Interfering elements on determination of hexavalent chromium in paper materials with UV-vis spectrophotometry

Regulation of hexavalent chromium is based on Waste Framework Directive 1994/62/EC, European Commission and publication of the World Health Organization. Herein, detection of hexavalent chromium was performed by alkaline digestion and instrumental analysis which was demonstrated in USEPA methods. However, UV-vis detection method could be affected by some metal ions reacted with diphenylcarbizide. Actually, various interfering elements, such as Ni, Fe, Al, and Cu, were detected and selected by ED-XRF in paper materials. In order to improve accuracy of analysis results of hexavalent chromium in paper materials based on USEPA methods, the interfering elements was removed by liquid-liquid extraction with carbonate media using tricaprylmethylammonium chloride and chloroform after alkaline digestion. Consequently, the temperature for alkaline digestion was between 85 and 95 degrees C. Hydrochloric acid was proper complex tricaprylmethylammonium-Cr(VI) in the procedure of liquid extraction. After that hexavalent chromium was completely extracted using of 1 M sodium hydroxide solution. The technique for analyzing the hexavalent chromium used in liquid-liquid extraction significantly reduced the errors caused by the interfering elements, Fe and Cu. Thus, application of the extraction method was efficient in removing the interfering elements, which increased the recovery ratio of the hexavalent chromium from paper materials by 90 %.