Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (1204 page)

   Readily extracted in neutral liquid–liquid or SPE extraction scheme

   Unstable in acidic and basic conditions

   Gas chromatography, GC/MS, liquid chromatography, LC/MS; may thermally degrade depending on gas chromatography, GC/MS operating parameters

   Limit of quantitation: 10–50 ng/mL

BARBITURATES

   Definition and Use

   Older class of CNS depressants. Largely replaced by benzodiazepines and newer hypnotics such as zolpidem. Current main use as anticonvulsants, in treatment of migraines, and in reduction of cerebral edema and intracranial pressure resulting from head injury

   Screening

   Immunoassays for automated chemistry analyzers

   Urine

•   Target analyte—secobarbital

•   Cutoff concentration—200 or 300 ng/mL

•   Cross-reactivity—approximately 100% with amobarbital, 60–90% with butabarbital, butalbital, pentobarbital, and phenobarbital

   Serum/plasma/blood

•   EMIT, ELISA, FPIA

•   Target analyte—secobarbital

•   Cutoff concentration—10–50 ng/mL ELISA; 1,000 ng/mL EMIT

•   Cross-reactivity—manufacturer kit reagent dependent:

○   Low cross-reactivity with amobarbital, phenobarbital, butabarbital, and butalbital and high cross-reactivity with thiopental and pentobarbital

○   FPIA generally demonstrates more cross-reactivity than EMIT to other barbiturates

   Confirmation: chromatography or UV–visible spectrophotometry

   Sample pretreatment required