Simultaneous determination of five quinoxaline-1,4-dioxides in animal feeds using an immunochromatographic strip

An immunochromatographic (ICG) strip was developed for the simultaneous quantitative determination of five quinoxaline-1,4-dioxides in animal feed. For this purpose, polyclonal antibodies (PcAb) with group-specific quinoxaline-1,4-dioxides were conjugated to colloidal gold particles as the detection reagent for ICG strips to test for quinoxaline-1,4-dioxides. This method achieved semi-quantitative detection of quinoxaline-1,4-dioxides within 5-10 min. The visual lower detection limits of the strip for quinocetone, cyadox, carbadox, mequindox and olaquindox were 10, 15, 15, 20 and 20 ng ml(-1), respectively. Using an ICG strip reader, the 50% inhibitions (IC50 values) were calculated to be 9.1, 13.5, 16.6, 20.2 and 21.3 ng ml(-1) for quinocetone, cyadox, carbadox, mequindox and olaquindox, respectively. When used to analyse samples of animal feed, acceptable recovery rates of 77.5-99.5% and coefficients of variation (CVs) of 4.3-10.7% were obtained. Levels measured with the ICG strip for 10 spiked samples were confirmed by HPLC with a high correlation coefficient of 0.9965 (n = 10). In conclusion, the method was rapid and accurate for simultaneous determination of five quinoxaline-1,4-dioxides antibiotics in animal feed.