Determination of Pb(II), Cu(II) and Fe(III) with Capillary Electrophoresis Using Ethylenediaminetetraacetic Acid as a Complexing Agent and Vancomycin as a Complex Selector

Abstract

IntroductionIn the past decades, capillary electropheresis (CE) has been considered to be a powerful method, and widely applied to analyze many of different substances, ranging from small inorganic ions to large bio-macromolecules, due to many advantages, such as high separation speed and efficiency, very low running costs and low sample volume injected (e.g., 2 -10 nl). Metal-ion analysis, 1-3 however, covers a relatively small part of CE applications compared with separations in the areas of pharmaceuticals, oligonucleotides, proteins and peptides. Considering metal-ion analysis, problems occur due to (i) the similar electrophoretic mobilities and (ii) the weak UV absorption of most metal ions.The former problem is because most transition metal ions have similar mobilities due to their similar size and identical charge. 4 To achieve an electrophoretic separation, the mobilities have to be modified by introducing a complex forming equilibrium. If different degrees of complexation result for the ions during the interaction with a ligand, their apparent electrophoretic mobilities should also be different. Various reports can be found in the literature describing organic acids as complexing agents for improving the resolution in CE separation. These include oxalic acid, lactic acid, tartaric acid and hydroxyisobutyric acid. [4][5][6][7] Ethylenediaminetetraacetic acid (EDTA) has also been used for this purpose. [8][9][10][11] EDTA is known to complex with metal ions in a 1:1 ratio, and the chelates are always negalively charged whatever the charge on the cations. 4,12 As a principally electrophoretic property, metal-EDTA anionic complexes could be successfully separated due to inherent differences in the electrophoretic mobilities. However, in practice, it also suffers from poor selectivities, and is not sensitive. Until now, on-column derivatization, also called in-capillary derivatization, has been applied to determine various types of analyte by one of three different strategies: zone-passing, at-inlet and throughout capillary derivatization. 2,8,[13][14][15] These studies have proven that the sensitivity could be sharply increased by using in-capillary derivatization.For the latter problem, the weak UV-absorption of most metal ions, several preconcentration methods have been developed to overcome the sensitivity problem, such as isotachophoresis, 16 [28][29][30] In addition, the sensitivity for the metal determination could be improved by using on-line preconcentration in micellar electrokinetic chromatography 45 and CE-laser induced fluorescence. 46 Increasing the optical path length by incorporating a bubble cell 31,32 or a U-shaped cell 33,34 is one of the means to improve the sensitivity of a UV detector. U-shaped cells, usually a bent capillary, with a few millimeters of the capillary parallel to the optical path, can provide a higher sensitivity, but a loss of resolution prevents this method from further development. 35 Vancomycin is a macrocyclic antibiotic containing in its structure 18 asymmetric cent...

Simultaneous determination of heavy metal ions by caillary zone electrophoresis using a complex selector

“…Макроциклический антибиотик ванкомицин был использован в качестве комплекс-селектора при капиллярном электрофоретическом опреде-лении этилендиаминтетраацетатных комплексов Fe(III), Co(II), Ni(II), Cu(II) [20] и Cu(II), Pb(II), Fe(III) [21]. Однако авторы столкнулись с рядом трудно-стей, обусловленных невысокой химической устой-чивостью ванкомицина, сильным поглощением реа-гента в УФ-области и склонностью его к адсорбции на стенках кварцевого капилляра.…”

“…Авторы [20,21] считают, что взаимодействие ванкомицина с комплексами Ме-ЭДТА обусловле-но, с одной стороны, комплексообразованием по типу «гость-хозяин» с частью молекулы антибиоти-ка, включающей три связанных макроциклических кольца, а с другой стороны -электростатическим взаимодействием ионизованных карбоксильных групп ЭДТА с вторичными аминогруппами молеку-лы ванкомицина.…”

“…Спектры поглощения комплексов Cd(II), Co(II), Ni(II), Mn(II), Zn(II) и Cr(III) практически совпа-дают. На основании анализа спектров для прямого спектрофотометрического детектирования были вы-браны длины волн 195 нм (обеспечивает наиболь-шую чувствительность детектирования комплексов всех исследуемых металлов) или 260 нм (обеспе-чивает возможность селективного определения комплексов Cu(II), Pb(II), Fe(III) и Bi(III)), в отличие от авторов [20,21], записывавших ЭФГ при 242 нм.…”

“…6). Метод частичного заполнения капилляра до-полнительным комплексообразующим реагентом был использован, например, авторами [21] при раз-делении ионов Cu(II), Pb(II) и Fe(III). Селективность разделения комплексов этих металлов с ЭДТА как при предварительном, так и при внутрикапиллярном комплексообразовании оказалась невелика, и ком-плексы Cu(II) и Pb(II) мигрировали совместно в виде одного раздваивающегося пика.…”

Bis(salicylaldehyde) orthophenylenediamine as complexing reagent in simultaneous determination of gold, chromium, iron, uranyl, and nickel using capillary zone electrophoresis

“…In Table V, the data are compiled for the reported [33][34][35][36][37][38][39] CE method for separation/determination of metal ions involved in current study. No method covers all the metal ions studied here; also, phenylenediamine-type Schiff base is not reported earlier for the CE separation of metal ions.…”