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1. Experimental purpose According to the standard GB/T 14931.1-94, the residual amount of oxytetracycline, tetracycline and chlortetracycline in livestock and poultry meat was determined. The minimum detectable concentrations were: 0.15, 0.20, 0.65 mg/kg.
2. Test principle The sample is extracted, directly filtered by microporous membrane filtration, separated by reversed-phase chromatography, detected by ultraviolet detector, and compared with the standard, the order of peak is oxytetracycline, tetracycline and chlortetracycline. Standard addition is quantified.
3. Reagents
3.1 Acetonitrile (analytical grade).
3.2 0.01 mol/L sodium dihydrogen phosphate solution: Weigh 1.56 g (±0.01g) of sodium dihydrogen phosphate (NaH2PH4.2H2O) dissolved in distilled water, dilute to 100 mL, filter through filter (select microporous membrane for 0.45 μm), spare.
3.3 Oxytetracycline (OTC) standard solution: Weigh oxytetracycline 0.0100g (±0.0001g), and use 0.1mol/L hydrochloric acid solution containing 1mg of oxytetracycline per ml.
3.4 Tetracycline (TC) standard solution: Weigh 0.0100 g (±0.001 g) of tetracycline, dissolve it with 0.01 mol/L hydrochloric acid solution and make up to 10.00 mL. This solution contains 1 mg of tetracycline per ml.
3.5 chlortetracycline (CTC) standard solution: Weigh chlortetracycline 0.0100g (±0.0001g), dissolve in distilled water and make up to 10.00mL, this solution contains 1mg of chlortetracycline per ml. The above standard products are converted at 1000 units/mg. The 3.3~3.5 solution should be stored below 4 °C and can be used for 1 week.
3.6 Mixing standard solution: Take 1.00 mL of each of 3.3 and 3.4 standard solutions, take 2.00 mL of 3.5 standard solution, place in a 10 mL volumetric flask, add distilled water to the mark. This solution contains 0.1 mg of oxytetracycline and tetracycline per liter, and 0.2 mg of chlortetracycline.
3.7 5% perchloric acid solution.
4. Instrument
4.1 High Performance Liquid Chromatograph (HPLC): with UV detector.
4.2 Oscillator: Tianjin Hengao Technology Development Co., Ltd.
4.3 Filter: Tianjin Hengao Technology Development Co., Ltd.
4.4 Ultrasound: Tianjin Hengao Technology Development Co., Ltd.
5. Chromatographic conditions
5.1 Column: ODS-C18 (5 μm) 6.2 mm × 15 cm.
5.2 Detection wavelength: 355 nm.
5.3 Sensitivity: 0.002 AUFS.
5.4 Column temperature: room temperature.
5.5 Flow rate: 1.0 mL/min.
5.6 Injection volume: 10 μL.
5.7 Mobile phase: acetonitrile / 0.01 mol / L sodium dihydrogen phosphate solution (pH 2.5 with 30% (V / V) nitric acid solution), 35:65 (V / V), degassed by ultrasonic for 10 min before use.
6. Method of operation
6.1 Sample determination: Weigh 5.00 g (±0.01 g) of minced meat (<5 mm), place in a 50 mL Erlenmeyer flask, add 25.0 mL of 5% perchloric acid, and shake for 10 min on a shaker. The sample was transferred to a centrifuge tube, centrifuged at 2000 r/min for 3 min, and the supernatant was filtered through a 0.45 μm filter membrane. 10 μL of the solution was taken for injection, and the peak height was recorded, and the content was found from the working curve.
6.2 Working curve: Weigh 7 portions of minced meat samples, each 5.00 g (±0.01 g), and add mixed standard solutions 0, 25, 50, 100, 150, 200, 250 μL (including oxytetracycline, Tetracycline is 0, 2.5, 5.0, 10.0, 15.0, 20.0, 25.0 μg, containing chlortetracycline 0, 5.0, 10.0, 20.0, 30.0, 40.0, 50.0 μg), operating according to 6.1, with peak height as ordinate, The working curve is plotted with the antibiotic content as the abscissa.