Atomic Spectroscopy Flashcards
Explain the purpose of monochromator in A.A spectroscopy.
Monochromator removes unwanted phtonos from flame sources (scattering), and allows a narrow bandwidth for detection
Explain why Beer’s law is not applied to A.A spec?
The abosorption band must be narrow enough to get defined peak. Otherwise, there would be a large range of wavelength (e.g white light) in the bandwidth from the exit slit
As a result, it will detect polychromatic light with various molar extinction coefficient, which is against Beer’s law since the law only defines monochromatic light.
Describe the process of electrothermal atomization.
Sample in graphite tube=>solven evaporation=.sample ashing=>pluming=>that absorb incident radiation=>discrete atomization
how does interference occur in spectral nature?
absorption and scattering caused by the sample matrix. e.g. formation of oxides or carbonaceous particles=> which increase Abs.
How to correct of interference in spectral nature?
1) increase the temperature to burn up all of the background/blank solvent
2) use D2 lamp and HCL lamp together to correct for scattering, D2 lamp get scattered but not absorbed, while HCL lamp both get scattered and absorbed. So by using a modulated chopper, both different radiation alternatively passes through chopper to get teh electrochemical atomizer. So, it uses UV light to see how much scattering from HCL, so the scattering is corrected by remove background from D2 lamp.
how does interference occur in chemical nature?
anions and cations can form into low volatile compounds
Why does A.A spec need to be modulated?
since flame is coloured=> broadband spectrumm, it can interfere measurement. So modulation removes scattering from source radiation.
How to correct for scattering light in A.A spec? (use the simple method, and it does not involve sample prep)
use the Smith-Hiefje method.
It corrects background noise by alternating low and high current operation of HCL When low current is operating, the total absorbance is obtained, including from atom of interest and other components in the matrix.
In high current, large amount of non-excited atoms absorb radiation that is produced from excited species=>broadened emission line. So emission gets reabsorbed by analyte of interest, hence the dip. So high current gives absorbance of entire background to correct for scattering (green area)
What is another technique for correcting scattering light, but too complicated to go over in the course”
Zeeman effect
How to correct for scattering light in A.A spec that involves sample prep?
filter cloudy solution
use no-scrated cuvette
Briefly describe how does HCL work?
Hollow cathode contains metal of interest to be dislodged by sufficiently large voltage. So it produces atomic cloud called sputtering=>atomic cloud of excited states=>emits radiation=>return to ground state=>back to cathode or deposit on glass wall.
Explain how to decrease chemical interference in A.A spectroscopy, using flame equilibria.
use ionizable suppressor, where ionizable compound is used to flood the region with electrons, So following the Le Chat principle, more electrons will push towards atomic form
Name A.A analytical techniques used for measurement?
sample prep
calibration curve
run standard solution in between 2-3 runs
What are the advantages of AES than AAS?
(Note: AES=Atomic emission spectroscopy
- can analyze multiple elements simultaneously, especially for complex sample.
- allows non-metal analyte
- low interference with other elements
- use plasma for wider range of elements
What is the typical block diagram for AES? Label and explain why the order of the components is in placed.
