Why is the light "chopped" into pulses in AAS?
Asked by
julia999 (
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March 18th, 2010
Hello,
I’m studying chemistry and I noticed that in a diagram of Atomic Absorption Spectrometer, it describes the light emitted by a hollow cathode lamp as being “pulsed”.
I was curious why it is pulsed. I cannot find a reason in the textbook or on the Internet, I was hoping someone could give me a clue.
Thanks!
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4 Answers
HCL’s require very high voltages to operate (a quick search found 500VDC as typical). Rather than convert household voltage (~120V) to 500V directly via a transformer (which would be relatively large), it’s much more efficient to produce short bursts of 500V by stepping up the 120V potential.
More on the step-up circuit here: http://en.wikipedia.org/wiki/Boost_converter
Thanks grumpy fish. I don’t think it would have to do with efficiency, though. I think the fact that the light is pulsed has something to do with the sample receiving small bursts of light rather than a constant stream. Perhaps something to do with the results the detector picks up…
These are my thoughts anyway.
Well—there is this: Smith-Hieftje correction (invented by Stanley B. Smith and Gary M. Hieftje) – The hollow cathode lamp is pulsed with high current, causing a larger atom population and self-absorption during the pulses. This self-absorption causes a broadening of the line and a reduction of the line intensity at the original wavelength.[9]
(From Wikipedia )
Okay that makes more sense. Thank you grumpyfish.
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