A simple and reliable method reducing sulfate to sulfide for multiple sulfur isotope analysis

Abstract

RationalePrecise analysis of four sulfur isotopes of sulfate in geological and environmental samples provides the means to extract unique information in wide geological contexts. Reduction of sulfate to sulfide is the first step to access such information. The conventional reduction method suffers from a cumbersome distillation system, long reaction time and large volume of the reducing solution. We present a new and simple method enabling the process of multiple samples at one time with a much reduced volume of reducing solution.MethodsOne mL of reducing solution made of HI and NaH2PO2 was added to a septum glass tube with dry sulfate. The tube was heated at 124°C and the produced H2S was purged with inert gas (He or N2) through gas‐washing tubes and then collected by NaOH solution. The collected H2S was converted into Ag2S by adding AgNO3 solution and the co‐precipitated Ag2O was removed by adding a few drops of concentrated HNO3.ResultsWithin 2–3 h, a 100% yield was observed for samples with 0.2–2.5 μmol Na2SO4. The reduction rate was much slower for BaSO4 and a complete reduction was not observed. International sulfur reference materials, NBS‐127, SO‐5 and SO‐6, were processed with this method, and the measured against accepted δ34S values yielded a linear regression line which had a slope of 0.99 ± 0.01 and a R 2 value of 0.998.ConclusionsThe new methodology is easy to handle and allows us to process multiple samples at a time. It has also demonstrated good reproducibility in terms of H2S yield and for further isotope analysis. It is thus a good alternative to the conventional manual method, especially when processing samples with limited amount of sulfate available.

Homogeneous sulfur isotope signature in East Antarctica and implication for sulfur source shifts through the last glacial-interglacial cycle

“…The DDU samples were processed through chemical conversion into Ag 2 S, as described in Geng et al . 31 , and then into SF 6 in a method similar to that described by Ono et al . 32 , with modification as described by Hattori et al .…”

Synthesis of Sulfur-35-Labeled Trisulfides and GYY-4137 as Donors of Radioactive Hydrogen Sulfide

“…Reduction of Na 2 SO 4 to H 2 S and Trapping H 2 S. The reduction of sulfate to sulfide was adapted from a known literature procedure. 51 Sodium sulfate (Na 2 SO 4 ) (493 mg) was added to a pre-dried Schlenk flask with a PTFE N 2 gas bubbler. The pressure of the gas was at 3 psi, and the Schlenk flask was connected with tygon tubing to five other flasks in sequence.…”

The geochemical riddle of “low-salinity gypsum” deposits

“… 34 S SO4 of gypsum sulfate from the Vena del Gesso basin was measured at IPGP (Paris) on gaseous SF 6 with a MAT-253 dual inlet mass spectrometer. The gypsum powder was first reduced with a "Thode" solution into H 2 S (Thode et al, 1961) that was subsequently trapped in NaOH solution and then precipitated into Ag 2 S by adding a AgNO 3 solution (Geng et al, 2018). The entire extraction procedure gave sulfur yields between 76 and 116% (n=29) with a mean of 95±2% (1σ), with the lowest yields explained by higher amount of non-sulfur bearing mineral phases such as clays.…”