Round robin tests for the spectrophotometric determination of chromium in waste water samples according to the JIS method

Abstract

Round robin tests were carried out by the members of Association for Environmental Analysis in Osaka to have an idea about the precision of the spectrophotometric method for the determination of chromium in waste water by a JIS method. Three kinds of synthetic waste water samples containing various co-existing substances were prepared. The diphenylcarbazide spectrophotometric method prescribed in JIS K 0102-1974 was adopted for the determination of total chromium in these samples. At first, Sample I was distributed to the laboratories and 74 data were collected. The mean value of the 74 data was 1.92 mg/l and the coefficient of variation was 14.0%. Second, Sample II containing a large amount of co-existing substances was analyzed. Decomposition of organic substances by either nitric-sulfuric acids or nitric-perchloric acids and separation of iron by cupferron-chloroform extraction were involved prior to the final determination. The coefficient of variation of 22.2% was obtained. Lower results were obtained when the absorbance of color-developed solution was high, exceeding 0.4. Third, Sample III which contained the same co-existing substances as Sample II was analyzed principally in the same manner as for the Sample II, but the details of analytical procedure was rigorously specified in all its aspect. The coefficient of variation of 19.5% came out, indicating that nothing gained in precision. It is difficult to get better than 20% of the coefficient of variation for the determination of total chromium in waste water containing a large amount of co-existing substances by the diphenylcarbazide spectrophotometric method prescribed in JIS K 0102-1974. © 1979, The Japan Society for Analytical Chemistry. All rights reserved.