STABILITY OF MERCURY DILUTE AQUEOUS-SOLUTIONS - AN OPEN ISSUE

In the framework of the activities of the European Commission Referenc e Laboratory (CRL) for residues at the Istituto Superiore di Sanita a number of analytical quality control trials on determination of trace analytes are being carried out. As regards trace elements it soon beca me apparent that the stability of Hg dilute aqueous solutions is rathe r unsatisfactory. An investigation was thus undertaken to ascertain th e conditions under which the concentration of this metal does not appr eciably change. Mercury solutions were prepared in high purity deioniz ed water in the concentration range 1-10 ng g(-1) and the effect of va rious amounts of HNO3 and K2Cr2O7 (alone or in combination) was elucid ated by measuring the variations with time in the actual concentration of Hg. Determinations were performed by both inductively coupled plas ma atomic emission spectrometry and inductively coupled plasma mass sp ectrometry. Results show that solutions added with 5% (w/w) HNO3 and 0 .01% (w/w) K2Cr2O7 do not undergo any significant alteration in the no minal content of the analyte for at least 1 month. Similar conclusions are reached in the case of solutions enriched in CaCO3, NaCl, NaNO3, KH2PO4, KNO3, and Mg(NO3)(2) . 6H(2)O to mimic acid digests of meat sa mples. The improvement ensuing from the adoption of this approach on t he performance of the Hg analytical quality control trials is discusse d in detail. (C) 1996 Academic Press, Inc.