What Are The Gases Needed in An AAS?
Flame Atomic Absorption Spectrometer (F-AAS)
The gas needed includes fuel and oxidant. The fuel is acetylene, and the oxidant can be compressed air or nitrous oxide. And the combination will be "acetylene + air" or "acetylene + nitrous oxide", to ignite the flame.
Specifications of gases needed are shown in the following table:
|
Gas required |
[Fuel] |
[Oxidant] |
[Oxidant] |
|
Purity |
99.9% |
O2, 21%; N2 78%; Ar 0.9%; CO2 300ppm; CH4 < 5ppm |
99.5% |
|
Minimum Pressure |
55 kPa (8 psi) |
330 kPa (47 psi) |
330 kPa (47 psi) |
|
Maximum Pressure |
96 kPa (14 psi) |
370 kPa (53 psi) |
370 kPa (53 psi) |
|
Minimum Flow Rate |
12 L/min |
24 L/min |
24 L/min |
Graphite Furnace Atomic Absorption Spectrometer (GF-AAS)
There are two kinds of gas are required by GF-AAS, the inert gas and auxiliary gas. Inert gas can be high-purity, oxygen-free nitrogen; or a high-purity, oxygen-free argon. The pressure have to be controlled in the range of 70-200kPa (10-30 psi). Insufficient pressure will affect the operation of the instrument. General use of the gas flow rate has to be about 3L / min (approximately 4–5 units on the flow meter).
Further, if there is a PAL auto sampler installed, the inert gas is also needed to be used in the pressurizing. Lacking of the inert gas, will prevent furnace operation.
Auxiliary gas is a second inert gas, the difference is that the gas is used to assist poured into a graphite furnace. General recommendations of using the auxiliary gas, in longer drying process, the cheaper nitrogen is recommended. In the ashing process, argon provides a better response. It's better to use argon.
Specifications of gases listed in the following table:
|
Gas required |
Nitrogen (high-purity O.F.N.) |
Argon (high purity grade) |
|
Purity |
Nitrogen 99.99% |
Argon 99.99% |
|
Gas Composition Recommendation |
Oxygen <10 ppm Methane <5ppm Carbon dioxide 0.1ppm Moisture at 15 °C <12ppm |
Oxygen <10 ppm Nitrogen <50ppm Carbon dioxide <5ppm Carbon monoxide <1ppm Hydrocarbons as CH <1ppm Hydrogen <1ppm Moisture at 15°C <12ppm |
|
Minimum Pressure |
70 kPa (10 psi) |
70 kPa (10 psi) |
|
Maximum Pressure |
200 kPa (30 psi) |
200 kPa (30 psi) |
|
Flow Rate |
3 L/min |
3 L/min |