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.

Keywords: Copper; Hydrogen sulfide; Mercaptans; Metal-complex; Off-odors; Reduction.