How Does the QuEChERS Method Solve the Problem of Matrix Dependencies?
Q: Extraction is often susceptible to matrix interference. One analytical method is fine in this matrix but it may become problematic in another matrix. Have you encountered this situation with QuEChERS? If so, how can the QuEChERS method be improved to overcome it?
A: For pesticide residues, most food samples do not exhibit matrix interference (except for some dry, oily samples). However, for some complex samples (such as tea, Chinese medicine, spices, liver, citrus oil, etc.), there will be adsorption of pesticide residues by the matrix, no matter what QuEChERS method you use. This is related to the method itself, because if the matrix contains impurities similar to the structure of the analyte, it is difficult to remove through the sample pretreatment process.
Of course, some means such as adjusting the extractant, adjusting the pH, adding QuEChERS extraction salts, changing the volume ratio, adding water, and adsorbent can also play a role. For example, under the influence of PH, Anastassiades found that when quantitatively extracting nicotine from mushrooms, the pH needs to be adjusted to 10-11. However, when extracting chlorothalonil from onions and leeks, the pH should be adjusted to 2, so as to reduce the adsorption of the substrate and improve the recovery rate. In addition, for the pesticides of worms, the above low pH value is also necessary.
Acidic herbicides, such as phenoxy alkanoic acids, tend to form covalently bonded residues. This type of pesticide is typical of legally used pesticides, so it must be released before liquid-liquid extraction. Usually, we can adjust the pH to 12 for alkaline hydrolysis for 30min (alkaline hydrolysis step), and then adjust it back to neutral for QuEChERS extraction.
If it is a certain type of pesticide, the targeted pre-treatment QuEChERS method can achieve good recovery, but at this time it will inevitably reduce the recovery of other pesticides. This situation will inevitably occur when multiple types of pesticides are extracted. For these complex situations, we rely on high-quality chromatography-mass spectrometry.
The instrument with high sensitivity allows us to allow the final extract to have a lower sample concentration (such as 0.1g / ml in some examples), and the highly selective chromatography-mass spectrometer allows us to ignore impurities that peak simultaneously with the target. If ruggedness or detection limits are compromised too much, gel chromatography or fractionated extracts may be a good solution.
But at this time, we must also consider what requirements the obtained data needs to meet, test time, cost, labor, equipment, and other factors. We don’t think QuEChERS is omnipotent, we just think it’s fast and easy to use. If it can be used, you will find that it will save a lot of QuEChERS method development time and workload.
Future development
With the development of LC / MS technology, the multi-residue analysis will be the development direction of QuEChERS in many types of animal residues, and medical and forensic testing. The development of QuEChERS is inseparable from the development of modern chromatography and mass spectrometry technology, and sample processing technology will continue to be inseparable from these detection technologies.
The enrichment of representative samples in testing is very important. When analytical chemistry continues to develop into small, micro, and nano-types, sample processing technology to get meaningful results will be increasingly difficult.
If one day, thousands of data from different parts of representative samples can be quickly obtained-we expect this to be a development direction of sample processing in the future, but in the analysis of multiple types and multiple residues, there is still a long way to go.
