Quantitative Analysis by Derivative Electronic Spectroscopy

Abstract

Absorption and emission spectroscopy in the ultraviolet and visible regions, apart from being the earliest physical techniques of analysis, have great utility in solving a variety of structural and analytical problems l-41. However, in many cases the quantitative determination of individual components in a mixture by UV-VIS spectroscopy becomes very difficult owing to the spectral similarities and overlapping of weak absorption bands of one component by strong absorption bands of other components. It was recently recognized that derivative spectrophotometry, introduced about three decades ago 5-81 and originally proposed by Rutherford 9], can be a very useful analytical tool for characterizing an analyte band that is overlapped by other absorption bands with different halfwidths. On differentiation, the intensity of the absorption band with a small halfwidth increases more than that of a band with a large halfwidth 10]. The central idea behind the development of the science of derivatized spectra rests upon the measurement of the first or the higher derivatives of the absorbance A or the luminescence intensity I with respect to the wavelength λ, e.g., dI/dλ, dA/dλ, d²I/dλ², etc. These derivatives, when plotted or scanned against wavelength, yield an array of derivative spectra.