Precise estimation of dodecylbenzenesulfonate in aqueous solution containing dissolved organic matter extracted from soil using UV‐spectrometry

Abstract

Precise estimation of sodium dodecylbenzenesulfonate (DBS) is essential for understanding its adsorption in soils, transport, toxicity, fate, and its application in the remediation of contaminated soil and groundwater. DBS can be easily identified by its conjugated double bond systems of benzene rings under the ultraviolet (UV) spectrum of a spectrophotometer. However, benzene group components of dissolved organic matter (DOM) also absorb light in the UV spectrum, and this effect is responsible for the excess quantities of DBS that are falsely measured by spectrophotometers. This study was conducted to propose a method for accurately measuring the DBS concentration of a solution containing DOM. To elucidate the influence of DOM during the UVspectroscopic measurement of DBS in an aqueous solution, 222.5 nm UV and 400 nm UV-vis spectra were measured. The DOM was extracted from a highly humic non-allophanic volcanic ash (Andosol) soil by using 1 mmol NaCl/L and 100 mmol NaCl/L solutions as the extractants. The absorbances at both 222.5 and 400 nm increased in proportion to the increase in the DOM concentration. The relationship between the absorbances at the two different wavelengths could be expressed as a linear relationship. On the other hand, the absorbance at 400 nm did not increase with the increase in the DBS concentration, whereas the absorbance at 222.5 nm increased with the increase in the DOM concentration. Therefore, we inferred that the influence of DOM on the absorbance value of the DBS-DOM complex solution at 222.5 nm could be eliminated by using the linear relationship between the two different absorbances of the DBS-free DOM solution. This method makes it possible to easily measure the DBS concentration of a solution from soil water, streams or industrial effluents containing DOM, without using reagents. Highlights• Dodecylbenzenesulfonate in a solution is overestimated in the presence of dissolved organic matter.• Dodecylbenzenesulfonate becomes precisely detectable using 222.5 and 400 nm spectrophotometry.

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

“…The slope of the linear line was smaller in the case of the 10 mmol/L NaCl background condition compared with that in 0.1 mmol/L NaCl (Figure 3b). The results at pH 12.5 were similar to those obtained by Hossain and Ishiguro (2021), although the relationship was slightly influenced by pH.…”

“…The absorbance at 400 nm in the UV–vis spectrum increased in proportion to the concentration of DS. However, as indicated by Hossain and Ishiguro (2021), DBS did not affect the absorbance of this spectrum. The slopes of the linear lines (DS concentration vs. 400 nm absorption) of certain NaCl solutions and pH values were similar to those obtained with the different concentrations of DBS solutions, except for a divergence at the higher pH condition with the 0.1 mmol/L NaCl solution.…”

“…The computation of accurately calculated DBS concentration was achieved following the previously proposed precise DBS estimation method of Hossain and Ishiguro (2021). Briefly, they found that the absorbances measured at 222.5 nm UV and 400 nm UV–vis spectra exhibited linear increases with a rise in the DS concentration.…”

“…As the DBS does not influence the 400 nm absorbance, they also found the relations as below: where x (DBS + DOM) was the 400 nm absorbance of the DBS–DOM complex solution. Finally, DOM influence was eliminated, and the precisely calculated DBS concentration ( C ) was obtained by placing the values of Equations (), (), and () in Equation () like below (Hossain & Ishiguro, 2021). …”

“…However, molecular‐scale spectroscopy and spectromicroscopy of the macromolecular structure have confirmed the conformation of humic substances under alkaline (pH ≥9.5) conditions, which may alter the absorbance characteristics of DOM at higher pH values (Chen & Schnitzer, 1976; Ghosh & Schnitzer, 1980). Therefore, it is assumed that the effect of NaOH induced elevated pH condition exhibits the influence of DOM on the absorbance characteristics of DBS‐DOM complex solution, which challenges the validity of the photometric method proposed by Hossain and Ishiguro (2021) under such high pH conditions.…”