Sugars’ Quantifications Using a Potentiometric Electronic Tongue with Cross-Selective Sensors: Influence of an Ionic Background

Glucose, fructose and sucrose are sugars with known physiological effects, and their consumption has impact on the human health, also having an important effect on food sensory attributes. The analytical methods routinely used for identification and quantification of sugars in foods, like liquid chromatography and visible spectrophotometry have several disadvantages, like longer analysis times, high consumption of chemicals and the need for pretreatments of samples. To overcome these drawbacks, in this work, a potentiometric electronic tongue built with two identical multi-sensor systems of 20 cross-selectivity polymeric sensors, coupled with multivariate calibration with feature selection (a simulated annealing algorithm) was applied to quantify glucose, fructose and sucrose, and the total content of sugars as well. Standard solutions of ternary mixtures of the three sugars were used for multivariate calibration purposes, according to an orthogonal experimental design (multilevel fractional factorial design) with or without ionic background (KCl solution). The quantitative models’ predictive performance was evaluated by cross-validation with K-folds (internal validation) using selected data for training (selected with the K-means algorithm) and by external validation using test data. Overall, satisfactory predictive quantifications were achieved for all sugars and total sugar content based on subsets comprising 16 or 17 sensors. The test data allowed us to compare models’ predictions values and the respective sugar experimental values, showing slopes varying between 0.95 and 1.03, intercept values statistically equal to zero (p-value ≥ 0.05) and determination coefficients equal to or greater than 0.986. No significant differences were found between the predictive performances for the quantification of sugars using synthetic solutions with or without KCl (1 mol L−1), although the adjustment of the ionic background allowed a better homogenization of the solution’s matrix and probably contributed to an enhanced confidence in the analytical work across all of the calibration working range.

Determination of Acid Dissociation Constants (pKa) of Bicyclic Thiohydantoin-Pyrrolidine Compounds in 20% Ethanol-Water Hydroorganic Solvent

The acid dissociation constants of potential bioactive fused ring thiohydantoin-pyrrolidine compounds were determined by potentiometric titration in 20% (v/v) ethanol-water mixed at25±0.1°C, at an ionic background of 0.1 mol/L of NaCl using the HYPERQUAD computer program. Proton affinities of potential donor atoms of the ligands were calculated by AM1 and PM3 semiempiric methods. We found, potentiometrically, three different acid dissociation constants for1a–f. We suggest that these acid dissociation constants are related to the carboxyl, enol, and amino groups.

Nitrogen Specific Ion Electrodes for Soil, Plant, and Water Analysis

The nitrate specific ion electrode and the ammonia and nitrogen dioxide gas-sensing combination electrodes offer simple methods of analyses of plants, soils, and water. The nitrate electrode measures activity of the nitrate ion in solution and is susceptible to interfering ions, particularly Cl. Considerable discrepancies exist in the literature concerning nitrate extracting solutions and buffering solutions used to eliminate interferences with the nitrate electrode. An evaluation of ionic strength adjusters, used to alleviate fluctuating ionic background interferences, indicates (NH4)2SO4 produces consistent results without adversely affecting life of the nitrate electrode. Ammonia electrode determination of total nitrogen in soil, plant, and water samples is a rapid method that eliminates the time-consuming distillation-titration step. The nitrogen dioxide electrode is relatively new and little information is available concerning methodology and its potential problems.