Page 183 - An Introduction to Analytical Atomic Spectrometry - L. Ebdon

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3 Turn the monochromator wavelength setting to 589 nm.

4 Set the slit width to 0.15 nm.

5 Ensure that the instrumental mode switch is set to flame emission.

6 Switch on the air compressor; ensure that the pressure and flow rate is correctly set.

7 Turn on the main valve on the acetylene cylinder and ensure that the cylinder and outlet pressures
and flow rate are correct. If the cylinder pressure is below the recommended value do not attempt to
ignite the flame, as this will result in acetone being ignited in the flame. (Acetylene when stored under
pressure is dissolved in acetone.)

8 After ignition aspirate water continuously. Using a 10 cm measuring cylinder, check that the
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uptake rate of the nebulizer is within the range quoted by the manufacturer. Adjust if necessary.

9 Ensure that the flame is blue with a very faint tinge of yellow above the primary cone. If it appears
to be too fuel lean or fuel rich, adjust the fuel flow rate control carefully.

10 After ignition aspirate water continuously.
11 Zero the emission reading.

12 Using the top standard (10 µg ml sodium and 1000 µg ml potassium), fine tune the
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monochromator setting to achieve maximum emission signal. Set the voltage of the photo multiplier
tube (PMT) until a reading of about 90 is obtained with this solution, then increase the scale expansion
control until a reasonable signal is achieved. The increase in signal is offset by an increase in noise.

13 Set the instrument integration time control to 1 s.

14 The effect of potassium. Take five replicate emission readings of each of the six potassium
standards. Remember to zero the instrument between each standard while aspirating a blank. Calculate
the mean emission and RSD for each standard and plot a graph of sodium emission intensity against
potassium concentration. The RSD is defined as standard deviation (s) of the emission intensities
divided by the mean emission intensity ( )[RSD = (s/ ) x 100].

15 Determination of sodium in a soil extract. Using the five sodium calibration standards already
prepared obtain five replicate readings for each sodium standard and calculate the mean emission
intensity and RSD for each standard. Aspirate the standards in ascending and descending order of
concentration. Aspirate a blank between each standard and zero the instrument. Using a statistical
software package construct a