Computer modeling of mass transfer frequently requires empirical validation. Improvements in the empirical chemical method of the catalytic oxidation of sodium sulfite are presented. The oxidation by oxygen was followed by monitoring the change in UV absorption at a wavelength of 260 nm. Liquid was pumped from the reaction vessel, a stirred cell, into a 0.5-mL quartz flow cell inside a UV absorption spectrometer. Different catalysts were investigated for controlling the reaction rate. Cobalt sulfate and cobalt chloride were both successfully used in the analysis. The real-time analysis of the oxidation of sodium sulfite did not require pH stabilization and makes this procedure superior to the standard iodometric titration. In addition, mass-transfer experiments can be miniaturized without loss of accuracy.