Improved Gas Chromatography/Mass Spectrometry Analysis of Barbiturates in Urine Using Centrifuge-Based Solid-Phase Extraction, Methylation, with d

• Published in: Journal of forensic sciences 1994-11, Vol.39 (6), p.1504-1514
• Main Authors: Liu, RH, McKeehan, AM, Edwards, C, Foster, G, Bensley, WD, Langner, JG, Walia, AS
• Format: Article
• Language: English
• ISSN: 0022-1198; 1556-4029
• DOI: 10.1520/JFS13737J

Effective solid-phase extraction, derivatization, and GC/MS procedures are developed for the simultaneous determinations of butalbital, amobarbital, pentobarbital, and secobarbital, using a deuterated pentobarbital (d5-pentobarbital) as the internal standard. Buffered (pH 7) urine samples were extracted with Bond Elute Certify II™ cartridge. Iodomethane/ tetramethylammonium hydroxide in dimethylsulfoxide was used for methylation, while a HP 5970 MSD equipped with a 13 m J & W DB-5 column (5% phenyl polysiloxane phase) and the Thru-Put Target® software package were used for GC/MS analysis and data processing. This protocol was found to be superior, in both chromatographic performance characteristics and quantitation results, over a liquid-liquid extraction procedure without derivatization using hexobarbital as the internal standard. Extraction recoveries observed from control samples containing four barbiturates range from 80% to 90%. Good one-point calibration data are obtained for all four barbiturates in the 50 to 3200 ng/mL range. Interestingly, the one-point calibration data for pentobarbital are inferior to the other three barbiturates-due to interference from the internal standard (d5-pentobarbital). The calibration data of pentobarbital are best described by a hyperbolic curve regression model. Precision data (% CV) for GC/MS analysis, over-all procedure, and day-to-day performance are approximately 2.0%, 6.0%, and 8.0%, respectively. With the use of a 2 mL sample size, the attainable detection limit is approximately 20 ng/mL.