ION-ASSOCIATION CAPILLARY ELECTROPHORESIS - NEW SEPARATION MODE FOR EQUALLY AND HIGHLY-CHARGED METAL-CHELATES

A new separation method for highly charged metal chelates based on ion association in capillary zone electrophoresis (CZE) has been developed. Metal chelates of Al(III), Co(III), Cr(III) and Fe(III) ions with 2,2'-dihydroxyazobenzene-5,5'-disulphonate could not be separated by a conventional CZE system (electrophoretic buffer: [NaH2PO4](tau) = 0.02 M, pH 7.0, V = 21.7 kV, i = 20 mu A, l = 50 cm), because they have fixed and identical (-5) charges. However, when 25 mM tetrabutylammonium bromide was added to the same electrophoretic buffer, each of the four chelates was well resolved and migrated in the order Fe(III), Co(III), Cr(III) and AI(III) with theoretical plate numbers of 210 000-250 000 per 50 cm within 11 min (V = 21.3 kV, I = 40 mu A). The detection limits (S/N = 3) as determined by spectrophotometric detection (lambda = 494 nm, I.D. = 50 mu m) were 1.00, 1.89 and 3.11 fmol for Al, Co and Fe, respectively, in 6.0 10(-9) dm(3) of sample solution injected. The effect on the separation of the sizes, types and the concentrations of quaternary ammonium ions added to the electrophoretic buffer was also investigated. As a result, some evidence was obtained that the ion-association reaction between the chelates and ammonium ions probably took the major role in the separation mechanism.