DESENVOLVIMENTO DE METODOLOGIA ANALÍTICA BASEADA NO PROCESSO DE FOTO-OXIDAÇÃO UV PARA A DETERMINAÇÃO DE Fe, Mn E Zn EM SUCOS DE FRUTA POR ESPECTROMETRIA DE ABSORÇÃO ATÔMICA EM CHAMA (FAAS)

Abstract

The fruits and products derived from their processing are sources of several essential nutrients to the organism. Fruit juices stand out among fruit products because of their popularity and health benefits. The knowledge of mineral content of these foods is important to evaluate their contribution in diet and for quality control products. However, most of work related to minerals determination in fruit juices makes use of conventional methods of sample preparation, such as wet digestion and dry ashing, which have several disadvantages. Thus, this work aimed at the optimization and validation of an alternative method using UV Photo-Oxidation process in sample preparation for determination of Fe, Mn and Zn in fruit juices by FAAS. The optimization of experimental conditions of UV Photo-Oxidation process was carried out by application of a 24 factorial design, which evaluated the volume of H2O2, pH of solution, concentration of buffer solution and UV irradiation time, obtaining the absorbance of samples at 280 nm.The conditions established by factorial design were applied to 14 fruit juice samples, which were subjected to Fe, Mn and Zn determination by FAAS. In order to evaluate the reliability of the developed method, a validation study was carried out, which evaluated parameters of linearity, limits of detection (LOD) and quantification (LOQ), precision and accuracy, applying appropriate statistical tests. Analytical curves obtained with external standard were employed for all elements analyzed, which showed adequate linearity in the concentration range investigated, with correlation coefficient r> 0.99, values of Fregression>>Fcritical and without lack of fit of linear model (Flof<Fcritical).The limit of quantification (LOQ) values for UV Photo-Oxidation method were below the first point of calibration curve and presented lower values than reference method (wet digestion), indicating a higher sensitivity of proposed method. The method precision was evaluated by comparison with reference method through an F-test of variance comparison, which indicated that there were no significant differences in precision between both methods. The precision was also evaluated by the analysis of repeatability and intermediate precision, using the relative standard deviations (RSD) and the Horrat value, and all values obtained being lower than established by AOAC (RSD (%) <7.3 and Horrat value <1.3), which indicates that this method has adequate precision. Accuracy was evaluated by comparison with reference method by applying a paired t-test and linear regression analysis. The results of paired ttest demonstrated that there are no significant differences between the methods used for determination of Fe, Mn and Zn, since tcalculated<tcritical. In addition, linear regression results, with high values of Fregression, suggested that the metal content determined by both methods presented a linear relation between them. Recovery tests were also performed for three metals analyzed, with recovery rates between 85 and 108%, which are within the limit established by AOAC for concentration range investigated. These results indicate that the proposed method has adequate accuracy for determination of Fe, Mn and Zn in fruit juices by FAAS. Thus, it can be concluded that UV Photo-Oxidation process is suitable for the treatment of fruit juice samples for determination of Fe, Mn and Zn by FAAS, representing a simpler and faster alternative with lower cost and lower generation of toxic waste to environment.