Radioimmunoassays for morphine-barbiturate (MOR-BARB), morphine, barbiturate, and amphetamine were evaluated by a direct comparison with differential elution extraction thin-layer chromatography, the "enzyme multiplied immunoassay technique," and XAD-2 resin extraction thin-layer chromatography for the detection in urine of drugs subject to abuse. Statistically significant (Psmaller than 0.01) concentrations for detection were: 50-100 mug/liter for MOR-BARB; 5 Mug/liter for morphine, 10 mug/liter for barbiturate, and 100 mug/liter for amphetamine. Unconfirmed and unaccounted-for radioimmunoassay positives (false) were: 0% for morphine in the radioimmunoassay for MOR-BARB and that for morphine alone; 2.8% for barbiturates in the MOR-BARB assay and that for barbiturates alone; 0-6% when a combination of these drugs was present in the MOR-BARB, morphine, or barbiturate assay; and 2.4% in the amphetamine radioimmunoassay. Less than 1% of all radioimmunoassay-negative samples were unconfirmed (false). Cross-reactivity was observed with drugs of a similar chemical structure in each of the radioimmunoassays tested. All the radio-immunoassays were easy to use, highly sensitive, and extremely reliable for detecting drug use or abuse.
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Mulé et al. (1975) studied this question.