Simulation of a variable-wavelength uv-visible spectrophotometer
with a 200 - 700 nm wavelength range, switchable tungsten and
deuterium light sources, four interchangable quartz cuvettes,
percent transmission and absorbance readout, auto-zero button, and
realistic sources of error and non-linearity. Students specify
sample characteristics, select wavelength, cell path length,
select deuterium or tungsten lamp, and perform measurements.
Realistic modeling of lamp spectral characteristics, cell
transmission variations, photon and detector noise, unabsorbed
stray light, and instrument non-linearity caused by finite
spectral bandpass.
Version 1.2 (June, 2000) has a fixed 5 nm spectral bandpass and
models a single absorber in solution. Allows the student to
specify the solute weight, solution volume, and the absorptivity,
peak wavelength, and peak width of the absorber in each of the
four cells. Useful for reinforcing the Beer-Lambert Law and its
limits and for introducing the effects of noise and non-linearity
due to optical deviations from the Beer-Lambert Law.
Version 1.3 is similar to version 1.2, with the addition of a
"Statistics" button that takes 30 absorbance readings
automatically (without removing and replacing the cell) and
calculates the mean (average), standard deviation, and percent
relative standard deviation of the absorbance.
Operating Instructions:
Specify the spectral characteristics and concentrations of the
absorbers in the four cell by typing values into the table (cells
C9 .. F13). Use the slider above to change the wavelength of the
instrument. Click on the buttons on the left to change the cell
path length and lamp type. Click on one of the four cell buttons
(#1 ... #4) to change the cell contents; this simulates removing
the cell, replacing its contents, and replacing it in the light
beam. Click the Auto-zero button to zero the instrument on the
current cell contents. Click the Read button to take another
reading of absorbance without disturbing the cells.
Download links: Version 1.2 (June, 2000): UVVis12.wkz;
Version 1.3 (June, 2000): UVVIS13.WKZ;
Wingz player application and basic set of simulation modules, for
windows PCs or Macintosh
Outputs:
AA20: total meas I-zero = sum($AA9..$AA19)
AB20: total meas I = sum($AB9..$AB19)
AB21: absorbance = log($AA$20/$AB$20)
I4: Absorbance (zero corrected) = $AB$21-$G$24
J4: %T = $AB$20/$AA$20
Statistics table (version 1.3):
Average absorbance =avg(AC23..AC53)
Standard deviation =stdev(AC23..AC53)
Relative standard deviation =J17/J16
Button scripts:
"Rinse and refill" buttons:
#1
put 0.02+0.01*rand() into background
put "Solution #1" into b14
put C33 into O6
put C12 into O7
put C13 into O8
recalc
#2
put 0.02+0.01*rand() into background
put "Solution #2" into b14
put D33 into O6
put D12 into O7
put D13 into O8
recalc
and so on for cells 3 and 4.
"Cuvette, cm" buttons:
"0.1"
put 0.1 into path
put 0.02+0.01*rand() into background
put "0.1 cm cell" into b15
recalc
and so forth for the 1.0 and 10 cm buttons.
"none"
put 0 into path
put 0 into background
put "No cell in lightpath" into b15
recalc
Lamp buttons
Tungsten:
put 600 into LampMax
put 2 into LampInt
put 120 into LampWidth
put "Tungsten lamp" into b16
recalc
Deuterium:
put 200 into LampMax
put .5 into LampInt
put 120 into LampWidth
put "Deuterium lamp" into b16
recalc
Autozero:
recalc
put $AB$21 into g24
Read:
recalc
Statistics: (version 1.3)
define reading
for reading=0 to 30
recalc
put I4 into "AC"&reading+23
end for (c) 1991, 2015. This page is part of Interactive
Computer Models for Analytical Chemistry Instruction, created
and maintained by Prof.
Tom O'Haver , Professor Emeritus, The University of Maryland
at College Park. Comments, suggestions and questions should be
directed to Prof. O'Haver at toh@umd.edu.
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