Determination of mercury isotope ratios in samples containing sub-nanogram amounts of mercury using inductively coupled plasma mass spectrometry

Abstract

The determination of sub-nanogram amounts of mercury demands systems of high sensitivity. To determine isotopic ratios a large signal is required to obtain a high number of counted ions. It was found that the precision in the isotope ratio determination in samples containing less than 300 pg of mercury is limited by the counting statistics. With 300 pg of mercury the precision was 0.2%(relative standard deviation) in the ²⁰²Hg: ¹⁹⁹Hg ratio. The detection limit was lowered by concentration of mercury vapour on gold traps, and the sensitivity of the instrument was increased 4–6-fold by addition of nitrogen or hydrogen to the central gas flow.