Transcript Eugene`s NSERC Poster

INVESTIGATING LIGHT-MATTER
INTERACTIONS USING A
MANUAL SPECTROMETER A NEW CHM151 LAB
Developed by E. Kwan, H. Ohorodnyk, I. Miller, A. Orozco, and A. Dhirani
with assistance from F. Bures and J. Jackiewicz (electronics)
as well as J. Ford and F. Shaw (machining).
Department of Chemistry, University of Toronto.
Introduction
Beer’s Law
 Intensity of a beam of light decreases exponentially with the
number of absorbing particles in the beam:
I/I0 = 10-A
where I is the final intensity, I0 is the initial intensity, and A is the
absorbance.
 A =  c b, where  is the extinction coefficient, c is the
concentration of the solution, and b is the path length.
Goals of Project
 Students explore the validity, limitations, and applications of Beer’s
Law
 Students are introduced to spectroscopy in a hands-on way
The Spectrometer
Light Detector and I-V
Converter
Double
Convex
Lens
Sample
Holder
Diffraction
Grating
Diffraction
pattern
Photodiode
Multimeter
Rails
Lamp
 Light intensity measured by photodiode and multimeter
 Detector position on rail determines wavelength detected
Samples
(1) Various
filters
(2) Copper (II)
Sulfate
(3) Chlorophyll
Geraniums
Filter ground up leaves
soaked in methanol
Extracted
chlorophyll
Blue Filters: Background Removal
3.5
 Red light intensity measured against number of filters
 Data fit to y = y0 + y1 e-x/t, an exponential decay
 y0 is the background (stray light)
3.0
2.5
Signal (V)
2.0
1.5
1.0
0.5
0.0
Chi^2 = 2.49934
R^2
= 0.99753
-x/1.3 1
y = 0.28 + 2.75*e
0
1
2
3
4
5
6
Numb er of Blue Filters
7
8
9
10
Blue Filters: Absorbance Plot
 Absorbance calculated as –log[(I-y0)/(I0-y0)]
 Absorbance increases linearly with numbers of filters
 Slope is 0.31 (represents absorbance per blue filter)
 Signal:noise ratio gets much worse
3.5
3.0
Absorbance
2.5
2.0
1.5
1.0
y = 0.31x + 0.02
2
R =0.99611
Std. Dev.=0.17359
0.5
0.0
0
1
2
3
Nu mb er of Filters
4
5
6
Green Filters: Absorbance Plot
2.0
 Absorbance increases linearly but with a different
slope, 0.15.
 Data measured at same red wavelength
1.5
Absorbance
1.0
0.5
0.0
y = 0.15x + 0.01
2
R =0. 99934
Std . De v.=0. 05805
-0.5
0
1
2
3
4
5
Number of Green Filters
6
7
8
Blue and Green Filters: Absorbance
3.0
 Slope is now 0.45, statistically the same as the sum of
0.31 + 0.15 => slopes add when filters combined
 So absorbance is additive
2.5
Absorbance
2.0
1.5
1.0
0.5
y = 0.45x + 0.02
2
R =0.99615
Std. Dev.=0.20074
0.0
-0.5
0
1
2
Number of Filter Pairs
3
4
Copper Sulfate Absorbance
1.75
1.50
1.25
 Absorbance increases linearly with
concentration
 Graph can now be used to determine
concentration of a solution by measuring
its absorbance
Absorbance
1.00
0.75
0.50
0.25
y = 10.6x + 0.01
2
R =0.99713
Std. Dev.=015755
0.00
-0.25
0.00
0.02
0.04
0.06
Concent ra tion (M)
0.08
0.10
0.12
Spectroscopy of Chlorophyll
Transmitted
Light
Green Diffraction
Maximum
Chlorophyll appears red!
Light Shield
Green Reflection
Chlorophyll viewed from the side
Chlorophyll
viewed in
normal light
 Green light transmitted
 Red light absorbed and re-emitted (sideways also)
 Some blue light converted to red light -> fluorescence (covered slit
with blue filter and observed red light out)
Special thanks to P.E. Trudeau and Y. Suganuma