In: Chemistry
Why do we need to increase the flow rate of air-acetylene flame when we switch over to nitrous oxide flame in AAS?
The AAS requires that the temperature of the flame should be very high i.e around 2300-3000 oC. So as to obtain this temperature, air-acetylene flame and/or nitrous oxide-acetylene flame is used. The temperature of the air-acetylene flame varies between 2250 - 2350 °C whereas that of nitrous oxide-acetylene flame is 2800-3000 oC.
Now when you want to swtich from air-acetylene flame to nitrous oxide-acetylene flame, there will be sudden massive increase in tyemperature of the flame. Due to this there will be fluctuation in AAS values. So as to minimize the variation in results of AAS, the rate of flow of air-acetylene flame is increased so that the temperature difference between the two observations can be decreased. This will not cause any large variation in readings of AAS. The increased rate flow will raise the temperature of air-acetylene flame and will give better results.