Titanium dioxide nanoparticles-coated column for capillary electrochromatographic separation of oligopeptides

Abstract

A novel column made through the condensation reaction of TiO2 nanoparticles (TiO2 NPs) with silanol groups of the fused-silica capillary is described. EOF measurements under various buffer constitutions were used to monitor the completion of reactions. The results indicated that the EOF was dependent on the interactions between buffers and the bonded TiO2 NPs. With formate/Tris buffer, EOF reversal at pH below 5 and cathodic EOF at pH above 5 were indicated. The pI of the bonded TiO2 NPs was found at approximately ph 5. Only cathodic EOF was illustrated by substituting the mobile phase with either glutamate or phosphate buffer. It was elucidated that both glutamate and phosphate buffer yield a negative charge layer on the surface of TiO2 NPs attributable to the formation of a titanium complex. The CEC performance of the column was tested with angiotensin-type oligopeptides. Some parameters that would affect the retention behavior were investigated. The interactions between the bonded phases and the analytes were explicated by epitomized acid-base functional groups of the oligopepetides and the speciation of the surface oxide in different pH ranges. The average separation efficiencies of 3.1 x 10(4) plates/m is readily achieved with a column of 70 cm (50 cm) x 50 mum ID under an applied voltage of 15 kV, phosphate buffer (pH 6.0, 40 mM), and UV detection at 214 nm.

Recent applications in CEC

“…Hsieh et al [8] used titanium dioxide nanoparticles to coat the inside of fused-silica capillaries. The covalently bonded TiO 2 exhibited a pI at pH < 5, so that a reversal of the direction of the EOF was observed at this pH.…”

Simultaneous separation of eight β‐adrenergic drugs using titanium dioxide nanoparticles as additive in capillary electrophoresis

“…Hsieh et al [28,29] reported that the TiO 2 NP-coated capillary would exhibit exceptional surface properties which are depending on buffer composition and pH. In order to study the effect of TiO 2 NPs upon EOF, phenylmethanol was used as the neutral EOF marker.…”

“…Fujimoto [27] demonstrated that titanium dioxide-coated capillaries can be used for the CE and CEC separation of carbohydrates and proteins. Hsieh et al [28] were the first to prepare TiO 2 NP-coated capillaries for the open-tubular CEC separation of oligopeptides. Next, this group attempted to use TiO 2 NP-coated columns for the CEC separation of proteins of similar molecular weight or pI's for further applicability evaluation [29].…”

“…Induced by a positive surface charge, the TiO 2 NPs are adsorbed on the negatively charged capillary wall and adsorb the negative ions in the solution onto them. Connor [28]). The adsorption of phosphate on TiO 2 NPs and TiO 2 NPs adsorbed on the capillary wall (increases in the zeta potential) may be the main contributor for the increase in EOF below pH 6.0.…”

Capillary electrochromatographic separation of proteins on a column coated with titanium dioxide nanoparticles

“…We have prepared TiO 2 NP-coated capillaries for the open-tubular CEC separation of oligopeptides [30]. The surface properties of the prepared columns are significantly affected by the composition of the mobile phase, and are therefore very attractive for our purpose.…”