Influence of high pH state of dodecylbenzenesulfonate and dissolved organic matter complex solution on the ultraviolet spectrometry of dodecylbenzenesulfonate

Dodecylbenzenesulfonate (DBS) is an anionic surfactant that is the most commonly used ingredient in modern cleaning agents. Globally, billions of liters of untreated DBS are released daily into natural water bodies, which may lead to fatal consequences in micro and macro living entities, and destroy the natural ecosystem. Therefore, a simple, precise, rapid, and inexpensive method for measuring DBS is crucial for developing countries. The conventional ultraviolet (UV) spectrophotometric method cannot accurately estimate the DBS concentration in a solution containing a considerable quantity of dissolved organic matter (DOM). Recently, a new spectrometric method was developed using the 222.5 nm UV and 400 nm UV-visible (UV-vis) spectra to precisely estimate DBS concentration in the DBS-DOM complex solution. However, this newly developed method is yet to be validated under higher pH conditions. The accuracy of DBS measurements from the DBS-DOM complex solution under lower pH (5.5 and 6.5) and higher pH (12.5) conditions was compared in this study using the previously developed method. With the higher pH, the influence of the electrolyte increased the absorbance under the 222.5 nm UV spectrum. However, such influence decreased with the increase in DBS and DOM concentration. The UV-vis absorbance at 400 nm decreased under higher pH values when the DOM concentration increased, owing to the conformational change in DOM. Despite the contrasting trends of the absorbances in the two spectra, the studied method was proven to be equally applicable and efficient, even under higher pH conditions.