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[Operating instructions] [Cell definitions and equations] [Student assignment handout]
This is a simulation of the spectroscopy of a linesource atomic absorption (AA) measurement. It is not a simulation of an AA instrument. What's the difference? An instrument simulation shows you how to work an AA instrument. This simulation shows you how AA spectroscopy works, that is, what goes on under the instrument's surface. The purpose of the simulation is to make it clearer how the various spectroscopic aspects relate to each other and to the measured absorbance, in a linesource atomic absorption measurement with continuumsource background correction in a steadystate (i.e. flame) atomizer. You can observe the spectral relationship of the hollow cathode lamp emission profile to the atomic absorption profile, observe the effect of different spectral line widths of both the absorbing atom and the hollow cathode lamp, correction of background absorption by continuumsource (D_{2}) method, overcorrection caused by structured background absorption, and the effect of nonabsorbing lines, lineoverlap interferences, and hyperfine structure.
Download links:
AtomicAbsorption.xlsx for
Excel
AtomicAbsorption2.ods for
OpenOffice Calc
AtomicAbsorption.wkz; for WingZ
(Wingz player application and basic set of simulation modules, for
windows PCs or Macintosh)
Other related simulations:
Instrumental Deviations from Beer's Law
Effect of Slit Width on
SignaltoNoise Ratio in Absorption Spectroscopy
Comparison of Calibration Curve
Fitting Methods in Absorption Spectroscopy
INPUTS:
shift = collisional shift of absorption line, pm.
abs. width = spectral width of atomic absorption line, pm.
source width = spectral width of hollowcathode lamp emission line, pm.
atom density = relative concentration of atoms in atomizer, arbitrary units.
stray light = relative intensity of continuum background radiation from hollowcathode lamp.
background abs. = nonspecific background absorption in atomizer.
nonabs. line = intensity of a nonabsorbing line from HCL. arbitrarily placed at 60 pm, relative to main resonance line.
interference = peak absorbance of matrix absorption line, arbitrarily placed at +60 pm.
hyperfine = relative intensity of hyperfine line, relative to main resonance line.
Array calculations:
A39..A139: wavelength = 100 to +100 (displacement in pm from resonance wavelength)
Total number of wavelength intervals = NumWavelengths
B39..B139: absorbance = PeakAbs/(1+((wavelengthshift)/AbsWidth)^2)+
Interf/(1+((wavelength80)/AbsWidth)^2)+
Hyper*PeakAbs/(1+((wavelength6)/AbsWidth)^2)
C39..C139: transmission = 10^(absorbanceBackAbs)
D39..D139: SourceIntensity = exp(((wavelength)/SourceWidth)^2)+StrayLight/100+
NonAbs*exp(((wavelength+60)/SourceWidth)^2)+
Hyper*exp(((wavelength6)/SourceWidth)^2)
E39..E139: TransmittedIntensity = transmission*SourceIntensity
Graph shows spectral profile in region ±100 pm around resonance line.
Gray line: SourceIntensity
Blue line: transmission
Red line: TransmittedIntensity
OUTPUTS:
Peak abs. = "true" peak absorbance at center of absorption line.
Width ratio = ratio of absorption width to source width.
Cont. A = absorbance measured with continuum source.
Uncorr. A = absorbance measured with line source.
Corrected A = atomic absorbance corrected for background absorbance (equals Uncorr. A  Cont. A).
measured I = total intensity transmitted through atomizer, measured at the detector over the entire spectral bandpass.
measured Izero = total incident intensity measured at detector over entire spectral bandpass.
delta I = difference between measured Izero and measired I.
SNR = signaltonoise ratio for photonlimited measurement.
Display calculations:
measured I = MeasI = sum(TransmittedIntensity)
measured Izero = MeasIzero = sum(SourceIntensity)
delta I = MeasIzeroMeasI
SNR = 1000*CorrectedA*sqrt(MeasI)
Peak abs. = Conc/(AbsWidth)
Width ratio = SourceWidth/AbsWidth
Cont. A = Ac =log((NumWavelengths))/(sum(transmission)))
Line A = Al = log(MeasIzero/MeasI)
CorrectedA = AlAc
BUTTONS:
Run calib. curve:
Varies concentration from 0 to 10 units in steps of 1 and records corrected absorbance.
