STABILIZED NEUTRAL ORTHOTOLIDINE, SNORT, COLORIMETRIC METHOD FOR CHLORINE

Using bis(2-ethylhexyi)suifosuccinate as a stabilizer produces a pH 7.0 orthotolidine method for free chlorine with a blue quinhydrone imine product which obeys Beer's law up to 1.0 X 10-4M. The succinate stabilizer makes it possible to use a neutral phosphate buffer at pH 7.0. Using this buffer minimizes the chloramine interference commonly present at lower pH with other methods and reagents and eliminates the iron, nitrite, alkalinity and acidity interference. The rate of monochloramine interference at pH 7.0 was 4.0 I. mole-1 min-1 first order in monochloramine and orthotolidine with a first order catalytic dependence on hydrogen ion concentration. This dependence on pH explains why earlier methods of lower pH, necessary because of product instability, give significant chloramine interference. The products of the chromogenic reaction in the presence of stabilizer, even at high temperature and pH, are more stable than the acid orthotolidine products. The rate of product decomposition at pH 7 and 34 °C is apparently zero order at 8 X 10-8M min-1. The two reagents used in the test are stable in solution for periods in excess of one year. © 1969, American Chemical Society. All rights reserved.