Highly stable, rapid colorimetric detection of carbaryl pesticides by azo coupling reaction with chemical pre-treatment

For rapid detection of carbaryl pesticides, we developed a simple colorimetric detection method based on azo-coupling reaction. Pretreating carbaryl pesticides with an organic base yielded 1-naphthol, which readily reacted with a diazonium salt with a dramatic color change. Since the resulting azo dye can further change color with the organic base used in the pretreatment, phosphoric acid was added to suppress the confounding colorimetric response. We report that this new colorimetric method can selectively detect carbaryl pesticides from other carbamate pesticides within a minute. Moreover, carbaryl can be detected below 10 parts per million (ppm), which is below its permissible exposure limit (similar to 15 ppm). Finally, we successfully estimated the concentrations of carbaryl pesticides on fruit samples in the presence of natural interferences. (C) 2018 Elsevier B.V. All rights reserved.