Modification of Method for Rapid Determination of 3 Illicit Drugs in Human Urine by GC-MS with Pretreatment by DLLME

A modification for the dispersion liquid-liquid micro extraction (DLLME) in the sample pretreatment of rapid determination of 3 illicit drugs (i.e., methamphetamine, MDMA and ketamine) in human urine by GC-MS in hyphenation was proposed. In the analytical procedure, after the urine sample (2.0 mL) was mixed with 100 μL of 20.0 mg·L^-1 internal standard solution of SKF525A, and its acidity was adjusted to pH 12, a modification of addition of 50 mg of PSA to the solution was made at this stage to remove impurities of fatty acid in urine, thus no precipitation of footy substance would happen in succeeding manipulations. After the addition of PSA, the mixture was centrifuged and the surpernatant was taken, to which 400 μL of iso-propyl alcohol (as dispersant) and 200 μL of CCl₄ (as extractant) were added. The mixture was shocked lightly for 1 min and centrifuged for 5 min. 1 μL of the extractant (CCl₄) at the shape bottom of the centrifuging tube was taken with a micropipet, and used for GC-MS determination of the 3 illicit drugs. Standard curves of the 3 drugs were found to have the same linearity range between 0.1 to 10.0 mg·L^-1 and same detection limit (3S/N) of 0.01 mg·L^-1. Test for recovery was made by standard addition method at 3 concentration levels, giving average recoveries of 76.4%, 83.2%, 103% for the 3 drugs respectively. Values of RSDs (n=5) found from the determined values of the 3 drugs were 6.7%, 5.3%, 6.7% (intraday) and 7.5%, 5.9%, 6.6% (interday) respectively.