Extraction is often susceptible to matrix interference. One analytical method is fine in this matrix but can become problematic in another matrix. If we encounter such a situation, how can we improve the QuEChERS method to overcome it?
For pesticide residues, most of the food samples do not exhibit matrix interference except for some dry and greased samples. However, for some complex samples such as tea, traditional Chinese medicine, spices, liver and citrus oil, regardless of the QuEChERS method we apply, there is always the adsorption of the substrate on the pesticide residue. This is related to the method itself.
When the matrix contains impurities similar in structure to the analyte, it is difficult to purify it by the sample pretreatment process. Of course, some means such as adjusting the extractant, adjusting the pH, adding salt, changing the volume ratio, adding water, adding adsorbent can be of some help.
For example, acidic herbicides like phenoxyalkanoic acids tend to form covalently bonded residues. Such legally used pesticides are quite typical and therefore must be released prior to liquid-liquid extraction. Usually, we can firstly perform alkaline hydrolysis for 30 minutes by adjusting the pH to 12, and then have it return to neutral for QuEChERS extraction.
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