AA Light Sources
2
Hollow Cathode Lamp Design
BaseGraded Seal
QuartzEnd Window
Pyrex Envelope
Anode
Cathode
Getter
Alignment Pin
Electrical Contacts
Lamp Element Code Contacts
Lamp CodeCircuit
GlassShield
3
HCL Operation
Hollow Cathode
Anode
Atom Atom
e-
Electrical DischargeNe+ + e-
Sputtering
EmissionExcitationRelaxation
PhotonSpecific toExcited Atom
En
Eo
En
Eo
4
Self-Reversal
Cloud of Ground State Atoms
Normal OutputOutputafter Reversal
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Choosing an Analytical Wavelength
Sample ConcentrationPrecisionDillution FactorsWavelength
• Calibration CurvatureRelative Sensitivity
• Concentration & DilutionRelative Intensity
• Signal to noise
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Lamp Data
Element Maximum Current
mA
Recommended Current
mA
Wavelength Slit nm Relative Sensitivity
Relative Intensity
Ni 10 4 232.0 0.2 1 5352.5 0.2 5 100351.5 0.2 10 30362.5 0.2 500 10
Cu 10 4 324.8 0.5 1 100327.4 0.5 2 50217.9 0.2 8 3218.2 0.2 10 2222.6 0.2 40 5244.2 1 270 15
7
Multi Element Lamps
Available for:
Ag-Cd-Pb-ZnAg-Cr-Cu-Fe-NiCa-MgCa-Mg-AlCo-Mo-Pb-ZnCu-Fe-Mn-ZnCu-Fe-Si-ZnCu-ZnFe-Co-Ni-Mn-Cu-CrNa,K
8
Using Multi Element Lamps
Use all normal recommended wavelengths
Refer to Data Sheet for recommended slit width
Refer to Data Sheet for recommended lamp currentThe SAME current is used for ALL elements in the lamp – may need to change in the method
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Multi Element Lamps
AdvantagesMore elements can be run without changing lampsLower initial cost
DisadvantagesMore complex emission profileSome secondary lines cannot be usedSome changes in sensitivity observedOperating current may be higherLine intensities may be lower
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How Can We Make LampsMore Intense?
We could increase the lamp current - but this results in the following undesirable changes
• The atom cloud extends beyond excitation region and cools down
• Atoms in the atom cloud may absorb light from the lamp (self-reversal)
• This causes broadening of the emission line and increased calibration curvature
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The High Intensity UltrAA Lamp
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The Varian UltrAA Lamp
QuartzWindow
Glass Shield
CathodeBoost Filament
Discharge Guide
AnodeBoost Anode
Glass EnvelopeShields
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UltrAA Lamp Operation
2 anodes are fitted inside the UltrAA lamp:• one for the normal HCL discharge• the second for a separate boost discharge which is directed
across the cathodeElectrons emitted by a heated filament are passed through the atom plume to re-excite the atoms by collisionThis increases the emission intensity of the lamp
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UltrAA Lamps - Elements Available
Single Element UltrAA LampsSb Cu Mn SiAs Ge Ni TeBi Au Pd TlB Fe Pt SnCo Pb Se
Multi Element UltrAA LampsAg-Cr-Cu-Fe-Ni Cu-Fe-Mn-ZnAg-Cd-Pb-Zn Cu-Fe-Si-ZnAs-Cu-Fe Cu-ZnCa-Mg-Al Fe-Co-Ni-Mn-Cu-CrCo-Mo-Pb-Zn Ni-Se
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UltrAA Lamps
Varian's boosted discharge lamps provide: • Improvements in intensity• Extended lifetime• Improved sensitivity• Improved calibration linearity
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Lead Lamp Comparison
0
0.5
1
1.5
2
2.5
0 10 20 30 40 50 60 70 80 90 100Concentration
Abso
rban
ce
UltrAA Lamp
Normal HCl Lamp
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Advantages of UltrAA Lamps
Reduced baselinenoise
Peak to peak baseline noise forSe is 0.013 Abs.for the conventionalHCL compared with0.008 Abs. for theUltrAA Lamp
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UltrAA Lamp Increased Sensitivity
Increased sensitivity• Typical signals for 75
µg/L Se are illustratedUltrAA Lamp
Conventional HCL
Abs
orba
nce
Tem
pera
ture
Bac
kgro
und
25000.50
0.50
Time (sec)
0.00 0
72.00 74.60
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Advantages of UltrAA Lamps
Enhanced calibration linearity• Typical calibrations for
Se using standards of 25, 50 and 75 ug/L Se are illustrated
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Advantages of UltrAA Lamps
Improved Characteristic Concentrationsand Detection Limits
Element Wavelength UltrAA Conventionalnm Lamp HCL
Characteristic Concentration (in µg/L with 20µL sample)As 193.7 0.25 - 0.3 0.31Pb 283.3 0.15 - 0.26 0.26Se 196.0 0.49 - 0.5 0.85 - 2.2
Detection Limits (3 sigma in µg/L with 20µL sample)As 193.7 0.35 - 0.7 0.3 - 1.4Pb 283.3 0.18 - 0.23 0.8Se 196.0 0.28 - 0.57 1.1 - 3.1
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Gold Lamp Comparison
0.0
0.5
1.0
1.5
2.0
2.5
0 20 40 60 80 100
Concentration
Abs
orba
nce
Boosted Lamp
Normal Lamp
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Comparison of Gold UltrAA and Normal Lamps at Detection Limit Levels
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
0.00 0.01 0.10 1.00 10.00
Concentration mg/L
Prec
isio
n %
242.8nm UltrAA Lamp 267.6nm UltrAA
242.8nm HCl 267.6nm HCl
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Lifetime of UltrAA Lamps
350
400
450
500
550
0 2000 4000 6000 8000
Operating Time Hours in mA-Hours
Phot
omul
tiplie
r Vol
ts
Lead
Selenium
Arsenic
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Key Benefits of the UltrAA Lamp
Improved analytical performance• Lower baseline noise levels• Increased sensitivity• Lower detection limits• Enhanced calibration linearity
Greater reliabilityLonger lamp lifetimes