CIRCULAR PAPER CHROMATOGRAPHIC METHOD FOR DETERMINING TRACE AMOUNTS OF COBALT, COPPER, NICKEL, AND ZINC IN ROCKS AND SOILS

Ascending, descending, and horizontal (circular) methods of paper chromatography were explored and compared. Circular chromatography was found to be the most suitable; it requires shorter development time, has more definite Rf values, less tailing, higher sensitivity, and better precision than ascending or descending methods.A methyl ethyl ketone: hydrochloric acid solution (93:7 v/v) is used as a developing solvent for cobalt, copper, and nickel, and a 1-butanol: 1 N hydro–chloric acid solution (7:3 v/v) is used as a solvent for zinc. Good separations were obtained with these solvents and no critical interferences were noted. Benzidine – rubeanic acid is used as a color indicator for cobalt, copper, and nickel; and dithizone (0.01%) for zinc. This method has an absolute sensitivity of 0.005 μg for zinc, and 0.02 μg for cobalt, copper, and nickel. Precision is estimated at ± 10%.Methods have also been developed for determining bismuth, silver, and tin.The separation of elements from complex mixtures by paper chromatography and by quantitative determination of the amounts present by emission spectrography have been investigated. This rarely considered process offers promise, because the sensitivity of several elements is higher in emission spectrography than in colorimetry.