Sensitive method for the determination of methadone in small blood samples.

Quantitation of low levels of methadone in small size samples required a sensitive and specific method of analysis. Methods for clinical application have been described for blood and urine samples using immunoassay techniques14, gas chromatography5-’ l and combined gas chromatography-mass spectrometry12-14. These methods are not sensitive enough for determination of plasma concentrations in small volume blood samples. The sensitivity of those methods was in the 4&50 ng/ml range; however, they required sample sizes of 4415 ml 5,7. These techniques were not appropriate to study the methadone-ethanol interaction in experimental animals. This report presents a simple and accurate method of quantification using the addition of an internal standard, extraction with an organic solvent and gas-liquid chromatography (GLC) determination. The internal standard selected, 4-dimethylamino1,2-diphenyl-3-methyl-2-butanol (chirald), is commercially available.