A GC-MS method suitable to conduct practical trace toxicological analyses of various opiates including hydrocodone or hydromorphone is presented both in scan and selected ion monitoring modes. Silylation can be a convenient reaction to derivatize unknown analytes in toxicological samples. However, silylation of drugs with tautomeric keto/enol groups in molecular structure can cause analytical problems due to poor reproducibility of conversion degree. After using N-Methyl-N-trimethyl-silyltrifluoracetamide (MSTFA) acceptable results were achieved.

        Key words: GC-MS toxicological analyses, silylderivatives, hydrocodone, hydromorphone