Isotopic fractionation of mercury induced by reduction and ethylation.

Isotope ratio measurements characterizing (202)Hg/(200)Hg in NIST SRM 3133 Mercury Standard Solution were undertaken by multicollector inductively coupled plasma mass spectrometry employing NIST SRM 997 Tl for mass bias correction by use of the slope and the intercept obtained from a natural logarithmic plot of each session of measurements of (202)Hg/(200)Hg against (205)Tl/(203)Tl. The calculated value of 1.285333 +/- 0.000192 (mean and one standard deviation, n = 40) for the mass bias corrected (202)Hg/(200)Hg was then used for mass bias correction of other Hg isotope pairs. Ratios of 0.015337 +/- 0.000011, 1.68770 +/- 0.00054, 2.3056 +/- 0.0015, 1.3129 +/- 0.0013, 2.9634 +/- 0.0038, and 0.67937 +/- 0.0013 (expanded uncertainty, k = 2) were obtained for (196)Hg/(198)Hg, (199)Hg/(198)Hg, (200)Hg/(198)Hg, (201)Hg/(198)Hg, (202)Hg/(198)Hg, and (204)Hg/(198)Hg, respectively. Reduction of Hg(II) to Hg(0) in solutions of SRM 3133 was then undertaken using SnCl(2), NaBH(4), UV photolysis in the presence of formic acid, and ethylation of Hg(II) using NaBEt(4.) These reactions induced significant isotope fractionation with maximum values of 1.17 +/- 0.07, 1.08 +/- 0.09, 1.34 +/- 0.07, and 3.59 +/- 0.09 per thousand (one standard deviation, 1SD, n = 5) for delta (202/198)Hg relative to the initial isotopic composition in the solution following 85-90% reduction of the Hg by SnCl(2), NaBH(4), UV photolysis, and ethylation with NaBEt(4), respectively. Mass-dependent fractionation was found to be dominant for all reduction processes.