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Published:
Journal of Analytical Toxicology,
ISSN 0146-4760,
Volume 24,
Number 8, November/December,
pp. 685-690
Analysis of Six
Anticonvulsant Drugs using Solid-Phase Extraction, Deuterated Internal Standards,
and Gas Chromatography–Mass Spectrometry
D.J. Speed1,*,
S.J. Dickson2, E.R. Cairns3, and N.D. Kim1
1Chemistry Department, University of Waikato, Private Bag, Hillcrest, Hamilton,
New Zealand; 2ESR, Kenepuru Science Centre, P.O. Box 50348, Porirua, New Zealand;
and 3AgriQuality New Zealand Ltd, National Chemical Residue Laboratory, P.O. Box
40063, Upper Hutt, New Zealand
A
rapid method for simultaneously determining the anticonvulsant drugs carbamazepine,
ethosuximide, phenobarbitone, phenytoin, primidone, and valproic acid is described.
Blank plus single-point calibration gives reliable quantitation from therapeutic
to high fatal concentrations, except for ethosuximide, for which it gives semiquantitative
results. Whole blood and liver tissue samples containing deuterated internal
standards were extracted using Bond Elut Certify columns. Butyl derivatives
were formed using n-iodobutane and TMAH under mild conditions and were extracted
into ethyl acetate as a cleanup step. Recoveries were greater than 50%, except
for valproic acid (42%). Sample preparation time was less than 2 h, and the
GC run time was less than 20 min per injection. At least two ion pairs formed
by electron impact ionization were monitored for each drug. Intraday CVs were
less than 6.28% (4.20%) and interday CVs less than 14.1% (for midtherapeutic
concentrations in blood [liver], except for ethosuximide). Linearity was observed
from subtherapeutic to high fatal levels for all drugs. This method has been
applied to forensic cases and has significantly reduced analytical time while
improving case-work quality. Results of a case study involving anticonvulsant
drugs are given. Reproduction
of editorial content of this journal is prohibited without publisher’s
permission.
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