Statistical Comparison of Wet and Dry-Ashing Digestion Methods for the Determination of Copper and Iron Species in Orange Peel, Flesh and Tree Leaves by Flame Atomic Absorption Spectroscopy

In this study, two methods of wet digestion and dry-ashing digestion are performed and compared statistically for the determination of iron (Fe) and copper (Cu) species in the orange peel, flesh and leaves by means of flame atomic absorption spectroscopy (AAS). In wet digestion, the effects of two reagents and their mixtures were studied. In dry digestion, various factors affecting the digestion were studied and optimal condition established. Based on the average concentration (mg L−1), standard deviation (n = 5) and relative standard deviation (RSD)%, the best conditions of dry digestion and wet digestion to extract Fe and Cu were chosen. Finally, some 12 measurements were performed based on the optimum conditions of dry and wet digestions and the best method was selected with regard to the obtained results. In orange tree leaves because texp (0.016) is smaller than ttheorical (2.18), it shows that there is no difference between the two methods for analysis of Fe. However, the determination of Cu in orange tree leaves was practical with wet digestion in that texp (57.14)˃ ttheorical (2.18) shows there is a difference between the two methods and wet digestion is more suitable than dry-ashing due to obtaining less RSD%. In flesh orange, it is seen that for both texp ˃ ttheorical, showing there is a difference between the two methods and wet digestion is more suitable than dry-ashing one. Furthermore, in both Fe and Cu species, the texp ˃ ttheorical, indicating that the two digestion methods are different and wet digestion was selected as a suitable method because of obtaining smaller values of RSD%. Finally, after comparison of the results, the wet digestion vessel for Fe and Cu extraction in the samples was suggested. The developed digestion methods were validated with certified reference materials.