Background Sulfonamides have been widely used in the prevention and clinical treatment of bacterial diseases in livestock and poultry. The use of sulfonamides increases the risk of veterinary drug residues in animal derived foods. The traditional reversed phase liquid chromatography methods for sulfonamides residues detection in animal derived foods have the problem of high consumption of organic solvents. Objective The aim of this study was to establish a green high-performance liquid chromatography method for the detection of sulfonamides residues in different animal-origin foods. Method The sample extraction solutions were purified by the Agela Cleanert PEP-2 cartridge and analyzed by the high-performance liquid chromatography method using ethanol as the green alternative solvent. Results The proposed method was validated in terms of linear range (20–1000 μg/kg), limit of detection (3.0–12.3 μg/kg), limit of quantitation (10–43 μg/kg), accuracy (80.7–101.3%), and repeatability and reproducibility (RSD <5.9% and RSD <8.5% respectively). Conclusions The proposed method is an environmentally friendly, sensitive and reliable high-performance liquid chromatography method for simultaneous determination of sulfonamide residues in animal-origin foods. Highlights In this work, we firstly developed a green high-performance liquid chromatography method for simultaneous determination of the residues of nine sulfonamides in milk and beef with ethanol as the green alternative solvent.

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Table S1. The structures and basic properties of the target compounds. Compounds Structure Log Po/w a Number of hydrogen bond a: the data about log Po/w and number of hydrogen bond donors comes from https://pubchem.ncbi.nlm.nih.gov (accessed January 14, 2019).

A new method for the measurement of aprotinin potency by CZE-UV detector was established for the first time. The on-line mixing of substrate, trypsin and aprotinin using at-inlet technology was realized by the established method. Enzymatic reaction, separation, and detection of substrate and product can be performed simultaneously online. The aprotinin potency can be measured within 4 min. The response surface methodology was used to optimize the incubation conditions of trypsin and substrate, and the optimized conditions were obtained under 17.39 mM phosphate buffer at pH 7.6, 1.40 min of incubation time. The repeatability of proposed method was evaluated in three different systems of capillary zone electrophoresis: (i) only substrate; (ii) trypsin and substrate; (iii) aprotinin, trypsin and substrate, and the RSDs of migration times and peak areas of substrate were less than 2.7 and 3.1%, respectively. The RSDs of migration times and peak areas of product were less than 2.1 and 3.0%, respectively. A formula was also developed to calculate the aprotinin potency in this method. In a word, the established CZE-UV method was convenient, fast, and environmentally friendly for the measurement of aprotinin potency.

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