Single superphosphate is currently one of the mostly used fertilizers as an alternative source for phosphorus and sulphur. Sulphur presents four stable isotopes (32S, 33S, 34S, and 36S) with natural abundances of 95.00; 0.76; 4.22; and 0.014% in atoms, respectively. Single superphosphate labeled with the 34S isotope was obtained from a chemical reaction in stoichiometric amounts between Ca(H2PO4)2 and Ca34SO4.2H2O. Calcium sulphate (Ca34SO4.2H2O) was enriched with 5.85 ± 0.01 atoms % of 34S. The Ca(H2PO4)2 reagent was obtained from a reaction between CaCl2.2H2O and H3PO4. The reaction between the Ca(H2PO4)2 thus produced and the labeled Ca34SO4.2H2O compound was then performed to obtain the 34S-labeled single surperphosphate. The thermal decomposition of the labeled superphosphate for the production of gaseous 34SO2 was carried out under a vacuum line at 900ºC in the presence of NaPO3. The isotopic determination of S (atoms % of 34S) was carried out on an ATLAS-MAT model CH-4 mass spectrometer. The production yield of Ca(H2PO4)2 and labeled single superphosphate were approximately 97 and 99% respectively, and the purity level of the labeled single superphosphate was estimated as 96%. No isotopic fractionation was observed in the production process of 34S-labeled single superphosphate.
isotopic determinations; sulphur; stable isotopes; mass spectrometry; labeled compounds
