Dual-template molecularly imprinted paper for the determination of drugs of abuse in saliva samples by direct infusion mass spectrometry

Abstract

Chromatographic separation improves method selectivity at the expense of analysis time. In this article, the use of a molecularly imprinted polymer (MIP) paper combined with direct infusion electrospray ionization tandem mass spectrometry (DI-ESI-MS/MS) in the selected reaction monitoring (SRM) mode is presented as an alternative to the classical workflow for the determination of cocaine and methamphetamine in saliva samples. The MIP paper is synthesized by dip-coating, just immersing the paper substrate into a polymeric solution (nylon-6 in formic acid) containing cocaine and methamphetamine as templates. The evaporation of the solvent induces the rearrangement of the polymeric chains around the template, creating selective cavities that are released when the MIP paper is washed. The MIP paper presents a better affinity for the analytes than for 6-acetylmorphine, which was selected as model interfering compound. Also, the MIP paper showed a better performance than the non-imprinted (NIP) one. The extraction can be easily performed in an Eppendorf tube, enabling the simultaneous extraction of several samples, which increases the sample throughput. Working at the optimum conditions, a matrix-matched calibration model was built for both analytes using deuterated analogs as internal standards. The limits of quantification and detection were 10 µg·L−1 and 3 µg·L−1, respectively, for both analytes. The precision, expressed as relative standard deviation, was better than 5.9%, and the recovery values were found in the interval 84.3–98.0%.