Validation of the Immunalysis® Microplate ELISA for the detection of methamphetamine in hair

The object of this study was to validate the Immunalysis Methamphetamine Microplate ELISA for detecting methamphetamine in hair. Twenty-nine scalp hair samples were obtained as routine cases submitted to the National Institute of Scientific Investigation in Seoul by the police. The hair samples were washed with 0.1% sodium dodecyl sulfate, distilled water, and dichloromethane. The samples were screened using the Immunalysis Methamphetamine Microplate ELISA and confirmed using gas chromatography-mass spectrometry (GC-MS). Twenty-eight hair samples were screened and confirmed as positive for methamphetamine. For ELISA analysis, the samples were extracted by incubation in monobasic phosphate buffer for 1 h at 60°C. For GC-MS, the samples were extracted for 20 h in methanol containing 1% hydrochloric acid. The methanol/acid solution was evaporated to dryness and the resulting residue was derivatized with trifluoroacetic anhydride. Methamphetamine and amphetamine were detected using selective ion monitoring (SIM) mode. The Immunalysis Methamphetamine Microplate ELISA demonstrated a sensitivity and specificity of 97% and 100%, respectively, using a cut-off concentration of 0.5 ng/mg d-methamphetamine. The ELISA kit showed 63% cross-reactivity with d,l-methamphetamine and did not cross-react to any significant extent with the licit l-methamphetamine isomer. The intra- and interassay precisions were 2.5% and 3.7%, respectively.