The Analysis of Overlapping Spectral Absorption Bands by Derivative Spectrophotometry

Abstract

In the measurement of absorption spectra, it is difficult to detect low intensity bands overlapped by bands of higher intensity. Their detection is greatly facilitated by measuring the first derivative of the transmission curve with respect to wavelength. A machine is under development in this laboratory to plot this derivative. A graphical study is here made of the behavior of the derivative curves for overlapping absorption bands of differing heights, widths and separation intervals and the derivatives are compared with the corresponding extinction and percent transmission curves. The curves here presented are intended as illustrations of the possibilities inherent in derivative spectrophotometry and for the identification of extinction or transmission curve types from measured derivatives.