Capillary electrophoresis studies of pectins

Capillary electrophoresis (CE) has been used to study a variety of pectins that originate from different sources (citrus, apple and beet) and have different anhydrogalacturonic acid (AGU) contents (86.2–63.2%). This CE method can be used for the quantitative detection of aqueous solutions of pectins in the concentration range 0.5–5 mg mL−1 using a 50 mM pH 7.0 phosphate background electrolyte and UV detection at 192 nm. Using lemon pectin calibration standards in the degree of esterification (DE) range 31.1–75.8%, the technique was used to determine the DE of a further 11 pectin samples. Results are shown to be in excellent agreement with those obtained by titration, irrespective of the pectin type and neutral sugar content. The method also allows determination of the intermolecular DE distribution (variation in DE between molecules), from the CE peak shape. Results for the DE distribution are compared with those obtained by ion-exchange chromatography in combination with size-exclusion chromatography (IEC-SEC). Both DE and DE distribution are obtained from CE in approximately 2 h, inclusive of sample preparation and calibration, in contrast to 2 days for the IEC-SEC method.