DETERMINATION OF CARBONYL SULFIDE AND HYDROGEN-SULFIDE SPECIES IN NATURAL-WATERS USING SPECIALIZED COLLECTION PROCEDURES AND GAS-CHROMATOGRAPHY WITH FLAME PHOTOMETRIC DETECTION

Hydrogen sulfide in natural waters can be found as dissolved uncomplexed species (i.e., ''free sulfide'', H2Saq + HS- + S2-), as dissolved metal sulfide complexes (''complexed sulfide''), and as particulate metal sulfides. To examine the distribution of hydrogen sulfide species and carbonyl sulfide in natural waters, a technique for their sampling and simultaneous determination was developed. Contamination and loss are minimized by using trace metal-clean and hermetic sampling techniques and apparatus. The analytical method is based on stripping an acidified 1-300-mL sample with helium, liquid nitrogen-cooled trapping of the evolved gases followed by gas chromatographic separation and flame photometric detection. To eliminate storage artifacts determinations are made in the field immediately after sample collection. Detection limits are 0.2 pmol/L for total dissolved sulfide and 1.3 pmol/L for OCS. Precision is better than 5 % (relative standard deviation) for both sulfur compounds at the 50 pmol/L level. The method can also determine hydrogen sulfide in the headspace of a sample (H2Sg); this concentration can in turn be used to calculate the concentration of free sulfide that is in equilibrium with H2Sg. In combination with selective chemical treatments, the method can also be applied to the determination of acid-volatile sulfide and chromium-reducible sulfur in suspended particles. The procedures have been used to analyze a variety of natural water and sediment samples.