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.

Recently, our laboratory has investigated the depletion of Vitamin A and its metabolites in experimental animals. High Pressure Liquid Chromatography (HPLC) was used to measure retinal oxidase activity by monitoring the conversion of retinaldehyde (RALD) to retinoic acid (ROIC). In order to obtain more information about these compounds, a Direct Exposure Probe mass spectrometric method was developed to confirm the presence of ROIC and RALD in HPLC peaks. A rapid negative ion chemical ionization (NICI) method using ammonia as reagent gas was developed to detect the presence of ROIC and RALD with picogram sensitivity. The ROIC and RALD peaks were collected from HPLC, extracted with hexane, evaporated under nitrogen and reconstituted in ethanol before placing onto a rhenium filament with current programmed from 0-1.3 A at 50 mA/sec. The instrument employed was a Finnigan 4510 operated in the NICI mode and scanned from m/z 100-650 with a source temperature of 80 C. Other parameters were electron energy 140 eV and filament current at 0.25 mA. Prominent ions were generated at m/z 284 and m/z 300 for RALD and ROIC which were subsequently monitored in the selected ion monitoring mode. In summary, we have developed a rapid retinoid identification method (2.5 minutes) which is more sensitive (pg vs ng) than HPLC and does not require elaborate sample preparation or derivitization. This method can be used as an important adjunct to HPLC enzyme studies.