Ultrasensitive determination of heavy metals at the sub-picogram per gram level in ultraclean Antarctic snow samples by inductively coupled plasma sector field mass spectrometry

Assessing changes in heavy metals concentrations in Antarctic snow dated fr om the last century is of high interest to determine to which extent the mo st remote regions of our planet are contaminated for these metals, and to h ave a better understanding into their long-range transport from the differe nt natural and anthropogenic source areas to the Antarctic continent. Such investigations are unfortunately very difficult because the concentrations to be measured are exceedingly low, down to the sub-picogram per gram level . They require a strict control of contamination problems from field sampli ng to laboratory analysis, and the use of ultrasensitive analytical techniq ues. We present here important advances in the analytical protocols for obtainin g reliable data on the occurrence of heavy metals in Antarctic snow. Utmost precautions were taken to obtain a series of large size ultraclean snow bl ocks from the wall of a 8.3 m clean hand-dug pit at a remote site in Coats Land, Antarctica. These blocks were then sub-sampled inside a laminar flow clean bench in a cold room, using ultraclean protocols, to provide high-res olution heavy metal times series. V, Cr, Mn, Cu, Ag, Ba, Pb, Bi and U were then determined directly, without any pre-concentration step, by the ultras ensitive inductively coupled plasma sector field mass spectrometry (ICP-SFM S) technique in clean room conditions. Calibration of the instrument was pe rformed using ultralow concentrations standards, and extreme precautions we re taken to ensure the cleanliness of the instrument and its introduction s ystem. The results show that it is possible to accurately measure a variety of heavy metals in Antarctic snow, down to the sub-picogram per gram level , using this approach. Examples of the data obtained for the Coats Land sit e are finally presented. For U, the observed concentrations range from 0.00 4 to 0.21 pg/g; they are the first data ever obtained for this metal for An tarctic snow and ice. (C) 2001 Elsevier Science B.V All rights reserved.