Development of a Mercury Vapour Air Analyser for Measurement of Hg in Solution

The Tekran 2537A mercury vapour analyser, designed to measure Hg in air by cold vapour atomic fluorescence spectrometry, has been modified to determine Hg in solution. The new ‘front-end’, required to generate Hg° vapour from acidified waters or acid leachates, is described. Using 1% NaBH4 as reducing agent, a 12 mL water sample can be analysed, at a rate of 1 every 6 min, for Hg to a detection limit of 0.8 ppt (ng L-1). Instrumental precision is typically 1% relative standard deviation (RSD) at levels of Hg from 10 to 200 ppt. Results for 10 analyses of the international water standard, NIST 1642b, are 1530±20 ppt Hg, agreeing well with the certified value of 1480±130 ppt. Nineteen geological standard reference materials (soils, sediments and tills) were used to assess accuracy. Results for these samples, digested in aqua regia in triplicate, showed good agreement with recommended values for all but two, SO-3 and TILL-1. However, results by this method for these two standards were confirmed by an independent method, direct atomic absorption spectrometry. Average method precision was shown to be 5% RSD over the range 10 ng g- 1 to 35 μg g-1 Hg.