Determination of uronic acids in sugarcane bagasse by anion-exchange chromatography using an electrode modified with copper nanoparticles

Abstract

Uronic, D-glucuronic and D-galacturonic acids are found in lignocellulosic materials and are known to be used in the food industry and chemical industries. They are present in the fibrous structure of sugarcane bagasse, where they are incapable of being detected owing to the lack of absorption of the chromophore and fluorophore groups in their molecular structure, thus restricting their detection by traditional spectrophotometric methods. The detection is only possible by means of derivatization. In this light, a modified detector with copper nanoparticles by potentiostatic electrodeposition was developed. D-Galacturonic and D-glucuronic acids are oxidized irreversibly at potentials of 0.45 and 0.48 V vs. Ag/AgCl, respectively, in cyclic voltammetry. This modified electrode was used in chromatography with pulsed amperometric detection in wall-jet cells. An anion exchange column, CarboPac PA10, was used for the separation of uronic acids under isocratic conditions, with the mobile phase containing 0.1 M NaOH plus 280 mM CH₃COONa. The separation of the acids was found to be complete within 15 minutes. The detection limit was 5.8 × 10⁻⁷ and 7.3 × 10⁻⁷ mol⁻¹ and the amperometric sensitivity was 3.6 ± 1.8 × 10⁶ and 1.9 ± 1.0 × 10⁶ μA l mol⁻¹ for D-galacturonic and D-glucuronic acids respectively. The aforementioned method developed was then applied to real samples of hydrolyzate bagasse. The amount of acid found in this sample was 15.8 ± 0.5 g kg⁻¹ and 12.5 ± 0.5 g kg⁻¹ for D-galacturonic and D-glucuronic acids respectively. The results demonstrate that the proposed method can be used for the detection of these acids without the need for derivatization, given its merits of exerting no interference, having considerable accuracy and shorter run time.