Direct and efficient liquid chromatographic‐tandem mass spectrometric method for opiates in urine drug testing – importance of 6‐acetylmorphine and reduction of analytes

Opiates comprise a class of abused drugs that is of primary interest in clinical and forensic urine drug testing. Determination of heroin, codeine, or a multi‐drug ingestion is complicated since both heroin and codeine can lead to urinary excretion of free and conjugated morphine. Liquid chromatography‐tandem mass spectrometry (LC‐MS/MS) offers advantage over gas chromatography‐mass spectrometry by simplifying sample preparation but increases the number of analytes. A method based on direct injection of five‐fold diluted urine for confirmation of morphine, morphine‐3‐glucuronide, morphine‐6‐glucuronide, codeine, codeine‐6‐glucuronide and 6‐acetylmorphine was validated using LC‐MS/MS in positive electrospray mode monitoring two transitions using selected reaction monitoring. The method was applied for the analysis of 3155 unknown urine samples which were positive for opiates in immunochemical screening. A linear response was observed for all compounds in the calibration curves covering more than three orders of magnitude. Cut off was set to 2 ng/ml for 6‐acetylmorphine and 150 ng/ml for the other analytes. 6‐Acetylmorphine was found to be effective (sensitivity 82%) in detecting samples as heroin intake. Morphine‐3‐glucuronide and codeine‐6‐glucuronide was the predominant components of total morphine and codeine, 84% and 93%, respectively. The authors have validated a robust LC‐MS/MS method for rapid qualitative and quantitative analysis of opiates in urine. 6‐Acetylmorphine has been demonstrated as a sensitive and important parameter for a heroin intake. A possible interpretation strategy to conclude the source of detected analytes was proposed. The method might be further developed by reducing the number of analytes to morphine‐3‐glucuronide, codeine‐6‐glucuronide and 6‐acetylmorphine without compromising test performance. Copyright © 2013 John Wiley & Sons, Ltd.