Analysis of Cathinones in Plasma Using LC-MS/MS

Significance of the topic

Designer cathinones, commonly known as "bath salts," represent a growing public health challenge due to their potent psychostimulant effects and evolving chemical structures that evade regulatory controls. Accurate measurement of cathinone concentrations in biological matrices is crucial for forensic investigations, toxicology screening, and regulatory compliance.

Objectives and Study Overview

This work aimed to evaluate matrix effects in plasma and to develop a straightforward LC-MS/MS method using standard addition (without internal standards) for quantifying cathinone and mephedrone in plasma samples. The approach focused on method simplicity and reliability in the context of emerging forensic requirements.

Methodology and Instrumentation

Sample Preparation:

• Sheep plasma spiked with cathinone and mephedrone standards (10–80 pg/µL).
• Dilute-and-shoot protocol: 1:1 dilution with methanol, centrifugation at 14 000 rpm for 10 min.

Chromatography:

• UHPLC: Phenomenex Kinetex C18 (2.1×100 mm, 1.7 µm), 30 °C, isocratic elution.
• Mobile phase A: water with 0.05% formic acid and 5 mM ammonium formate.
• Mobile phase B: methanol with 0.05% formic acid; flow rate 0.5 mL/min; injection volume 10 µL; auto-sampler 15 °C.

Mass Spectrometry:

• Shimadzu LCMS-8030 triple quadrupole with DUIS interface.
• Nebulizing gas: 1.5 L/min; drying gas: 15 L/min; DL 250 °C; heat block 400 °C.
• MRM transitions: cathinone 150.2>132.1 and 150.2>117.1; mephedrone 178.2>159.8 and 178.2>145.1.

Main Results and Discussion

Chromatographic peaks for cathinone and mephedrone were sharp and well resolved at low picogram-per-microliter levels. Standard addition calibration showed:

• Cathinone average recovery: 98.4%, CV 5.6%.
• Mephedrone average recovery: 100.2%, CV 5.4%.

These results demonstrate that the dilute-and-shoot standard addition method effectively compensates for plasma matrix suppression without requiring solid-phase extraction or internal standards.

Practical Benefits and Applications

• Rapid turn-around: minimal sample prep and no SPE.
• Cost efficiency: eliminates need for labeled internal standards and complex cleanup.
• Forensic relevance: suitable for routine toxicology screening and pharmacokinetic studies addressing new psychoactive substances.

Future Trends and Opportunities

• Expansion to a broader panel of cathinone analogues (e.g., butylone, MDPV).
• Integration with high-resolution MS for untargeted screening.
• Automated standard addition workflows for high-throughput laboratories.

Conclusion

The developed LC-MS/MS method employing a dilute-and-shoot standard addition strategy provides accurate, reproducible quantitation of cathinone and mephedrone in plasma. Its simplicity, robustness, and avoidance of internal standards make it an attractive tool for forensic and clinical toxicology.

Reference

Concheiro, M. et al. (2013) Matrix effects on cathinone detection in LC-MS/MS analysis of biological samples.