An evaluation of the Charm test--a rapid method for the detection of penicillin in milk

Using the Charm radioactive assay technique as a rapid test for the determination of penicillin in milk in experiments with milks containing known concentrations of penicillin, the coefficient of variation was found to be 15 and 11% for raw whole and reconstituted skim-milks respectively. Storage of reagents for up to 4 d increased the variance of the test by more than 20% and the estimated penicillin concentration 0.4%/d of storage up to 25 d. In comparison with the Bromocresol Purple Test, which was capable of 100% accuracy in defining a threshold of 0.02 i.u. penicillin/ml milk, the Charm Test falsely classified 15.6% of the samples.