Analytical performance evaluation of EMIT II monoclonal amphetamine/methamphetamine assay: more specificity than EMIT...

We evaluated a new EMIT II monoclonal amphetamine/methamphetamine assay for screening human urine by comparing it with the EMIT d.a.u. monoclonal amphetamine/methamphetamine assay and a fluorescence polarization assay. The EMIT II assay has a cutoff of 1 mg/L d-methamphetamine. The EMIT II and EMIT d.a.u. assays were run on a BM/Hitachi 704 analyzer; for the fluorescence polarization assay we used a TDx analyzer. All EMIT II positive samples were also analyzed by the fluorescence polarization assay. We used gas chromatography/mass spectrometry (GC/MS) for confirmation of the presence of amphetamine or methamphetamine. Within-run CVs for the Level 1 (1 mg/L) and Level 2 (3 mg/L) calibrators for the EMIT II assay were 0.47% and 0.53%, respectively. Corresponding between-run CVs were 1.48% and 1.60%, respectively. Of the 1007 samples screened for amphetamines, 50 were positive by the EMIT d.a.u. assay; 21 samples (not a subset of the 50 samples) were positive by the EMIT II assay. However, 19 samples that tested positive by EMIT II also tested positive by the EMIT d.a.u. assay. Subsequent testing of the EMIT II positive samples by the fluorescence polarization assay detected in six positive samples. By means of chiral derivatization wer identified two specimens containing primarily l-isomers of amphetamine and methamphetamine. Sympathomimetic amines were identified in several of the samples not containing amphetamine or methamphetamine.