Effects of moisture on the cold vapour determination of mercury and its removal by use of membrane dryer tubes
Continuous-flow vapour generation is now a well-established sample-introduction technique for mercury and the hydride-forming elements. One of the problems associated with this technique is moisture carryover, which originates during the gas–liquid separation process. Excessive moisture carryover causes gradual loss in sensitivity and baseline drift for atomic absorption and atomic fluorescence spectrometry and inductively coupled plasma detection system. Chemical desiccants and physical moisture traps can be used to reduce moisture for short periods of time, although these may give rise to contamination and analyte losses. A more effective way to remove moisture carryover has been found by using a semi-permeable Nafion membrane dryer tube, which continuously desolvates the wet gaseous stream. This device improved the long-term stability and enhanced sensitivity. A relative standard deviation of 2% was achieved for 90 runs of a 1 µg l–1 standard, obtained over a period of 3 h.