Investigation of photochemical reaction products of glucose formed during direct UV detection in CE

Abstract

In CE, saccharides are accessible to direct UV detection due to a photochemical reaction in the detection window of the separation capillary resulting in the formation of UV absorbing substances. Employing a CE method that allows long in-capillary irradiation with subsequent UV and MS detection, the present study could identify several reaction products of glucose. Among these were UV absorbing substances so far unknown to be formed during direct UV detection with the chemical formulas C4 H6 O2 , C5 H6 O4 , C5 H8 O3, and C6 H8 O5 . Investigations of the impact of the irradiation time revealed differences between these reaction products suggesting differing reaction mechanisms especially for the smallest products. More detailed information could be obtained by experiments with isotope-labeled substrates performed to determine the parts of glucose that are converted to the particular reaction products. In addition, structural formulas for the reaction products were suggested based on HPLC-MS/MS measurements of off-line irradiated glucose solutions which revealed the existence of functional groups such as carboxylic acid or aldehyde groups.

Recent advances in capillary electrophoresis separation of monosaccharides, oligosaccharides, and polysaccharides

“…The photochemical reaction of saccharides during direct UV absorbance detection has been recently investigated by Schmid et al. . A similar method has also been applied by Oliver et al.…”

Size-Based Characterization of Polysaccharides by Taylor Dispersion Analysis with Photochemical Oxidation or Backscattering Interferometry Detections

“…Experiments revealed that the conversion reaction of carbohydrate to MDA is sensitive to the residence time under the UV light since MDA can further degrade into non-UV absorbing products 24 . Besides MDA, minor photooxidation reaction products, either with UV absorbing (C 4 H 6 O 2 ) or non-UV absorbing (gluconic acid) compounds could be detected 25 . Photo-initiator Irgacure® 2959 added in the background electrolyte could significantly increase sensitivity by 40% for mono-and disaccharides in CE-UV method, providing LOD of 0.005 to 0.02 mM respectively 26 .…”

“…Later, Oliver et al., suggested that the photooxidation of the saccharides, and thus their detection, could be enhanced by the application of the electric field. Schmid et al , investigated in more detail the occurring photochemical reactions using CE-MS and HPLC-MS/MS. Experiments revealed that the conversion reaction of carbohydrate to MDA is sensitive to the residence time under the UV light as MDA can further degrade into non-UV-absorbing products .…”

Ultrafast Photodynamics of Glucose

“…On the experimental side, the fact that continuous UV irradiation of carbohydrates leads to strongly UV-absorbing photoproducts has been exploited in the last years in the context of analytical techniques, such as the quantification of carbohydrate contents in beverages by spectrophotometric detection 16 , or as an alternative detection approach in capillary electrophoresis [17][18][19] . Usually, the detection process within the latter method involves UV absorption of the separated analytes.…”

“…Investigation of the reaction products formed from glucose samples in this way has also confirmed that the degradation process is initiated by a ring opening reaction in which the bond between the C 1 carbon and the ring oxygen is broken. 18,19 A detailed theoretical insight into the optical absorption and possible photochemical relaxation pathways of the glucose molecule has been gained by investigations of Tuna et al 14 . Glucose represents a building block found in various naturally occuring polymeric carbohydrates and thus can be considered as a basic representative of this class of molecules.…”