Sample preparation is one of the most important steps in most analytical procedures to determine trace sedative-hypnotic drugs in biological samples with complex matrices. An ideal biological sample preparation technique should be simple, inexpensive, efficient, selective, and compatible with various analytical techniques. It should give a recovery as high as possible, use the minimum amount of solvent, and be environmentally friendly. Therefore, researchers are making great efforts to develop rapid, accurate, precise, and sensitive methods for the determination of sedative-hypnotic drugs in real biological samples [1].
The main aim of my study was the development of a new sensitive and specific method based on fast gas chromatography with negative-ion chemical ionization mass spectrometry (GC/NICI-MS) using a mixed-mode solid phase extraction for the quantification of sedative-hypnotic drugs in biological samples.
One of the greatest challenges with a residue analysis of sedative-hypnotic drugs is the selection of a sorbent suitable to achieve an acceptable sensitivity to all compounds characterized by different physicochemical properties. In this research, a mixed-mode polymeric sorbent with ion-exchange properties was applied. This sorbent is capable of hydrophilic-lipophilic and ion-exchange interactions [2-4], and therefore it is suitable for achieving an efficient extraction of all herein-investigated analytes by a single extraction step. For that reason, biological sample preparation conditions including a selection of the solvent for washing and elution steps, pH values were optimized. To the best of my knowledge, this method has been used for the first time for the optimization of sample preparation at pH 1.0.
The developed method for the determination of sedative-hypnotic drugs in biological samples was validated following the recommendations for new methods [2,5,6]. The linear relationships with the correlation coefficients (r2) better than 0.996 were evaluated. It was determined that extraction efficiency ranged from 82.9 (±6.2) % to 94.6 (±3.4) %. The precision (RSD) for analytes was 4.08-9.52 %, while the accuracy was in the range of 93.0-106.3 %. Moreover, this method has several advantages: elimination of interferences, low volume of samples (0.2 mL), a multi-residue analysis, and very fast chromatographic separation of analytes (3.9 min). According to the results, the developed method is accurate, precise, effective, selective, sensitive, and specific enough to detect analytes after a long time of use of a single oral administration of some psychoactive substances. Furthermore, this method enables reaching the highest specificity for major analytes and meets the requirements of good laboratory practice, especially when applied to pharmacodynamic investigations. Ultimately, the developed method has been applied in routine toxicological analysis during the investigation of both clinical and forensic cases. This research was supported by the State Forensic Medicine Service, Lithuania