Infra‐red analysis by the derivative method

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Abstract
Derivative infra‐red spectra have been obtained by means of an analogue computer and utilized in qualitative and quantitative analysis. The second derivative with respect to time of the light intensity, obtained when the spectrometer is scanning at a fixed rate, may be used to detect and fix the position of minor changes of absorption, while the second derivative of the logarithm of the light intensity approximates very closely to the second derivative of optical density and is a quantitative function of the absorbing material.The value of the derivative function is zero or very small over considerable intervals of the wavelength scale and analyses for a particular component in complex mixtures may frequently be made by a single measurement of the magnitude of the quantitative derivative function at an appropriate wavelength without interference from other components. m‐Cresol and o‐cresol have been directly estimated in commercial m‐cresol, and m‐ and o‐cresol and phenol have been assayed in crude tar phenols without prior fractionation and by a single independent measurement for each.The success of analyses using wide slits is attributed to the triangular form of the spectrometer slit function.
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