Page 192 - An Introduction to Analytical Atomic Spectrometry - L. Ebdon

Page 178

The requisite weight of the spike required to do this can be calculated using the equation.

where R = isotope ratio of A to B, A x = atom fraction of isotope A ( Cd) in sample, B x = atom fraction
106
of isotope B ( Cd) in sample, A = atom fraction of isotope A ( Cd) in spike, B = atom fraction of
111
106
s
s
isotope B ( Cd) in spike, W = weight of sample, W = weight of spike, C = concentration of element
111
s
x
x
in sample and C = concentration of element in spike, and M and M = molar mass of element in sample
s
x
s
and spike respectively.
The equation can be rearranged and the appropriate values substituted to calculate W :
s
B.7.3.2 Calculation of Unknown

Equation B.2 can also be rearranged into the appropriate form to calculate C as follows:
x

B.7.4 Instrument Start-up

A demonstration of the correct procedure for the ICP-MS instrument will be given. This will be an
opportunity to get to know the instrument by discussions with the demonstrator and hands-on 'knob
twiddling'. The following aspects will be covered.

B.7.4.1 Preparation.

A complex instrument such as ICP-MS requires careful preparation before use if reliable results are to
be obtained. Useful preparative steps include:

• acid washing of spray chamber, torch and other glassware;

• cleaning of sampler and skimmer cones;

• preparation and alignment.

B.7.4.2 Ignition

This procedure is automated in most modern instruments; however, it is as well to be aware of things
that can go wrong beforehand in order to