Detection and quantification of new psychoactive substances (NPSs) within the evolved “legal high” product, NRG-2, using high performance liquid chromatography-amperometric detection (HPLC-AD)
The global increase in the production and abuse of cathinone-derived New Psychoactive Substances
(NPSs) has developed the requirement for rapid, selective and sensitive protocols for their separation and
detection. Electrochemical sensing of these compounds has been demonstrated to be an effective
method for the in-field detection of these substances, either in their pure form or in the presence of
common adulterants, however, the technique is limited in its ability to discriminate between structurally
related cathinone-derivatives (for example: (±)-4’-methylmethcathinone (4-MMC, 2a) and (±)-4’-methyl-
N-ethylmethcathinone (4-MEC, 2b) when they are both present in a mixture. In this paper we demonstrate,
for the first time, the combination of HPLC-UV with amperometric detection (HPLC-AD) for the
qualitative and quantitative analysis of 4-MMC and 4-MEC using either a commercially available impinging
jet (LC-FC-A) or custom-made iCell channel (LC-FC-B) flow-cell system incorporating embedded graphite
screen-printed macroelectrodes. The protocol offers a cost-effective, reproducible and reliable sensor
platform for the simultaneous HPLC-UV and amperometric detection of the target analytes. The two
systems have similar limits of detection, in terms of amperometric detection [LC-FC-A: 14.66 μg mL−1
(2a) and 9.35 μg mL−1 (2b); LC-FC-B: 57.92 μg mL−1 (2a) and 26.91 μg mL−1 (2b)], to the previously
reported oxidative electrochemical protocol [39.8 μg mL−1 (2a) and 84.2 μg mL−1 (2b)], for two synthetic
cathinones, prevalent on the recreational drugs market. Though not as sensitive as standard HPLC-UV
detection, both flow cells show a good agreement, between the quantitative electroanalytical data,
thereby making them suitable for the detection and quantification of 4-MMC and 4-MEC, either in their
pure form or within complex mixtures. Additionally, the simultaneous HPLC-UV and amperometric detection
protocol detailed herein shows a marked improvement and advantage over previously reported
electroanalytical methods, which were either unable to selectively discriminate between structurally related
synthetic cathinones (e.g. 4-MMC and 4-MEC) or utilised harmful and restrictive materials in their design.
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