An Introduction to
Flame Atomic Absorption
Spectrometry (FAAS)
Steve Badger
and
Charity Wessel
Introduction
• FAAS, developed in the 1950s, is a
common method of quantitative
analysis of many elements
• FAAS is extensively used to
determine trace quantities of
elements in biological, environmental,
clinical, geological, and edible samples.
– Elemental health hazards can be
detected with 0.0331% error.
Theory of Operation
• Structure of an atom
– Atoms consist of a nucleus
and electrons.
• The nucleus contains
protons and neutrons.
• The negatively charged
electrons are located in
orbitals around the
nucleus.
– When electrons occupy the
innermost available orbital,
their energy is at a
minimum (ground state).
Theory of Operation, continued
• When atoms are
subjected to heat or
some form of EMR, one
or more electrons jump
to a higher energy
level, leaving a vacancy
in the inner shell
• We say the electron is
excited
• As this happens, energy
is absorbed
Theory of Operation, continued
•When the excited
electron in the outer
orbital returns to the
lower energy level of the
inner, vacant orbital,
energy is released in the
form of a photon
Theory of Operation, continued
•Because the atoms of
each element have a
different electronic
structure, each one emits
light of different
wavelengths
•In FAAS, the
concentration of an
element present in a
sample can be measured
by noting the absorbance
caused by the excited
sample
Instrument Design
• FAAS components:
– Fuel (acetylene)
– Oxidizer (air, N2O)
– Hollow Cathode Lamp
(HCL)
– Nebulizer
– Burner Head
– Flame
– Exhaust hood
Instrument Design: Acetylene
• Acetylene is a flammable,
compressed gas that is used as a
fuel for FAAS.
• During FAAS operation, the valve
connected to the acetylene
cylinder is opened completely.
• Storing the tank in a lab can be
extremely dangerous.
• That is why the tanks are
supported upright with a metal
chain.
Instrument Design: HCL
• The HCL is a glass
tube filled with an
inert gas (neon, argon,
or helium) and the
pure element to be
subjected to FAAS.
• The atoms of the
element become
ionized and excited
when the FAAS is on.
Instrument Design: HCL
• The spectrum emitted by
the HCL corresponds to the
element in the cathode
• For example, if a Cd HCL is
used, the characteristic
wavelengths of Cd are
emitted
Do you recall emission spectra
from general chemistry?
7.3
Instrument Design: HCL
• Single-element
HCLs generally
achieve greater
sensitivity
• On the other hand,
multi-element
HCLs save money
Instrument Design: Burner Head
• The burner head is
made of titanium
• This is where the
sample atoms are
excited
Instrument Design: Nebulizer
• The nebulizer
changes liquid
sample to a mist
• This arrow is
pointing to the
nebulizer
Instrument Design: Flame
• The flame is ignited
by pushing the red
burner button on
the instrument
• The maximum
temperature of the
air-acetylene flame
is 3,095°C
Typical Units of Concentration
Parts Per Million (ppm)
A unit of concentration often used
when measuring levels of pollutants
in air, water, body fluids, etc.
1.00 ppm is equal to 1.00 mg/liter
And 1.00 g/mL
Typical Units of Concentration
Parts Per Billion (ppb)
Another typical concentration unit
used when measuring trace levels of
pollutants in air, water, body fluids,
etc.
1.00 ppb is equal to 1.00 g/liter
Preparation of Standards
• Typically 4-5 standards and a blank are
prepared to construct a calibration curve
(a/k/a a standard curve)
– When preparing your solutions, think about the
need for precision, low contamination, and
minimal waste
– Standard solutions should be prepared using
appropriate glassware and distilled water
• Consult a reference to determine
appropriate concentrations of standards
for a given element
Constructing a Calibration Curve
• As with other analytical
techniques, FAAS requires
careful calibration
• The absorbance of the
standards are plotted
versus concentration
• The plot often deviates
from a straight line
Preparation of Samples
A standard reference should be
consulted to determine appropriate
methods of preparing various samples
for FAAS
Operation
• Open the valve on top of
the acetylene cylinder
completely.
• Turn on the exhaust vent
using the switch on the
hood.
• Turn on the workstation
connected to the FAAS.
• Load the FAAS software.
Operation: Optimization
•
Only a few steps are required for
optimization
–
•
The software steps you through the
optimization, because a method has
already been created for doing so
After optimization, you are now
ready to start the analysis
Analysis
• Again, the software leads you
through the procedure
• Sequentially aspirate the blank
(distilled water), the calibration
standards, and the samples
Evaluation of Results
• After the analyses are complete, look
at the calibration curve printed out
by the FAAS system’s printer
Limitations of FAAS
• The chemical form of the analyzed element is
not detected
– For example, if copper was being analyzed, all that
would be known is how much copper is present.
– It would not be known if it is copper(II) cyanide,
copper(III) sulfate, etc.
• The preparation of the standards and samples
can be time consuming
• The whole FAAS procedure requires detailed
work
• Some elements cannot be examined by FAAS
• The FAAS procedure destroys the sample
Conclusion
FAAS is an accurate
method of quantitative
analysis for many
elements