Pitfalls in trimethylsilylation of anabolic steroids. New derivatisation approach for residue at ultra-trace level.

Mixtures such as N-methyl-N-trimethylsilyl-trifluoroacetamide (MSTFA), ammonium iodide and dithioerythreitol (DTE) or MSTFA, trimethyliodosilane and DTE were used for derivatisation of anabolic steroids extracted from 2 g kidney fat and present at ng kg(-1) level. They are leading to unexpected products. Their identity and mechanism of formation have been discussed. A new silylation mixture was developed to overcome these pitfalls: N,O-bis-trimethylsilyl-acetamide was used in combination of 2.5% of MSTFA/I(2) (1000:10 (v/w)). A single product consisting in ether-TMS and/or enol-TMS derivative was observed for all tested steroids with a stability demonstrated for at least 48 h. Quantitative application was proved even at the low ng kg(-1) level in a complex biological matrices, i.e. kidney fat.