Enhanced spectrophotometric determination of chromium (VI) with diphenylcarbazide using internal standard and derivative spectrophotometry

In the present work, erioglaucine A was applied as internal standard to enhanced spectrophotometric determination of chromium (VI) with diphenylcarbazide. The following procedure was used: (1) addition of internal standard and formation of ion pairs of Cr (VI) with benzyltributylammonium bromide (BTAB) (sample volume 100 ml), (2) extraction to 10 ml of methylene chloride, (3) evaporation in nitrogen stream, and (4) redissolution in a micro-volume with addition of diphenylcarbazide for color development (final volume 200 mul). The preconcentration factor achieved was about 400 and it was shown that, using internal standard, the analytical errors due to sample treatment were reduced. The analytical signals for chromium and internal standard were obtained at 591.30 and 653.50 nm from first derivative spectra, normalized against (1)D(653.50nm). The analytical characteristics evaluated were: detection limit = 0.06 mug l(-1), quantification limit = 0.19 mug l(-1), precision for 1 mug l(-1) 14.2%, and for 10 mug l(-1) 3.2%, correlation coefficient of linear regression was 0.9985. The proposed procedure was applied to determination of chromium (VI) in tap water. Total chromium was determined by electrothermal atomic absorption spectrometry, the recovery of hexavalent chromium added was then evaluated and compared with the results of the proposed procedure. In this experiment, good agreement was obtained between results obtained by the two methods.