Limitations to the use of solid-phase microextraction for quantitation of mixtures of volatile organic sulfur compounds

A study of the range of volatile organic sulfur compounds produced by brass ica plants has highlighted limitations to the use of Carboxen/PDMS fibers f or their analysis by solid-phase microextraction (SPME), These fibers are s ometimes advocated for the analysis of sulfur gases, but a quantitative com parison of analytical data derived by SPME and by direct gas sampling of st andard mixtures of volatile low molecular weight sulfur compounds at 0.01-1 0 mg/L has identified potential errors associated with their use. Higher mo lecular compounds displace lower molecular weight compounds as a consequenc e of competition for active sites on the fiber, and the relative proportion s of the components adsorbed onto the fiber depend on their ratio in the he adspace, As their relative concentrations change from sample to sample, the varying interactions result in irregular analytical responses, reflected i n erratic calibration curves. Standards containing single components are no t valid; only a standard containing all components found in the sample to b e analyzed, and at the same relative concentrations, is appropriate. In pra ctice, this may preclude the use of the fibers for quantitative analysis of multicomponent mixtures.