Influence of Dissolved Organic Matter on the analysis of a solution of anionic surfactant, Dodecylbenzenesulfonate [an abstract of entire text]

概要

Surfactants are amphiphilic compounds that lower the surface tension between two surfaces e.g. between liquids, between a gas and a liquid, or between a liquid and a solid. Their heads are polar or hydrophilic, and their tails are hydrophobic. Every day a billion liters of untreated effluent are released into the soil-water system of our environment from industrial and household cleaning activities. Most of those cleaning agents are detergent, soap, and shampoo based on anionic surfactants such as Dodecylbenzenesulfonate (DBS).

Andosols have a thick dark A-horizon with a very high organic matter content which is able to produce the Dissolved organic matter (DOM) in aqueous. About 50 to 70 percent of DOM is usually covered by humic substances such as humic acids, fulvic acids, and humin, which have much importance in hydrochemistry and toxicology. In an aqueous solution, DOM gives a dark yellowish-brown to a black colour appearance depending on the quantity and ratio of the different organic portions dissolved in the solution. It is found that the high turbidity of the soil solution is caused by the presence of the DOM, especially when the humic substance is present in a considerably higher quantity.

The untreated discharge of DBS into the natural water bodies increases pollutant load in the soil–water system, hampers the soil physicochemical properties, and becomes deadly to micro and macro living entities in the natural ecosystem. Precise measurement of DBS is crucial for understanding its interaction with DOM and soils, transport, toxicity, fate, and its application in soil reclamation. The measurement of DBS to explore the interactions among the soil, DOM and surfactants were complex, time-consuming and expensive tasks because of using different costly reagents, electrodes, and high-priced equipment. To identify such interactions of DBS in a natural aqueous medium easily, no convenient method for the precise, simple, fast, and cost-effective measurement of the DBS traced so far.

Both DBS and DOM absorb the UV light at 222.5 nm. However, DOM also absorbs visible light with a wavelength of 400 nm, while DBS does not. It is believed that the influence of DOM can be eliminated by using this phenomenon and a precise method of DBS measurement can be developed on this principle. The possible conformation of humic substances under alkaline (pH ≥ 9.5) conditions may alter the absorbance characteristics of DOM, which challenges the validity of the mentioned method under high pH conditions (Ghosh and Schnitzer, 1980). Therefore, it is essential to check the validity of a UV/UV-vis measurement method in higher pH sate for the true applicability of the proposed method in the real world. The dissolution of DOM from soil affected by kinetic agitation is yet to be revealed, which is crucial to the availability of DOM that may interfere with the estimation of DBS from natural water.

In this study, we proposed and improved a precise estimation method of DBS using UV/UV-vis spectrometry for the DBS-DOM complex solution. Dissolution characteristics of DOM from the highly humic volcanic ash soil with electrolyte solutions were also investigated.