Thermal Infrared Enthalpimetry Method for the Determination of Hypochlorite in Bleaching Solutions

Thermal infrared enthalpimetry (TIE) was used for hypochlorite determination in commercial hypochlorite-based bleaching solutions. Experimental parameters were evaluated for the reaction with a hydrogen peroxide solution. The most relevant conditions were 5% H2O2 (m/m) solution, stirring speed of 250 rpm, dispensing rate of 0.57 mL s-1, and 10 s after reaction for the simultaneous temperature readings of four replicates. Agreement to reference method NBR 9425 ranging from 98.2 to 103.2% was achieved, with a low variation among measurements (relative standard deviation < 3.5%). The number of analytical operations was reduced, and only H2O2 solution was required as a greener reagent. A low amount of residues was generated (2.4 and 152.8 mL for each replicate in TIE and official method, respectively), and the application of the green analytical procedure index (GAPI) showed the greenness of the proposed method.