US EPA

1431961 

Technical Report 

Colorimetric Determination Of Uranium With 1-Ascorbic Acid 

Smith, GG; Orlemann, EF; Smales, AA; Rothenberger, CD; Grimes, WR 

1947 

NIOSH/00136983 

S 

AECD-2101 

A colorimetric method for determining uranium (7440611) was developed and tested. Ascorbic-acid in a 10 percent aqueous solution was added to hexavalent uranium in a weak acidic solution. The solution was buffered with ammonium-acetate. The intensity of the yellow color formed was determined by the measurement of the optical density of the solution with a Beckman spectrophotometer. The effects of varying pH from 1 to 11 were studied. The amounts of acid and buffering agent were varied to determine optimum color production. The method was tested on known concentrations of uranium. The effect of foreign ions on color formation was tested with more than 20 ions. About 20 minutes was required for formation of the colored complex. Color intensity was linearly related to uranium concentration up to at least 15 milligrams per milliliter of solution. In the pH range of 4.5 to 4.8, color intensity was independent of pH, but pH of 4.0 prevented iron precipitation. With an increase in ascorbic-acid and a decrease in acetate ion concentration optical density increased. In the absence of acetate ions color was unstable. Chloride, nitrate and perchloride ions had no appreciable effect on color. Anions capable of forming stable complexes with a weak acid solution caused large negative errors dampening the color. Moderate amounts of various elements tested were without effect, though chromium, vanadium, and significant amounts of nickel, zinc, and molybdenum did interfere with the determination. Accuracy of the method was within about 2 percent. The authors conclude that variables must be controlled for high accuracy if the method is to be used. 

DCN-125078; Radioactive heavy metals; Quantitative analysis; Analytical chemistry; Analytical methods; Photometry; Laboratory techniques; Trace analysis; Research; Chemical analysis