Professor Went: Burners Flashcards
1
Q
What are the advantages and disadvantages of Laminar Flow Burners?
A
Pros
- Long path length for increased sensitivity
- Clean flame as large droplets are drained away
Cons
- Wasteful (10% of sample –> flame)
- Atomic residence time and concentration is small in flame
- Flicker and instability results in noise, limiting detectability
2
Q
What are some commonly used flames?
A
- Air-acetylene burners are very common
- Acetylene-nitrous oxide is useful for elements, which tend to form heat-stable oxides.
- Hydrocarbon flames absorb heavily below 200 nm.
- Ar-H2-Air is colourless and useful for As 193.5 nm and Se 197.0 nm
3
Q
Is spectral line interference an issue with using burners?
A
- Because source lines are narrow, interference due to overlapping lines is rare
- Normally possible to use another absorption line
- Interferences are also caused by solid particles, unvaporised solvent droplets or molecular species
- Background measurements are important.
4
Q
What are ionisation interferences?
A
M –> M+ + e-
This lowers the population of absorbing free atoms
Exacerbated by hotter flames.
Solved by ionisation suppresors, which are easily ionised, supply excess of electrons in flame to reduce ionisation of analyte
5
Q
What is Refactory Compound Formation?
A
- Sample solution may contain a chemical, usually an anion, that will form a refractory compound with the test element in the flame.
- E.g. calcium + phosphate –> Calcium pyrophosphate
- Problems occur when analyte metal reacts with gases in the flame. Al, Ti, Mo, V react with O and OH species in flame to form oxides and hydroxides
- Acetylene-nitrous oxide useful in reducing fuel-rich enviro
- CN and NH decompose refactory oxides
6
Q
What are physical interferences?
A
- Includes most parameters that affect rate of sample uptake in burner and atomisation efficiency
- Variation in gas flow rate, sample viscosity, flame temperature etc.
- Can usually be accounted for by frequent calibration.
