| Summary: | Specific spectroscopic techniques were validated for assay of four pesticides applied for cucumber in Egypt; mandipropamid (MAN), metalaxyl (MET), thiophenate methyl (THO) and carbendazim (CAR). First method is derivative method for the quaternary mixture of the studied pesticides; by using the first derivative THO was assayed at 281 nm, while MAN and CAR were assayed using second derivative at 236.4 and 256.2 nm, respectively and MET was assayed using third derivative at 221.6 nm. Second method is double divisor ratio spectrum derivative method that used for assay of MAN at 289 nm and MET at 233.2 nm using a double divisor of 30 μg mL−1 of each of THO and CAR, then both THO and CAR were determined at 259 and 267.4 nm, respectively, using a double divisor of 4 μg mL−1 of each of MAN and MET. The obtained results were within the acceptable range regarding to the Egyptian committee of agricultural recommendations. Keywords: Mandipropamid, Metalaxyl, Thiophenate methyl, Carbendazim, Derivative spectrophotometry, Double divisor ratio spectra derivative spectrophotometry
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