Gas chromatographic-sulfur chemiluminescent detector procedures for the simultaneous determination of free forms of volatile sulfur compounds including sulfur dioxide and for the determination of their metal-complexed forms

Abstract

Three different procedures for the quantitative assessment of free and metal complexed volatile sulfur compounds (VSCs) and for the determination of truly free SO2 have been developed, taking advantage of a GC-sulfur chemiluminescent detector system (GC-SCD) with cryotrapping. The inertness of the inlet systems, together with the column used (SPB-1 sulfur) makes it possible to obtain a non-saturated perfectly Gaussian peak for SO2, well resolved from H2S. In the main procedure, the injection of 1 mL of the headspace of a sample prepared in complete anoxia and equilibrated at 30 °C makes it possible to get highly sensitive signals for all VSCs and free SO2. Detection limits are 3, 35 and 60 ng/L for H2S, MeSH and EtSH, 13 μg/L for truly free SO2 (at pH = 3.4, or 0.46 μg/L for molecular SO2), and better than 1 μg/L for other relevant sulfur volatiles. Method precision is also satisfactory and linearity covers the whole range of occurrence of these compounds. A second procedure, not making use of the cryotrapping unit, gives also satisfactory results, although with higher detection limits (0.03, 0.25 and 0.37 μg/L for free H2S, MeSH and EtSH, respectively). For the analysis of free plus metal-complexed forms, it has been demonstrated that the headspace injection of the vapors on a 1:10 brine dilution of the sample heated at 70 °C for 25 min, gives good estimates of the free + metal-complexed forms of H2S and wine mercaptans.