Improved gas chromatography/mass spectrometry analysis of barbiturates in urine using centrifuge-based solid-phase extraction, methylation, with d5-pentobarbital as internal standard.
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.
Liu
R H
RH
Department of Criminal Justice, University of Alabama at Birmingham.
McKeehan
A M
AM
Edwards
C
C
Foster
G
G
Bensley
W D
WD
Langner
J G
JG
Walia
A S
AS
D000654:Amobarbital / Q000652:urine; D001463:Barbiturates / Q000652:urine*; D002138:Calibration; D008401:Gas Chromatography-Mass Spectrometry / Q000379:methods* / Q000592:standards; D006801:Humans; D008745:Methylation; D010424:Pentobarbital / Q000652:urine; D015203:Reproducibility of Results; D012631:Secobarbital / Q000652:urine
D001463:Barbiturates; D012631:Secobarbital; D000654:Amobarbital; D010424:Pentobarbital; C004470:butalbital