Chapter 4 Basic Operation
4-66
AA-6800/6650 Instruction
4.8.5 Flame Conditions When Analyzing Organic Solvent Samples
Since an organic solvent itself will burn in the flame, the flame will not be completely combusted using the
normal flame conditions, as the result, the measurement accuracy will be decreased. To perform an accurate
measurement, it is necessary to decrease the sample spray amount as well as decrease the acetylene gas flow
rate, compared with the aqueous solution. The procedure for setting the flame conditions when using organic
solvent is as follows.
(1) Replace the suction nozzle with the provided polyethylene capillary tube.
(2) While solvent is being sprayed into the flame, decrease the acetylene gas flow rate so that the color of the
flame is from blue or slightly red (in the case of air-acetylene flame). Next, while organic sample is being
sprayed, try various acetylene flow rates and burner heights until the maximum S/N ratio (signal to noise
ratio) is achieved.
(3) Overly decreasing the acetylene flow may cause the flame to go out when spraying of the organic sample
is stopped. In this situation, increase the acetylene gas flow rate in 0.1 L/min increments until the flame no
longer goes out at the end of spraying the organic solvent sample, and then adjust the flame condition by
increasing the support gas flow rate. When using a nitrous oxide-acetylene flame, be sure that the red
feather (red portion of the flame) is more than 2 - 3 mm.
If a stable flame is not achieved after performing the above procedure, continue with the steps (4) to (6)
outlined below, and then search for the optimal flame conditions using steps (2) to (3) again.
(4) R
eturn the acetylene flow rate to its normal value.
(5) Rotate the support gas pressure adjusting knob so that the support gas pressure is in the range of 0.1 to
0.25 MPa, and decrease the amount of sample sprayed.
(6) Increase the support gas flow rate by rotating the support gas flow adjusting knob to approach the flow rate
used prior to decreasing the support gas pressure.
CAUTION
In case of flashback, set the safety valve at the back of the chamber as it was if it is out of place. Also,
remove the spray unit to check it and if the disperser is separated, mount it as it was. Check the tube from
the drain outlet is firmly connected.
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