TLC studies and separation of heavy metal cations on soil amended silica gel layers developed with surfactant-mediated solvent systems

Thin-layer chromatography (TLC) of ten heavy metal cations was performed on soil, silica gel and soil mixed with silica gel sorbent phases using aqueous solutions of cetyl trimethyl ammonium bromide (CTAB), sodium dodecyl sulphate (SDS), polyoxyethylene dodecyl ether (Brij-35) and iso-octylphenoxypolyethoxy ethanol (TX-100) surfactants; with or without added urea, nitrate or chloride of ammonium and sodium phosphate as mobile phases. In all, twenty-nine stationary and twenty-five mobile phases were used in order to examine the mobility pattern and to find out the best TLC system for metal cations separation from their multicomponent mixtures on soil mixed with silica gel layers. The mobility of all cations was insignificant on pure soil layers irrespective of the nature of mobile phase used. Addition of silica gel into soil bed leads to the increase of mobility and facilitates the separation of metal cations. Amongst surfactant solutions, CTAB at concentration level of 0.5 M was found to be most effective, the analytical potentiality of which was further improved in the presence of urea. The TLC system comprising of silica gel plus 0.6 M urea (1:1, v/v) as mobile phase was found most favourable for achieving separations of metal ions from their multicomponent mixtures. A few such separations worth mentioning include, Fe3+-Cu2+-Ni2+-Hg2+, Zn2+-Cd2+-H2+ Ni2+-Cu2+-Fe3+, Zn2+-Fe3+-Ni2+-Hg2+, Pb2+-Cd2+-Hg2+ and Ni2+-Cu2+-Pb2+. R-F values of metal ions on soil amended with alumina, kieselguhr, cellulose and fly ash layers have also been determined. Salting - in effect exhibited by certain metal ions like Cd2+, Ni2+ or Co2+, Ag+, Hg2+ has been reported. Effect on mobility of metal ions, by replacing urea with different fertilizers in the CTAB containing mobile phase has also been examined.