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This review discusses the results of research in the use of bulk liquid membranes in separation processes and preconcentration for analytical purposes. It includes some theoretical aspects, definitions, types of liquid membranes, and transport mechanism, as well as advantages of using liquid membranes in laboratory studies. These concepts are necessary to understand fundamental principles of liquid membrane transport. Due to the multiple advantages of liquid membranes several studies present analytical applications of the transport through liquid membranes in separation or preconcentration processes of metallic cations and some organic compounds, such as phenol and phenolic derivatives, organic acids, amino acids, carbohydrates, and drugs. This review presents coupled techniques such as separation through the liquid membrane coupled with flow injection analysis.

In the present paper we studied the competitive transport of p-nitrophenol (pNP) and 2,4-dinitrophenol (2,4-dNP) from aqueous media using the technique of liquid membranes. This technique is very efficient, economic and selective when compared to other removal techniques of phenolic derivatives. The paper presents the influence of the sodium carbonate concentration from the stripping phase, the influence of the concentration ratio [2,4-dNP]/[pNP] upon the selectivity of the transport process and some kinetic aspects of the transport of 2,4-dNP in the presence of pNP through bulk liquid membranes.

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Transport through liquid membranes of various chemical species is a viable method for different applications in analytical or technological domain. This paper presents the transport and separation results of two compounds of pharmaceutical importance: salicylic acid and aspirin, using bulk liquid membrane technique. We studied the effect of the feed source and receiving phase pH on the transport efficiency of the two compounds throught chloroform membrane. These results were correlated with speciation diagrams of salicylic acid and aspirin. The speciation diagrams shows that in these pH conditions, for aqueous phase of the membrane system, the two compounds are mostly undissociated form and therefore active for transport. In this system it can be achieve separation of the two compounds, salicylic acid and aspirin, using a suitable complexing agent in the feed source such as Fe 3+. In this way salicylic acid forms an inactive complex structure for transport while aspirin crosses the membrane and it is recovered in a percentage of 80% in the receiving phase membrane system.

The paper presents a study of the phenomena that take place at membrane system interfaces in the process of indole-3-acetic acid (IAA) transport. The results were obtained in a bulk liquid membrane system using trioctylamine, tributylphosphate, trioctilphosphine oxide as carriers in chloroform. The main equilibriums that take place at the interface feed phase% membrane phase were identified and the diffusion coefficient of the indole-3-acetic acid complex (DLS) and the extraction constant (Kex) were assessed. The influence of the chemical potential gradient on these parameters was considered.

In this present paper the behavior of two important pharmaceutical compounds, namely: nicotinic acid (vitamin PP/B3) and para-aminobenzoic acid (vitamin B10) to the transport through a liquid membrane of chloroform containing Aliquat 336 have been studied. The influence of operational parameters such as: solute concentration in the feed phase, stripping agent concentration in the stripping phase, transport time was monitored. The assessment of the obtained results allowed establishing of optimal transport conditions as well as identification of a kinetic transport model for nicotinic acid corresponding to consecutive irreversible 1st order reactions. The maximum transport efficiency was 96% and it was obtained at a concentration of 10-4 mol/L nicotinic acid in the feed phase and a concentration of 1 mol/L sodium hydroxide in the stripping phase. The transport time necessary to achieve this efficiency was 6 h. The results obtained led to important conclusions regarding the possibility of separating these two compounds. Analytical control of the process was done spectrophotometrically. The maximum absorbance was obtained at their characteristic wavelengths, namely 262 nm for nicotinic acid and respectively 267 nm for para-aminobenzoic acid.

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