An Immunoassay for Drug Screening in the Forensic Laboratory

In forensic toxicology, immunoassays are the key sample-screening techniques for drugs in human fluids. Samples that show positive results using immunoassays are presumptive specimens; therefore, the presence of the drug must be confirmed by an alternative analytical technique. The purpose of this laboratory procedure is to introduce the fundamentals of the enzyme multiplication immunoassay technique, EMIT, to undergraduates in a forensic laboratory and lead the laboratory class into a discussion and application of analytical instrumentation for confirmatory analyses. The EMIT technique is based on a colorimetric reaction, the product of which can be measured spectrophotometrically. In this experiment, students used commercially available kits containing calibration standards to construct a calibration curve of the drug theophylline. A solution containing an unknown amount of theophylline in synthetic urine was then analyzed and compared to the calibration curve to determine if the concentration of theophylline is within the therapeutic range, 10 to 20μg/mL. Ninety percent of students in this particular class were able to accurately determine the concentration of theophylline in the unknown sample.