Polarography is by no means the only method suitable for the measurement of U concentration in the final solution. Spectrophotometry can also be used and is, in some cases, even more sensitive; but if spectrophotometry is used, the interference from chromium (Table I) should be considered. Chromium does not interfere in the polarographic determination since, although it extracts into TOA and back-extracts into 0.17V HC1, the reduction wave of Cr(III) appears at potentials more negative than -0.5V vs. SCEin47VHCl.The method is simple, rapid, and accurate. Six to eight determinations can be carried out per day by a trained technician. The relative standard deviation is 2% at the 95% confidence level in samples that contain 0.05 to 0.2 mg of uranium per milliliter.