Abstract
Rohypnol (flunitrazepam) has been successfully determined in coffee by high performance liquid chromatography dual electrode detection (LC-DED) in the dual reductive mode. Initial studies were performed to optimise the chromatographic conditions and these were found to be 50% acetonitrile, 50% 50mM pH 2.0 phosphate buffer at a flow rate of 0.75mLmin−1, employing a Hypersil C18, 5μm, 250mm×4.6mm column. Cyclic voltammetric studies were made to ascertain the redox behaviour of Rohypnol at a glassy carbon electrode over the pH range 2–12. Hydrodynamic voltammetry was used to optimise the applied potential at the generator and detector cells; these were identified to be −2.4V and +0.8V for the redox mode and −2.4V and −0.1V for the dual reductive mode respectively. A linear range of 0.5–100μgmL−1, with a detection limit of 20ngmL−1 was obtained for the dual reductive mode. Further studies were then performed to identify the optimum conditions required for the LC-DED determination of Rohypnol in beverage samples. A convenient and rapid method for the determination of Rohypnol in beverage samples was developed using a simple sample pre-treatment procedure. A recovery of 95.5% was achieved for a sample of white coffee fortified at 9.6μgmL−1 Rohypnol.
Highlights
CH3 O N O2N F (I)Rohypnol (5-(2-Fluorophenyl)-1-methyl-7-nitro-1,3-dihydro-2H-1,4-benzodiazepin-2-one, flunitrazepam) (I) has received a great deal of attention due its medical [1] and increased elicit usage [2,3,4,5,6,7]
The psychotropic sedative effects and memory loss exhibited by Rohypnol has led to it being increasingly reported in sexual assaults and increasingly involved in robberies, where the victim is rendered unable to resist the attacker and has an incomplete recollection of the attack
We have reported on a variation of this system, which we described as the dual reductive mode [23]
Summary
Benzodiazepin-2-one, flunitrazepam) (I) has received a great deal of attention due its medical [1] and increased elicit usage [2,3,4,5,6,7]. In the series configuration the first upstream electrochemical cell can be used as a “generator” where an electroactive product can be formed which is detected at the following downstream “detector” cell This approach provides a number of advantages, the main one of these being that the electrochemically generated can be more oxidised or reduced than the parent compound. We have reported on a variation of this system, which we described as the dual reductive mode [23] For certain compounds such as p-nitrophenol, by selection of the correct experimental conditions, species can be formed at the generator electrode which can be reduced further at the detector electrode at potentials close to 0 V. In the final section we investigate the possible advantages of both the redox mode the dual reduction mode for the determination of Rohypnol in beverage samples
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