Electromagnetic Spectrum and Beer-Lambert Law

Visible Light and Electromagnetic Spectrum

• Visible light represents a small segment of the electromagnetic spectrum, encompassing colors such as red, yellow, green, blue, and violet.
• The visible spectrum consists of electromagnetic radiation wavelengths ranging from 400 nm to nearly 800 nm.

Beer-Lambert Law

• The Beer-Lambert law establishes a linear relationship between absorbance and the concentration of an absorber of electromagnetic radiation.
• The law is expressed as: A = aλ · b · c, where:
  • A = measured absorbance
  • aλ = wavelength-dependent absorptivity coefficient
  • b = path length of the light through the sample
  • c = analyte concentration.

Spectrophotometer Functionality

• Light of a specific wavelength is generated using a prism or diffraction grating within a monochromator.
• Wavelength selection is performed electronically, optimizing the measurement process.
• A reaction mixture is analyzed in a colorless cuvette with known volume and thickness for accurate readings.

Light Measurement Process

• Light first passes through a monochromator, then through the reaction mixture in the cuvette.
• Transmitted light is detected by a photocell or photomultiplier tube, converting optical signals into electrical energy.
• The electrical signal is measured and displayed using a galvanometer.

UV-VIS Spectrophotometry

• Advanced spectrophotometer models can operate at ultraviolet wavelengths, thus broadening testing capabilities.
• Deuterium lamps serve as the UV source in UV-VIS absorption spectrophotometers, enhancing the analysis of various substances.

Absorption Analysis

• Light absorption is directly correlated to the concentration of colored compounds in a solution.
• The wavelength of maximum absorption is specific to different compounds, allowing for specific concentration determinations.
• The method can assess concentrations of substances that exhibit color directly or after chemical reactions.

Components of a Spectrophotometer

• The spectrophotometer comprises two main parts:
  • Spectrometer: Generates light of selected wavelengths.
  • Photometer: Measures the intensity of light transmitted through the sample.
• A cuvette containing the sample is positioned between the spectrometer and photometer to evaluate light absorption.

Key Components Described

• Light Source:
  • Tungsten lamp is used for the visible region, emit varying intensity based on wavelength.
• Monochromator:
  • Filters to isolate the desired wavelength from the light source.
• Cuvette:
  • Transparent container for holding samples and blanks.
• Radiation Detector (Phototube):
  • Converts absorbed radiant energy into a measurable electrical signal.
• Readout Device:
  • Displays output from the photodetector.

Important Material Note

• Pyrex glass is transparent in the visible region but absorbs virtually all UV light, necessitating the use of quartz or silica cuvettes in UV-range applications.

Explore the fundamentals of the visible light spectrum, which is a small fraction of the entire electromagnetic spectrum. This quiz also delves into the Beer-Lambert law, which illustrates the relationship between absorbance and concentration in electromagnetic radiation. Test your understanding of these key concepts in optics.