Effects of biological matrices and sample collection conditions on the reliability of methamphetamine analysis

Breast milk and urine samples from thirty-nine mother-infant pairs were tested for the methamphetamine-level measurement reliability under four separate conditions: freezethaw cycle, short-term storage, long-term storage and on-instrument/extract storage. The four different conditions yielded methamphetamine levels within ±10% variation of that obtained from the freshly prepared samples. For most consistent results, milk samples should be frozen immediately after collection, while urine samples can be kept at room temperature for up to six hours before the longer-term storage. Finally, the use of an autosampler only has minimal effects on the measurement reliability.