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O polimero polivinilpirrolidona (PVPP) proporciona uma alternativa analitica ao inves do po-de-pele e caseina, como um agente complexante na quantificacao de taninos. Neste trabalho foi estudado a especificidade do PVPP em complexar com compostos polifenolicos, na presenca de rutina. Os acidos galico e tânico, catequina e pirogalol foram utilizados como substâncias de referencia (PRS), junto com o extrato aquoso das folhas do Psidium guajava L. A especificidade da complexacao foi avaliada pelo metodo espectrofotometrico e por cromatografia liquida de alta eficiencia (CLAE) com arranjo de diodos (DAD). As analises para a mistura das PRS e rutina, demonstraram claramente que a complexacao com PVPP nao e uma reacao especifica e independe da quantidade de polimero utilizada. As analises por CLAE-DAD do extrato de Psidium guajava revelaram picos caracteristicos de flavonoides, alem de catequina e acido galico. Todos os picos destes flavonoides, catequina e acido galico decresceram quando adicionou-se o PVPP. Isto confirma a falta de especificidade. Desde que a ligacao PVPP-polifenois depende de caracteristicas estruturais particulares, a extensao desses resultados a outras especies vegetais deve ser evitada. Cross-povidone, or polyvinylpyrrolidone (PVPP) affords an analytical alternative instead of hide-powder and casein as binding agent in the content assay of vegetable tannins. In this work we studied the specificity of PVPP to bind polyphenolics in the presence of flavonoids. Gallic acid, tannic acid, catechin and pyrogallol were used as polyphenolic reference substances (PRS), along with an aqueous extract from Psidium guajava L. leaves. The binding specificity was assayed by UV-Vis and High Performance Liquid Chromatography-Photodiode array (HPLC-PDA) methods. The analyses of PRS-rutin mixtures showed clearly that PVPP binding is a non-specific reaction, unrelated to the amount of PVPP used. HPLC-PDA analysis revealed peaks which could be characterized as flavonoids in the Psidium guajava extract, beside catechin and gallic acid. All these flavonoids, catechin and gallic acid peaks decreased as PVPP was added; this confirms the lack of specificity. Since the polyphenolic-PVPP reaction depends on specific structural features, any extensive conclusion should be avoided.

Study of the Specificity of Cross-Povidone (PVPP) as binding agent in the quantification of polyphenolic compounds