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Abstract
Transport of L-cysteine (L-cys) from potassium chloride solutions through emulsion liquid membranes containing dicyclohexyl-18-crown-6 (CE) has been investigated. The mechanism of transport is based on ion-pair formation between (K · CE)+ complex and L-cys-. The effect of parameters influencing the process, that is, pH of the external phase, carrier concentration, receiving phase concentration, emulsification, and stirring speed were examined and discussed. The highest performance for transport of L-cysteine (1 × 10−4 M) was achieved by adjusting the ionic strength of the feed phase at 0.01 M and pH 10 (KCl/KOH mixture). The membrane was prepared by emulsification (at 11000 rpm) of the mixture of crown ether (6 × 10−4 M), 4% emulsifier (ECA-4360) and liquid paraffin. The optimized organic to aqueous volume ratio of the emulsion globules and treat ratio was found to be 1:3 and 0.1, respectively. Hydrochloric acid solution (2 M) was used as stripping phase. The extraction step was completed after 30 min. by stirring the phases (700 rpm). The process shows an excellent selectivity towards L-cysteine with respect to amino acids L-tryptophan, L-tyrosine, L-leucine, L-methionine, L-arginine, L-asparagine, L-aspartic acid, L-glycine, L-serine, and L-threonine. UV-Vis. Spectroscopy and TLC method using ninhydrin, as indicator, were used for amino acids analysis.