ISSN: 0022-1198
CODEN: JFSCA
Page Count: 11

Improved Gas Chromatography/Mass Spectrometry Analysis of Barbiturates in Urine Using Centrifuge-Based Solid-Phase Extraction, Methylation, with d⁵-Pentobarbital as Internal Standard
McKeehan, AM
Technical director, laboratory staff, quality control supervisor, laboratory staff, laboratory manager, and laboratory director, Environmental Health Research and Testing, Inc., AL

Walia, AS
Technical director, laboratory staff, quality control supervisor, laboratory staff, laboratory manager, and laboratory director, Environmental Health Research and Testing, Inc., AL

Edwards, C
Technical director, laboratory staff, quality control supervisor, laboratory staff, laboratory manager, and laboratory director, Environmental Health Research and Testing, Inc., AL

Foster, G

Langner, JG
Technical director, laboratory staff, quality control supervisor, laboratory staff, laboratory manager, and laboratory director, Environmental Health Research and Testing, Inc., AL

Liu, RH

Bensley, WD
Professor and program director, graduate student, and graduate student, University of Alabama at Birmingham, AL

(Received 2 March 1994; accepted 16 May 1994)

Abstract

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.

Keywords:
toxicology barbiturates, chemical derivatization, drug urinalysis, GC/MS, internal standard, selected ion monitoring, solid-phase extraction

Paper ID: JFS13737J
DOI: 10.1520/JFS13737J
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