1. Method development for graphite furnace atomic absorption involves optimizing the dry, pyrolysis, and atomization steps for a particular analyte and sample type. This includes running blanks and standards to assess instrument performance. 2. Optimization of the dry step focuses on fully drying the sample without boiling or spattering. A two-step dry can help ensure complete drying. 3. Optimization of the pyrolysis and atomization steps focuses on selecting temperatures that give the best peak shape and sensitivity for the analyte. Lower temperatures are generally used for atomization in a transversely heated graphite atomizer compared to a longitudinal heated furnace.

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Method Development

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Method Development in GF-AA
 Introduction
- Look up the default temperature program
- Run a series of blanks
- Run a standard using default conditions, assess the
performance of the instrument (e.g.. check characteristic
mass)
- Optimize dry, pyrolysis, and atomization steps for the
particular application
- Analyze spike of representative sample(s) or standard
reference material to assess validity of the method
- Run a Standard Reference Material
- Check precision

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Find the Defaults
Don’t forget the modifier!

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Method Development
Dry Steps
 Optimization of Sample Drying
- Drying should be smooth with no boiling or spattering
- Use pre-heated injection whenever possible
(temperature near or at the beginning of the initial dry
step)
- With platform in place, drying temperature is usually 20-
40o
C above the boiling point of the solvent; can vary
depending on the temperature of the cooling water
- The default programs are set for 25 mL of solution

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Method Development
Dry Steps
 Optimization of Sample Drying (cont.)
- In THGA, verify drying without the extraction
system first, watching for condensation on the
small dental mirror
- A two-step dry is excellent for insuring drying of
the sample
- The sample should be dry with 10 sec. remaining
in the dry step
- A completely dry sample will prolong tube lifetime

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Typical Program
Dry Step(s)
Conditions:
20 mL sample
5 mL modifier
THGA
Two step dry

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Method Development
Sample Pyrolysis
 Optimization of Sample Pyrolysis
- Original guidelines for wall atomization were a 1 sec.
ramp for each 100o
C between the final dry step and the
pyrolysis step. This approach has proven to be useful
using the platform in analyzing diverse environmental
samples.
- Typically, it is sufficient to hold at the pyrolysis
temperature for 15-20 sec. depending on the sample.
- If the samples are relatively free of matrix, it may not be
necessary to pyrolyze the sample at all. If this is the
case, omit the modifier and the pyrolysis step

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Method Development
Pyrolysis Study in a THGA
0
0.05
0.1
0.15
0.2
0.25
200 400 600 800 1000 1200
Temperature o
C
Abs-sec
PO4 + Mg(NO3)2
PO4
Pd + Mg(NO3)2

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Conditions:
20 uL sample
5 uL modifier
THGA
Typical Program
Pyrolysis
Using the
Phosphate/Magnesium
Nitrate Modifier

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Method Development
Pre-Atomization Cool Down Step
 Pre-Atomization Cool Down Step
- Studies indicated it is often advantageous to cool the tube off prior to
atomization in a HGA
- Heating rate is maximized
- Careful measurements indicated a broader isothermal zone is present
within the graphite tube

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Method Development
Atomization Study
 Optimization of Atomization
- Generally, THGA furnaces utilize atomization
temperatures that are 200-300o
C lower than a
HGA
- Many furnace users rely on peak shape and/or
sensitivity to determine the optimum temperature
- Generally, in a HGA, a symmetrical peak (peak
height = peak area) is considered “ideal”

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HGA Platform Atomization
“Ideal” Peak

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HGA Method Development
Pb: Effect of Atomization Temperature
0.610
0
5.00
Time (sec)
1400o
C
1600o
C
1800o
C
2200o
C

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THGA Method Development
Pb: Effect of Atomization Temperature

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Conditions:
20 uL sample
5 uL modifier
THGA
•0 sec ramp
•Stopped gas flow
•Read step
Method Development
Atomization

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Method Development
Clean-out
•Gas on
•Do not exceed
2650 degrees
More aggressive clean-out
may be necessary for
refractory elements

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Furnace Program Temperatures
Furnace
Step
Analyte
Dependent
Matrix
Dependent
Volume
Dependent
Dry No Yes Yes
Pyrolysis Yes Yes No
Atomization Yes No No

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Quality Control Methods
 Precision
 Accuracy
 Spike Recovery
 Reference Samples

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Using the Software for
Quality Control
 Checks
- Calibration Curves
- Spike Recoveries and Duplicates
- Precision
 QC
- After calibration, ongoing, at the end
- Actions based on when it fails
- Use the software to implement your QC policy

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Checks - Calibration

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Checks - Spikes and Duplicates

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Checks - Precision

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QC - Identifying

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QC - Scheduling

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QC - Actions (Calib. and Periodic)

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QC - Actions (End and Retry)

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Reference Materials
 NIST, National Institute of Standards and
Technology
 Environmental Resource Associates
 High Purity Standards
 Brammer Standard Co.
 Conostan Metallo-Organic Standards
 BCR, European Community

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Graphite Furnace
Atomic Absorption
Workbook Exercises