Determination of Total Sulfur and Chlorine in Plant Materials by Ion Chromatography

Abstract

A simple and precise ion chromatographic (IC) method for simultaneous determination of total S and Cl in plant materials has been developed. It involves combustion of a plant sample (20–100 mg) in a Schoniger‐type oxygen flask containing 25 mL of deionized water. The SO^2‐₄ and Cl^‐ formed in the aqueous solution (the S and Cl gases produced are absorbed by water) are determined by using a Dionex Model 10 IC. The IC method is based on separation of the anions by a separator column containing Dionex low‐capacity anion exchange resin in the HCO^‐₃ form and on converting the various anions to their corresponding acids by a suppressor column containing a strong acid cation exchange resin in the H⁺ form. A solution 3.0 mM NaHCO₃ + 1.8 mM Na₂CO₃ is used as the eluent, and electrical conductivity is used as the mode of detection. Results obtained for total S in a variety of plant materials by the IC method agreed closely with those obtained by the methylene blue method after digestion with NaOBr. The average total S values of 15 plant samples by the two methods were 0.255 and 0.259%, respectively. Comparison of the results obtained for Cl by the IC method and by a colorimetric method involving the use of mercuric thiocyanate and ferric ammonium sulfate showed that the averge Cl values for the plant samples were 0.380 and 0.377%, respectively. The recovery of total N and P was not quantitative. A single operator can perform about 40 analyses in a normal working day.