Search

This work proposes an on-line digestion system employing 70% (w/w) hydrogen peroxide and UV radiation for producing hydroxyl radicals for the determination of chromium in beer samples by electrothermal atomization atomic absorption spectrometry (ETAAS). The digester system consists of a closed wooden box, which is painted black internally, containing a PTFE tube wrapped around a 15 W UV lamp. During the mineralization step, a peristaltic pump is employed to propel the sample solution over the UV lamp. The experimental factors UV irradiation time and hydrogen peroxide volume were optimized using a two-level full factorial design. Degradation curves at different pH conditions demonstrated that the digestion of beer is faster at alkaline pH. The results demonstrated that, in the presence of 70% H2O2 and 15 W UV radiation, 75% of the chromophore species is degraded with an irradiation time of 25 min. The degradation kinetic curves of beer samples under different conditions were also evaluated. The apparent kinetic constant (kapp) found for the process assisted by 70% H2O2 and 15 W UV light was 0.0668 min−1 (R2 = 0.9936). The on-line digestion procedure with a sample flow rate of 2 mL min−1 for 45 min allowed the determination of chromium in beer samples by ETAAS, utilizing the external calibration technique, with the analytical line 357.9 nm, in the presence of magnesium as chemical modifier with limits of detection and quantification of 0.86 and 2.90 μg L−1, respectively. The method accuracy was confirmed by the analysis of the certified reference material of ERM-CA713 wastewater provided by the European Reference Materials. Six beer samples were digested and the chromium was determined. The contents found varied from 4.26 to 33.28 μg L−1. Addition/recoveries tests were also performed to evaluate the accuracy method. The recoveries obtained varied from 93.2 to 96.4%.

This work presents a critical review of multivariate techniques employed for optimization of methods developed in food analysis. A comparison between the response surface methodologies has been performed, it evidencing advantages and drawbacks of these. Applications of the main chemometric tools (central composite and Box Behnken designs and Doehlert matrix) often utilized for optimization of sample preparation procedures and also instrumental conditions of analytical techniques for determination of organic and inorganic species in food samples are shown. Also, a brief discussion on the use of multiple responses and robustness test in food analysis has been presented.

This paper proposes a closed inline system for decomposition of wine, aiming at the determination of lead using electrothermal atomization atomic absorption spectrometry (ETAAS). The system is built using a 0.8 mm diameter PTFE tube, which is wrapped around an 8 W UV lamp. The sample in the presence of 70% hydrogen peroxide is circulated on an 8 W UV lamp at the flow rate of 1 mL min−1 for 45 min. Under these conditions, the carbon content varied from 10% to 2% for a red wine sample before and after digestion, respectively. The system has allowed the determination of lead in wine samples using the analytical line 283.306 nm in the presence of aluminum as the chemical modifier and pyrolysis and atomization temperatures of 800 and 1800 °C, respectively. Then, lead can be quantified employing the external calibration technique with limits of detection 0.27 and quantification 0.89 µg L−1, and characteristics mass of 18 pg. The precision expressed by relative standard deviation (RSD%) was 2.13%, calculated using six replicates of a digested solution of a wine sample with the lead content of 16.35 µg L−1. For evaluation of the accuracy method, two wine samples were analyzed simultaneously by the method proposed and also by inductively coupled plasma mass spectrometry (ICP-MS). A statistical test demonstrated no significant difference between the means obtained by these two techniques. Also, experiments involving addition/recovery tests confirmed the method's accuracy. The system was employed for digestion and determination of lead in four Brazilian wine samples. The lead content varied from 2.19 to 43.48 µg L−1.