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-μgg^-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 (∼15min 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 100μgS⁰g^-1 for a 5g sample (R²=0.994, mean CV=6.4%), and the methodological detection limit was 0.01μgS⁰g^-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 1g drywall samples, indicating that the methodology should be robust across a range of complex matrices.