Volume 29, Issue 2 (April 1984)
Sampling Errors in the Determination of Cocaine in Seized Drugs
Experiments in which 28-g (1-oz) seizures of cocaine plus diluent (mannitol, inositol) were ground in a mortar for only a few minutes before removal of 20-mg portions for assay (by gas chromatography using bupivicaine as internal standard) showed the standard deviation of the sampling operation to be several times larger than the standard deviation of the analytical operations. Measurement of the particle size distribution of ground mixtures allowed estimation of the weight of sample required to lower the sampling standard deviation to any specified level. The sample weight required was shown to depend in a predictable way on the percentage of cocaine present in the material.