Quantitation of methamphetamine and amphetamine in urine by capillary GC/MS. Part I. Advantages of trichloroacetyl derivatization.

A urine assay for methamphetamine and amphetamine that is compatible with our existing high-volume GC/MS assays for other drugs of abuse has been developed. Trichloroacetic anhydride is used for derivatization and its derivative is substantially less volatile than other commonly used derivatives. The internal standard is the primary amine 2-methylphenethylamine. The procedure utilizes an initial liquid-liquid extraction, a liquid-liquid back extraction for specimen cleanup, and derivatization for removal of excess trichloroacetic anhydride and acid by-product. A GC temperature of about 180 degrees C results in retention times of approximately 2.8, 3.2, and 4.3 min for amphetamine, the internal standard, and methamphetamine, respectively. Five ions are monitored: 91+, 118+, 188+ for amphetamine; 105+, 118+ for 2-methylphenethylamine; and 91+, 118+, 202+ for methamphetamine. Full scan GC/MS data from a variety of other derivatives are examined and used to illustrate the advantages of derivatizing molecules with strongly electronegative atoms near the reaction site. This situation forces fragmentation patterns in which positive charges are located on larger and structurally acceptable identifying mass fragments of the original methamphetamine or amphetamine molecule.