A study of techniques for the preservation of mercury and other trace elements in water for analysis by inductively coupled plasma mass spectrometry (ICP-MS)

Abstract

The storage of aqueous solutions in high density polyethylene (HDPE) bottles containing nitric acid (0.15 to 2.0% (v/v) was shown to be unsuitable for the preservation of dissolved mercury (Hg²⁺) either as a single element or as part of a multi-element solution. At concentrations ranging from 0.05 to 10.0 ug l⁻¹ more than 10% of the dissolved mercury was lost within the first three days and up to 50% of the mercury was lost within nine days after solutions were prepared. However mercury was stable in the presence of hydrochloric acid (HCl) or sodium chloride (NaCl). Solutions of either 40 mg l⁻¹NaCl in 0.15% (v/v) nitric acid (HNO₃) or 0.01% (v/v) HCl in 1% (v/v) HNO₃ were found to be effective for preserving mercury for more than 50 days. The stabilising mechanism is most likely the formation of HgCl₄²⁻ complex ions that prevent the adsorption of mercury on the inner walls of the HDPE container. The elements Al, Ag, As, Ba, B, Cd, Cr, Co, Cu, Mn, Mo, Ni, Pb, Sb, Se, Tl, V and Zn were stable up to 12 months when preserved in 1.0 to 2.0% (v/v) nitric acid or a mixture of 1% (v/v) HNO₃ plus 0.01% (v/v) HCl. The recommended acid combination for the preservation of mercury and multi-elements for the simultaneous determination by ICP-MS is 1% (v/v) HNO₃ plus 0.01% (v/v) HCl. Chloride related polyatomic interferences in ICP-MS determination from this acid mixture were less than 0.1 ugl⁻¹ for all elements investigated, making it an ideal preservation medium for ICP-MS analysis.