AAS SPECTROSCOPY

1. ATOMIC ABSORPTION
SPECTROSCOPY

2. Atomic Absorption (AA) spectroscopy
•
•
Atomic absorption spectroscopy is a quantitative
method of analysis that is applicable to many metals
and a few nonmetals.
A few examples include:
Al in blood serum
Ca in blood serum, plants, soil, water
Cu in alloys
Cr in sea water
Fe in plants
•
•
•
Only a drop of sample needed
The metals need not be removed from other
components (AA is a highly selective technique)
Sensitive in the ppm range (even ppb with the right
equipment)

3. Principles of AAS
•
•
When metals are exposed to heat, they absorb
light.
Each metal absorbs light at a characteristic
frequency. For example:
Metal
λ (nm)
Zn
214
Fe
248
Cu
325
Ca
423
Na
589

4. •
•
•
The metal vapor absorbs energy from an
external light source, and electrons jump from
the ground to the excited states
The ratio of the transmitted to incident light
energy is directly proportional to the
concentration of metal atoms present
A calibration curve can thus be constructed
[Concentration (ppm) vs. Absorbance]

5. Use of each components of the AA spectrometer: fuel, atomizer,
monochromatic light source, monochromatic detector, read out.
• A block diagram of the AA spectrometer appears
below.

6. Overview of AA
spectrometer.
Light Source
Sample
Compartment
Detector

7. •
•
•
The source of light is a lamp whose cathode is
composed of the element being measured.
Each analyzed element requires a different lamp.
For example, a hollow cathode lamp for
Aluminum (Al) is shown below

8. •
The cathode lamps are
stored in a compartment
inside the AA spectrometer.
The specific lamp needed
for a given metal analysis is
rotated into position for a
specific experiment.

9. •
•
•
The sample is made up, typically in water
A flame is created, usually using ethyne &
oxygen (fuel)
The flame gases flowing into the burner create a
suction that pulls the liquid into the small tube
from the sample container. This liquid is
transferred to the flame where the sample is
atomized [mixing the sample with air to create
fine droplets]. The metal atoms then absorb
light from the source (cathode lamp).

10. Light beam
Sample is
vaporized
in the flame.
Aspirator
tube sucks the
sample into the
flame in the
sample
compartment.

11. •
•
•
The light passes through a monochromater (a
device used to select a particular wavelength of
light for observation)
The intensity of the light is fairly low, so a
photomultiplier tube (PMT) is used to boost the
signal intensity
A detector (a special type of transducer) is used
to generate voltage from the impingement of
electrons generated by the photomultiplier tube

12. A typical photomultiplier tube

13. •
The read out specified by
the user is displayed on
the computer screen for
each sample measured.

14. The resulting
data can be
presented in
a variety of
ways, but
typically a
print out is
made.

15. Concentration of a solution from a calibration curve.
•
•
•
AA can be used to identify the presence of an
element (qualitative analysis), or the
concentration of a metal (quantitative analysis)
Quantitative analysis can be achieved by
measuring the absorbance of a series of
solutions of known concentration.
A calibration curve and the equation for the line
can be used to determine an unknown
concentration based on its absorbance.

16. Disadvantages of AAS
 only solutions can be analyzed
 relatively large sample quantities
required (1-2mL)
 less sensitivity
 problems with refractory elements

17. Advantages of AAS
 inexpensive (equipment, day-to-day
running
 high sample throughput
 easy to use
 high precision