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

Abstract

Detection of drugs of abuse in urine samples depends on their composition, absorption,
distribution, physical and chemical properties, concentrations, elimination properties, and the
techniques employed. This study compared the performance of centrifugation and solid phase
extraction (SPE) methods in the determination of levels of drugs of abuse and their metabolites in
urine samples collected from drug abusers. Analysis was performed using liquid chromatographytandem
mass spectrometry (LC-MS-MS). Calibration was done using both internal and external
standards. The recovery values were generally greater in centrifugation method than in SPE
method, 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 were
satisfactory. The concentrations of 6-monoacetylmorphine (6-MAM), morphine and cocaine were
up to 3.37, 4.21 and 0.03 μg/mL, respectively in samples prepared by centrifugation method, while
in samples prepared by SPE method were up to 6.67, 6.66 and 0.13 μg/mL, respectively. The mean
concentrations and detection frequencies of 6-MAM and morphine were higher in samples
prepared by centrifugation method than those of SPE method. Cocaine had the same mean
concentrations and detection frequencies in samples prepared by both methods. There were no
significant differences in the concentrations of the drugs of abuse between the samples prepared by
centrifugation and SPE methods, although the levels of the drugs in the samples prepared by
centrifugation method were slightly greater than those prepared by SPE method.