USING A FLAME PHOTOMETER

Many flame photometers are quite simple instruments and they must always be calibrated against standard solutions.
A photometer relatively cool flame is suitable for the excitation of the element from groups 1, 2 and the lanthanides.
Air and gas line are attached to the back of the instrument. In this case the air is supplied by small pump.
The gas supplied passes through a secondary regulator valve before entering the instrument.
Before making any readings, unlock the air valve and adjust the air pressure to the value recommended in the instrument manual, then lock the valve.

The regulated air and gas supplied enter a mobilized unit where they are mixed with the sample solution.
The air flow into the nozzle at the front of the unit draws solution up the pump tube and converts it into a mist.
This then enters the nebulizer where it mixes with the gas.
The nebulizer mixture of gas air and solution is passed to the boiler.
Excess liquid from the nebulizer passes in a stand pipe which stops air and fumes escaping and allows excess liquids to run to waste.

Check regularly that the drainage system is functioning correctly. If it is not, the instrument will not give reliable readings.
The way in which this automated instrument works is best seen with the protective hood around the burner assembly removed.
Switching on the instrument automatically open valve in the air and gas supplies, and this instrument automatically ignites the fume air mixture.

The presence of a flame is sensed by a detector and indicated on the front of the panel.
 If ever the flame is extinguished during operation a signal from the detector shut off the gas supply.
When using older instrument without the safety features, take care to follow the operation instruction   exactly, since there may be a risk of forming explosive gas/air mixtures.
The presence of elements such as the alkaline metals colors the flame, this is the color produced by potassium, and this that of sodium.
The light from the flame passes through window to a photo detector which covers the opening and its normally hidden inside the hood.
This instrument is set up to measure calcium, potassium or sodium.
Movement of the bar moves the flame photos in front of the detector, each of these only let the light of the wave length specific to the element in question to reach the detector.

The rate at which the instrument draws up liquid in aspiration rate should be checked using a blank solution in this case, water at the beginning of the round.
This is easily done by drawing the solution from a graduated vessel. A rate of 1cm3 in about 10seconds is satisfactory.
If the instrument does not aspirate or aspirate very slowly, the nozzle may need cleaning, this can be done by removing the nozzle, taking off the delivery tube and passing a fine wire through the nozzle.

The male knob at the end of the nozzle is used to adjust the aspiration rate this should seldom necessary.
Before starting the run, the flame must be set to give maximum sensitivity to the element that is to be measured.
Ensure that the fuel control is well opened, switch on and when the flame is ignited aspirate the blank solution in this case distilled water.
Use the blank control to set the meter reading to zero.
Then replace the blank solution by dilute solution of the element to be measured, in this case sodium.

Check that the correct filter is in place, and then reduce the flame fume until the meter reading is at the maximum.
 Now aspirate the blank solution again to remove any traces of sodium from the nebulizer.
When the meter readings return to zero, the instrument is ready to be calibrated against standard solutions.
A range of standard solutions should have been made up in advance.
The concentration should be chosen so that likely the concentration of the unknown sample lies in the middle of the range.
Start with the most concentrated standard solution.
When the reading is stabilized uses the coarse, and then the fine sensitivity control to bring the meter reading to the concentration of the standard solution.

Once this is done the settings of the instrument should not be altered until the analysis is completed.
Aspirate the blank solution to clean the nebulizer, and then aspirate the next standard solution.
Note the meter reading, remove the standard solution and aspirate the blank solution again.
Continue with this procedure until readings have been recorded for all the standard solutions.
Now aspirate the blank solution again, and then aspirate the unknown sample, and record the meter reading.
Finally aspirate the distilled water for a couple of minutes to finally clean up the nebulizer, and then switch off.
For non automated instrument carefully follow the shut down procedure.

If the ordinary solution contains solute, it is important to filter it order wise the nebulizer may become blocked.
It is vital to select the filter paper that will not absorb the ion that must be measured, if in doubt seek advice.
Finally wash up the sample vessel and the filter to ensure the entire soluble sample is transfer to the measuring flask, and then make it up to volume.
Plot the calibration reading, this record may give a sign curve that is why calibration is necessary.
Then read off the part per million value corresponding to the analytical sample