On-column laser-based refractive index detector for capillary electrophoresis

Abstract

The Interference pattern from side-illuminated capillary tubes has been exploited to develop a sensitive universal refractive Index (RI) detector suitable for nanollter on-column capillary separation techniques. A 2-fold benefit Is obtained by surrounding the capillary tube with a RI-matching fluid: the fringe pattern Is simplified, and thermal noise Is reduced. The key to RI detection In CE, provided that the instrument delivers sufficient sensitivity, has been found to be thermal stability. A thermal stability of AT = 2.0 X 10"* °C is achieved In a Peltier cooled RI cell having a highly symmetric design aimed to ensure fast thermal response from the thermoelectric system. The linear dynamic range extends to more than 3 orders of magnitude with a typical RMS noise level of 3 X 10-* RIU and baseline drifts of 2 X 10-* RIU h1 at 1 Hz. This Is about 1 order of magnitude above the calculated shot noise limit for these tube dimensions. These noise levels correspond to an angular deflection of the selected fringe of 100 nrad, which has been obtained by using a large position-sensitive photodiode. The optical geometric arrangement of the photodiode, with respect to the fringe width, has been optimized theoretically. A detailed description of the Instrument and Its noise sources is presented, and the technique Is demonstrated In CE In the analysis of underlvatlzed carbohydrates using a 50-jim tube.

Microcolumn liquid chromatography: instrumentation, detection and applications

“…Laser-based RI detection has, among others, been applied by Bornhop and co-workers [130][131][132] and Bruno et al [133,134]. The capillary flow cell developed by Bruno et al [134] is based on the so-called forward scatter, off-axis technique. With the use of an RImatching fluid surrounding the capillary flow cell, and active temperature control of the flow cell assembly, improved performance is feasible.…”

Holographic refractive index detector for application in microchip-based separation systems

“…This method has been successfully applied to HPLC, CE and flow-injection analysis. 29 The 'off-axis' method for CE was also demonstrated by Bruno et al 30 in the analysis of underivatized sugars in a 50 mm id capillary. They identified Joule heating as the major source of experimental noise.…”

Suspended Microchannel Resonators for Ultralow Volume Universal Detection

“…As UV absorption does not scale favorably due to path length dependency [12,15] and nonlinear response to sample concentration [16], effort is being directed towards maintaining high sensitivity with RID while scaling the detection volume down to the nanoliter regime. For example, Wang et al…”