D
2
(deuterium lamp) method –– highly sensitive background correction
1. Detection sensitivity is superior to the SR method. Therefore, this method is suitable for the analysis of samples with a simple matrix requiring high
sensitivity, such as the measurement of trace levels of impurities in ultrapure water or environmental analyses.
2. As the lighting frequency is higher than with the SR method, it can eliminate noise due to emission components of the flame or graphite tube to permit
accurate atomic absorption measurements.
3. The original hollow cathode lamp can be used.
Features
Principle
The deuterium lamp method involves lighting the hollow cathode lamp and the
deuterium lamp alternately at high speed. After separation by the monochromator,
the light from the deuterium lamp has a bandwidth from 0.1 to 5 nm. Therefore, an
atomic absorption with a line width of only about 1/1000 nm is almost unobservable
compared to the background absorption due to wide-bandwidth molecular
absorption. However, as the light from the hollow cathode lamp has approximately
the same bandwidth as the atomic absorption band, the total of the atomic
absorption and the background absorption can be observed. With the deuterium
lamp (D
2
) method, light from both sources passes through the atomizer. The
difference in absorbance is determined to conduct background correction.
The SR method is suitable for samples containing elements that cause
problems with spectral interference, as shown in the table to the left.
Measured Element
Al
Analytical Line (nm) Coexisting Element Absorption Line (nm)
309.28 Mg 309.30
As
193.76 Fe 193.73
Ca
422.67 Fe 422.64
Cd
228.80 Ni 228.84
Cu
324.75 Fe 324.73
Ga
294.36 Ni
285.18
Mg
285.21 Fe
Fe
Fe
Fe
Fe
Fe
294.39
Ni
232.00 232.04
Pb
217.00 216.95
Sb
217.58 217.55
Se
196.03 196.05
Si
251.61 251.69
FeZn 213.856 213.8589
Examples of elements and wavelengths causing spectral
interference problems due to neighboring lines
Atomic absorption + background absorptionHollow cathode lamp spectrum
Atomic absorption
D
2
lamp spectrum Background absorption
Examples suitable for D
2
method (where no difference results between SR and D
2
methods)
Example: Measurement of trace levels of lead in 2% NaCl solution by molecular absorption (analysis of Pb in 2% NaCl solution)
BGC-SR method
BGC-D
2
method
It can be seen that the sensitivity is higher with the BGC-D
2
method.
Background signal
Atomic absorption signal
15
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