Food safety in general has become a top priority as food importing and processing have become greater sectors of the industry. Moreover, increasingly efficient methods for food testing have become necessary to test for the presence of pesticides and other residual compounds. These concerns extend to the growing cannabis industry as well and the myriad of consumables that have become available in recent years -- a trend is certain to continue as more states adopt cannabis friendly regulations regarding it’s use and presence in foods.
Pesticides can be a necessary evil to prevent crop damage by mold and insects, however, the persistence of even trace amounts can pose a danger to consumers. Highly sensitive and selective methods are needed as a result. Although attention has been given to the development of novel methods for pesticide analysis, liquid-liquid extraction using a technique such as QuEChERS (Quick, Easy, Cheap, Effective, Robust, Safe) has shown to be an effective method for both food and cannabis product related testing.
To start with the basics of the method, the sample is first homogenized in a blender or (cryo)mill and placed in a vessel. Acidified acetonitrile is added to the material (1:1 with solution or with added water) and incubated with shaking and/or homogenizer balls if necessary. After incubation, QuEChERS salts are added and the mixture is shaken or vortexed, followed by centrifugation.
A key to the method is that although acetonitrile is miscible in water, it is salted out during the extraction process, thereby permitting the separation of organic compounds and water-soluble matrix materials. The resultant extract of the QuEChERS process has four layers: The top is the extract containing organic compounds and pesticides; next is the insoluble matrix component layer; followed by the water-soluble matrix components; and finally, the excess extraction salts at the bottom.
For pesticide analysis, a clean up step using a dispersive solid phase extraction (dSPE) kit provides further conditioning of the extract. This method improves performance by pulling out further interfering matrix components, while removing excess water to improve analyte partitioning. The resultant extract can be dried under nitrogen and resuspended in an appropriate solution for HPLC, GC-MS or LC-MS analysis. Quantitation, as discussed in subsequent articles, typically requires the use of analytical standards appropriate for the chosen analytical platform.
Several groups have applied extraction modifications to selectively isolate and analyze a greater number of pesticide residues from a wider variety of plants and consumables. Modifications of the salts and solution components lends to QuEChERS methods tailored toward the pesticides of interest. For instance, buffered extraction salts are amenable to more labile pesticides. Dispersive kit components are associated with removal of specific matrix components, such as organic acids, sugars, and lipids. Finally, standardized methodologies such as those approved by the Association of Official Chemists (AOAC) or the European Committee for Standardization (CEN) often dictate which kits and components are compatible with appropriate performance guidelines.
The data produced by high-performance instruments are only as solid as the quality of analyte material going in. With a greater range of compounds and concentrations used as pesticides in modern food production, it is imperative that analytical labs achieve the sensitivity and reliability needed to maintain high quality food safety. Modern methods aim to achieve greater depth of sample extraction in this regard.