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Published:
Journal of Analytical Toxicology,
ISSN 0146-4760,
Volume 32, Number 5, June,
pp.355-363
A New Method
for Simultaneous Determination of Cyclic Antidepressants and their
Metabolites in Urine Using Enzymatic Hydrolysis and Fast GC–MS
Sumandeep Rana, Victor P. Uralets, and Wayne Ross
Redwood Toxicology Laboratory, Santa Rosa, California 95403
A method for the simultaneous determination of
six commonly prescribed cyclic antidepressants and their major
metabolites in urine is presented. This method can be used for
quantitation of amitriptyline, nortriptyline, imipramine, desipramine,
doxepin, desmethyldoxepin, and maprotiline in human urine, in
addition to the qualitative determination of their hydroxylated
metabolites. This method is suitable for confirmation of drug
abuse in health care professionals and overdose cases where the
identity of the abused cyclic antidepressant may not be known.
Samples are spiked with internal standard and hydrolyzed with β-glucuronidase
from Escherichia coli. Hydrolysis is found to be essential
to the extraction procedure as the tertiary cyclic antidepressants
are found to be extensively conjugated in urine. The secondary
cyclic antidepressants, on the contrary, are found to be minimally
conjugated. Drugs are extracted from alkalinized urine into solvent
and derivatized with MSTFA/ammonium iodide/ethanethiol reagent.
This reagent produces more stable derivatives compared to reagents
previously employed. Gas chromatographic (GC)–mass spectrometric
analysis is performed in electron ionization mode by selective
ion monitoring, using hydrogen as a carrier gas, a short narrow
bore GC capillary column, and fast temperature program, allowing
for a rapid analytical cycle. While maintaining specificity for
these drugs, concentrations in human urine ranging from 50 to
20,000 ng/mL can be measured with intraday and interday precisions,
expressed as variation coefficient, of less than 2.8% for all
analytes.
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