Quantitative selected ion monitoring (QSIM) of drugs and/or drug metabolites in biological matrices.

From a modest beginning, QSIM has established itself with over three hundred applications in the 1970s as not only a reference technique for other methods but also as a useful method in its own right for the quantitation of drugs in biological matrices. Relative to its potential sensitivity, the actual sensitivity of QSIM drug assays is disappointing, although a number of QSIM drug assays report LOQs of 250 pg ml-1 or less. The mean reported precision of QSIM drug assays (approximately 6%) is similar to that of traditional GC and LC assays, but is an order of magnitude less than either what is theoretically possible or what has been demonstrated in a few selected QSIM assays.