Script:
manual recalc
column letters
define standard
for standard=0 to 10
put standard into C3
put C3 into "J"&standard+2
recalc
put H3 into "K"&standard+2
end for
put 1 into C3
automatic recalc
Plot and fit:
Plots analytical calibration curve on separate sheet, fits straight line to low absorbance
(linear) region.
Script:
{ INSTRUCTIONS: Put data to be fit into two adjacent columns, the xaxis data }
{ (i.e. independent variable) in the first column and the yaxis data (i.e. }
{ (the dependent variable) in the second column. The first row of each column }
{ should contain column labels. Select the data range and run this script. }
{ The script creates a new sheet containing a copy of the data values, the best }
{ fit data, an ANOVA table, and an XY plot of the data and best fit lines. }
{ Print page 2 of this new sheet to get report contain ANOVA table and plot. }
repaint off
column numbers
Define datarange,numrows
select range R1C10..R20C11
Copy
select range R1C1
New Worksheet ""
window size (12780, 7540)
paste values
Select last cell
numrows=row()
select range "R1C1..R"&numrows&"C1"
Copy
select range R1C3
Paste
datarange="$R1$C2..$R4$C3"
Select range datarange
select more range R1C5
select more range R1C6
column letters
Regress
column numbers
select range R1C4
Put "Fit at low conc." Into R1C4
select range R2C4
Put "=R2C3*$R2$C5+$R1$C5" Into R2C4
select range "R2C4..R"&numrows&"C4"
Copy Down
select range "R1C1..R"&numrows&"C4"
Unselect Add Chart Range frac(R25C6..R51C11,0,62,149,252) Using "R1C1..R"&numrows&"C4"
select object 1
XY
Legend Bottom
select chart 1 series 1
symbol color 0
symbol width 20
symbol type 3
symbol size 7 points
line fg 0
line bg 16777215
line pattern 0
line width 40
select chart 1 series 2
line fg 0
line bg 16777215
line pattern 1
line width 20
select range R1C2
select more chart 1 axis 3
axis title range
select range R1C1
select more chart 1 axis 1
axis title range
column letters
Select All
precision 4
text size 9
show cells
select range G52..K52
text size 9
precision 4
unselect
zoom window
select range F23..K52
Report Print Range
Hide Headings
Hide Tool Box
Hide Entry Bar
Hide Cell Grid
window size (9520, 8640)
Put "Intercept =" Into R52C7
Put "=$R1$C5" Into R52C8
Put "Slope =" Into R52C10
Put "=$R2$C5" Into R52C11
select range K52
repaint on
Operating Instructions
shift  Collisional ("red") shift of the absorption line, pm. 
abs. width  Spectral width of the the analyte's atomic absorption line, pm. 
source width  Spectral width of the hollowcathode lamp emission line, pm. 
atom density  Relative atom density of analyte atoms, arbitrary units. 
stray light  Relative intensity of continuum background radiation from
the hollowcathode lamp. 
background abs. 
Absorbance of the nonspecific background absorption in the atomizer 
nonabs. line  Intensity of a nonabsorbing line from the HCL,
arbitrarily placed at 60 pm, relative to the main resonance line. 
interference  Peak absorbance of a matrix absorption line, arbitrarily
placed at +60 pm, relative to the main resonance line. 
hyperfine  Relative intensity of the hyperfine line, relative to
intensity of the "main" line. 
Peak abs.  The "true" peak absorbance at the center of the absorption line. 
Width ratio  Ratio of the absorption width to the source width. 
Cont. A  Absorbance measured with the continuum source. 
Line A  Absorbance measured with the line source. 
Corrected A  Atomic absorbance corrected for background absorbance. (This is simply equal to Line A  Cont. A). 
measured I  Total intensity transmitted through the atomizer measured
over the entire spectral bandpass. 
measured Izero  Total incident intensity measured over the entire spectral bandpass. 
delta I  Difference between measured Izero and measured I. 
SNR  Theoretical signaltonoise ratio for photonnoiselimited measurement. 
Run calib. curve  Varies the atom density from 0 to 10 units in steps of 1
and records the corrected
absorbance.

Plot and fit  Plots the resulting analytical calibration curve on a separate sheet, fits a straight line to the low absorbance (linear) region, and displays the slope and intercept of the line. 