Modeling the Effect of Polychromatic Light in Quantitative Absorbance Spectroscopy

Abstract

This laboratory experiment is the first in a semester-long instrumental analysis course. Students measure the emission profiles of various light sources including light-emitting diodes (LEDs), the transmission of interference and absorption filters, and the absorptivity of colored complexes of Fe2+. They use this information to model the effect of polychromatic radiation on the shape of the calibration curve and to assess possible optical configurations for a field spectrophotometer used to determine the concentration of soluble iron in environmental systems. This experiment serves as a hands-on examination of many of the fundamental concepts in electronic absorbance spectroscopy. The typical components of a spectrophotometer and their functions are clearly illustrated (e.g., continuum vs line sources, filters vs monochromators). Topics in quantitative absorbance spectroscopy including Beer's law, deviations from linear behavior, and figures of merit are also covered. The students gain experience with the use of spreadsheets for data analysis and macro programming in Excel. The data collected in this lab are applied to current topics in analytical research including environmental analysis and the miniaturization of analytical instruments.