In analytical toxicology, the extraction step is critical: the double aim is to separate xenobiotics from endogenous compounds and to clean-up the extract. Extraction processes such as liquid-liquid extraction and off-line solid-phase extraction are often efficient, but time consuming. Proteins precipitations with methanol or acetonitrile are quicker but only dedicated to whole blood or plasma-serum matrices. For more than ten years, another approach has been used for the determination of pesticides in food matrices (Anastassiades M et al. 2003). This method, named QuEChERS (Quick, Easy, Cheap, Effective, Rugged and Safe), is based on a quick extraction with an acetonitrile and salt combination. The aim of this presentation is to report biological and forensic toxicological applications of this method initially dedicated to pesticides in food.

200 to 500μL of acetonitrile were added to the sample (100μL of whole blood, urine, serum or plasma), followed by a small amount (i.e. 300mg) of QuEChERS salts (4g MgSO₄/1g NaCl/1g Sodium citrate dehydrate/0,5g Sodium citrate sesquihydrate). The mixture was vigorously shaken and then centrifuged at 13,000rpm for 10min. Before injection in the chromatographic system, the upper layer was diluted, or not, depending on the final application in LC-MS/MS.

Some examples of QuEChERS method applications together with the comparison with our previous methods are presented in the following table.

This approach was also successfully applied to the development of several new methods: antiepileptics, anticoagulants, curares, ivabradine… Despite the lower sample volume used and the simple sample preparation (coupled with a dilution of the sample), the obtained limits of detection that have been reached in LC-MS/MS were close or inferior to those obtained by GC-MS, using a time consuming extraction with a higher volume of sample. Among the previous methods cited, some of them have been successfully evaluated by the Comité Français d’Accréditation, according to the ISO 17025 standard.

In our opinion, the QuEChERS sample preparation is almost universal. The main benefit is the short time required for sample preparation and its efficiency in cleaning up the extract. The main limitation is the absence of a major concentration of the analytes. Nevertheless, in case of applications requiring a very low limit of detection, we can foresight that this problem could be solved with the next generation of mass spectrometers.
Table Abstract O28.CompoundUsual methodQuEChERS methodInstrumental methodSample volume (mL)Time prep (h)LOQ (μg/L)Instrumental methodSample volume (mL)Time prep (h)LOQ (μg/L)Dextropropoxyphen and metaboliteGC/MS1210LC/MS20.10.7510Verapamil and metaboliteGC/MS1220LC/MS20.10.7510TropatepineGC/MS1210LC/MS20.10.7510Opiates and cocaineGC/MS13.510–25LC/MS20.115AmphetaminesGC/MS12.510