AN ION-EXCHANGE SEPARATION OF METAL-CATIONS ON A C-18 COLUMN COATED WITH DODECYL-SULFATE

The retention mechanism was studied for the cations of the alkaline earth metals and Zn2+, Ni2+, Co2+, Cd2+ and Bi3+ on a C18 column permanently coated with sodium dodecylsulphate, with aqueous mobile phases containing cupric chloride or sulphate, or cerous nitrate. The dependencies of the logarithm of the capacity ratio on the logarithm of the eluent concentration were linear, demonstrating that ion-exchange was the predominating separation mode; the slopes of these dependencies were in good agreement with the values predicted from the ion-exchange theory. Indirect UV photometric detection yielded limits of detection (LOD) of 21, 44, 120 and 275 ng in the volume injected, 20-mu-l, for Mg2+, Ca2+, Sr2+ and Ba2+, respectively, with the 10(-2) M copper(II) chloride mobile phase; the respective LOD values decreased to 0.8, 1.6, 3.0 and 6.7 ng with the 5 x 10(-4) M cerium(III) nitrate eluent. The method was found to be primarily suitable for determination of the alkaline earths and was applied to analyses of surface and mineral waters.