K.C. Honeychurch , H . Li, S. Pericleous , M. Antoniou , A. Abed and J.P . Hart - PowerPoint PPT Presentation

Redox Mechanisms of Rohypnol and Mogadon and Their Exploitation in an Assay Using Dual Electrode

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Redox Mechanisms of Rohypnol and Mogadon and Their Exploitation in an Assay Using Dual Electrode ECD Following HPLC

K.C. Honeychurch, H. Li, S. Pericleous, M. Antoniou, A. Abed and J.P. Hart

Talk Outline
  • Importance of the 1,4-benzodiazepine class of drugs
  • Cyclic voltammetric behaviour of Flunitrazepam (Rohypnol), and Nitrazepam (Mogadon)
  • Possible mechanism for their voltammetric behaviour
  • Optimisation of Liquid Chromatographic Separation and dual electrode detection conditions
Importance of the 1,4-benzodiazepine class of drugs
  • Widely used and prescribed drugs for sleeping and anxiety related disorders.
  • Reviews have highlighted the forensic importance of this class of compounds.
    • DFSA
    • robberies
  • Concern has also focused on the effects of such compounds in the environment.
    • Levels in drinking water.
    • pregnant women and children.
    • Aquatic environment
    • chronic effects seen at sub-µg/l.
  • Gas chromatography requires derivatization
  • Immunoassays show cross reactivity.
  • Consequently, need for new rapid sensitive methods

Nitrazepam

Flunitrazepam

Cyclic Voltammetric Behaviour

(b)

(a)

Cyclic voltammograms obtained in the presence (solid line) and absence (dotted line) of 1 mM flunitrazepam in 50 % 0.2 M pH 2 phosphate buffer-50 % acetone. Scan rate 50 mV/s, starting and end potential 0.0 V. (a) initial switching potential +2.0 V, second switching potential ‑2.0 V. (b) initial switching potential ‑2.0 V, second switching potential +2.0 V. (c) ip versus pH and (d) Ep versus pH.

ipαv½

(d)

(c)

O2

R1

O1

R2

R2

O1

R1

O2

Honeychurch et al. Anal. Methods, 2012, 4, 132-140.

Honeychurch et al, Anal. Chem. 2006, 78, 416-423.

High-Performance Liquid Chromatography Coupled with Dual Electrochemical Detection (LC-DED)
  • “Generator” and “Detector” Cells
  • “Generator” cell- analyte is electrochemically converted to a product that can be then more readily electrochemically determined at the “Detector” cell.
  • Advantages - lower working potentials:
  • lower background currents
  • less interferences -
  • oxygen – no degassing, number of common other interferences not seen.

HPLC

chart recorder

detector

generator

Rheodyne injector

Faraday cage

Thermostatically controlled Column

3 mm diameter GCE

3 mm diameter GCE

4X10‑5 AUFS

0

12

8

4

minutes

Optimisation of Chromatographic Conditions

pH 6.6

pH 2.7

N

F

pH 2.3

pKa 1.8 flunitrazepam

pKa 3.2 nitrazepam

Effect of mobile phase pH on peak separation.

50 % acetone, 50 % 100 mM phosphate buffer, 0.8 mL/min, UV detection λ = 380 nm. C18 column

Hydrodynamic Voltammetry

Generator

Detector

Conclusions
  • We have demonstrated the cyclic voltammetric behaviour of flunitrazepam and nitrazepam.
  • We have the shown the possibility to determine these drugs by LC-DED.
  • Future work will focus on accessing the analytical performance of the LC-DED method.
Acknowledgements
  • We are grateful to the University of the West of England and HEFCE for financial support. Gwen M. Davidson, Emma Brown and Jonathan Toner are thanked for their work with some preliminary studies. Alison Halliday, Paul Bowdler and Mervyn Lewis are thanked for their technical assistance.

References

Kevin C. Honeychurch, Ai Teng Chong, Khalil Elamin and John P. Hart, Novel electrode reactions of diazepam, flunitrazepam and lorazepam and their exploitation in a new redox mode LC-DED assay for serum, Anal. Methods, 2012, 4, 132-140.

Kevin C. Honeychurch, Gemma C. Smith, and John P. Hart, Voltammetric Behavior of Nitrazepam and Its Determination in Serum Using Liquid Chromatography with Redox Mode Dual-Electrode Detection, Anal. Chem. 2006, 78, 416-423.

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