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High-throughput flow injection analysis-MRM3 (FIA-MRM3) spectrometry for alternative fast screening of the isomeric methamphetamine and phentermine in blood for forensic toxicology cases in Malaysia

Background: Methamphetamine (MA) and phentermine (PTM) are critical isomeric compounds that often coexist in biological specimen in toxicology cases which have similar nominal mass. The dependency of high-resolution mass spectrometer and special chiral stationary phase column for separation of isomeric compound impedes screening throughput especially in meeting high sampling demand. Aim: In the absence of such equipment for identification, we introduce the flow injection analysis (FIA)-MRM3 technique and demonstrated its capabilities for quick identification of both isomeric compounds without liquid chromatography (LC) separation through the addition of selectivity criteria in the MRM3 mode. Method: 20 to 100 ng/mL of MA and PTM, respectively, in whole blood sample (WBS) and dried blood stain (DBS) were used to develop the method for the identification and relative quantification. Twenty whole blood samples which were reported positive of the drugs were randomly selected and were individually stained onto the Flinders Technology Associates (FTA) card for DBS study. Results: The peaks from the two isomeric compounds were successfully discerned for all the tested specimens using the FIA-MRM3 spectrometry technique. The limit of detection (LOD) and limit of quantification (LOQ) for MA and PTM were comparable to normal liquid chromatography-tandem mass spectrometry runs at 2.23 and 2.07 ng/mL, respectively, for WBS (n = 30). For DBS, the LOD and LOQ were 3.40 and 2.86 ng/mL, respectively. The accuracy and inter-day precision for DBS and WBS were in the range of 99.97–111.19% and 7.17–9.55%, respectively. Conclusion: These results demonstrated that the technique is highly adoptable in the screening of isomeric compounds of similar masses in a simple and rapid analysis.