Effect of the [BMIM][BF4] as a mobile phase additives on the adsorption behavior of tryptophan by reversed-phase high performance liquid chromatography

Ionic liquids are widely recognized as important components of 'green' chemistry. As a novel class of solvents, room temperature ionic liquids, have properties that make them desirable alternatives for many industrial applications. They possess wide range of solubilizing capability for polar and apolar molecules as well as for ions. They have interesting electrochemical properties such as significant dielectric constant, a high electrical conductivity, good thermal and chemical stabilities, low volatility and flammability. The absence of vapor pressure has gained then the label of environment-friendly solvents. This variety has enormously increased the ionic liquid applications and potential in a variety of chemical processes.;In the analytical field, ionic liquids are applied in liquid-liquid extraction. They are used as stationary phases in gas chromatography and matrices in laser desorption ionization. In capillary electrophoresis, ionic liquids are used as running electrolytes and in reversed-phase liquid chromatography, they reduce the silanol effects when employed as mobile phase additives.;The adsorption data of tryptophan were collected on two different C18 silica columns (Xterra and Prevail) and then comparision between the two columns were made. The mobile phases used were an aqueous mixture of methanol, acetic acid and 1-butyl-3-methylimidazolium tetrafluoroborate ([OMIM][BF4]) or the solutions of the ionic liquid [BMIM][BF4] without methanol. The adsorption isotherm and profiles of tryptophan depends on the composition of mobile phase and the concentration of Ionic liquid used. Overloaded band profiles of tryptophan are used to determine best values of isotherm coefficients by the inverse method (IM) of chromatography. It helps in isotherm determination with minimum solvent and sample consumption. Here it is important when using the IM to choose a good isotherm model. The model can be guessed from the shape of the overloaded band profiles. This method is useful for purification process and drugs in the industrial field because the parameters for adsorption isotherm is known in a very short time when compared to that of Frontal analysis.;Our results indicate that the shape of the profiles, the isotherms, and the retention of tryptophan was affected by the amount of IL added to the mobile phase. The amount of analyte adsorbed on the column and the retention factor can be manipulated by changing the amount of BMIM in the mobile phase. Mobile phase containing no methanol as modifier and containing only BMIM can be used as mobile phase to elute the amino acids. There is a good agreement between the values of parameters obtained by Frontal analysis and by the inverse method.