Paper spray mass spectrometry applied to the detection of cocaine in simulated samples

Abstract

Paper spray mass spectrometry (PS-MS) is applied for the fast detection of cocaine in simulated samples that mimic real materials seized on streets. The simulated samples were prepared by using similar formulations to those usually employed by drug dealers. Hence, colourless and cheap materials (wheat flour, boric acid and sodium bicarbonate) and adulterants (lidocaine and caffeine) were selected to prepare two distinct bases (or excipients): A and B. The simulated drug samples were formulated by mixing each base with increasing amounts of cocaine (varying from 0.1 to 5.0% m/m). All samples were extracted with methanol and the extracts were dropped on a triangular-shaped paper and analyzed by paper spray mass spectrometry in the positive ion mode, PS(+)-MS. The results indicated that protonated cocaine (m/z 304) was easily distinguished, even in the mass spectra of the most diluted sample. Furthermore, the occurrence of the ion of m/z 235 (protonated lidocaine) in all mass spectra allowed for the identification of this adulterant in the simulated samples (protonated caffeine of m/z 195 was detected in only one of them). The characteristic fragmentation pattern of protonated cocaine was also used as a confirmation test for the occurrence of this drug. Moreover, a linear relationship between the ratio of the relative intensities of protonated cocaine (m/z 304) and lidocaine (m/z 235, taken as the internal standard) versus the cocaine content was verified for the simulated samples prepared with base B (R² = 0.996). Some other figures of merit (limit of detection, linear range and relative standard deviation) were also obtained for the analyses with the simulated samples prepared with base B. These results therefore point to the application of the present methodology not only to the fast detection of cocaine but also to estimate its content in real samples.