Tandem dispersive liquid-liquid microextraction followed by high performance liquid chromatography for simple determination of thebaine and ketamine in biological fluids

A simple and efficient method named tandem dispersive liquid-liquid microextraction is applied for the determination of thebaine and ketamine in biological fluids. Thebaine is an ideal starting material that can be transformed into several opiates [1]. Ketamine induces loss of consciousness, amnesia, immobility, pain relief and sedation while the cardiopulmonary functions and the protective airway reflexes remain unchanged [2].This method, which is based upon two consecutive dispersive microextractions, is totally accomplish in 7 minutes, and by performing a fast back-extraction step, it provides a high sample clean-up [3]. The back extraction step is performed in less than 2 min, and very simple tools were required for this purpose. In addition to the increase in the sample clean-up, the analytes were extracted into the aqueous solution. Thus this step could cause eliminating the problem of injection of the organic solvent into the final instrument analyzer as well. On the other hand, unlike most methods coupled with DLLME for improving the sample clean-up, back-extraction of the analytes was a green step in the proposed method [4]. In order to achieve the best extraction efficiency, optimization of the variables affecting the method is carried out. Under the optimized experimental conditions, the relative standard deviations for the method was in the range of 8.9–9.7%. The calibration curves were obtained in the range of 3–1000 μg L−1 with a reasonable linearity (R2 0.995), and the limits of detection ranged between 1.0 and 1.5 μg L−1 (based on S/N = 3). Finally, the applicability of the proposed method was evaluated by the extraction and determination of the drugs under study in the human plasma samples.