PROCEDURE FOR THE DETERMINATION OF 8 CHOLESTEROL OXIDES IN POULTRY MEAT USING ON-COLUMN AND SOLVENT VENTING CAPILLARY GAS-CHROMATOGRAPHY

A procedure for the determination of eight relevant cholesterol oxides in poultry meat has been developed. The method consists of the enrich ment of cholesterol oxides by means of the combined use of solid-phase fractionation and thin-layer chromatography. Florisil and silica colu mns of 10 g permitted the handling of the total cholesterol oxides con tent included in the lipid bulk obtained after the Folch's extraction of 20 g of muscle meat. The determination of cholesterol oxides under their trimethylsilyl derivatives was performed by using capillary gas chromatography. The use of a fused-silica open tubular capillary colum n 30 m x 0.25 mm I.D. coated with 5% phenylmethylsilicone and with a f ilm width of 0.25 mu m permitted the separation of all the species. Tw o modes of injection (on-column and solvent venting) were evaluated an d compared for the analysis of cholesterol oxides. On-column capillary gas chromatography (cGC) gave better absolute areas relative standard deviation (R.S.D.) values: 3% to 6% vs. 5% to 7% for solvent venting cGC. Regression analysis for each cholesterol oxide was performed for the two modes of injection. The possibility of large volume injection (10 mu l) by using the solvent venting mode was also evaluated in orde r to increase the sensitivity of the detection of cholesterol oxides. R.S.D. values for absolute areas ranging from 6% to 14% were obtained. The validation of the method was carried out within the range of 0.1- 1 ppm. Absolute and relative recovery values ranging from 80% to 100% were obtained, Statistical analysis revealed that the method was repro ducible. cGC-mass spectrometry was also used to confirm the peaks dete cted by cGC: the total ion chromatogram mode was used for the analysis of samples containing concentrations down to 0.1 ppm of cholesterol o xides. The analysis of fresh and cooked chicken meat revealed the pres ence of cholesterol oxides proceeding from the autoxidation of the cho lesterol B-ring. Finally, saponification was found to be not as accura te as the described procedure for cholesterol oxides analysis.