Microwave-assisted preparation of boron acid modified expanded graphite for the determination of chloramphenicol in egg samples

A rapid and simple method for the synthesis of boron acid modified expanded graphite (B-EG) with the assist of microwave irradiation was developed. The synthesis process can be completed in one-step, where H₂SO₄ and H₃BO₃ were used as intercalating agent and KMnO₄ was used as oxidizing agent. The obtained B-EG was worm-like and lamellar structure with plenty of small dispersed particles. The B-EG was successfully used as solid phase extraction absorbent for the enrichment and separation of chloramphenicol in egg samples, followed by liquid chromatography tandem mass spectrometry analysis. The predominant conditions affecting extraction efficiency were optimized. Under optimal conditions, the detection limit of the method was 0.27 ng g⁻¹. The relative standard deviations of within-day and between-day were in the range of 2–6% and 2–8%, respectively. The method was successfully used to detect chloramphenicol in five egg samples. At the spiked concentration of 50 ng g⁻¹, the satisfactory recoveries (87–94%) were obtained.