MCR-ALS applied to the quantification of the 5-hydroxymethylfurfural using UV spectra: Study of catalytic process employing experimental design

Abstract

Study of the production of 5-hydroxymethylfurfural (5-HMF) from glucose, applying niobic acid as catalyst, and the quantification of 5-HMF by selective analytical methods are the goals of this work. The high-performance liquid chromatography (HPLC) was used as reference method. The developed alternative method proposes the use of ultraviolet (UV) spectroscopy technique in combination with multivariate curve resolution alternating least squares (MCR-ALS). In addition, a partial least squares (PLS) regression model was built to compare MCR-ALS and HPLC results. Regression models using MCR-ALS and PLS were built for 5-HMF in the presence of levulinic acid in the range of 2.0–16.0 mg L−1. For HPLC the range used was of 10–800 mg L−1. The models were evaluated by analyzing statistical parameters of quality such as root mean square error (RMSE) and correlation coefficient (R). The calibration parameters obtained for MCR-ALS, PLS and HPLC were, respectively: RMSEC of 0.68, 0.27 and 4.92 mg L−1 and R equal to 0.988, 0.998 and 0.999. Central composite design (CCD) was used to optimize the two variables of reaction, i.e., time and mass of catalyst for glucose conversion into 5-HMF. The samples were analyzed by UV-MCR-ALS, UV-PLS and HPLC. The predicted concentrations of 5-HMF obtained by MCR-ALS and PLS versus HPLC predictions were evaluated. Both correlations were equal to 0.995. According to paired t-test results at a significance level of 0.05 both model predictions were statistically equal to the values predicted by HPLC. The results show that UV-MCR-ALS method can predict the concentration of 5-HMF in reaction mixtures with accuracy and obtain the relative concentration and pure spectra in a mixture without chromatographic separation.