Micellar thin‐layer chromatographic separation of heavy metal cations: Effect of organic and inorganic additives on migration behavior

Abstract

The migration behavior of heavy metal cations on cellulose layers using aqueous micellar, hydro-organic, and water-organic-surfactant mobile phases was investigated. Anionic, cationic, and nonionic surfactant systems were examined over a 0.001-5% concentration range. Brij-35, a nonionic surfactant capable of forming charged complexes with some metal ions, was identified as the best surfactant. The effect of the presence of organic additives, such as dimethylsulfoxide, dimethylformamide, methanol and acetone, on the mobility of metal ions was also studied. Acetone was found to be the most effective additive at 10% concentration with 3% Brij. Quantitative determination of UO 2 2+ by spectrophotometry after preliminary thin-layer chromatographic (TLC) separation from Fe 3+ and Hg 2+ was also performed. A maximal recovery of 93% was obtained. This TLC method is rapid, with development times averaging 2 min.Paper no. S1098 in JSD 2, 523-529 (October 1999). KEY WORDS:Acetone, Brij-35, DMSO, heavy metal cations, micelles, TLC, uranium.Micellar liquid chromatography (MLC) has increased in popularity because of its unique advantages, such as the capability to simultaneously separate ionic and nonionic compounds and to provide faster analysis, higher detection sensitivity, and selectivity (1-5). The most fascinating feature of micellar systems is their dual hydrophobic and hydrophilic character, which provide electrostatic and hydrophobic sites of interaction within the aqueous mobile phase, resulting in unique separation capabilities of both ionic and nonionic solutes. As a result, micellar mobile phases have been extensively used in reversed-phase chromatographic separation of various organic compounds. In comparison, the use of micellar mobile phases in inorganic chromatography has been limited. Efficiency of mobile phases in the separation of cations (6,7) and anions (8,9) has been reported and reviewed by Okada (10). Mullins and Kirkbright (11) used MLC as an alternative to ion chromatography for the separation of several inorganic anions using a cationic micellar eluent. Kirkman et al. (12) used a variety of micellar eluants to examine the chromatographic behavior of ionic, nonionic, chelated, and organometallic metal species. Although micellar mobile phases offer enhanced selectivity, they suffer from a serious loss of efficiency when compared to traditional hydro-organic mobile phases. Dorsey et al. (13) reported that addition of low concentrations of different organic solvents to micellar mobile phases improves efficiency by reducing the adsorbed amount of emulsifier (surfactant). This unique phenomenon in MLC was attributed to the existence of a competing equilibrium in MLC and an influence of micelles on the role of organic modifiers. Khaledi et al. (14) observed simultaneous enhancement of separation selectivity and solvent strength in MLC using hybrid eluants comprising cationic or anionic micellar-organic solvents for different groups of ionic and nonionic compounds.A few studies reported the use of surfac...