Use of factorial design for optimization of microwave-assisted digestion of lubricating oil

Abstract

A eficiência dos procedimentos de digestão em fornos de microondas pode ser afetada por parâmetros experimentais críticos, como massa de amostra, volume da mistura ácida, potência de radiação aplicada e o tempo da digestão. Neste trabalho foi proposta a utilização de um planejamento fatorial completo para a otimização da digestão de amostras de óleo lubrificante em forno de microondas, com recipientes fechados. O teor de carbono residual e a acidez final das soluções foram determinados em todos os digeridos provenientes do forno de microondas, como resposta ao planejamento fatorial. Cálcio, Cu, Mg, P, S e Zn foram determinados nos digeridos ácidos e a exatidão foi checada utilizando-se um material de referência certificado, NIST SRM 1848-Lubricating Oil Additive Package. Os resultados encontrados para as amostras e para o material de referência certificado estão em concordância a um nível de confiança de 95%. Tempo de digestão, potência de radiação aplicada, massa de amostra e as interações entre essas variáveis foram significativas (P < 5%), aplicando-se a análise de variância (ANOVA).This work proposes the use of factorial design for optimization of microwave-assisted digestion of lubricating oil. The accuracy of digestion procedures is affected by critical experimental parameters, such as sample amount, concentrated acid volumes, microwave radiation applied power, and digestion time. The effects of these key variables on the microwave-assisted digestion efficiency were investigated. The residual carbon content and the acidity were determined in all digestates after microwave-assisted digestion as response of the factorial design. Calcium, Cu, Mg, P, S, and Zn were determined in oil digestates obtained by using two systems: a cavity-and a focused-oven. The accuracy was checked using one standard reference material, NIST SRM 1848 -Lubricating Oil Additive Package. All determined and certified values are in agreement at a 95% confidence level. The digestion time, microwave applied power, sample mass, and the interaction between these variables were significant according to P-values when the analysis of variance (ANOVA) was used.Keywords: factorial design, microwave-assisted digestion, lubricating oil, metals IntroductionThe proposal of a new analytical method requires the optimization of the experimental variables and its validation. The first one involves the selection of the values of the factors that have an influence on the analytical signal and lead to the best results for the analytical process. The optimization of the proposed method allows us to understand effects that are not explained in a traditional way, such as those in which the analytical response is a multimodal function of the independent variables or when the effects of the variables are not additive and there is interaction among them. 1 Sample preparation involves digestion or extraction of the analytes before the analysis, 2 so this step is time limiting, requiring up to 60% of the complete analysis time, and is responsible for up to 30% of ...

Microwave Assisted Acid Digestion of Biomorphic Ceramic Obtained from Beech Wood Infiltrated with Nickel Oxide: Factorial Design

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Evaluation of digestion procedures for simultaneous determination of Ca, P, Mg, K and Na in biodiesel by inductively coupled plasma optical emission spectrometry

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