Direct determination of monosaccharides in honey by coupling a sensitive new Schiff base Ni complex electrochemical sensor and chemometric tools

Abstract The determination and quantification of saccharides is of considerable importance in the food industry among other fields. In this work, we describe for the first time the preparation of the Schiff base Ni complex, NiII-(N,N’-bis(2,3-dihydroxybenzylidene)-1,2-diaminobenzene) (Ni(II)-2,3dhS) obtained by reaction of the tetradentate Schiff base ligand containing ortho quinone functional groups (N,N’-bis(2,3-dihydroxybenzylidene)-1,2-diaminobenzene) and Ni2+, as well as its application in the development of an electrochemical sensor. Coupled to chemometric tools, the sensor allowed the direct determination of glucose and fructose in honey, without the need of previous separation steps or chromatographic techniques. For this purpose, the new Schiff base Ni complex has been electropolymerized onto screen-printed electrodes modified with carbon nanotubes. The electropolymerization process has been exhaustively characterized by operando spectroelectrochemical techniques to confirm the generation of the desired polymer. The resulting modified electrodes present a strong electrocatalytic activity towards the oxidation of glucose and fructose in alkaline solution and have been employed in combination with partial least squares regression (PLSR) to resolve mixtures of glucose and fructose in a complex matrix, as honey. The multivariate model was based on PLSR analysis and showed good predictive capability for the two analytes in sample standard honey with an average error of 8% and relative standard deviations below 9%.