Comprehensive Analysis of Analogues of Amine-Related Psychoactive Substances Using Femtosecond Laser Ionization Mass Spectrometry

Determination of three ephedrine psychoactive substances in sewage using solid-phase extraction-ultra-performance liquid chromatography-tandem mass spectrometry

RATIONALE

In recent years, ephedrine psychoactive substances have attracted much attention due to their prevalence in water bodies and potential threat to aquatic ecosystems. Psychoactive substances have been considered as a new type of environmental pollutant due to their unpredictable potential risks to the behavior and nervous system of non-target organisms. A rapid, sensitive, selective, and robust method for the quantification of three ephedrine psychoactive substances in sewage is needed.

METHODS

An ultraperformance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) method was developed for the simultaneous determination of three ephedrine psychoactive substances in water. The optimal processing conditions were determined by optimizing the chromatography-mass spectrometry and solid-phase extraction (SPE) conditions (e.g., the SPE column, sample pH, washing, and elution), and the treatment conditions were determined; this was achieved via positive ion scanning in multiple reaction monitoring mode. Poly-Sery MCX was selected as the extraction column, with samples loaded at pH 3. And 4-mL solution of 2% formic acid (FA) aqueous solution was used as the eluent; the target compounds were eluted with 5 mL of 5% NH4OH in acetonitrile (ACN) solution. The best results were obtained when the residue was resolubulization in ACN after nitrogen evaporation.

RESULTS

The developed UPLC-MS/MS showed a good linear relationship in the range of 0-50.00 μg/L, with determination coefficients (R2) greater than 0.9990. The detection limit and quantitation limit were 0.05-0.10 and 0.20-0.50 μg/L, respectively. Recovery rates of the target compounds in blank sewage at three different concentrations ranged from 92.37% to 106.31%, with relative standard deviations (RSDs) of 0.77%-4.83% (n = 7).

CONCLUSIONS

This method has been successfully applied to the analysis of surface water and domestic sewage, and the samples were processed stably, indicating that the method is practical for the determination of ephedrine psychoactive drugs in water bodies.

Determination of Barbiturates by Femtosecond Ionization Mass Spectrometry

Barbiturates are highly susceptible to dissociation in mass spectrometry (MS) because of their long side chains combined with a nonaromatic ring consisting of several carbonyl and amine groups. As a result, they exhibit extensive α-cleavage and subsequent rearrangement, making the identification of these compounds difficult. Although a library of electron ionization MS (EIMS) is available, most barbiturates have very similar fragment patterns. Accordingly, it would be desirable to develop a technique for soft ionization, providing a molecular ion and large fragment ions as well. In this study, a molecular ion was clearly observed, in addition to large fragment ions, for a variety of barbiturates based on multiphoton ionization MS (MPIMS) using a tunable ultraviolet femtosecond laser as the ionization source (fs-LIMS). This favorable result was achieved when the optimal laser wavelength for minimizing the excess energy remaining in the ionic state was used. An examination of the photofragmentation pathways suggested that an H atom in the side chain was abstracted by an oxygen atom in the carbonyl group in the ring structure thus initiating fragmentation and subsequent rearrangement. Barbiturates that are substituted with alkyl groups (amobarbital and pentobarbital) had narrower spectral regions for optimal ionization than the other barbiturates with alkyl and alkenyl groups (butalbital and secobarbital) and more with alkyl and phenyl groups (phenobarbital). All of the barbiturates studied provided unique mass spectral patterns in fs-LIMS, which was useful for the reliable identification of these compounds in practical trace analysis.