Practical demonstration of the importance of wavelength in Ultraviolet Visible spectroscopy

Abstract

In the present work, the design of a series of experiments was carried out with the objective of providing teachers of analytical chemistry courses with tools that allow them to demonstrate in a practical way the importance of the analysis wavelength in the measurements of absorbance in the, discipline of visible ultraviolet spectroscopy. Initially, a series of experiments based on the absorption of radiation by methylene blue and bromothymol blue (with pH regulated at 3.7) at different concentrations are proposed. To do this, the red (665 nm) and violet (405 nm) colored beam was passed over the solution to be studied and the attenuation of the intensity (or power) of the radiation beam was observed qualitatively after leaving the solution cell, considering that the greater the attenuation or decrease in the intensity of the radiation, the greater the absorbance of the sample. Finally, an experiment is proposed in the laboratory based on the realization of calibration curves of methylene blue and bromothymol blue (regulated at pH 3.7) at different wavelengths (665 and 425 nm), to provide quantitative information to the student about the importance of the selection of the wavelength in applications of visible ultraviolet absorption spectroscopy.