Analysis of tetracycline residues in bovine milk by CE‐MS with field‐amplified sample stacking

A rapid, sensitive, and robust CE‐MS method has been developed for the determination of tetracycline, oxytetracycline, and chlortetracycline in milk. Field‐amplified sample stacking with electromigration injection (FASS‐EMI) was used for the online concentration of tetracyclines. The conditions of separation, MS detection, and stacking were systematically optimized. The optimum buffer composition was 35 mM Tris, 1.1% formic acid, 5% methanol, and 15% ACN. By using the online concentration method of field‐enhanced sample stacking (FESI)‐EMI stacking, the sensitivity was increased six‐ to seven‐fold. The RSDs (n = 6) of the relative migration time of tetracyclines were 1.1–1.4% for intraday and 2.4–2.9% for interday. The RSDs (n = 6) of the relative peak area of tetracyclines were 3.2–4.6% for intraday and 4.7–6.1% for interday. The LODs (S/N = 3) were 7.14 ng/mL for tetracycline, 11.4 ng/mL for oxytetracycline, and 14.9 ng/mL for chlortetracycline. The method has been successfully used to analyze tetracyclines residues in bovine milk.