Clinical Research Squadron, Wilford Hall Medical Center, Lackland AFB, TX 78236-5319, USA

Clobenzorex was monitored by acquiring four prominent ions in the mass spectrum at m/z 91, 118, 125 and 364. All 4 ions were evaluated to assess the best 3 ions to select for routine monitoring. Interference was occasionally seen at m/z 91 and/or m/z 118 but in most cases, particularly at low concentrations, either ion gave acceptable results. HP-1 and DB-17 capillary columns were used to ensure elimination of interference from related amines.

Several attempts were made to quantitate clobenzorex using either methamphetamine-d11, fenfluramine, benzphetamine or diphenylamine as internal standard. Results using these internal standards proved to be unacceptable due to poor accuracy and reproducibility of the quantitative results (>20% of target levels). The compound, 3-Chlorobenzyl-amphetamine (3-Cl-clobenzorex) was synthesized in our lab and evaluated in this study for the quantitation of clobenzorex. This 3-chloro analog of clobenzorex was selected for its anticipated similar behavior in the extraction and derivatization to the compound of interest. The compound proved to behave as predicted and was chromatographically separated from clobenzorex.

Using a calibrator at 25 ng/mL, the limit of detection (LOD) was determined to be 1 ng/mL, the limit of quantitation (LOQ) was 5 ng/mL and the linear range from 5 to 100 ng/mL. When using a calibrator at 10 ng/mL, the LOD and LOQ were 1 ng/mL and the linear range was shown to be 1 to 25 ng/mL. All characteristics (variability, accuracy, etc.) were determined using 3-Cl-clobenzorex as the internal standard. Precision studies showed 3-Cl-clobenzorex to produce accurate and reliable quantitative results (within-run RSD < 6.1%, between-run RSD < 6.0%).