An enzyme-assisted and nitrogen-blowing salt-induced solidified floating organic droplet microextraction for determination of clenbuterol and ractopamine in swine feed via capillary electrophoresis

•The developed method overcomes traditional SFODM disadvantage.•Enzymes play essential role in eliminating interference.•The extraction recoveries are more than 74.1%.•The limits of detection are 1.1–1.5 μg/kg in swine feed samples.•This method is a rapid, low cost method for analysis of CLB and RCT in feed.

A simple and sensitive analytical methodology, based on enzyme-assisted extraction and nitrogen-blowing salt-induced solidified floating organic droplet microextraction (NS-SFODM), was developed and optimized for isolation and determination of clenbuterol (CLB) and ractopamine (RCT) in swine feeds. β-Gluocronidase/arylsulphatase (50 μL) was added into 2 g of powdery feed to eliminate interference and to improve extraction efficiency. In the NS-SFODM procedures, the down-layer salt and aqueous phase was discarded by opening the bottom cap, and the remaining solidified solvent was easily and relatively wholly collected by a medical spoon, resulting in a high extraction efficiency. The optimal parameters for NS-SFODM procedures and capillary zone electrophoresis (CZE) operations were as follows: 40 μL of 2-DC as extraction solvent, sample pH of 12.0, saturated (NH4)2SO4 of 4.0 g, nitrogen-flowing time of 1.0 min, and 10.0 mM sodium tetraborate running buffer. Under optimized conditions, the limits of detection (at S/N = 3) were 1.1 μg/kg for RCT and 1.5 μg/kg for CLB, the mean enrichment factors reached more than 124-fold and the extraction recoveries were more than 74.1% for CLB and RCT. The newly developed procedure is proved to be an accurate, precise and reliable sample-pretreatment method that substantially reduces sample matrix interference and gives very good enrichment factors and low detection limits for analyzing trace amount of CLB and RCT in feed samples.