Determination of sulfates in urban air by pyrolysis-gas chromatography with flame photometric detection

Abstract

An analytical technique has been developed for the determination of sulfates of ammonia (volatile sulfates) in suspended particulate matter (SPM) by pyrolysis-gas chromatography with flame photometric detection (Py-GC/FPD). This method is based on the determination of SO 2 generated by pyrolysis of sulfates, about 30% of which are converted to SO 2 when pyrolysis is performed at 315° C. This technique has several advantages such as small sample size, rapid analysis, simplicity of sample handling and low detection limit (30 ng as sulfur). Atmospheric concentrations of sulfates are measured by Py-GC/FPD and compared with results obtained by ion chromatography (IC). The analytical results of sulfates show a good correlation ( r = 0.920 between Py-GC/FPD and IC. However, the average concentrations of sulfates obtained by PY-GC/FPD are 18% higher than the results of water soluble sulfates (WSS) obtained for daytime samples (7:00–19:00) by IC. In contrast, the concentrations of sulfates in night-time samples (19:00-7:00) obtained by Py-GC/FPD are 12% lower than those of WSS obtained by IC. These analytical results demonstrate that Py-GC/FPD is a useful technique for specific analysis of sulfates of ammonium amongst various types of sulfates. However, a contribution of sulfur-containing components other than sulfates to SO 2 cannot be neglected when Py-GC/FPD is used.