SPECTROSCOPY
Fascinating Light
Fireworks
 Various colors
 Due to atomic spectra of various
elements
 Na (yellow), Sr (red), Ba (blue)
 Light transmitted through space
http://www.fireworkslondon.co.uk/images/template
_5_06.jpg
Aurora borealis or “Northern Lights”
 Light transmitted through space
http://www.geofffox.com/MT/images/Northern-Lights-large.jpg
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Spectroscopy
 The science that deals with the interactions of
electromagnetic radiation (EMR) or light with matter
Electromagnetic radiation (EMR) - or simply light, is energy
traveling through space.
3
Light = Electromagnetic Radiation
Electric field
http://static.flickr.com/35/121582712_
5c0f8d193a_m.jpg
Magnetic field
http://www.cs.cornell.edu/People/egs/
magnetos/friends.html
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In vacuum, EM waves travel at a constant speed of 3.00 x 108 m/s
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High energy
High frequency
Short wavelength
Image available at herschel.jpl.nasa.gov
Low energy
Low frequency
Long wavelength
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Visible light, the light that we see with our
eyes, is only a small portion of the EM
spectrum
- Associated with rainbow colors
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A Continuous Spectrum
A prism can break white light up into the visible light spectrum,
resulting into a continuous spectrum. Here the spectrum
shows a smooth transition between colors (or wavelengths).
Continuous
spectrum
Image available at
http://solarsystem.nasa.gov/deepimpact/science/spectroscopy.cfm
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A Line Spectrum
When a gaseous element is heated to its excited state, it emits
light (wavelengths) in discrete patterns called a line spectrum
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Image available at http://ausgo.aao.gov.au/IYAcontest/news.html
Fascinating Light
Fireworks
 Light transmitted through space
 Basically show the emission spectra
of various elements in firework
mixture
Image available at http://www.fireworks-london.co.uk/images/template_5_06.jpg
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Examples of everyday life spectroscopy (matterlight interaction)
Matter
Suntan
Chlorophyll
Tuning circuits
Light (EMR)
UV light
visible light
radiowaves
Effect
Tans or burns skin
Synthesis of food
Produces sound
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Amount of Light Absorbed Related to
Concentration
 The higher the absorbance (A), the higher is the
amount or concentration of substances (ex. blue dye)
in solution
 We can use a spectrometer, measure absorbance and
calculate the amount of blue dye in solution
A SPECTROMETER
NOTE: This process only works for
colored solutions.
Spectrometer image available at: http://www.cofc.edu/~kinard/
Amount of Light Absorbed Related to
Concentration
 The higher the absorbance (A), the higher is the
amount or concentration of substances (ex. blue dye)
in solution
 We can use a spectrometer, measure absorbance and
calculate the amount of blue dye in solution
 How exactly is absorbance related to
concentration?
Use of Standards in Measurements
How long is the object in this picture?
What do we need to
measure its length?
Use of Standards in Measurements
The ruler is a standard used
for measuring length.
Blue dye standard solutions
are used for measuring the
amount of blue dye in
commercial drinks.
How much blue dye is in Gatorade?
 Use a spectrometer
 Measure absorbance of light, A
 Compare with A of known amounts or concentrations of
blue dye (called blue dye standards)
 Each blue dye standard has a fixed amount of blue dye
 Much like each scale in a ruler --- has a fixed
measurement)
 Create a graph of A versus known amount of
blue dye standards = Standard Curve
 Using A of sample (ex. Gatorade) with unknown amount of
blue dye, extrapolate to determine amount of blue dye in
sample
Absorbance and concentrations
of blue dye standards
Standard No.
ppm (mg/L)
concentration of
standard solution
Absorbance
at 630 nm
1
2
3
4
2.00
4.00
6.00
8.00
0.248
0.478
0.702
0.898
Standard Curve for Blue Dye
1.000
Absorbance at 630 nm
0.900
0.800
0.700
0.600
0.500
0.400
y = 0.115x
R² = 0.9946
0.300
0.200
0.100
0.000
0.00
2.00
4.00
6.00
8.00
10.00
ppm concentration (mg/L) of blue dye standards
ppm (mg/L)
Absorbance at
Standard No. concentration of
630 nm
standard solution
2.00
4.00
6.00
8.00
?
0.248
0.478
0.702
0.898
0.402
1.000
Standard Curve for Blue Dye
0.900
Absorbance at 630 nm
1
2
3
4
Sample 1
0.800
y = 0.115x
R² = 0.9946
0.700
0.600
A Sample
0.500
0.400
0.300
ppm blue dye in sample
0.200
0.100
0.000
0.00
2.00
x
4.00
6.00
8.00
10.00
ppm concentration (mg/L) of blue dye standards
Percent (%) vs. Parts-per-million (ppm)
Percent = parts per hundred (pph)
Parts-per-million = one part in a million parts (ppm)
or simply
Example
ppm = % x 10,000
%
ppm
Normal CO2 level
0.036
360
Permissible CO level
0.0009
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Toxic gas; lethal level in ppm scale
21
ppm (mg/L)
Absorbance at
Standard No. concentration of
630 nm
standard solution
2.00
4.00
6.00
8.00
?
0.248
0.478
0.702
0.898
0.402
1.000
Standard Curve for Blue Dye
0.900
Absorbance at 630 nm
1
2
3
4
Sample 1
0.800
y = 0.115x
R² = 0.9946
0.700
0.600
A Sample
0.500
0.400
0.300
ppm blue dye in sample
0.200
0.100
0.000
0.00
2.00
x
4.00
6.00
8.00
10.00
ppm concentration (mg/L) of blue dye standards