Effects of non-ionic surfactants on isotachophoretic separations of 2-arylpropionic acids

Non-ionic surfactant (Brij 35, Tween 20, Tween 80 and Tergitol NPX) modified capillary isotachophoresis was investigated for the separation of 2-arylpropionic acids (fenoprofen, flurbiprofen, ibuprofen, ketoprofen and naproxen) and benzoic acid and its derivatives (salicylic, acetylsalicylic and gallic acids). The relative step height (RSH) values of analytes were found to be dependent on the type and concentration of the surfactant. The strength of the affinity of the 2-arylpropionic acids to the non-ionic micelles was found to be as follows: flurbiprofen > fenoprofen > ibuprofen > naproxen > ketoprofen. In general, the RSH values of 2-arylpropionic acids increase with an increase in the concentration of surfactants. However, the RSHs of benzoic, salicylic and gallic acids are not considerably affected. Separation of all acids was obtained with the Tween 20 (1.5%, w/v) in the leading electrolyte 10 mmol L−1 hydrochloric acid/l-histidine (pH 6.0). Changes in the fluorescence intensity of fenoprofen, flurbiprofen and naproxen were also investigated in micellar media (Tween 20, Tween 80 and Brij 35). The strength of the affinity of the 2-arylpropionic acids to the Tweens micelles was found to be as follows: flurbiprofen > fenoprofen > naproxen, which is consistent with the isotachophoretic results. On the contrary, the strength of the affinity to the Brij micelles was found to be as follows: fenoprofen > naproxen > flurbiprofen.