This document discusses light sources and background corrections for Atomic Absorption Spectroscopy (AAS). It describes two main light sources: hollow-cathode lamps and electrodeless discharge lamps. Hollow-cathode lamps consist of a tungsten anode and metal cathode enclosed in a glass tube with inert gas. An applied voltage excites the gas to produce characteristic radiation from the coated metal. Electrodeless discharge lamps contain inert gas and metal salt excited by radio waves. The document also discusses methods to correct for spectral interferences, including continuum source correction, Zeeman effect background correction, and source self-reversal using high and low lamp currents.

1. Light sources for Atomic Absorption Spectroscopy (AAS)
And
Background corrections
Prepared by-
Dr. Mallikarjunaswamy C
Assistant Professor
Postgraduate Department of Chemistry
JSS College of Arts, Commerce and Science
Ooty Road, Mysuru-570025

2. Radiation Sources
1. Hollow-Cathode Lamps
This type of lamp consists
1. Tungsten Anode
2. Cylindrical Cathode
• these two sealed in a glass tube filled with inert Argon/Neon gas
• The cathode is constructed by using desired metal.
• A voltage is applied across the anode and cathode.
• The Argon gas is ionized to Ar+ at the anode.
• The Ar+ ions are drawn toward the cathode and when they strike the surface, sputter off some of the
coated atoms into the gas phase.
• In the sputtering process, some of the atoms are excited and emit the characteristic lines of radiation
while returning to ground state.
• The efficiency of the hollow-cathode lamp depends on its
 geometry and
 the operating voltage.
• High voltages, and thus high currents, lead to greater intensities.

3. Limitations
• The greater voltage and current is increase in Doppler broadening of the emission lines from the lamp.
• The greater currents produce an increased number of unexcited atoms in the cloud.
• The unexcited atoms, in turn, are capable of absorbing the radiation emitted by the excited ones.
• This self-absorption leads to lowered intensities, particularly at the center of the emission band.
• HCL has high precision and low detection limit.
2. Electrodeless Discharge Lamps
• Constructed from a sealed quartz tube containing a
few Torr of an inert gas such as argon and a small
quantity of the metal (or its salt) whose spectrum is
of interest.
• The lamp contains no electrode but instead is
energized by an intense field of radio-frequency or
microwave radiation.
• Ionization of the argon occurs to give ions that are
accelerated by the high-frequency component of the

4. Source Modulation / Interferences of Flame Noise
• It is necessary to eliminate interferences caused by
emission of radiation by the flame.
• Of course, interferences removed by the bandpass
monochromators.
• However, emitted radiation equal to monochromator setting is inevitably present in the flame because of
excitation and emission of analyte atoms and flame gas species.
• We can account for flame noise and changes in the flame noise by using a device called a chopper.
• A chopper is a spinning wheel that alternately lets source light through to the flame and then blocks the
source light from reaching the flame.
• When the chopper blocks the source, the detector only reads the
background flame noise.
• When the chopper lets the light through, both flame noise and
source noise is detected.
• By subtracting the combined source/flame signal from only the
flame background it is possible to measure the magnitudes of Po and P and to determine whether
the introduction of the

5. Correction of Spectral Interferences
1. Continuum-source correction method
• In this technique, a deuterium lamp provides a
source of continuum radiation throughout the UV
region.
• The output of the hollow cathode lamp will be
 diminished by atomic absorption,
 molecular absorption and
 scatter.
• The continuum lamp will only be diminished by
 molecular absorption and
 scatter, since any contribution from atomic absorption is negligible.

6. 2. Background Correction Based on the Zeeman Effect
• The Zeeman effect, named after Dutch physicist Pieter Zeeman, is the effect of splitting of a spectral line into several
components in the presence of a static magnetic field.
• Application of Zeeman effect is based on the differing response of the two types of absorption lines to polarized radiation.
• The π line absorbs radiation polarized that is parallel to the external magnetic field.
• The σ lines, in contrast, absorb radiation polarized perpendicular to the field.

7. 3. Background Correction Based on Source Self-Reversal/ Smith-Hieftje method
• It is based on the self-reversal or self-absorption behavior of radiation emitted from hollow-cathode lamps when they are
operated at high currents.
• High currents produce large concentrations of nonexcited atoms, which are capable of absorbing the radiation produced from
the excited species.
• To obtain corrected absorbances, the lamp is programmed to run alternately at low and high currents.
• The total absorbance is obtained during the low-current operation.
• At High Current absorbance by the analyte is at a minimum, (due to insufficient energy for atom excitation) absorbance due to
background interference is measured.