QUANTITATIVE-DETERMINATION OF TOTAL SULFUR IN PLANT-TISSUES USING ACID DIGESTION AND ION-CHROMATOGRAPHY

Total sulfur determination in plant material can be done either by expensive and sophisticated equipment such as an inductively coupled plasma atomic emission spectrophotometer (ICP-AES), or tedious and time consuming procedures like the Johnson and Nishita or oxygen combustion method, or by S-auto-analyzers. Since ion-chromatography has demonstrated versatility in inorganic ion analysis, it was adopted in this paper to measure SO4 in wet acid digests of plant materials. Plant tissues (200 mg) were digested with 2 mL HNO3 + 1 mL 70% HClO4 and subsequently evaporated to dryness in order to minimize the HClO4 concentration for efficient ion-chromatography. Magnesium oxide was dissolved in HNO3 at a rate of 1.25 g L-1 to provide cations to prevent the losses of S gases. Dionex OmniPac PAX-500 analytical column was used to provide simultaneous anion exchange and reverse-phase ion-chromatography. Using 25 mM NaOH in 45% acetonitrile as eluent at a rate of 0.8 mL min-1, the analysis time was 10 min/sample. A complete recovery of total S from plant materials and with sulfur added as cysteine, methionine, glutathione, and sulfate is demonstrated. The method is simple, accurate, reproducible, and can be automated.