On-line infrared detection in aqueous micro-volume systems

On-line hyphenation of quantum cascade laser and capillary electrophoresis

We report the first successful hyphenation of a Fabry Pérot quantum cascade (QC) laser to a capillary electrophoresis system. This involved use of a dedicated IR-transparent flow cell, made of CaF2, constructed by means of SU-8 based lithography and low temperature wafer bonding techniques. Adenosine, guanosine, xanthosine and adenosine-5'-monophosphate were separated in a borate-containing separation electrolyte (10 mM, pH 9.3). Functional group (carbohydrate) detection was accomplished by use of the 1080 cm(-1) emission line of the available QC-laser. The assessable optical path length could be increased, from the normally available 10-15 microm in CE-FTIR analyses, to 60 microm using this powerful mid-infrared laser and aqueous solutions.

Attenuated Total Internal Reflectance Infrared Microspectroscopy as a Detection Technique for Capillary Electrophoresis

A novel detector for capillary electrophoresis (CE) using single-bounce attenuated total internal reflectance (ATR) Fourier transform infrared (FT-IR) microspectroscopy is presented. The terminus of the CE capillary is placed approximately 1 microm from the internal reflectance crystal at the focus of an ATR infrared microscope. Using pressure driven flow injection, concentration and volume detection limits have been determined for 25- and 10-microm-i.d. silica capillaries. Upon injection of 820 pL of succinylcholine chloride in a 10-microm capillary, a concentration detection limit of approximately 0.5 parts per thousand (ppt), or 410 pg, is found. The injection volume detection limit using a 108 ppt solution is 2.0 pL (216 pg). Sample separations using a programmed series of pressure, voltage, and again pressure on 25-, 50-, and 75-microm-i.d. capillaries are shown. CE separations of citrate and nitrate, as well as succinylcholine chloride with sodium salicylate using acetone as a neutral marker, are demonstrated. Several advantages of this CE-FT-IR technique include: (1) minimization of postcolumn broadening as a result of a small detector volume; (2) the ability to signal average spectra of the same aliquot, thereby improving the signal-to-noise in a stopped-flow environment; and (3) simplicity of design.