Seven Common Methods in Pesticide Residue Detection Pretreatment

Original Title: Seven Common Methods in Pesticide Residue Detection Pretreatment 1. Soxhlet extraction (Automatic Rope Extraction) Soxhlet extraction is a classical extraction method, which is still widely used in sample preparation for pesticide residue analysis. The United States Environmental Protection Agency (EPA) uses it as one of the standard methods to extract some pesticide targets, such as Fe, which may cause the decomposition of some organochlorine pesticides). In addition, hlet eapan's "JAP Positive List Detection Method for Pesticide Residues in Food, Veterinary Drugs and Feed Additives". In these two methods, the extraction solvent generally used is mostly polar solvent,wiped film evaporator, and acetonitrile is mostly used in the standard method. Because the water content in these samples is generally high, if a single non-polar solvent is used for extraction, the extraction effect will be reduced due to its strong hydrophobicity and limited ability to infiltrate or penetrate the sample. There is also an important pretreatment step, namely solid-liquid separation, in the oscillation method and the tissue mashing method (homogenization method), as well as the ultrasonic extraction and microwave extraction methods mentioned later. This step can be achieved by filtration (suction filtration) and centrifugation. Filtration may be carried out with simple filter paper or by suction filtration with a filter aid such as Celite 545.
If centrifugal separation is used, care should be taken to prevent the container from breaking. Expand the full text In these two extraction methods, in order to avoid the loss caused by liquid transfer, part of the liquid is usually extracted directly from the extraction liquid for subsequent operation. 3. Ultrasonic extraction method Ultrasonic extraction has the advantages of no heating, simple operation, time saving and high extraction efficiency. It is also widely used in sample pretreatment of pesticide residue analysis, such as EPA3550 method. Ultrasonic extraction is generally carried out by using an ultrasonic cleaner (Fig. 2) or a special needle extractor (such as an ultrasonic cell disruptor, Fig. 3). No matter what kind of extraction equipment, it uses the "cavitation" effect of ultrasonic wave. Ultrasonic extraction has obvious characteristics and does not need heating, which is especially suitable for the extraction of thermally unstable targets. At present, the ultrasonic cleaner is mostly used as the extraction instrument in the laboratory. Generally, before ultrasonic extraction,50l rotovap, the sample to be extracted should be soaked in the extraction solvent for a period of time, so that they can fully contact and penetrate each other. In the ultrasonic extraction, it is preferable to use a mixed extraction solvent and extract in steps to improve the extraction efficiency of the target substance. Ultrasonic extraction method also has certain requirements for glass containers, if the he like. Now the supercritical fluid extraction instruments (such as ASI in the United States) have been greatly improved, and the performance, function and volume of the instruments have been greatly improved. Due to the use of special equipment and consumables, the literature on SFE analysis of pesticide residues in China is still relatively small compared with other methods. The biggest advantage of supercritical fluid extraction is the use of organic solvents (basically not used or rarely used), and it is easy to extract some macromolecular compounds, cbd centrifugal extractor ,thin film distillation, heat-sensitive and chemically unstable substances. Of course, the cost of equipment is a problem that many laboratories must consider. 5. Accelerated solvent extraction Accelerated solvent extraction was selected as the standard method by the EPA (EPA 3545). Accelerated solvent extraction (ase) is easily automated (sequential extraction) and is currently used as a pretreatment for the analysis of pesticide residues in soil and biological samples (Figure 4). Compared with Soxhlet extraction and ultrasonic extraction, accelerated solvent extraction consumes less solvent, has a high degree of automation and is relatively simple to operate, but the biggest problem of accelerated solvent extraction is the cost of analysis, that is, the instruments and consumables are relatively expensive (especially the filter membrane, disposable), which is difficult for the general laboratory to bear. The efficiency of accelerated solvent extraction is higher, but the general co-extract is relatively more, which will affect the subsequent purification operation. At present, online purification has been reported (for example, there is relevant purification information on the website of Diane Company), that is, the adsorbent required for purification is loaded under the sample to achieve the purpose of extraction-purification. However, for the detection of different samples and pesticide residue targets, the specific method needs to be determined by many experiments.
ASE has a high degree of automation, simple operation, easy parameter setting, and automatic filtering in the subsequent operation, which greatly reduces the labor intensity of the experimenter and avoids the loss of the target. When extracting d-solid separation can also be achieved by means of filtration; the extraction efficiency of microwave extraction is higher Moreover, the co-extraction of pigments in samples, such as plants, is smaller, which makes the purification slightly easier.
Relatively speaking, open microwave extraction is slightly inferior to closed extraction in terms of the amount of samples proA uniform fraction of the sample is placed on the surface of the solid phase particles to form a semi-solid column, which is then washed and eluted using an operation similar to SPE. Its advantages are as follows: Depending on the mechanical shearing force of filler particles and the impurity removal effect of C18 and other fillers, the sample homogenization and extraction are completed in the same process without solvent and impurity removal steps; C18 and the like can destroy the cell membrane of the lipid, so that the cell components are released and redistributed in the filler; and the sample matrix and the components to be tested are uniformly distributed in the filler. The various components of the sample are dissolved and distributed in the bonding phase on the surface of the filler according to the polarity according to the law of similar dissolution; The retention of components is related to the filler, sample matrix and solvent; The MSPD sample processing speed is fast, the amount of solvent is small, and the amount of sample is also small, so the detection method (instrument) is required to have high sensitivity. The commonly used detection methods include the determination of chloropropanol in soy sauce,wiped film evaporator, the determination of pesticide components in apple juice, the extraction and determination of persistent compounds (polychlorinated biphenyls), etc. Return to Sohu to see more Responsible Editor:.
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