Chlorine is an essential element for the physiology of plants. Accuracy profile was used to validate an analytical method of chlorine determination in plant samples performed by a wavelength dispersive X-ray fluorescence (WDXRF) instrument. The samples were dry plant powders and were pelletized before analysis. The calibration of the WDXRF instrument was carried out by employing plant materials with known mineral contents supplied from inter-laboratory studies. Interferences between elements were corrected by using the method of the influence coefficients, which were computerized according to the routine program linked to the equipment. The measured samples were reference materials. The accuracy profile of chlorine shows the measurements (trueness and precision) obtained under intermediate precision conditions. It aimed to compute an acceptability interval where a known proportion of future results will be located. The quality system also included the systematic analysis of an internal reference sample in each batch of samples routinely analysed. The performance of the method, over a period of three years was reported through a control chart. The yearly variation coefficients were less than 5.0% for chlorine. Finally, a comparison with another analytical method, ion chromatography, was established.