STUDIES ON COLORIMETRIC DETERMINATION OF ANTIMONY(Ⅰ)AN IMPROVED RHODAMINE B METHOD

The rhodamine B method has been recommended by Maren for the deter- mination of very small amount of antimony in biological material.However we found that Maren's original method was deficient in several ways.A study with a view to improving it was made and a revision of the method was proposed below. Sulfuric acid solution of antimony is prepared after destruction of the organic matter as discribed by Maren.To it are added 4 ml of saturated NaCl solution and about 5 drops of ceric ammonium sulfate solution (0.1N) until the yellow color develops.Allow the solution to stand for about 20 minutes,add 8 ml of 3N H₃PO₄ and a few drops of HONH₂·HCl solution (1%) to remove the excess of ceric ammonium sulfate,transfer it immediately to a separatory funnel con- taining 10 ml of C₆H₆ and 5 ml of 0.02% aqueous rhodamine B solution,shake for one minute,and then,draw off the C₆H₆ layer into a test tube.After the water droplets settled on standing,the transmittancy of the C₆H₆ solution was determined at 565 mμ.The color intensity of the samples containing Sb in the range of 0.01—25 γ/ml is reproducible and obey Beer's law. This revised method can be applied directly to water soluble pentavalent Sb- compounds without destruction of the organic matter.