The analysis of carbamate and urea herbicides by fluorimetry of their dansylated amine moieties
Carbamate and urea herbicides have been analysed by thin-layer chromatography and fluorimetry of the 1-dimethylaminonaphthalene-5-sulphonyl (dansyl) derivatives of their aniline hydrolysis products. The herbicides were hydrolysed with 1 M sodium hydroxide solution at 80 °C for 40 minutes and then the liberated anilines and amines were extracted into hexane. Aliquots of the hexane solution were spotted on to a chromatographic plate and made to react in situ with at least a ten-fold excess of dansyl chloride, which was spotted over them. Next, the plate was sprayed until moist with a 20 per cent. solution of triethanolamine in propan-2-ol and the spots were analysed fluorimetrically in situ. The hydrolysis and coupling reaction of the herbicides, fluorescence phenomena and chromatographic properties of the derivatives were investigated. Detection limits of 1 ng per spot taken at a 3:1 signal to noise ratio and a reproducibility of 3 to 5 per cent. relative standard deviation can be expected and the calibration graphs are linear up to 300 ng per spot. Natural water samples can be analysed to determine concentrations of herbicides of a few parts per billion (109) with high recoveries and without the necessity of a clean-up step.