Efficient capillary zone electrophoretic separation of wood-derived neutral and acidic mono- and oligosaccharides

Abstract

Neutral and acidic monosaccharides, commonly present as structural units in wood-derived hemicelluloses, were derivatized by reductive amination using 6-aminoquinoline (6-AQ) and subsequently separated as their borate complexes by capillary zone electrophoresis. By using a quite concentrated (420 mmol 1 −1) alkaline borate buffer, a fused-silica capillary column with a small inner diameter (30 μm nominal I.D.) and a constant power of 1200 mW (corresponding to an applied voltage of approximately 21 kV), optimal separation was achieved. Under these conditions, the monosaccharides investigated were separated with a resolution, R s , of 1.0–1.2 or greater. On-column UV detection at 245 nm was found to provide highly sensitive detection of the 6-AQ-derivatized monosaccharides. The minimum detectable concentrations were on the order of 10 −6 mol 1 −1 (corresponding to an estimated limit of detection of a few fmol). The linear calibration range of the method, including the 6-AQ derivatization step, was found to be about two orders of magnitude. Several neutral β(1–4)- d-xylooligomers and acidic oligosaccharides containing 4-O-methyl- d-glucuronic acid units, which are common structural elements in hemicelluloses such as birch and spruce xylan, were also efficiently separated as 6-AQ derivatives, using the same buffer system. Finally, the usefulness of this analytical method has been demonstrated using a spruce wood xylan sample subjected to chemical and enzymatic hydrolysis.