A green on-line digestion system using 70% hydrogen peroxide and UV radiation for the determination of chromium in beer employing ETAAS

Abstract

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%.