A new sensitive chemiluminescence (CL) procedure for the detection of hexythiazox (HXTZ) is presented, based on the quenching effect of the HXTZ in the luminol–H2O2 system using gold nanoparticles (GNPs) as a catalyst. The Box–Behnken design matrix and response surface methodology (RSM) have been applied in designing the experiments for studying the interactive effects of the three most important variables pH, luminol, and H2O2 concentrations on the CL intensity of luminol catalysed by GNPs. Under the optimal conditions, the CL intensity was linear with HXTZ concentration in the range of 0.017–0.42 μg mL−1, and the limit of detection (LoD) was 0.011 μg mL−1. The procedure has been successfully applied to the detection of HXTZ residues in citrus fruits and water samples at trace levels. Mean recoveries obtained were between 84.0% and 95.3%, with a repeatability precision of <6%. Meanwhile, the possible mechanism of the inhibited CL intensity was discussed.
