A Spectrophotometric Determination of Barium Complexation with Methylthymol Blue
Abstract
In this work, a spectrophotometric titration of methylthymol blue (MTB) with barium chloride was performed at pH = 7.5, 9.6, and 12.2 to determine the stoichiometry of complexation between the two as well as formation constants and absorptivity coefficients. Complexes of 1:1, 2:1, and 3:1 Ba:MTB were suggested by the experimental data upon fitting with appropriate models using Beer’s Law. The molar absorptivities of free MTB species at 605 nm were determined to be ����2������4− = 5.0 (± 0.2) x 103 L·mol-1·cm-1, ����������5− = 7.3 (± 0.3) x 103 L·mol-1·cm-1, ��������6− = 1.3 (± 0.2) x 104 L·mol-1·cm-1. At pH = 9.6, ������2��2������ and the formation constant of that complex were determined to be 6.0 (± 0.2) x 103 L·mol-1·cm-1, and 7 (± 4) x 102, respectively. Similarly at pH 12.2, ������2��������−, and its formation constant were determined to be 8.2 (± 0.1) x 103, and 1.2 (± 0.4) x 102, respectively. Formation constants of 3:1 complexes were unable to be determined with certainty due to a lack of constraints at high barium concentration. Binding activity was largely influenced by barium concentration and pH, presumably due to the dominant species of MTB present in solution.
