Spray-inlet microwave plasma torch ionization tandem mass spectrometry for the direct detection of drug samples in liquid solutions.

Rationale: Drug abuse or dependence results in a series of social problems, including crime and traffic accidents. Spray-inlet microwave plasma torch tandem mass spectrometry (MPT-MS/MS) was developed and used for the direct detection of such drugs in liquid solutions.

Methods: Drug sample solutions were directly sprayed into the flame of an MPT by a sampling pump and the ions produced by Penning ionization and ion-molecule reactions were guided into a quadrupole time-of-flight (QTOF) tandem mass spectrometer for mass analysis. The MPT was operated at 40 W and 2.45 GHz in a 700 mL/min argon flow both for the inner and middle plasma.

Results: Intact quasi-molecular and molecular ions of various drugs were successfully characterized by spray-inlet MPT-MS/MS. The analysis of one sample was finished within 30 s. Furthermore, the method exhibited excellent efficiency, precision and sensitivity, and the limits of detection and limits of quantification of the samples in methanol were in the range of 5.25-60.0 and 17.5-200 ng g , respectively. Excellent linearities with coefficients of determination (R ) of 0.9627-0.9980 were verified in the range 0.05-50 μg g . Four different beverages purchased locally were also analyzed with spray-inlet MPT-MS/MS, and caffeine was directly determined in two of the beverages. By adding six standard drug samples to sport drinks (each drug was 1 μg g ) and Chinese spirit (each drug was 0.1 μg g ), all the drugs except for caffeine were detected successfully.

Conclusions: This study indicates that spay-inlet MPT-MS/MS is an effective method for direct and rapid identification of drug solutions, and it has substantial potential for fast and sensitive drug residue detection.