Determination of total chromium in tannery waste water by inductively coupled plasma-atomic emission spectrometry, flame atomic absorption spectrometry and UV–visible spectrophotometric methods

The determination of total chromium in different streams of tannery effluents were carried out by the digestion of samples in a HNO3/H2SO4 mixture followed by KMnO4 oxidation, which resulted in the complete conversion of Cr(III) to Cr(VI). The Cr(VI) (Cr2O72−) species present in these samples were estimated by inductively coupled plasma-atomic emission spectrometry (ICP-AES), flame atomic absorption spectrometry (FAAS) and UV–visible spectrophotometry (1,5-diphenyl carbazide method). The results obtained from these methods were critically evaluated. UV–visible spectrophotometry was found to be better suited for this analysis when compared with the other two methods. Since these solutions contain relatively high concentrations of chromium (200–2400 mg/l), the need for preconcentration did not arise. The higher values obtained in the case of ICP-AES and FAAS methods can be attributed to the matrix effect arising out of high concentration of mineral acids and electrolytes. In addition, the values obtained in the latter methods (ICP-AES and FAAS) are comparable with each other, indicating that the interferences influence the results almost equally in both techniques. The statistical treatment of data indicates that the differences between the methods are within the acceptable range.