Recherches sur l'analyse des mélanges liquides par spectrographie Raman

Abstract

By technical improvements in the exact determination of the photographic plate contrast factors, the sensitonietric calibration and the densitometry, the following observations have been established : a) That for binary mixtures of non-associated compounds the theoretical proportionality between the intensity ratio of two lines and the molar ratio of the mixture has been confirmed over the range tested; deviations from this law observed by earlier workers have all been traced either to overlapping of lines or sensitometric errors. b) For binary mixtures of strongly associated liquids, the spectrum of the mixture is not always exactly the sum of the spectra of the components; new lines may appear. The proportionality relationship is conserved by the lines, due to vibrations within the molecule of groups not involved in the association, while other groups give strongly perturbed radiations. The study of these perturbations may throw useful light on the nature of association linkages in liquids. c) For ternary mixtures of alcohols, the influence of a third constituent on the intensity ratios of some of the lines of the first pair seems to be negligible. Since the line intensity ratios are proportional to the molar ratios, it should be possible to make use of relative diffusion coefficients for the analysis of more complex mixtures. Our work has improved the precision of the analytical determinations; the mean error does not exceed 0–8% and is often less than 0.5% for non-associated liquids; while for associated liquids the maximum error is only 3%.