Aqueous Two-phase Extraction Effect Of Mixed Cationic And Anionic Surfactant System

Aqueous two-phase extraction of mixed cationic and anionic surfactant system is a new method for liquid-liquid extraction, which is especially suitable for bioactive substances. The aqueous two-phase systems (ATPS) formed by cetyltrimethylammonium bromide (CTAB)/sodium dodecylsulfonate (AS)/water and CTAB/AS/(0.1 mol kg-1 sodium bromide (NaBr) aqueous solution) systems have been chosen as the extraction media. The extraction effects of these ATPS on three different kinds of dyes and five anthraquinones in rhubard have been investigated.Firstly, the effects of the cationic water-soluble dye methylene blue and anionic water-soluble dye xylenol orange on the critical micelle concentrations (cmc) of CTAB, AS and CTAB/AS mixed systems have been investigated by surface tension method. The results showed that, the effect of methylene blue on the cmc of CTAB was unobvious, while the addition of methylene blue reduces the cmc of AS or CTAB/AS mixed systems with excess AS. The effect of xylenol orange on the cmc of AS was unobvious, while the addition of xylenol orange reduces the cmc of CTAB, but increases the cmc of CTAB/AS mixed systems with excess CTAB. The interactions between ion dyes and CTAB/AS are complex. Interactions such as electrostatic interaction, hydrogen bonding and hydrophobic interaction influence the changes of cmc.Secondly, the partition of methylene blue, xylenol orange, and oil-soluble dye Sudan Ⅲ in ATPS formed by CTAB/AS/(0.1mol·kg-1 NaBr aqueous solution) has been investigated. The experimental results indicated that for ATPS with excess AS (ATPSa), the extraction effect on methylene blue and Sudan Ⅲ is obvious, whereas the extraction effect on xylenol orange is unobvious; For ATPS with excess CTAB (ATPSc), the extraction effect on xylenol orange and Sudan Ⅲ is obvious, whereas the extraction effect on methylene blue is unobvious. The extraction efficiency of ATPS for a substance is dependent on two factors:the hydrophobicity and electrical property of the substance being extracted. Hydrophobic Sudan Ⅲ is easy to be extracted to the surfactant-rich phase in ATPS. Cationic water-soluble dye methylene blue is easy to be extracted to the surfactant-rich phase in ATPSa due to the strong electrostatic attraction between the dye and negatively charged aggregates. Anionic water-soluble dye xylenol orange is easy to be extracted to the surfactant-rich phase in ATPSc due to the strong electrostatic attraction between the dye and positively charged aggregates. The improved Diamond-Hsu model has been used to correlate the partition coefficients of methylene blue in ATPS, the correlation results are in good agreement with the experimental results.Lastly, the extraction effects of ATPS formed by CTAB/AS/ (0.1molkg-1 NaBr aqueous solution) on the five anthraquinones in rhubarb have been studied. For emodin, the extraction effect of ATPS formed by CTAB/AS with water or NaBr aqueous solution having different concentration as solvent has been investigated. Experimental results illustrate that the extraction efficiency of the concentrated top phase in ATPSa or ATPSc formed by CTAB/AS/(0.1mol kg-1 NaBr aqueous solution) on emodin, chysophanol, chusophanol and aloe emodin are nearly 100%; The extraction efficiency of the top phase in ATPSC on rhein is nearly 100% either, however, the extraction effect of the top phase in ATPSa on rhein is not satisfactory, the acidity of rhein is kind of strong, rhein dissociates into hydrogen ions and thus its acid ions are negatively charged in aqueous solution, therefore rhein is easy to be extracted by ATPSc due to electrostatic attraction. The extraction effect of ATPS on emodin is dependent on the solvent. When water or NaBr aqueous solution with low concentration is used as solvent, the extraction effect of ATPS on emodin is unobvious. For ATPSc, the extraction effect becomes obvious when the concentration of NaBr increases to about 0.01 mol kg-1, and for ATPSa, the extraction effect becomes obvious when the concentration of NaBr increases to about 0.04 mol kg"1.