Application And Optimization Of QuEChERS Method In The Detection Of Pesticide Residues In Tea
Status quo of QuEChERS method
Based on the significant advantages of the QuEChERS method and the continuous development of instrument detection technology, analysts continue to expand the application field of the QuEChERS method. At present, the QuEChERS method is widely used in the detection of pesticide residues in high moisture samples such as fruits and vegetables, but also in oils and fats, grains, soil, Chinese herbal medicines, detection of pesticide residues in samples of animal origin, food, and milk, eggs, the muscle tissue of drug residues in samples. In addition, its research and application areas include food additives, polycyclic aromatic shorts, biotoxin, drug residues detection, and identification of illegal additives in traditional Chinese medicine.
Due to the many advantages of the QuEChERS method, analysts have also conducted more research on its application in the detection of pesticide residues in tea, and have made some progress.
Used an improved QuEChERS method to analyze 86 pesticide residues in green tea, black tea, and dark tea. They have extracted with triphenyl phosphate-added acetonitrile. The pH was adjusted with an agaric acid buffer solution. Anhydrous calcium chloride replaced anhydrous sulfuric acid. Magnesium removes excess water and is detected by LC-MS / MS and GC-MS / MS; the results show that the recovery rate of most pesticides among 86 pesticides is between 70% and 120%. When used the improved QuEChERS method to analyze the triazole fungicide residues in the tea leaves, acetonitrile was used as the extraction solvent. After purification by C18, PSA, and Flory silica, a liquid-liquid microextraction process was added to effectively reduce the interference of the matrix, the recovery rate of the obtained pesticide is between 91% -118%.
Compared with other plant-derived foods, tea is rich in alkaloids, tea polyphenols, and pigment compounds, which are easy to interfere with the detection. Therefore, optimizing the pretreatment conditions of tea samples is particularly important to reduce the detection limit and improve detection efficiency. When using the QuEChERS method for pretreatment, it is usually necessary to optimize the sampling volume, the types of extractants and purifiers and their amounts, etc., to meet the requirements of pesticide residue testing.
1. Optimization of sampling volume and sample pretreatment
The QuEChERS method was originally designed for vegetables and fruits with high water content, and the sampling volume is usually 10g. For tea leaves with low water content, the sampling volume should be appropriately reduced, usually 2g or 5g. Under the same conditions, reducing the particle size of the sample can increase its uniformity, making detection at a smaller sample size possible; however, if the sample particle is too small, it will affect the effect of centrifugal separation and supernatant absorption. Therefore, the appropriate particle size is particularly important for the feasibility and effectiveness of the detection.
Studies have found that the particle size of dried tea samples is 20-50 mesh is more appropriate; at the same time, in order to ensure that the analyte in the tea is easily extracted, a certain amount of water for soaking is often added. However, someone believes that for non-polar pesticides, the extraction of dry tea samples after soaking in water does not improve the extraction effect of such pesticides, but will increase the leaching of water-soluble impurities such as caffeine and increase subsequent purification difficulty.
It can be seen that whether water added during the pretreatment of tea samples depends mainly on the polarity of the target pesticide. For the detection of polar pesticides, pretreatment with water immersion can be used to improve the recovery rate of pesticides. For non-polar pesticides, on the basis of ensuring a higher recovery rate, organic solvent extraction can be used directly to reduce the leaching of water-soluble impurities.
2. Selection of extractant
The choice of extractant is one of the key factors for the development of a multi-residue analysis method. The choice directly affects the level of pesticide recovery and the difficulty of subsequent purification. Common extraction solvents used in the QuEChERS method include acetonitrile, ethyl acetate, and acetone. Compared with ethyl acetate and acetone, when acetonitrile is used to extract pesticides in tea, there are fewer co-extracted substances. At the same time, sodium chloride is added. By salting out, acetonitrile and water are easily separated. Therefore, acetonitrile is the most commonly used extraction solvent for the analysis of pesticide residues in tea under the QuEChERS method.
However, under the action of acetonitrile, some pesticides (such as dicofol, etc.)