New approach to derivatisation for oestradiol esters detection in animal blood plasma using negative chemical ionisation GC-MS.

In 1996, the EU prohibited the use of substances with anabolic action for food-producing animals (EU Directive 96/22/EC). In cases of illegal use of steroid hormones, these substances are usually applied to the animals in the form of esters. The reliable determination of intact steroid esters in animal tissues or body fluids is an unequivocal proof of illegal treatment of animals with EU prohibited anabolic substances. Previously our laboratory developed a sensitive method for determination of oestradiol benzoate and other steroid esters in blood plasma using LC-MS/MS, validated according to Commission Decision 2002/657/EC. This study describes a GC-MS method which has been developed for five oestradiol esters in blood plasma. The sample preparation procedure consisted of protein precipitation, phospholipids removal and cleaning on an alumina column. Oestradiol esters were derivatised with 2, 3, 4, 5, 6-pentafluorobenzoyl chloride (PFBCl) and pyridine in dichloromethane. The measurement of oestradiol esters was carried out by GC-MS/NCI with Cool On-Column injection. Methane was used as a negative chemical ionisation reagent gas. The method for determination of oestradiol esters in blood plasma has been validated according to Commission Decision 2002/657/EC. Decision limits for all analytes were observed below 0.05 ng mL-1. The method is robust for bovine and porcine plasma analyses and can be applied both for screening and confirmatory determination in routine residue monitoring.