Detection of Tetracyclines in Animal Muscle Using SPE-HLB Sorbent：

1. Extract an appropriate amount of sample with Na₂EDTA-McIlvaine buffer, centrifuge, and take the supernatant as the solution to be cleaned up (see GB/T 20764-2006 for details).

2. Conditioning: Wet the KBsphere® SPE-HLB cartridge with 5 mL methanol and 10 mL water, respectively.

3. Loading and washing: Load the solution to be cleaned up onto the cartridge, allow it to pass through slowly, and wash the cartridge with 5 mL of 5% methanol-water.

4. Elution: Elute with 15 mL ethyl acetate, blow dry under nitrogen, make up to volume with mobile phase, and determine by HPLC-UV.