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Abstract
The determination of the acidity of oils by catalytic thermometric titrimetry using paraformaldehyde as the thermometric end-point indicator was investigated. The sample solvent was a 1:1 (v/v) mixture of toluene and 2-propanol and the titrant was 0.1 mol L-1 aqueous sodium hydroxide. Paraformaldehyde, being insoluble in the sample solvent, does not present the inconvenience of other indicators that change the properties of the solvent due to composition changes. The titration can therefore be done effectively in the same medium as the standard potentiometric and visual titration methods. The results of the application of the method to both non-refined and refined oils are presented herein. The proposed method has advantages in relation to the potentiometric method in terms of speed and simplicity.
Highlights
The standard methods employed for the determination of acidity of oils are based either on titrimetry with visual indicators or, mainly in the case of coloured samples, on potentiometric titrimetry.[1]
Visual indicators cannot be employed for coloured samples, and potentiometric titrimetry may be subject to the noxious effect of the sample solutions on the glass electrode
We report our results on the determination of the acidity of some crude and refined oils by catalytic thermometric titrimetry, employing paraformaldehyde as the end-point indicator
Summary
Pós-Graduação em Química, Centro de Tecnologia e Ciências Exatas, Universidade Federal do Maranhão, Campus do Bacanga, Av. dos Portugueses, s/n, 65080-04 São Luis-MA, Brazil. Investigou-se a determinação da acidez de óleos graxos pela técnica da titulação termométrica catalítica empregando-se paraformaldeido como indicador termométrico de ponto final. O paraformaldeido, sendo insolúvel no solvente, não apresenta o inconveniente, que ocorre com outros indicadores de ponto final, de alterar a composição do solvente da amostra mudando suas propriedades, inclusive a solubilidade da amostra no mesmo. Os resultados da aplicação do método à amostras de óleos graxos brutos e refinados são apresentados. The sample solvent was a 1:1 (v/v) mixture of toluene and 2-propanol and the titrant was 0.1 mol L-1 aqueous sodium hydroxide. Paraformaldehyde, being insoluble in the sample solvent, does not present the inconvenience of other indicators that change the properties of the solvent due to composition changes. The titration can be done effectively in the same medium as the standard potentiometric and visual titration methods.
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