Detection of antibiotic residues in milk

The paper method, that is, the PD method (Paper Disc). Commonly used paper methods are Bacillus subtilis paper method and Adiposeia thermophila paper test method. These two methods are mainly used to detect β-lactam antibiotics in milk. The operation process is basically the same, and the selected strains are different from the antibiotic residues in milk. The existing detection methods: 1. Paper method: Paper method , that is, the PD method (Paper Disc). Commonly used paper methods are Bacillus subtilis paper method and Adiposeia thermophila paper test method. These two methods are mainly used to detect β-lactam antibiotics in milk, and the operation process is basically the same, and the selected strains are different. The results of the B. subtilis paper test are prone to false positives. In order to determine whether the positive substance is penicillin (or β-lactam), the heated milk sample is treated with penicillinase to inactivate penicillin in the milk sample. Then test again, the detection limit can reach 0.01 IU / mL. The Astragalus faecalis paper test method is not only used to detect β-lactam antibiotics in milk samples, but also indicates whether other bacteriostatic substances are still present, and the detection limit can reach below 0.008 IU/mL. The results are generally available within 4 hours. Therefore, in practice, the A. thermophilus paper method is more widely used than the B. subtilis paper method. In addition, Shen Baosheng (1991) made further research and improvement on the paper method. The improved paper method can not only determine the type of antibiotics, but also improve the detection rate and accuracy. The minimum detectable amount of chloramphenicol is 0.01mg/kg, oxytetracycline 0.05mg/kg, streptomycin 1mg/kg, Erythromycin 0.05mg/kg, penicillin 0.0025mg/kg. 1.1 Microbiological detection method: Microbiological detection method is a widely used method. The measurement principle is based on the anti-microbial physiology and metabolism inhibition of antibiotics to determine the antimicrobial residues in the sample, such as the paper method (PD). ), TTC method, swab method (STOP), etc. Using the traditional microbiological detection method, the disadvantages are: (1) long time; (2) the color rendering state is judged by the naked eye, which is easy to produce errors, and the reddish person cannot make an accurate judgment; (3) the operation is complicated. The advantage is that the cost is low and the general laboratory can operate. Among them, the paper method and the TTC method are two commonly used microbial detection methods for detecting drug residues in milk. 1.2 TTC method: TTC method, ie tripheye tetrazolium chloride, is the detection method for checking antibiotic residues in milk (GB5409-85) prescribed in China's food hygiene standards. The method is simple, fast, and requires no special equipment. It can be reported in 3~4h, which is very suitable for use in pasture, dairy and food hygiene inspection departments. The sensitivity (minimum detectable amount) of the TTC test used to detect various antibiotics was: penicillin 0.004 U/mL, streptomycin 0.5 U/mL, gentamicin 0.4 U/mL, kanamycin 5 U/ mL. At present, the trend is to study more sensitive, accurate, simple and rapid microbial detection methods. For example, in the United States and Canada, the swab method and the bovine antibiotic and sulfonamide test method (CAST) are used. In addition, a new experimental method, the Rapid Antibiotic Screening (FAST), has been added in the United States in recent years. Although these rapid microbiological assays sometimes produce some false positives, they are allowed to some extent; if such a situation arises, further confirmation experiments can be performed. 2, physical and chemical detection method: physical and chemical detection method is to use the special reaction or property of the group in the antibiotic molecule to determine its content, such as high performance liquid chromatography, gas chromatography, mass spectrometry, combined technology, etc. Qualitative, quantitative and drug identification, the sensitivity is higher, but some test procedures are more complicated, and some test costs are higher. In the detection of antibiotic residues in milk, the most commonly used physical and chemical detection methods are high performance liquid chromatography and combined technology. 2.1 High Performance Liquid Chromatography High performance liquid chromatography (HPLC) is a widely used physical and chemical detection method. It introduces the theory of gas chromatography. It uses high-pressure pump, high-efficiency stationary phase and high-sensitivity detector to achieve separation. Fast, efficient and automated. Almost all compounds, including highly polar/ionic analytes and macromolecules, can be determined by HPLC. The separation mechanism of HPLC is the same as that of conventional column chromatography, but the packing is finer (ф 5～10μm), driven by high pressure pump, high column efficiency (105 trays/m), fast speed and sensitivity similar to GC. Compared with GC, HPLC mobile phase participates in the separation mechanism, and its composition, ratio and pH can be flexibly adjusted, such as ion-pair chromatography, micellar chromatography, chiral separation chromatography, etc., so that many extremely difficult analytes can be analyzed. . Reversed phase HPLC is the fastest growing and has become the routine analytical method for most antibiotic residues. The main reasons are: (1) the chemically bonded stationary phase (C18 or C8) is stable and does not leaching; (2) using water-soluble organic solvents such as water, methanol or acetonitrile as the mobile phase, does not interfere with UV detection, and has low cost; 3) The polar impurities in the sample flow first, and the sample can be repeatedly injected after the peak of the analyte is detected, and the analysis speed is fast. The most common detection methods are concentration type UV detectors and fluorescence detectors. UV detectors (UVD) are the most popular, followed by fluorescence detectors and electrochemical detectors (EChD). Because the amount of drug residues in the milk sample is small, the background interference is often very serious, so the sensitivity of the UV detector detection residue is generally improved by the pre-column derivatization reaction. Peng Li et al reported the detection of residual chloramphenicol in milk by high performance liquid chromatography (HPLC), the residual chloramphenicol in milk was extracted with ethyl acetate, and the sample was detected at 278 nm with a UV detector. The average yield is 94.8%, the coefficient of variation

Rechargeable Vape Pod

Suizhou meters simi intelligent technology development co., LTD , https://www.msmsmart.com