Understanding and improving direct UV detection of monosaccharides and disaccharides in free solution capillary electrophoresis

• Capillary electrophoresis (CE) of carbohydrates in highly alkaline buffer.
• Direct UV detection of a radical intermediate created via in-situ photo-oxidation.
• Identification of some photo-oxidation end products with NMR spectroscopy.
• Importance of oxygen in the photo-oxidation mechanism.
• Addition of a photo-initiator increases the detection sensitivity.

Direct UV detection of carbohydrates in free solution capillary electrophoresis at 270 nm is made possible by a photo-oxidation reaction. Glucose, rhamnose and xylose were shown to have unique UV absorption spectra hypothesizing different UV absorbing intermediates for their respective photo-oxidation. NMR spectroscopy of the photo-oxidation end products proved they consisted of carboxylates and not malondialdehyde as previously theorized and that oxygen thus plays a key role in the photo-oxidation pathway. Adding the photo-initiator Irgacure® 2959 in the background electrolyte increased sensitivity by 40% at an optimum concentration of 1 × 10−4 mM and 1 × 10−8 mM for conventional 50 μm i.d. capillaries and for the corresponding extended light path capillaries, respectively.

Figure optionsDownload as PowerPoint slide