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

Rapid, inexpensive, and convenient methods for quantifying elemental sulfur (S0) with low or sub-μg g−1 limits of detection would be useful for a range of applications where S0 can act as a precursor for noxious off-aromas, e.g., S0 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 (∼15 min per sample) for quantifying S0 in complex matrices. Following dispersion of the sample in PEG-400 and buffering, S0 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 μg S0 g−1 for a 5 g sample (R2 = 0.994, mean CV = 6.4%), and the methodological detection limit was 0.01 μg S0 g−1. Interferences from sulfite or sulfate were not observed. Mean recovery of an S0 containing sulfur fungicide in grape macerate was 84.7% with a mean CV of 10.4%. Mean recovery of S0 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.

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► An inexpensive and convenient approach for quantifying elemental sulfur was developed.
► Sulfur is converted to hydrogen sulfide and quantified by a sulfide detection tube.
► Detection thresholds are comparable to the best existing methods.
► The method has good recovery and linearity across complex matrices.
► The method should be appropriate for both field and laboratory applications.