Page 186 - An Introduction to Analytical Atomic Spectrometry - L. Ebdon
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be obtained. If it is too high, then the tube will experience unnecessary wear and its lifetime will be
shortened. An added problem for many analytes is that they may react with the graphite and form
extremely refractory carbides, which will also decrease the atomic absorption signal. The optimum
atomize temperature may be found by constructing an 'atomize curve'.
B.5.3 Procedure
1 First, optimize the temperature programme. In the first instance, only the dry temperature need be
optimized, and so aliquots of water can be dispensed into the tube. A temperature range of 100-140°C
can be tried, and the temperature that gives complete drying without frothing or spitting selected.
2 Prepare a series of copper standards ranging from 0 to 100 ng ml , in 2% nitric acid.
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3 Set the ash temperature to 400°C for 10 s, which should be low enough to prevent any losses of
copper before the atomize stage, and set the atomize temperature to 1700°C for 5 s. Set the tube-clean
cycle to 2500°C for 5 s.
4 Deliver 10 µl of a standard solution into the graphite furnace and run the furnace program.
5 Repeat the above procedure while increasing the atomization temperature to 2300°C in stages of
100°C. Plotting a graph of peak area against atomize temperature will yield a sigmoid-shaped curve.
The optimum atomize temperature is that which is just on the higher plateau region.
6 Once the optimum drying and atomize temperatures have been selected, the optimum ash
temperature can be determined. Select the optimum dry and atomize temperatures and an ash
temperature of 400°C. Note the peak area produced at atomization, and then repeat the experiment
increasing the ash temperature to 1200°C in 200°C steps. A graph of ash temperature against signal
should then be plotted. The optimum ash temperature is that just before the signal starts to decrease.
7 Using the optimum temperature programme, prepare a calibration curve.
8 Take a portion of deionized, distilled water and get a volunteer to dip his/her finger into it for 15 s.
Determine the concentration of copper in this sample and a sample of tap-water.
