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.