Preparation, Set-up, Use & Shut-down
Preparation
The flame photometer is a wonderful laboratory instrument that provides consistent
reliable results in a remarkably short period of time. It has its place in laboratories, of
course, but it can also be found as an in-line part of a production line in everyday processes,
too.
You cannot simply turn it on and expect it to function, however. There are steps to
be followed to achieve accurate results. Some things you have to do every time you prepare
to use it; some things only need to be done periodically.
One of the most important preparations is to possess or install a water deioniser. Distilled water from the local grocery market is insufficiently pure. For set up, it is advised to prepare de-ionised (DI) water in the cleanest possible equipment. This is essential to establish a completely reliable 0 ppm reading for the water carrier.
Once you have a source secured, you need to obtain or make control samples with
known properties for calibration purposes. The five most likely candidates for testing will be
a selection of either; Barium, Calcium, Lithium, Potassium, and Sodium.
Assembling a collection of Calibration Standards of Sodium (Na) samples, you might elect to have a range of standards such as 25ppm, 50ppm, and 75ppm, for example. This allows you to generate a far more accurate calibration curve. Your calibration standards should always be in the range of particular interest, never allow your sample concentration to extend beyond the highest point of the calibration curve as results are only extrapolated at this point and no element has a completely linear calibration curve.
If your instrument allows for it then a multi-ion calibration standard should be produced, a multi-ion standard ensures that the calibration standard matches your sample composition and matrix as close as is possible and therefore produces more accurate results. All of the BWB instruments allow for multi-ion calibration curves to be generated.
Next you will need an air compressor, the compressor is used to mix air with the propane (butane or sometimes methane) gas to produce a hot blue flame, without the correct mix of air the flame will burn rich and will appear yellow in colour. This type of flame is not well suited for flame photometry. The compressor also works through the nebuliser to draw your liquid sample into the mixing chamber, this process known as venturi is similar in principle to a carburettor in a motor vehicle. The BWB range of instrument all include a built in compressor so there are no additional requirements.
If your instrument doesn’t have a built in compressor, it is important to carefully select an appropriately designed compressor. The flame inside the device is particularly sensitive to pressure changes in the fuel stream, and compressors that work from pistons, diaphragms or similar mechanisms cause pulsations within the flow, these pulses can
dramatically affect readings. Large pumps experience an increase in pressure during the
compression-stroke and a significant fall-off on the refill-stroke. While bottled compressed
air removes this variable, it is the more expensive option operationally speaking.
Set-up
Presuming a typical setup, the flame photometer would be placed on a firm level
surface, either with an exhaust hood above, or plenty of space between the chimney and
anything flammable overhead. Connect the fuel-supply safely and properly according to the
manufacturer’s instructions.
Connect the compressed air (if required) safely and according to instructions. Turn
on the compressor and set its pressure and flow rate according to the flame photometers
manufacturers instructions. Plug in the unit and let it complete its self-diagnostic and start
up routine, if the instrument includes this feature.
Open the main valve of the fuel tank slowly. Open the fuel valve, slowly on the flame
photometer and press the start button until the flame lights. On more elderly models, it
may require the operator to physically light the gas stream, usually by applying a flame
above the burner while the chimney is removed. The flame will generally be bright, high,
and orange-yellow when it starts. Use the gas/air control knob on the flame photometer to
adjust the gas/air ratio until the flame becomes a passive, steady blue flame, to the height
advised by the manufacturers instructions. Adjust the fuel control knob if the flame is still
too high or low and alter the air to attain the steady blue flame again. Replace the chimney,
if removed.
The BWB instrument range all feature an automatic ignition sequence and automatic
air flow adjustment with the built in compressor. For these instruments, open the manual
gas valve on the side of the instrument approximately 1 turn and press the ‘Turn on Flame’
command, once lit, simply adjust the height of the flame using the gas control knob to the
height as indicated in the manual.
Use
Place a beaker of DI water on the sample tray and place the sample tube in the water
and let it run for the warm up period as indicated by the manufacturer. The flame should be
unaffected in changes to visible colour.
Calibrate the instrument using the instructions supplied from the manufacturer, this
process can vary from one instrument to another. Older models use a variety of knobs on
the front panel to adjust a digital readout, typically discplyed on a LCD, to set the 100%
reading and blank reading. Other, more advanced models such as those offered by BWB
offer digital calibration, simply enter the concentration of each element into the instrument
menu and the system will monitor the flame for a stable reading and begin the aqcusition
proves to generate a calibration curve.
Once the system is calibrated you can begin running your samples for analysis. Now
you can bring in an “unknown” sample. Take the sample tube out of the DI water, and place
it in the sample. It may wander a count or two in each direction when it reaches maximum,
so after 30 seconds, note the middle number of any variance, and record that number. The
BWB systems also offer automatic analysis and result determination so that user error can
be removed from the process.
It is advised that you check the calibration periodically in case the Zero or Control
Value has drifted. This can be performed using a calibration standard and ensuring that the
system samples the standard within the allowable percentage of error.
Shut-down
Upon completion of testing, you need to shut the instrument down. First allow it to
run for a few minutes with just DI water, so its internal parts are flushed of any
contaminants and ready for the next user.
Turn off the fuel regulator knob, and close the valve on the fuel gas cylinder. Leave
the air running for another five minutes with the sample hose still in the DI water.
Finally, turn off the flame photometer, and shut down the air compressor.
Alternatively, with a BWB flame photometer, simply navigate the menu to ‘Turn off
flame’ after allowing the DI water to flush the system for about 5 minutes.
The Takeaway
The flame photometer is a very useful piece of equipment and can be operated by
most technicians with minimal training. It has a small learning curve for users and yet can
still obtain reliable and exceptionally accurate results.
There are tasks where the analyses of inorganic metals in bio-samples are essential,
such as research, genetics labs, and more. However, there are applications in industry, such
as food and beverage processing, municipal water quality monitoring, municipal waste
water treatment, and more, where it is absolutely vital.
Sometimes it is necessary to spend hundreds of thousands or millions to obtain Gas
Chromatograph-Mass Spectrometers or similar analytical equipment. In many cases that is
well-beyond the actual need, so don’t overbuy. If the majority of your work can be done
with a Flame Photometer, that is your best deal.