Rev. Bras. Ciênc. Solo.2012;36(6):1787-93.

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Isotope determination of sulfur by mass spectrometry in soil samples

Alexssandra Luiza Rodrigues Molina Rossete, Josiane Meire Toloti Carneiro, Carlos Roberto Sant Ana Filho, José Albertino Bendassolli

01/Dec/2012

DOI: 10.1590/S0100-06832012000600012

Sulphur plays an essential role in plants and is one of the main nutrients in several metabolic processes. It has four stable isotopes (³²S, ³³S, ³⁴S, and ³⁶S) with a natural abundance of 95.00, 0.76, 4.22, and 0.014 in atom %, respectively. A method for isotopic determination of S by isotope-ratio mass spectrometry (IRMS) in soil samples is proposed. The procedure involves the oxidation of organic S to sulphate (S-SO₄^2-), which was determined by dry combustion with alkaline oxidizing agents. The total S-SO₄^2- concentration was determined by turbidimetry and the results showed that the conversion process was adequate. To produce gaseous SO₂ gas, BaSO₄ was thermally decomposed in a vacuum system at 900 ºC in the presence of NaPO₃. The isotope determination of S (atom % ³⁴S atoms) was carried out by isotope ratio mass spectrometry (IRMS). In this work, the labeled material (K₂³⁴SO₄) was used to validate the method of isotopic determination of S; the results were precise and accurate, showing the viability of the proposed method.