Phase quantification of two chlorothalonil polymorphs by X-ray powder diffraction Original Research Article

Quantitative analysis method of phase composition of two chlorothalonil polymorphs (alpha and beta) co-existed with each other was studied by X-ray powder diffraction. With the content of polymorph alpha between 1.6% and 98%, the integral area of the strongest peak of polymorph alpha (2θ: 25.5 ± 1°) was not a linear function of its content. In the polymorph alpha matrix the detection limit of polymorph beta (2θ: 26.5 ± 0.1°) was 0.099%, while in the polymorph beta matrix, the detection limit of polymorph alpha was 1.6%. The expressions of the calibration curves were given. The relative density of polymorph alpha and beta was estimated to be equal to 0.90. The calibration curves joined into one linear and went through the origin (95% confidence interval). In the mixtures of the two polymorphs, the limits of prediction of alpha content from the determined integral areas mentioned above were less than ±0.026 (95% confidence limits). Some phase transformation samples were determined by the means of this quantitative analysis method.