Simultaneous detection of sulfamethazine and sulfaquinoxaline using a dual-label time-resolved fluorescence immunoassay

A dual-label time-resolved fluoroimmunoassay (TRFIA) was introduced for the simultaneous quantification of sulfamethazine (SM₂) and sulfaquinoxaline (SQX). Lanthanide (Eu³⁺ and Sm³⁺)-labelled antibodies were used because lanthanides have higher stabilities and narrower emission spectra than most fluorescent dyes. The sensitivity of the TRFIA for SM₂ was 0.02 ng ml^?1, and the average recoveries and the intra- and inter-assay CVs were 77.2–107.6%, 5.4–10.5%, and 6.0–11.2%, respectively. The sensitivity of the TRFIA for SQX was 0.04 ng ml^?1; and the average recoveries and the intra- and inter-assay CVs were 74.1–102.8%, 4.6–10.9%, and 8.7–11.2%, respectively. The method was used to analyse chicken tissue and egg samples, and the results agreed well with the results of HPLC and enzyme-linked immunosorbent assay (ELISA) analyses, with correlation coefficients (R²) of 0.9415–0.9724. The TRFIA developed is a simple, fast and sensitive method for the high-throughput simultaneous screening of SM₂ and SQX in edible animal tissues.