Derivative spectrophotometric determination of the herbicides picloram and triclopyr in mixtures

A derivative spectrophotometric method for the determination of the her- bicides picloram (4-amino-3,5,6-trichloropicolinic acid) and triclopyr (3,5,6-trichlo- ro-2-pyridyloxyacetic acid) in mixtures was developed in this work. Derivative spe- ctrophotometric determination of the selected herbicides was preceded by investiga- tions concerning the influence of pH, in the pH interval from 1 to 9. At pH 3.2, pi- cloram and triclopyr solutions are stable under daylight for nine months. This pH was used for all subsequent determinations. It was also found that the use of the first de- rivative of the spectra at 232 nm was optimal for the determination of picloram, while use of the second derivative of the spectra at 211 nm was best suited for the deter- mination of triclopyr. The calibration curves are linear in the concentration range 0.8 - 13 µg cm -3 with correlation coefficients -0.9998 for picloram and 0.9996 for triclopyr. The limit of detection of the developed method is 0.08 µg cm -3 for piclo- ram and 0.03 µg cm -3 for triclopyr. Derivative spectrophotometry was shown to be an appropriate method for the determination of picloram and triclopyr in mixtures and in pesticide formulations, unlike the deconvolution method.