Estudo do efeito de matriz na determinação de fósforo em espécies arbóreas de floresta tropical seca por espectrofotometria com azul de molibdênio

Abstract

Dry tropical forest soils have a shortage of phosphorus. Tris nutrient after absorption by plants, is returned to the soil by the nutrient cycling process, an ecosystem process essential for the conservation of forest ecosystems. Thus, the analysis of leaf material and the nutritional status of leaves are important because they allow understanding the dynamics and maintenance of forest ecosystems. The visible spectrophotometric method with molybdenum blue stands out in the determination of phosphorus, mainly due to its level of sensitivity. However, the matrix effect during analysis may compromise the reliability of the results obtained. Given the above, this research aimed to evaluate the effect of matrix on the determination of phosphorus in tree species of dry tropical forest by spectrophotometry with Molybdenum Blue. The study included the two most representative species in the forest environment in Araripina, Pernambuco, in the dry and wet periods. Digestion of the plant material was performed with 98% sulfuric acid and 30% hydrogen peroxide in the presence of catalysts. The determination was made by molybdenum blue spectrophotometry, associated with standard addition and five matrix dilution ratios. The data showed a decrease in absorbance resulting from the matrix effect and consequently the quantified P content. The pH of the plant extract also affected the analytical determination of phosphorus, however, less significantly than the matrix effect. Samples submitted to matrix dilution and standard addition showed a more efficient phosphorus recovery. The species Croton Limae and Guapira Opposita presented higher phosphorus contents in the wet period, due to the influence of rainfall. Guapira Opposita was the species with the highest P content in both evaluation periods, and the one with the lowest influence of the matrix effect. Thus, the matrix effect influences the phosphorus quantification by the molybdenum blue method, especially in low P species. This effect can be minimized by using matrix dilution combined with standard addition.