Abstract: Taking Solid-Phase Extraction (SPE) as pre-treatment process, a laboratory experiment was conducted by adopting the technology of High Performance Liquid Chromatography-Tandem Mass Spectrometry (HPLCMSMS) to develop a method to determine the concentrations of 13 steroids in feedlot wastewater. Atmospheric Press Chemical ionization (APCI) source was applied and operated in negative ion model, with the parameters of Chromatography and Spectrometry being optimized. Quasi-molecular ion peak ［M+H］⁺ appeared in the full scan of the first quadrupole of mass spectrometer (Q1) of Testosterone propionate and other 6 steroid compounds, while quasi-molecular ion peak ［M+H-H₂O］⁺ appeared in the full scan of Q1 of rest 6 steroid compounds. The linear range of the 9 points calibration curve for the 13 target compounds was determined to be from 1 to 1000 ng·ml^-1, and the calibration curve regression correlation coefficients (R) were always above 0.9990 for all sample batches. The average recovery rate of all target compounds was 83.75%-111.50%, and the methodological stability was determined to be acceptable, with the relative standard deviations between 2.02%-14.21%(n=6). Except that the limit of detection (LOD) of Mestradiol and Oestriol was higher than 15 ng·ml^-1, all the other target compounds had a LOD lower than 5 ng·ml^-1. In the determination of real samples from feedlot wastewater, the developed method represented a good profile to all target compounds at different concentrations in each stage of treatment.

Key words: feedlot wastewater, steroids, HPLC-Tandem Mass, APCI, determination, golden apple snail (Pomacea canaliculata), cold tolerance, seasonal variation, supercooling, sex ratio.