CONTINUOUS-FLOW DETERMINATION OF AQUEOUS SULFUR BY ATMOSPHERIC-PRESSURE HELIUM MICROWAVE-INDUCED PLASMA-ATOMIC EMISSION-SPECTROMETRY WITH GAS-PHASE SAMPLE INTRODUCTION

A simple continuous-flow generation of volatile hydrogen sulfide and s ulfur dioxide by acidification of aqueous sulfide and sulfite ions, re spectively, is described for the determination of low concentrations o f sulfur by atmospheric-pressure helium microwave-induced plasma atomi c emission spectrometry (MIP-AES) in the normal ultraviolet (UV) and v acuum ultraviolet (VUV) regions of the spectrum. For measuring spectra l lines in the WV region, the monochromator and the enclosed external optical path between the MIP source and the entrance slit of the monoc hromator have both been purged with nitrogen to minimize oxygen absorp tion below 190 nm. Sulfur atomic emission lines at 180.73, 182.04 and 217.05 nm have been selected as the analytical lines. Of the various a cids examined, 1.0 M hydrochloric acid is the most favorable for both the generation of hydrogen sulfide from sulfide ions and sulfur dioxid e from sulfite ions. Either. generated hydrogen sulfide or sulfur diox ide is separated from the solution in a simple gas-liquid separator an d swept into the helium stream of a microwave-induced plasma for analy sis. The best attainable detection limits (3 sigma criterion) for sulf ur at 180.73 nm were 0.13 and 1.28 ng ml(-1) for the generation of hyd rogen sulfide and sulfur dioxide, respectively, with the Corresponding background equivalent concentrations of 20.9 and 62.2 ng ml(-1) in su lfur concentration, The typical analytical working graphs obtained und er the optimized experimental conditions were rectilinear over approxi mately four orders of magnitude in sulfur concentration. The present m ethod has been successfully applied to the recovery test of the sulfid e spiked to waste water samples and to the determination of sulfite in some samples of commercially available wine.