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 heavymetals concentrations in Antarcticsnow dated from the last century is of high interest to determine to which extent the most remote regions of our planet are contaminated for these metals, and to have a better understanding into their long-range transport from the different 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-picogrampergramlevel. They require a strict control of contamination problems from field sampling to laboratory analysis, and the use of ultrasensitive analytical techniques. We present here important advances in the analytical protocols for obtaining reliable data on the occurrence of heavymetals in Antarcticsnow. Utmost precautions were taken to obtain a series of large size ultracleansnow blocks 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-resolution heavymetal times series. V, Cr, Mn, Cu, Ag, Ba, Pb, Bi and U were then determined directly, without any pre-concentration step, by the ultrasensitiveinductivelycoupledplasmasectorfieldmassspectrometry (ICP-SFMS) technique in clean room conditions. Calibration of the instrument was performed using ultralow concentrations standards, and extreme precautions were taken to ensure the cleanliness of the instrument and its introduction system. The results show that it is possible to accurately measure a variety of heavymetals in Antarcticsnow, down to the sub-picogrampergramlevel, using this approach. Examples of the data obtained for the Coats Land site are finally presented. For U, the observed concentrations range from 0.004 to 0.21 pg/g; they are the first data ever obtained for this metal for Antarcticsnow and ice.

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