This document summarizes the major components of instrumentation used in absorption and emission spectroscopy experiments. It discusses common light sources, wavelength selectors like monochromators and filters, sample containers, detectors such as phototubes and photodiode arrays, and examples of single beam and double beam spectrophotometers. Key components are the light source, wavelength selector to produce monochromatic radiation, sample holder, and detector to measure the detectable output over the wavelength region of interest.

1. Chapter 20: Instrumentation
Major Components
Depends on Type of Experiment
Absorption
Fluorescence
Emission
Source
Wavelength Selector
Sample
Detector
Signal Processor
Most Common
Placement depends on experiment

2. http://www.youtube.com/watch?v=O39avevqndU

4. Instrument Components
Light Source
Detectable Output over wavelength region of interest
Continuum Source
Line Source
From Skoog etal
From Skoog, West, Holler

6. Common:
Visible: Tungsten filament Lamp (320-2500 nm)
UV- Deuterium Lamp (160-320 nm)
IR: Heated Inert Solid (Globar, Nernst Glower)
AA: Hollow cathode lamp (line source)

7. Instrument Components
2. Wavelength Selector
Restrict radiation to a narrow band
Two Types
Filter – removes “wide” bands
Monochromator

8. Monochromator
A. Prism
B. Grating
•Lenses/mirrors to focus the radiation
•Entrance and exit silts to restrict unwanted radiation
•Dispersing Element to produce the “monochromatic”
radiation

9. Grating monochromator

10. Instrument Components
Bandwidth – wavelength range passed by selector
High Quality: ~ 0.1 nm (monochromator)
Filter  50 nm
From Skoog, West, Holler

11. Sample Container
Holds the sample
Must be transparent in the region of interest
UV: Quartz
Vis: Glass
IR: Salt Crystals

12. 1. In the equation, A = εbc, what quantity is represented by "ε" ?
a) Absorptivity
b) Molar absorptivity
c) Path length
d) Concentration
2. Can one measure a smaller amount of a compound if it has
a high or low absorptivity
a) higher
b) lower

13. Instrument Components
Radiation Detectors
Stable
Sensitive in region of interest
Rapid
Examples:
Phototube
Photomultiplier tube (most sensitive)
Photodiode array (multichannel)
CCD
Heat detectors (IR)

14. Phototube
From Skoog, West, Holler

15. PMT
Why is it better then a phototube
for measuring low light levels?

17. Types of Instruments
Single Beam (Spectronic 20)
Double Beam (separated in time or space)
Multichannel
Single Beam Spectrophotometer
Simple, Inexpensive
Wavelength range: 340 – 625 nm
Bandwidth: 20 nm
Wavelength accuracy: 2.5 nm

18. Spec 20
From Skoog, West, Holler

19. Double Beam Spectrophotometer
More complex
Compensates for drifts in detector/source
Wavelength range: 195-850 nm
Bandwidth: 4 nm
Photometric accuracy: 0.5%T

22. Photodiode Array
200-1000 nm
Resolution 1-2 nm
Time: 0.1 s
No scanning
From Skoog, West, Holler
Advantages/Disadvantages?

23. An 8.64 ppm solution of [FeSCN]Cl (149 g/mol) has a T of 0.295
at 580 nm when measured in a 1.00-cm cell. Calculate
the molar absorptivity coefficient for the complex
at this wavelength.

24. Cytochrome c has a molar absorptivity of 106,000 M-1
cm-1
.
A solution is prepared by diluting a 10.0 uM solution by a
hundred. What would be the absorbance of the
diluted solution if measured in a 1.00 cm cell.