A simple solid-phase radioimmunoassay for morphine and related opiates using a mixture of labelled morphine and antiserum pre-precipitated by polyethylene glycol.

A novel, solid-phase radioimmunoassay for morphine and related opiates is described in which radiolabelled morphine, antiserum and polyethylene glycol are premixed before being added to the samples or standards. The mixture can be stored at 2 degrees C and used for several months until decay of the 125I label leads to excessively long counting times. The method was developed using the Roche Abuscreen radioimmunoassay for morphine and has the particular advantages of simplicity (only 2 pipetting steps required instead of 5) and economy (800 assay tubes can be prepared from a 100-tube Abuscreen plus a 50% saving in operator time). The procedure can be applied to other assays providing the polyethylene glycol-precipitated antiserum is stable and that the antibody affinity for the labelled compound is not so high as to prevent displacement of the labelled compound from the antibody binding sites by unlabelled drug.