Comparison of centrifugation and solid phase extraction (SPE) methods of sample preparations in determination of residues of drugs of abuse in urine

Detection of drugs of abuse in urine samples depends on their composition, absorption,distribution, physical and chemical properties, concentrations, elimination properties, and thetechniques employed. This study compared the performance of centrifugation and solid phaseextraction (SPE) methods in the determination of levels of drugs of abuse and their metabolites inurine samples collected from drug abusers. Analysis was performed using liquid chromatographytandemmass spectrometry (LC-MS-MS). Calibration was done using both internal and externalstandards. The recovery values were generally greater in centrifugation method than in SPEmethod, but the recoveries in both methods were within an acceptable range. Linearity values (R2)ranged from 0.9789 to 0.9944 with an average of 0.99. The LOD and LOQ values weresatisfactory. The concentrations of 6-monoacetylmorphine (6-MAM), morphine and cocaine wereup to 3.37, 4.21 and 0.03 μg/mL, respectively in samples prepared by centrifugation method, whilein samples prepared by SPE method were up to 6.67, 6.66 and 0.13 μg/mL, respectively. The meanconcentrations and detection frequencies of 6-MAM and morphine were higher in samplesprepared by centrifugation method than those of SPE method. Cocaine had the same meanconcentrations and detection frequencies in samples prepared by both methods. There were nosignificant differences in the concentrations of the drugs of abuse between the samples prepared bycentrifugation and SPE methods, although the levels of the drugs in the samples prepared bycentrifugation method were slightly greater than those prepared by SPE method