Screening of a Novel Solvent for Optimum Extraction of Anionic Surfactants in Water

Abstract

Anionic surfactants (AS) are detrimental aquatic pollutants due to their well-characterized toxicity to aquatic organisms. The concentration of AS in aquatic environments is increasing because of their extensive use in many industries and households. The standard reference method for AS analysis is to determine a methylene blue active substance (MBAS) complex formed between AS and the methylene blue (MB) cation by using chloroform. However, chloroform has a low AS extraction efficiency and other limiting properties, such as a high density and volatility, which make the conventional AS analytical method time-consuming and labor-intensive. In an effort to replace the use of chloroform, this study was carried out to screen novel solvents for their ability to extract AS in water samples. Criteria were based on AS extraction efficiency, physicochemical properties, and the stability of the solvent under different environmental conditions. Organic solvents, such as methyl isobutyl ketone (MIBK), 1,2-dichloroethane (DCE), dichloromethane, benzene, and n-hexane, were assessed. In extraction of the anionic surfactant sodium dodecyl sulfate (SDS), the mixture of MIBK-DCE (3:1) proved to be an optimum solvent as an alternative to chloroform. It not only enhanced SDS extractability but also improved properties, such as having a lower volatility, a lower density than water, and a quicker phase separation. Among solvents screened, no one single solvent in SDS extraction could meet such criteria. The performance of the MIBK-DCE (3:1) mixture in SDS extraction was stable, irrespective of pH and ionic strength of the SDS solution, washing process, and presence of cations. Anionic interference from halogen and polyatomic and organic anions in SDS extraction by MIBK-DCE (3:1) existed only at an elevated concentration, which is not occurring in the natural aquatic environment. Results demonstrated that a MIBK-DCE (3:1) mixture solvent could be used in AS analysis for a wide range of aquatic samples and it could be the basis for the development of a new analytical method to replace conventional chloroform.

A Simplified Method for Anionic Surfactant Analysis in Water Using a New Solvent

“…Elimination of anionic interferences by the washing process is the prerequisite step for analysis of AS in aquatic samples [10][11][12][13][14]16]. Any washing procedure should remove the methylene blue-anion (MB + A − ) complex present in an aqueous or solvent phase.…”

“…Ideal criteria for the solvent to be used in the analysis of AS in different types of water are that it should have a high extractability, a short phase separation time, a low volatility, a low solubility in water, a lower density than water, and a lower potential health hazard [14][15][16]. However, chloroform has a low AS extraction efficiency and a relatively high density and volatility [10,[14][15][16][17][18][19]. Yoon et al [16] reported that no single solvent in SDS extraction could, among several solvents screened, meet such ideal criteria.…”

“…However, chloroform has a low AS extraction efficiency and a relatively high density and volatility [10,[14][15][16][17][18][19]. Yoon et al [16] reported that no single solvent in SDS extraction could, among several solvents screened, meet such ideal criteria.…”

“…Yoon et al [16] showed that for a wide range of aquatic samples a mixture of two solvents, methyl isobutyl ketone (MIBK) and 1,2-dichloroethane (DCE), in a 3:1 ratio {MIBK-DCE (3:1)}, was selective and sensitive for SDS analysis, and it enhanced SDS extractability. As compared to chloroform, the solvent MIBK-DCE (3:1) had a lower volatility, a lower density than water, and a quicker phase separation.…”

“…The chloroform method suffers from salt interference, for example chloride ions in sea water [12,14,21,22]. Yoon et al [16] found that, for SDS extraction by MIBK-DCE (3:1), anionic interference from halogen ions and polyatomic and organic anions existed only at elevated concentrations, which do not occur in natural aquatic environments. A sample with a complex matrix, as found in wastewater and seawater, requires a method that has good selectivity and sensitivity for AS to avoid such anionic interferences [12,14,15,20].…”