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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 work proposes an on-line preconcentration system using ion-imprinted polymer (IIP) for determination of bismuth in seawater employing atomic fluorescence spectrometry (AFS). The polymer was synthesized using 2- (5-bromo-2-pyridylazo) -5-diethylaminophenol (Br-PADAP) for complex formation, ethylene glycol dimethacrylate (EGDMA), cross-linking reagent and methacrylic acid (AMA) reagents, used as the functional monomer, 2,2-azobisisobutyronitrile was used as the radical initiator. The polymer was characterized employing the Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The determination of bismuth was performed employing hydride generation atomic fluorescence spectrometry (HG AFS) and the experimental conditions were optimized using a Box Behnken design involving the factors sample pH, eluent concentration and sodium tetrahydroborate concentration. So, using the optimized conditions the system allows the determination of bismuth with limits of detection and quantification of 26 and 88 ng L−1, a preconcentration factor of 19.8. All these parameters were determined using a sample volume of 25 mL. The precision expressed as relative standard deviation (RSD%) was 3.7% for a bismuth(III) solution of concentration 0.25 µg L−1. The system proposed was applied for the determination of bismuth in four seawater samples collected in Salvador City, Bahia State, Brazil. The concentrations obtained varied from 0.38 to 0.45 μg L−1. The accuracy was evaluated by addition/recovery test, and the recoveries found varied from 92% to 101%.

This study describes the preparation of a novel ion-imprinted polymer (IIP) to apply pre-concentration of cadmium ions in water samples of the Pontal Bay in Ilheus, Brazil. First, cadmium ion was complexed with 2-(2-thiazolylazo)-p-cresol (TAC). Subsequently, there was the polymerization using ethylene glycol dimethacrylate and methacrylic acid monomers along with the radical azobisisobutyronitrile initiator. The mold ions were removed using 2:1 (v v-1) nitric acid. The thermal stability of the polymer was evaluated by thermogravimetry and the characterization was performed by Fourier transform infrared spectroscopy. The maximum adsorption capacity for IIP (qmax = 84.75 mg g-1) could be described by the Langmuir isotherm. The variables: sample flow rate, pH and eluent (nitric acid) were optimized using Box-Behnken design with determination by flame atomic absorption spectrometry (FAAS). The enrichment factor, as well as the limits of detection and quantification (LOQ), were found to be 44, 0.14 and 0.46 µg L-1, respectively. Selectivity was evaluated by using solutions containing CdII, CuII, NiII, PbII, CoII, SO42-, and Cl- ions. The concentration of cadmium ions in the samples varied between < LOQ to 1.25 µg L-1.