Performance evaluation of a high-pressure microwave-assisted flow digestion system for juice and milk sample preparation

Application of atmospheric pressure glow discharge generated in contact with liquids for determination of chloride and bromide in water and juice samples by optical emission spectrometry

Novel atmospheric pressure glow discharge (APGD) microplasma systems, sustained between a miniaturized flowing anode (FLA) or cathode (FLC) and a He jet, were investigated for the direct determination of Br and Cl, using optical emission spectrometry (OES). The impact of the most crucial operating parameters, i.e., the acid type and its concentration, the discharge current, the gas flow rate, and the sample flow rate, was studied for each of the proposed APGD-based systems. Under the optimized conditions, the analytical figures of merit were determined. The susceptibility to the matrix effects of both developed methods was verified as well. It was found that the mechanism of the analytes transport into the discharge likely relied on the cathode sputtering in the case of FLC-APGD and the formation of the volatile Br and Cl species for FLA-APGD. The DLs of Br and Cl were established to be relatively high, i.e., 0.15 and 1.5 mg L^-1 for FLA-APGD and 2.1 and 18 mg L^-1 for FLC-APGD. However, both studied methods turned out to be resistant to the presence of foreign ions in a sample, at relatively high concentrations. Hence, the proposed methods could be successfully applied for the determination of Br and Cl in water and juices samples and no major differences between the results obtained using the external standard calibration and the standard addition method were found.

Chemometric tools in the optimization of a microwave-assisted digestion procedure for guarana-based drink samples and data analysis from elemental, caffeine, and epicatechin contents

In this work, a method was developed for the determination of Na, K, Ca, Mg, P, S, Fe, Zn, Mn, and Cu by ICP OES and caffeine and epicatechin by HPLC-DAD in industrialized guarana-based beverages. The acid digestion in microwave oven was optimized by constrained mixture design. The optimum volumes found for the reagents were 2.60 mL (HNO₃), 1.80 mL (H₂O₂), and 0.60 mL (HCl) for a final volume of 10 mL, resulting in a final digestate with residual acidity of 0.8 mol L^-1 and 9% for residual carbon content. The detection limits found for the studied elements were between 0.0010 and 0.050 mg L^-1. Precision (%RSD) was always below 6%. Accuracy was assessed by analyzing a certified reference material and addition and recovery tests. PCA and HCA were applied to caffeine, epicatechin and elemental concentrations aiming to evidence latent information.