Rapid determination of cholesterol oxidation products in milk powder based products by reversed phase SPE and HPLC-APCI-MS/MS

A rapid and sensitive HPLC-APCI-MS/MS method for the determination of cholesterol oxidation products (COPs) in milk powder based foods is reported. The method consists in the direct saponification of the sample and purification of oxysterols by reversed phase C18-SPE followed by HPLC-MS/MS analysis. By this procedure, the extraction and enrichment of oxysterols are combined in a unique step, reducing sample manipulation and the possible formation of artifacts. LOD and LOQ were in the concentration ranges of 2–8 ng g1 and 8–30 ng g1, respectively. The precision (CV%) was in the range 10–36% in fresh samples with a total COPs amount from 212 to 645 ng g1 and 6–14% for an oxidized sample with a higher amount (3651 ng g1). The recovery ranged from 74 ± 8% for 7-ketocholesterol to 101 ± 12% for 7ahydroxycholesterol at 200 ng g1 and from 82 ± 2% for 7-ketocholesterol to 117 ± 10% for 5a,6a-epoxy cholesterol at 500 ng g1 spiked levels, respectively.