Gas phase detection of cocaine by means of immunoanalysis
Immunoanalytical techniques based on an indirect competitive ELISA to determine cocaine in the gas phase are described. A test-gas generator was developed and evaluated by determining saturation vapour pressures and the sublimation enthalpy of cocaine base. To achieve quantitative recovery of the drug, the saturated air stream was sucked through a retention fluid. For validation of the test gas generator, samples were analysed with a microtitre plate cocaine-ELISA based on monoclonal antibodies. To simplify the sampling and analysis procedures by analysing the retention fluid directly in the sampling vessel, particle-based immunoassay formats were developed. According to the ELISA format, avidin was immobilized on the particles. The application of various solid particles consisting of different materials with a wide range of diameters (0.5–550 µm) to the analysis of cocaine standards and gas samples showed good correlation with the results obtained with the microtitre plate ELISA with an average IC50 value (end-point of the test; concentration at 50% binding) of 9.7 ng ml–1. The particle-based assays showed IC50 values in the range of 5–54 ng ml–1 and signal background ratios ranging from 2 to 11. The application of particle-based assays for direct analysis of cocaine in the sample fluid was successfully performed with glass beads, precoated with avidin and a biotin–cocaine conjugate. Recovery of cocaine from the gas phase depended on the volume of sample fluid and on the geometry of the sample tube.