Abstract: A quick confirmative method was developed for determining the residues of 17 glucocorticoids, 11 progesterones, 3 androgens and 8 estrogens in infant formula by liquid chromatography-tandem quadrupole mass spectrometry (LC-MS/MS). The sample was extracted with acetonitrile at first. Then the lipid substances were removed by centrifugation under freezing condition and liquid-liquid extraction with hexane of the extract. The purification was carried out on hydrophilic-lipophilic solid-phase extraction columns and methanol was used as the eluted solvent. The detection of 39 analytes was carried out in the positive or negative multi-reaction monitoring (MRM) mode, separately. Acetonitrile-0.1% formic acid was used as the mobile phase and an ordinary silica gel C18 column was selected to separate the analytes in the positive mode. Acetonitrile-0.1% aqueous ammonia as mobile phase and the separation was carried out on an ultra-performance C18 column with a wide pH range in the negative mode. The limits of quantification (LOQ, S/N≥10) were 0.02~5 μg/kg. The overall recoveries varied from 59.5% to 117.9%, and the relative standard deviations (RSD) were between 6.4% and 16.3%. The real sample tests showed that the simple and accurate method can be used for determining the residues of multi-endogenous and chemically synthesized hormones in milk powders.

Key words: frozen delipidation, hormones, infant formula, solid-phase extraction (SPE), liquid chromatography-tandem mass spectrometry (LC-MS/MS)