Convenient, inexpensive quantification of elemental sulfur by simultaneous in situ reduction and colorimetric detection

Rapid, inexpensive, and convenient methods for quantifying elemental sulfur (S-0) with low or sub-mu g g(-1) limits of detection would be useful for a range of applications where S-0 can act as a precursor for noxious off-aromas, e.g., S-0 in pesticide residues on winegrapes or as a contaminant in drywall. However, existing quantification methods rely on toxic reagents, expensive and cumbersome equipment, or demonstrate poor selectivity. We have developed and optimized an inexpensive, rapid method (similar to 15 min per sample) for quantifying S-0 in complex matrices. Following dispersion of the sample in PEG-400 and buffering, S-0 is quantitatively reduced to H2S in situ by dithiothreitol and simultaneously quantified by commercially available colorimetric H2S detection tubes. By employing multiple tubes, the method demonstrated linearity from 0.03 to 100 mu g S-0 g(-1) for a 5 g sample (R-2 = 0.994, mean CV = 6.4%), and the methodological detection limit was 0.01 mu g S-0 g(-1). Interferences from sulfite or sulfate were not observed. Mean recovery of an S-0 containing sulfur fungicide in grape macerate was 84.7% with a mean CV of 10.4%. Mean recovery of S-0 in a colloidal sulfur preparation from a drywall matrix was 106.6% with a mean CV of 6.9%. Comparable methodological detection limits, sensitivity, and recoveries were achieved in grape juice, grape macerate and with 1 g drywall samples, indicating that the methodology should be robust across a range of complex matrices. (C) 2011 Elsevier B.V. All rights reserved.