Module 3a: Photometry and Spectrophotometry
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majority of analytic techniques fall into one of four basic disciplines within the field of analytic chemistry which are
> spectrometry luminescence electroanalytic methods chromatography
five types of Spectrophotometry/Photometry/Colorimetry
a. Spectrophotometry b. Flame Emission Spectrophotometry c. Atomic Absorption Spectrophotometry d. Reflectance Spectrophotometry e. Mass Spectrophotometry
Light energy is a form of ________ radiation
Electromagnetic
light travels in packets of radiant energy called _____ or _____
photons or quanta
light energy is characterized by _______ and _______
frequency and wavelength
definition: FREQUENCY
number of vibrations of wave per second, has a direct relationship with energy
definition: WAVELENGTH
distance between two successive peaks in nanometers, has an inverse relationship with energy and frequency
light is used to describe radiant energy from the spectrum _____ to ____ nm
290 to 750 nm (ultraviolet to visible light)
differentiate: PHOTOMETRY and SPECTROPHOTOMETRY
both are measurements of the luminous intensity of light, but spectrophotometry measures only light at a selected wavelength
define: Planck’s theory
theory that energy is transmitted through units of quanta or photons where the more waves there are (higher frequency), the more light energy
basic components of a spectrophotometer according to the path of light
• Light source • Entrance slit • Monochromator • Exit slit • Cuvette with sample • Photodetectors • Meter or Readout devices
define: Beer’s Law
The concentration of a substance is directly proportional to the amount of light absorbed, or is inversely proportional to the log of the transmitted light.
Beer’s law formula
A = abc A (absorbance) a (proportionality constant defined as absorptivity) b (light path in cm) c (concentration in g/l)
light that has already passed through sample
transmitted light
light that hasn’t passed through a sample
incident light
percent transmittance is the ratio of ____
sample beam signal/ blank beam signal
% transmittance when all light is absorbed
0%
% transmittance when no light is absorbed
100%
used to measure the light transmitted by a solution to determine the concentration of the light-absorbing substance in the solution.
spectrophotometer
Most common light source in the visible portion of the spectrum, with most emitted in the infrared region.
Tungsten/Tungsten Iodide Lamp
Tungsten/Tungsten Iodide Lamp does not supply sufficient radiant energy or measurements below ____ nm
320 nm
Provide sources of continuous spectra in the UV region with some sharp emission lines.
Hydrogen and deuterium lamps
Deuterium lamps provide continuous emission down to ___ nm.
165 nm
Advantage of deuterium lamp over Hydrogen lamp
more stable and has longer life