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Estimation and comparison of ζ‐potentials of silica‐based anion‐exchange type porous particles for capillary electrochromatography from electrophoretic and electroosmotic mobility
Author(s) -
Sánchez Muñoz Orlando L.,
Hernández Ever Pérez,
Lämmerhofer Michael,
Lindner Wolfgang,
Kenndler Ernst
Publication year - 2003
Publication title -
electrophoresis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.666
H-Index - 158
eISSN - 1522-2683
pISSN - 0173-0835
DOI - 10.1002/elps.200390049
Subject(s) - zeta potential , electrokinetic phenomena , microelectrophoresis , electrophoresis , chemistry , electrochromatography , electro osmosis , chromatography , analytical chemistry (journal) , capillary electrophoresis , capillary electrochromatography , ionic strength , particle (ecology) , electrolyte , isoelectric point , silanol , electrophoretic light scattering , materials science , dynamic light scattering , aqueous solution , nanotechnology , organic chemistry , oceanography , electrode , geology , nanoparticle , enzyme , catalysis
Mobilities of different chromatographic particles obtained from two electrokinetic methods were determined and compared. The particles were all based on porous silica, between 3 and 15 μm diameter, and were either native, or derivatized. As intermediate of chemical modification 3‐mercaptopropyl‐modified silica particles (TP‐silica) are obtained. These particles were finally transformed into weakly basic anion exchangers with O ‐9‐( tert ‐butylcarbamoyl)quinine (tBuCQN) as chiral selector. The electrophoretic mobility of the particles was determined from their migration velocity in an electric field using microelectrophoresis. Electrokinetic chromatography with a capillary column packed with the same particles was used to measure the electroosmotic flow generated. All measurements were carried out in background electrolytes of equal ionic strength (10 −2 mol/L), at pH varying between 3.5 and 9.5. From these data a rough estimation of the ζ‐potential was made, taking Helmholtz‐Smoluchowski conditions into consideration. With both methods the ζ‐potential of the native silica particles is negative throughout, and its value increases with pH. The weakly basic tBuCQN particles have positive ζ‐potentials at pH lower than about 7.5, but exhibit a negative ζ‐potential above this pH, indicating the dominating effect of residual silanol groups at the silica surface. The ζ‐potential for these anion‐exchange particles ranged between +30 and −40 mV. The ζ‐potentials derived with electrophoresis and electroosmosis agree, showing the adequacy of the approach, although many limitations must be taken into account in the treatment of the electrokinetic phenomena in such porous systems. These restrictions in interpreting mobility and ζ‐potential were discussed.