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 t o enhanced spectrophotometric determination of chromium (VI) with diph enylcarbazide. The following procedure was used: (1) addition of inter nal standard and formation of ion pairs of Cr (VI) with benzyltributyl ammonium bromide (BTAB) (sample volume 100 ml), (2) extraction to 10 m l of methylene chloride, (3) evaporation in nitrogen stream, and (4) r edissolution in a micro-volume with addition of diphenylcarbazide for color development (final volume 200 mu l). 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 anal ytical signals for chromium and internal standard were obtained at 591 .30 and 653.50 nm from first derivative spectra, normalized against D- 1(653.50nm). The analytical characteristics evaluated were: detection limit = 0.06 mu g l(-1), quantification limit = 0.19 mu g l(-1), preci sion for 1 mu g l(-1) 14.2%, and for 10 mu g l(-1) 3.2%, correlation c oefficient of linear regression was 0.9985. The proposed procedure was applied to determination of chromium (VI) in tap water. Total chromiu m was determined by electrothermal atomic absorption spectrometry, the recovery of hexavalent chromium added was when evaluated and compared with the results of the proposed procedure. In this experiment, good agreement was obtained between results obtained by the two methods. (C ) 1997 Elsevier Science B.V.