DECOLORIZATION REACTIONS BETWEEN CHROMIUM(VI) AND 3 COLOR REAGENTS - DETERMINATION OF CHROMIUM(VI) BY FLOW-INJECTION ANALYSIS

Chromium (VI) can oxidize and decolor three colour reagents. i.e. 1,8-dihydroxy-2-(4'-chloro-2'-phosphonophenylazo)-7-(6''.8''-disulfonaphthylazo)- .6-disulfonaphthalene (RI); 1,8-dihydroxy-2-(4'-chloro-2'-phosphonophenylazo)-7-(4''-Sulfonamidephe-nylazo)-3.6-disulfonaphthalene (RII): and 1.8-dihydroxy-2-(4'-chloro-2'-phosphonophenylazo)-7-(D-hippuric acid azo)-3.6-disulfonaphthalene (RIII). Loss of absorbance of three colour reagents at maximum absorption wavelengths is proportional to the concentration of chromium (VI) in solution. We have made use of the decolorization reactions between chromium (VI) and three colour reagents to determine chromium in steel by flow injection analysis. and relative error in sample determination is less than 5.0%. Response is linear from 0.84 to 6.72 mug/mL and optimum measuring acidity is 1.3-1.7 mol/L H2SO4 in three systems. The effect of interference ions on determination has been studied.