QUANTITATIVE INFRARED DETERMINATIONS IN MIXTURES OF UNKNOWN QUALITATIVE COMPOSITION

Abstract

The basic rule that quantitative infrared determinations may only be made in systems of known qualitative composition is subject to well-known qualifications. The ""known qualitative composition"" may be replaced by a composition which is known not to interfere at selected wave lengths, or which produces a reproducible interference which may be handled by techniques employing ""blanks"" or ""base-line-density"" methods. Mixtures of truly unknown composition may introduce substantial inaccuracies into base-line-density methods. One possible solution is to select analytical wave lengths where the interference is least, with the objective of obtaining checks at several such wave lengths. A second approach, of a statistical nature, involves measurement of the component with a maximum number of base-line-density correlations, discarding results on a statistical basis, and averaging the remaining data. A valuable limiting value for a given component in a given mixture is obtained by referring the true absorbance of the mixture at selected wave lengths to the absorbance-concentration curve for that component. The lowest value so obtained is a limiting maximum value for the component.