Quantitation of methamphetamine and amphetamine in urine by capillary GC/MS Part II. Derivatization with 4-carbethoxyhexafluorobutyryl chloride.

An analytical procedure for methamphetamine and amphetamine has been developed using 4-carbethoxyhexafluorobutyryl chloride. This derivatizing reagent has all the previously reported advantages of trichloroacetic anhydride (TCAA) in that it produces stable derivatives having both a higher mass fragmentation pattern and lesser volatility than derivatives of trifluoroacetic anhydride (TFAA) or heptafluorobutyric anhydride (HFBA). In addition, the assay uses deuterated internal standards for both methamphetamine and amphetamine. The procedure employs a liquid-liquid extraction and back extraction followed by acylation of the amines to their respective 4-carbethoxyhexafluorobutyramides. Excess derivatizing reagent is converted to the diethyl ester with anhydrous ethanol. At a column temperature of approximately 180 degrees C, the retention times for amphetamine and methamphetamine are 4 min and 5.5 min respectively. The monitored positive ions are: 248, 266, 294 (amphetamine); 270, 298 (amphetamine-d6); 262, 280, 308 (methamphetamine); 287, 315 (methamphetamine-d9). As a result of this high mass fragmentation pattern, which eliminates the 91 and 118 ions as criteria for both identification and quantitation, potential interferences from phentermine and phenethylamine are totally eliminated.