Precise determination of sulfur isotopic ratio in aqueous solutions by inductively coupled plasma mass spectrometry

Abstract

Analytical procedures for complete separation of SO₄²⁻ in aqueous solutions and precise sulfur isotopic ratio determination using inductively coupled plasma double focusing sector field mass spectrometry (ICP-SMS) operated at low resolution (m/Δm = 300) were developed. A platinum guard electrode and an Aridus sample delivering apparatus were combined to reduce ¹⁶O¹⁶O⁺ interferences at m/z 32 and to enhance analytical sensitivity. A precision of better than 0.1% for successive measurements of seawater and IAPSO was achieved with 2–5 μl aqueous solutions in less than a minute of measurement time. The sulfate concentrations measured in rains, seawater and pore waters agree well with those obtained by ion chromatography. The downcore δ³⁴S variations in porewater at Site 1202 are greater than 50‰, highlighting the effects of sulfate reduction. The sulfur isotopic compositions in rains and seawater samples reflect sensitively the source and oxidation/reduction conditions.