Isotope determination of sulfur by mass spectrometry in soil samples

• Main Authors: Alexssandra Luiza Rodrigues Molina Rossete, Josiane Meire Toloti Carneiro, Carlos Roberto Sant Ana Filho, José Albertino Bendassolli
• Format: Article
• Language: English
• Published: Sociedade Brasileira de Ciência do Solo 2012-12-01
• Series: Revista Brasileira de Ciência do Solo
• Subjects: preparo de amostras; amostras de solo; diluição isotópica; isótopos estáveis; 34S
• Online Access: http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-06832012000600012&lng=en&tlng=en
• ISSN: 1806-9657

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 (K2(34)SO4) was used to validate the method of isotopic determination of S; the results were precise and accurate, showing the viability of the proposed method.