Liquid Analysis by Dry-Extract Near-Infrared Reflectance on Fiberglass

Nonvolatile residues of liquid samples were retained on fiberglass filters, and near-infrared reflectance spectroscopy was used for a rapid nondestructive analysis of the residue. However, neither log(1/R) nor (1 – R)²/2R computations gave results that varied in a linear manner with solute concentration. Nonlinear curve fitting of experimental data to a mathematical model [log 1/R = h + s(1 – exp(–kC))] has shown a good correlation with the model. On the other hand, NIR analysis by multiple linear regression has been evaluated for rapid determination of both total and individual sugars in aqueous solutions containing glucose, fructose, and sucrose mixtures. The concentration ranges of glucose, fructose, and sucrose are, respectively, 20–50 g/L, 20–50 g/L, and 0–50 g/L. Standard errors of performance for prediction are 1.8 g/L for sucrose, 3.5 g/L for glucose, 3.0 g/L for fructose, and 5.3 g/L for total sugars (range 0–150 g/L). The results of this study show its potential application in beverage analysis (fruit juices, lemonade) and other liquid systems.