Determination steps of oxytetracycline, tetracycline, chlortetracycline and doxycycline residues in milk and milk powder

12.

(1) Liquid chromatography measurement conditions

Column: Kromasil 100-5C ₁₈ , 5 μm, 150 mm×4.

(2) Liquid chromatography determination

The working solution are mixed standard sample, the concentration of abscissa, the peak area of the vertical axis, the standard curve, the samples were quantified using a standard curve, the sample solution oxytetracycline , tetracycline , chlortetracycline , strong mold The response value of the element should be within the linear range determined by the instrument

Figure 12-11 Liquid chromatograms of oxytetracycline, tetracycline, chlortetracycline, and doxycycline standard substances

12.

(1) Selection of extraction conditions

Tetracycline antibiotic molecules contain several hydrophilic hydroxyl groups, are easily soluble in water and lower primary alcohols, and are relatively stable in neutral and acidic solutions

Milk is rich in protein and calcium, which affect the extraction of tetracycline antibiotics

(2) Optimization of purification conditions

In the experiment, the combined effect of WCX, Oasis HLB single-solid phase extraction column and Oasis HLB solid phase extraction column plus carboxylic acid cation exchange column was compared

Figure 12-12 Chromatogram of blank milk sample after purification by HLB solid phase extraction column

Figure 12-13 The chromatogram of a blank milk sample after purification by HLB and Carboxylic Acid dual solid phase extraction column

Table 12-28 The elution effect of different solvents on HLB column

(3) Optimization of chromatographic conditions

The Kromasil 100-5 C ₁₈ (150 mm×4.