32 February / March 2017 NaCl to 800 mg MgSO4 : 200 mg NaCl. The
volume of acetonitrile was also minimised to account for the reduction. The compounds of interest explored in this method are also quite diverse in regards to polarity. In further studies, Lehotay et al. found that buffering the extraction to lower the pH greatly improved the recovery of several compounds [6]. With this approach, samples were extracted at a higher pH to promote analytes into their unionised form, and thus making it easier for them to partition into the organic phase of the initial extraction.
Several studies have been done to introduce QuEChERS to the forensic community [5,7- 8]. In a recent investigation by Dulaurent et al. [7] a single step QuEChERS approach was taken in order to reduce the amount of time for the extraction and increase throughput. The authors produced sound results, even with the elimination of the dSPE step. For the purposes of this investigation, dSPE was executed to further clean up samples (Figures 2 and 3) and introduce a higher threshold of sample purity to the instrumentation at hand. Three dSPE sorbent combinations were explored for maximum clean-up: MgSO4
+ C18 + C18 , MgSO4
+ Primary Secondary Amine (PSA) sorbent, and MgSO4
+ PSA. PSA and C18
were included in the evaluation due to the high anticipated lipid content of the liver samples and both sorbent’s enhanced ability to irreversibly retain such interferences. To evaluate the varying combinations in question, a small experiment was done by preforming the dSPE step of the procedure utilising the basified acetonitrile extraction solvent spiked with the drugs in question. The final ‘extracts’ were then compared to neat standards that were spiked into the same extraction solvent. Eliminating the matrix factor from this investigation allowed for observations to be made in regards to how the analytes would respond to the sorbents in question by removing any bias that may have occurred do to analyte enhancement or suppression upon analysis. While some analyte loss was noted with all of the sorbent combinations, MgSO4
+C18
only demonstrated minimal analyte loss, where any combinations featuring PSA were
Figure 3
affected at a much greater extent. Many of the analytes compromised in the presence of PSA featured two ionisable groups and contained partial negative charges at the basified pH. The loss is most likely attributed to the PSA forming ionic bonds with the analytes that possess that negative charge.
Conclusion
The QuEChERS method was conceptualised around the need to extract various types of compounds from a diverse group of matrices in a single, universal method. The expansion of the QuEChERS methodology outside of the food safety industry not only demonstrates its superior ability for sample extraction and clean-up, but also
signifies how rugged the technique is. While the method itself has not proven to be a guaranteed, single solution to all of the challenges analysts face, it has begun to offer new advantages to the forensic toxicology community when overcoming complex matrices.
References
1. Anastassiades M, Lehotay SJ, Stajnbaher D, Schenck FJ. Fast and easy multiresidue method employing acetonitrile extraction/ partitioning and dispersive solid-phase extraction for the determination of pesticide residues in produce. J AOAC Int. 86 (2003) 412.
2.
Quechers.com Figure 2
3.
sampleprep.unitedchem.com/products/ quechers
4. Levine, Barry, Ph.D.,DABFT,DABCC-T, ed. Principles of Forensic Toxicology. 3rd ed. Washington DC: ACC, 2009. Print.
5. Westland, Jessica L., and Frank L. Dorman. QuEChERS Extraction of Benzodiazepines in Biological Matrices. Journal of Pharmaceutical Analysis 3.6 (2013): 509-17.
6. Steven J.Lehotay,Kyung AeSon, Hyeyoung Kwon, Urairat Koesukwiwat, Wusheng Fu, Katerina Mastovska, Eunha Hoh, Natchanun Leepipatpiboon. Comparison of QuEChERS sample preparation methods for the analysis of pesticide residues in fruits and vegetables. Journal of Chromatography A – 2010
7. Dulaurent, Sylvain, Souleiman El Balkhi, Lauranne Poncelet, Jean-Michel Gaulier, Pierre Marquet, and Franck Saint-Marcoux. “QuEChERS Sample Preparation Prior to LC-MS/MS Determination of Opiates, Amphetamines, and Cocaine Metabolites in Whole Blood.” Analytical and Bioanalytical Chemistry 408.5 (2016): 1467-474.
8. Plössl F, Giera M, Bracher F. Multiresidue Analytical Method Using Dispersive Solid- phase Extraction and Gas Chromatography/ ion Trap Mass Spectrometry to Determine Pharmaceuticals in Whole Blood. Journal of Chromatography A 1135.1 (2006): 19-26.
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