Separation and kinetic study of chromium(III) chloro complexes by capillary electrophoresis

Three Cr(III) species (dichlorotetraaquachromium(III), [CrCl(2)(H(2)O)(4)](+); monochloropentaaquachromium(III), [CrCl(H(2)O)(5)](2+); and hexaaquachromium(III), [Cr(H(2)O)(6)](3+)) have been separated and determined by capillary electrophoresis. The first two complexes could be detected in direct mode in phosphate buffer, but because the absorption of complex [Cr(H(2)O)(6)](3+) is poor in the UV range, indirect UV detection had to be used. For indirect detection 5 mM imidazole was added to the buffer solution. The formation and decomposition of the different Cr(III) complexes were monitored in time after the preparation of solutions of CrCl(3). 6H(2)O. The slowest process was the decomposition of [CrCl(H(2)O)(5)](2+); 300 h after preparation of a solution of CrCl(3). 6H(2)O of pH 1 the solution contained only [Cr(H(2)O)(6)](3+). The effects of pH and the content of some matrix ions on the rates of conversion of the complexes were studied. The kinetic characteristics of this complex system could be investigated adequately by means of capillary electrophoresis.