Photo-oxidation using UV radiation as a sample preparation procedure for the determination of copper in fruit juices by flame atomic absorption spectrometry

The present work proposes the photo-oxidation using UV radiation/H2O2 as an alternative procedure for pretreatment of industrialized fruit juice samples for determination of copper by flame atomic absorption spectrometry (FAAS). For optimization of the photo-oxidation procedure the following variables were studied: pH and volume of buffer solution, volume of concentrated hydrogen peroxide and irradiation time. The sample degradation was monitored by molecular absorption spectrometry in the spectral range of 200-800 nm. The established conditions were: pH 10, volume of buffer of 1.0 mL, volume of concentrated hydrogen peroxide of 1.5 mL and irradiation time of 90 min, for a 5 mL volume of the photo-digested sample. An external calibration technique with aqueous standard was used for copper quantification. Under these conditions, the method allows the copper determination with limits of detection and quantification of 7 and 22 mu g L-1, respectively. The precision, expressed as relative standard deviation (RSD), was 1.43 and 0.27% for copper concentrations of 0.2 and 2.0 mu g mL(-1), respectively. The accuracy of the method was evaluated for five industrialized fruit juice samples (orange, grape, mango, passion fruit and peach) and the results compared with those obtained after acid digestion of the samples and determination by FAAS. No significant difference was observed between the results obtained by both procedures, applying a paired t-test at the 95% confidence level.