Ion-exchanger colorimetry-VIII Microdetermination of copper in natural waters

A microdetermination method for copper by ion-exchanger colorimetry has been developed. The porphyrin alpha,beta,gamma,gd-tetrakis(4-N-methylpyridyl)porphine was used as the colour reagent. After the complexation at pH 4.5 and 40 degrees , the surplus ligand was converted into the protonated species by addition of sulphuric acid. The complex and the ligand were easily sorbed on the cation-exchange resin, Dowex 50W-X2-H(+) (100-200 mesh). The resin-phase absorbances of the complex species at 424 nm and of the resin background at 510 nm were used for the measurements. There were no interferences by the foreign ions expected to be present in natural waters, at up to 1000 times the concentration of copper. With a 1 -litre sample the detection limit is 0.072 mug/l. It is possible to determine copper at mug/l. or lower levels in natural waters.