Determination of opiates, cocaine and benzoylecgonin in urine by solid phase extraction and liquid chromatography : tandem mass spectrometry

Abstract

ABSTRACT

In forensic toxicology it is important to have a specific and reliable detection of illicit drugs in biological species. At Norwegian Institute of Public Health (NIPH), Department of Drug Analysis, urine samples screened positive for illicit drugs are analysed to confirm and determine the drugs that are present.

In the present work an ultra performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) method for the determination of opiates (morphine, codeine, 6-monoacetylmorphine, pholcodine, oxycodone, ethylmorphine), cocaine and benzoylecgonine in urine has been developed and validated. Sample preparation was performed on a mixed mode cation solid phase extraction (SPE) cartridge. For optimized chromatographic performance with narrow, symmetrical peaks and repeatable retention times, a basic mobile phase of 5 mM ammonium bicarbonate, pH 10.2 and methanol (MeOH) as organic modifier was chosen. MS/MS parameters were optimized to obtain selective and robust detection. The desolvation gas temperature was found to be an important parameter with great influence on both peak shape and intensity. Deuterium labelled internal standards were used for most of the analytes.

The between-assay retention time repeatability was highly satisfactory with relative standard deviation (RSD) values within 0.1-0.6%. Limit of detection (LOD) and limit of quantification (LOQ) were satisfactory with values in the range 0.003-0.05µM and 0.01-0.16µM, respectively. Between-assay repeatability within the calibration range also was highly satisfactory with RSD values below 10% at four concentration levels for all analytes, except pholcodine which had a maximum RSD of 18%. Linear range up to 3-10µM were obtained for all analytes. Specificity was investigated by determination of the retention times of 98 drugs and internal standards in total. Co- eluting compounds were in all cases separated by the MS/MS detection. Matrix effects were investigated, but no or only minor matrix effects were observed.

Since August 2007, the method has been routinely used for determination of the opiates in approximately 400 urine samples.