Non-aqueous Capillary Isotachophoretic Determination of Heavy Metal Ions as Chloro Complexes after Extraction of the Diethyldithiocarbamate Chelates

Abstract

A sensitive capillary isotachophoretic method (CITP) in non-aqueous systems was developed. for the simultaneous determination of heavy metal ions extracted as the diethyldithiocarbamate (DDTC) chelates. Perchlorate, chloride and hydrogen ions were used as a leading (0.005 mol·dm^-3), a terminating (0.01 mol·dm^-3) and a counter ions, respectively; N, Ndimethylfgrmarnide (DMF) was used for the solvent of migrating system.1, 2-Dichloroethane and nitrobenzene were found to be most suitable solvent for the extraction of metal chelates and the extracts could be injected as sample solution for CITP without any pretreatment. The tolerable injection-amounts of the solvents, 1, 2-dichloroethane and nitrobenzene were 20 and 25 μl, respectively. The DDTC chelates injected are converted into the corresponding chloro complex anions by reaction with the counter cation H+and terminating anion Cl^-. The reaction is represented for divalent metal ion as follows,
M(DDTC)₂+2H⁺+nCl^- [MCl_n]^(n-2)-+2H·DDTC
The separation was achieved through the equilibria among the chloro complexes with the chloride and the 'hydrogen ions supplied from the terminating, leading zones, respectively. The H·DDTC liberated was readily decomposed to diethylammonium ion and carbon disulfide under the system. The calibration curves obtained by injecting 10 μi of DDTC chelate extracts from mixed solution of Fe(III), Cd(II), Zn(II), Pb(II) and Mn(II) were found to be linear in the range of 2-10 nmol. The proposed method was also applicable to the separation of trace metal ions shown in Fig.8 at the concentration as low as 1×10^-6mol·dm^-3. The order of decreasing effective mobilities of the chloro complexes in this system was Ga(III), Fe(III), Hg(II), Cd(II), Zn(II), Sb(III), Pb(II), Mn(II) and In(III).