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

摘要

Erioglaucine A was applied as internal standard to enhanced spectrophotometric determination of Cr (VI) with diphenylcarbazide. The following procedure was used: addition of internal standard and formation of ion pairs of Cr (VI) with benzyltributylammonium bromide (BTAB) (sample volume 100 ml); extraction to 10 ml of methylene chloride; evaporation in nitrogen stream; and redissolution in a micro-volume with addition of diphenylcarbazide for colour development (final volume 200μlitre). 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 Cr and internal standard were obtained at 591.30 and 653.50 nm from first derivative spectra, normalized against JD653.50nm. The analytical characteristics evaluated were: detection limit = 0.06μg/litre, quantification limit = 0.19μg/litre, precision for 1μg/litre 14.2% and for 10μg/litre 3.2%, correlation coefficient of linear regression was 0.9985. The proposed procedure was applied to determination of Cr (VI) in tap water. Total Cr was determined by electrothermal atomic absorption spectrometry, the recovery of hexavalent Cr 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 2 methods.