Page 175 - An Introduction to Analytical Atomic Spectrometry - L. Ebdon

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Appendix B:
Practical Exercises

B.1 Calculations

A variety of units are used in practical atomic spectrometry. Instrumental readings for AAS are
generally recorded in units of absorbance, and for AES and MS in counts per second (cps).
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Concentrations are normally expressed as a weight or mass per volume, e.g. µg ml = µg cm = mg 1
-1
= mg dm . Very often 1 µg cm is referred to as 1 ppm and so on. The use of the term parts per million
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-3
(ppm) should be discouraged as it lacks rigour and is ambiguous. For example, if the cadmium content
of a 1% solution of steel in aqua regia is reported as 1 ppm, does this mean 1 µg cm in the solution
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(i.e. 100 µg g in the solid) or 1 µg g in the solid? The term parts per billion (ppb) can cause further
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-1
confusion because different definitions of billion are used. Generally, the American billion, 10 , is
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intended, i.e. 1 ppb = 1 ng cm = 1 µg .
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1 The following blank-corrected readings were obtained for the determination of nickel in steel, using
nickel standards dissolved in iron solution (10 g l ). The determination was performed by atomic
-1
absorption spectrometry using an air-acetylene flame and the 232 nm nickel line.
Nickel concentration (mg 1 - 1 2 4 6 8 10 12
1 )
Absorbance 0.06 0.11 0.22 0.34 0.44 0.55 0.60

Plot the calibration curve for these data and comment upon any observed deviations from linearity.