Desenvolvimento e validação de métodos cromatográficos para determinação dos produtos de oxidação de álcoois

Abstract

The present work describes the development and validation of analytical methodologies based on chromatography for the identification and quantification of products obtained in the oxidation of alcohols. For this study, gold catalysts, supported on silica (AuNP/SiO2) and in the core-shell form (AuNP@SiO2), were synthesized and characterized for structural, morphological and chemical composition confirmation. In one of the catalyst characterization steps, to determine the gold content, a new flame atomic absorption spectrometry methodology was proposed, based on the preparation of samples in acid medium (different strategies, E1, E2, E3) using microwave oven and capable of differentiating the way AuNP is in silica. With the application of E2 (HNO3:HCl + MW) and E3 (HNO3:HCl:HF + MW) it was possible to confirm the location of AuNP (supported or in the core-shell form), with results proven through transmission electron microscopy. For the application of these catalysts in the oxidation reactions of benzyl alcohol (model), a chromatographic method using a polar column (method I) was developed and validated. The reaction system was evaluated through the application of an experimental design, in which conditions such as catalyst mass, reaction temperature and reaction time were evaluated. The presence of a base, potassium carbonate (K2CO3), in the reaction system was evaluated univariately by applying different catalysts. In order to reduce the quantities of reagents used in the reaction, it was sought to optimize its conditions, such as dilution of the system in water, requiring new reaction tests. These tests were carried out with a commercial gold and palladium (AuPd) catalyst as an example of another catalytic system. After optimization of reaction conditions, another chromatographic method (method II) was developed and validated using a nonpolar column, since method I does not allow the analysis of aqueous samples due to the instability of the polar stationary phase, based on polyethylene glycol, which undergoes hydrolysis. The validation tests proved that both proposed methodologies are accurate in the concentration ranges evaluated: method I (0.001 to 0.2 g mL-1) and method II (0.0001 to 0.01 g mL-1), meeting the guidance requirements for validation. Both methods presented analysis time ≤ 6 minutes, correlation coefficients ranging from 0.9957 to 0.9999 and recovery in the range of 80.1 to 101.4%. The developed methods were robust to instrumental variations and to the evaluation of benzyl alcohol oxidation reactions promoted by different catalysts. In the third stage of the work, a methodology based on high performance liquid chromatography (HPLC) for the determination of glycerol oxidation products was validated. The methodology proved to be selective in the identification of 07 compounds. The AuNP/SiO2 and AuNP@SiO2 catalysts were applied in glycerol oxidation reactions, proving that the proposed methodology was efficient in the separation and identification of the products regardless of their conversion and selectivity.