DETERMINATION OF STEROLS IN SEWAGE-SLUDGE BY COMBINED IN-SITU TRIMETHYLSILYLATION/SUPERCRITICAL FLUID EXTRACTION AND GC/MS

Sterols were quantitatively extracted from freeze-dried sewage sludges with high (60-80%) organic matter contents by simultaneous supercritical fluid extraction and BSTFA derivatization. The sterol trimethylsilyl derivatives were finally analyzed by capillary GC/MS. This protocol yielded similar results but was more rapid than the U.S. EPA method of ultrasonic extraction with a (1:1) methylene chloride/acetone mixture, followed by trimethylsilylation acid GC/MS. Sample preparation by combined TMS/SFE and quantitative analysis by GC/MS were applied to the determination of several free sterols in sewage sludges from four different origins. Coprostanol, a fecal sterol, was present in all municipal wastewater digested sludges at the highest concentration, ranging from 2.28 to 4.05 mg/g, and accounted for 38-62% of the total detected sterols.