or prepare standards. Part of this paper looks at the most sensitive multi-elemental analytical tool, i.e. inductively coupled plasma mass spectrometry (ICP-MS). Some of the most common causes of interference will be reviewed, as well as ways of reducing this interference by specific instrument developments and particular care taken during inductively coupled plasma mass spectrometry analysis. Sub-ppt values for limits of quantification are achievable when the ultrapure water used is produced by a system for which all parts have been carefully selected and whose configuration has been specifically developed for ultratrace purposes. This specific water purification system is described and typical values that can be achieved for blanks with inductively coupled plasma mass spectrometry technology are shown.

Subnanomolar Detection Limit of Stripping Voltammetric Ca2+-Selective Electrode: Effects of Analyte Charge and Sample Contamination

“…Moreover, the presence of subnanomolar Ca 2+ in ultrapure water is undetectable by measuring its resistivity (18.2 MΩ·cm at 25 °C), which is determined by 10 –7 M of H + and OH – . In addition, the detection of trace Ca 2+ by ICPMS is challenging owing to 40 Ar interference …”