Immersed single-drop microextraction combined with gas chromatography for the determination of sufentanil and alfentanil in urine and wastewater samples

An immersed single-drop microextraction (SDME) method coupled with gas chromatography flame ionization detection (GC-FID) was developed for the extraction and determination of sufentanil and alfentanil. These drugs were extracted from 4 mL stirred sample solution (pH 10.0) into a microdrop of 1-octanol, containing impurity C of fentanyl as internal standard. After the extraction, the microdrop was withdrawn into the syringe and injected directly into a GC injection port. The parameters influencing the extraction efficiency including the nature of the extracting solvent, pH and ionic strength of the solution, stirring rate and extraction time were investigated. At the optimized condition, (1.5 mu L 1-octanol as extracting solvent, stirring rate of 200 rpm, pH 10.0 and 30 min sampling time at room temperature, no salt addition), enrichment factors were 153 and 103 for sufentanil and alfentanil, respectively. Very good dynamic linear ranges (DLRs) were obtained in the range of 50 to 1000 ng mL(-1) for sufentanil and 60 to 1000 ng mL(-1) for alfentanil. Limits of detection (LODs) were 5 and 6 ng mL(-1) for sufentanil and alfentanil, respectively. Relative standard deviations (RSD) for five replications of both drugs were found to be less than 9%. Finally, the method was successfully applied to the extraction and determination of the sufentanil and alfentanil in urine and wastewater samples.