Confirmation of drugs of abuse in urine drug screens by direct exposure probe mass spectrometry

Abstract

A direct exposure probe (DEP) mass spectrometric method was developed to confirm the presence of cocaine (C), phencyclidine (P), benzoyl ecognine (BE) and 11-norcarboxy tetrahydrocannabinol (11-nor-c-THC) in previously screened urine specimens. Essentially, a urine sample is lyophilized overnight and reconstituted in 30 microliters of a 3:1 mixture of ethyl acetate:methanol. One microliter is placed on a rhenium filament and left to air dry. The specimen was analyzed by negative ion chemical ionization DEP using ammonia as reagent gas at 0.20 Torr with an ion source temperature of 100 degrees C. An electronics setting of 1700 V (EM), 0.30 mA filament current, and 100 eV with scanning at m/z 100-650 (1 sec/SCAN) resulted in simple spectra with easily identifiable molecular ions for C, BE, P and 11-nor-c-THC. The sensitivity of the assay was 1 ng for the drugs of abuse. The method was validated by analyzing 50 urine samples that have been previously screened and confirmed for drugs at the University of Illinois Toxicology Laboratory. The results showed that the DEP method confirmed 87%, 71%, 100%, and 85% of the BE, C, P and 11-nor-c-THC. In summary, a rapid and sensitive DEP method for the confirmation of drugs of abuse in urine has been developed which can serve as a useful adjunct to gas chromatographic/mass spectrometric confirmation.

Forensic science

“…A direct exposure probe (DEP) mass spectrometric method has been developed for confirmation of drugs of abuse in urine which has been previously screened (379). Mass spectra of several commonly abused drugs and their deuterated analogues have been compared ana evaluated with emphasis on the selection of suitable ions for selective ion monitoring when the isotopic analogues are used as the internal standards in a quantitative process (380).…”