1979 Volume 28 Issue 11 Pages 713-714
Finely divided ion exchange resin particles can collect ions from solution more rapidly than the beads of conventional size, and by the addition of oppositely charged resin particles, they coagulate each other to form a bulky material which is easily separated by filtration. The coagulated resins are collected on a filter paper as a uniform and thin layer which is directly subjected to the spectrophotometric measurements. A trace amount of chromium(VI) is determined as follows. A 100-ml sample solution containing less than 1.0μg of chromium(VI) and sulfuric acid in the concentration of approximately 0.01 mol dm-3 is taken into a separatory funnel. Then 3.0 ml of anionic resin suspension (7.22×10-3 meq ml-1), 1.0 ml of cationic resin suspension (13.3×10-3 meq ml-1) and finally 1 ml of 0.4% diphenylcarbazide in 50% acetonewater solution are added. The mixture is shaken for 12 min and the resulting coagulated material is collected onto a filter paper (Toyo Roshi No. 5A) set on a holder. The purple colored resins thus obtained form a disk of 17 mm diameter and about 0.3 mm in thickness. To stabilize the coloration, the filter strip is dipped into an acetate buffer solution for 10s and then the absorbance is measured against reagent blank at the absorption maximum of 550 nm and at 700 nm where the complex has no absorption. The net absorbance is obtained as the difference. The working curve deviates slightly from the proportionality, the relative standard deviation being 2.1% (n=6) for 1 μg of chronium(VI) and 3.3% (n=5) for 0.4μg. The sensitivity of the present method is approximately 100-fold higher than the ordinary solution method using 1-cm cell. As a 1-μg portion of chromium(VI) is quantitatively recovered from 400-ml sample solution, the sensitivity is 400-fold higher than the ordinary method.
