The Development and Application of QuEChERS
Pesticide is used more during the growth and storage of crops, and the widespread use of pesticides can cause residues on crop products to enter the human body through the food chain, thereby endangering human health. As food safety issues become more prominent, governments and related agencies have developed residue limits for a variety of pesticides on different crops.
Among them, the International Tobacco Scientific Research Collaborating Center formulated the Guiding Limits for pesticide residues in tobacco in 2003, a total of 99 pesticides; and then revised and expanded in 2008, now contains 118 kinds of pesticides.
The increase in pesticide types and the strictness of the limit indicators have proposed five series of standards for the analysis and detection of various pesticide residues in tobacco. The first three are multi-pesticide residue analysis methods, which contain about 160 kinds of pesticides. The detection means used mainly include gas chromatography (GC), gas chromatography-mass spectrometry (GC-MS), and liquid chromatography-tandem mass spectrometry (LC-MS/MS).
QuEChERS method
The pretreatment method is mostly based on the QuEChERS method, which is characterized by infiltration of the pulverized tobacco sample, extraction with acetonitrile, the addition of a salting-out package, centrifugation, and adsorption with N-propyl ethylenediamine (PSA) to purify. Since 2003, QuEChERS and its improved methods have been widely used in the analysis of various pesticide residues in substrates such as vegetables, fruits, grains, tea, and tobacco.
Compared with other commonly used pre-processing technologies (such as SPE, GPC, etc.), the advantages of QuEChERS lie in the following:
1) More than 200 compounds can be detected at the same time, and the recovery rate is higher than 80%.
2) The internal calibration method is used to calibrate, which has high precision and accuracy.
3) There are about 30 or 40 pre-weighed samples that can be processed in one hour. It can be operated simply and has a short detection period.
4) Only use acetonitrile as a solvent. It has low consumption and price. And it is low environmental pollution and little risk to the experimenter.
5) It is simple to use the instruments, mainly centrifuges, and centrifugal test tubes.
QuEChERS has undergone several major optimization changes since it was developed. The first improvement was the use of the buffer in the extraction process. The recovery of some compounds is susceptible to the influence of pH, which can be effectively solved by using the buffer. The second improvement is the purification effect.
The use of C18 filler together with PSA can improve the purifying effect of samples, especially for oil-rich samples. The third is to select suitable adsorbents for different sample matrices to improve the purification effect. For example, adding a small amount of graphitized carbon black can adsorb chlorophyll, carotenoids, and other impurities.
The Application of QuEChERS Kits
In fact, the application of QuEChERS kits is the extraction of samples by acetonitrile or acidic acetonitrile after homogenization. Afterward, the laboratory workers use QuEChERS salts, including magnesium sulfate and buffer salt, to make salting stratification.
Also, by using the dispersive solid-phase extraction and combination of other adsorbents and most of the chaff interferents, such as organic acid, aliphatic acid, and carbohydrate in the base materials. Lastly, operating the elimination by centrifugation and taking the supernatant to make analysis, so that the laboratory workers can achieve the aim of purification.
In general, the steps for using QuEChERS Kits include five steps.
1. Grinding and weighing of samples.
2. Extraction and separation by acetonitrile of a single solvent.
3. Eliminate water by adding magnesium sulfate and another kind of salt.
4. Eliminating impurities by adding PSA and another adsorbent.
5. Using GC-MS, and LC-MS to test the liquid supernatant.
Basically, the QuEChERS salts include buffer salt and anhydrous magnesium sulfate. Under normal conditions, the buffer salt can make the extraction environment at a mild PH level, and make sure the target compound stay stable. On the other side, the anhydrous magnesium sulfate has the water absorptivity, and can completely separate the acetonitrile extraction solution from the water in the base material.
