Transport of citric acid across a supported liquid membrane containing various salts of a tertiary amine

Four types of salts of tri-n-octylamine (TOA salts) were prepared by equilibrating xylene solutions of TOA and aqueous solutions of nitric, hydrochloric, sulfuric, and citric acids. A comparison was made for the transport of citric acid from aqueous solutions through a supported liquid membrane using these TOA salts and pure TOA as mobile carriers. The strip phase was either deionized water or sodium carbonate solution. Experiments were performed as a function of total TOA concentration and different loadings of TOA salts in the membrane phase. In contrast to the use of pure TOA, it was generally shown that the amount of citric acid transported increased for all TOA salts in long-term tests (over 8 h). Under the conditions studied, such an enhancement decreased in the order for TOA salts: citrate > nitrate > sulfate > chloride, regardless of the strip phases employed.