Roche Diagnostics, Somerville, NJ, USA

Urine from 9 different donors and a serum control was spiked with secobarbital. Mean recovery in urine from a standard curve produced with serum calibrators was: 100.1% at 2.38 µg/mL, 105.2% at 0.87 µg/mL, 99.98% at 0.45 µg/mL, 94.4% at 0.2 µg/mL, 98% at 0.17 µg/mL, and 97.2% at 0.12 µg/mL. Precision in urine was evaluated according to NCCLS Guideline EP5-T2 where the total precision at 0.276, 0.241, 0.222, 0.177, 0.136, and 0.087 µg/mL was 4.77, 4.78, 5.24, 6.93, 6.67, and 13.46% respectively. The sensitivity for detection of barbiturates in urine, as determined as that concentration which can be detected with 95% confidence, was 0.05 µg/mL.

Clinical samples, N = 60, were evaluated by GC/MS for phenobarbital, butabarbital, and secobarbital, LOD 25 ng/mL, the commercially available OnLine cassette COBAS INTEGRA Barbiturates (BARB) which uses KIMS (kinetic interaction of microparticles in solution) technology, LOD 17 ng/mL, and the SBARB urine application, LOD 0.05 µg/mL. The diagnostic sensitivity of the two immunoassays vsv GC/MS was 100% and the diagnostic selectivity was 90.9%.

Interference was evaluated by spiking secobarbital into water and urine containing either 7.5 g/L hemoglobin, 1.5% ascorbic acid, 2 mg/mL oxalic acid, 5% liquid hand soap, 2% glucose, 220 mg/L calcium hypochlorite, 0.5N sodium chloride, 1% ethanol, 5 mg/mL creatinine, 0.5% human albumin, 1% acetone, 0.25 mg/mL bilirubin, or 6% urea. Recovery of secobarbital was > 90% for all the interfering substances evaluated.

The cassette COBAS INTEGRA SBARB assay may be used for the analysis of barbiturates in serum, plasma, urine and saliva.