A void exists in capillary separations for a simple, nanolilter volume, optical detection that has high sensitivity and can be used universally. The need for such a detector is particularly evident in the area of biological analysis, where the desired solute has little native absorbance or fluorescence. The micro-interferometric backscatter detection (MIBD) system has the potential to fill this void. MIBD has been employed for refractive index (RI) detection in CE and will be used to perform RI and polarimetric detection of poorly absorbing or non-fluorescent biologically important solutes in capillary electrochromatography (CEC). MIBD is a significant advance in biological research instrumentation for several reasons. The folded, yet simple and inexpensive, optical train is easy to align; the fused silica capillary is directly probed without modification; and multi-pass signal enhancement affords ultra-high sensitivity (micromolar) in nanoliter volumes. Preliminary results also indicate MIBD can be used as a capillary-scale polarimetric detector, allowing optical activity detection (polarimetry) in sub-nanoliter volumes with CEC. CEC is a powerful hybrid separation technique that uses features of both high-performance capillary electrophoresis (HPCE) and liquid chromatography (HPLC). Doing CEC on etched and functionalized capillaries, with inner diameters ranging from 20 to 100 mm, rapid and efficient separation of anionic and neutral compounds is possible, while avoiding some of the limitations encountered in packed capillaries. The power of MIBD with CEC will allow new insights into the functionality of biologically significant species such as hormones, messengers and membrane constituents. As a first step to providing enhanced knowledge about these important species, CEC-RI and CEC-polarimetry will be used to quantify angiotensins, inositol phosphates and phospholipids.
