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 2-8ngg-1 and 8-30ngg-1, respectively. The precision (CV%) was in the range 10-36% in fresh samples with a total COPs amount from 212 to 645ngg-1 and 6-14% for an oxidized sample with a higher amount (3651ngg-1). The recovery ranged from 74±8% for 7-ketocholesterol to 101±12% for 7α-hydroxycholesterol at 200ngg-1 and from 82±2% for 7-ketocholesterol to 117±10% for 5α,6α-epoxycholesterol at 500ngg-1 spiked levels, respectively.