Figure 1.

Use of safranin-o leuco dye as a visual oxidation indicator. a) Bio-Rad® AG1x8 resin in Poly-prep column including a stop-cock valve to control flow without indicator dye showing original color of the resin; b) Dowex® 1x8 resin in Pierce polystyrene column including top and bottom frits to control flow without indicator dye showing original color of the resin; c) Solution of safranin-o in the oxidized form (1 drop of 1% solution in 4 M HCl); d) Anoxic safranin-o (colorless, reduced form) in 4 N HCl after reduction with Ti(III); e) Example of anoxic resin (no pre-treatment) after addition of reduced safranin-o solution with visible oxidation (pink color on resin); f) Anoxic resin after pre-treatment with Ti(III) and addition of reduced safranin-o solution (no color change observed).