Separation of eight aromatic acids using the same buffer with and without PIL as additive: (A) without PIL and (B) with PIL. Conditions: BGE, 100 mM NaH₂PO₄ (pH = 6.0) containing 0.006% (w/v) PIL, other conditions are the same as in Fig. 1. Peaks: 1, o-phthalic acid; 2, salicylic acid; 3, 4-aminobenzenesulfonic acid; 4, toluene-p-sulfonic acid; 5, 3-nitrobenzoic acid; 6, 4-chlorobenzoic acid; 7, p-hydroxybenzoic acid; 8, p-aminobenzoic acid.

Researchers of the Key Laboratory for Natural Medicine of Gansu Province, Lanzhou Institute of Chemical Physics, CAS, has developed a simple and reliable co-electroosmotic capillary electrophoresis system for the fast determination of aromatic acids by employing poly (1-vinyl-3-butylimidazolium bromide) as the background electrolyte modifier.

 Firstly, PVBIm+ Br− has been synthesized according to the conventional radical polymerization. Then a co-directional movement of negatively charged analytes and the reversed EOF was accomplished by employing this PIL as a BGE modifier. The co-electroosmotc CE system was further applied in the separation of eight aromatic acids. The electrophoretic conditions including the concentration of PIL and pH of BGE were investigated. The results proved that the coelectroosmotic capillary electrophoresis, which was dynamically modified with polymeric ionic liquid, provided better separation than the normal mode. Successful separation and identification of eight aromatic acids have been achieved under optimized conditions (100mM NaH2PO4, PVBIm+ Br− 0.006% (w/v), pH= 6.0). High efficiency (355,000–943,000 (plates/m)) and short analysis time (less than 3.5 min) were obtained.

This technique proposed is simple, reliable, and provides good reproducibility in terms of migration time of samples. The RSDs (n = 3) were less than 0.33% except p-aminobenzoic acid (0.9%). Analogous to the previously reported ILs used as BGE additives in CE, the separation mechanism relies on the association of aromatic acids with imidazolium cations of the PIL either coated on the capillary wall or electrophoretically migrated in the bulk solution. Furthermore, the present CE method was applied to determine the concentration of salicylic acid and benzoic acid in a common drug for external use. Excellent RSDs for the peak area and migration time of the aromatic acids in the sample solution were obtained.

 The detailed report of the work was published in Talanta (Talanta 82 (2010) 56–60).