When using a flame photometer, flame stability can be affected by a number of different factors and outside influences.
These include atmospheric conditions such as humidity, oxide concentrations, pressure changes and oxygen content of the air.
But what about the stability and reproducibility of results?
Here, we will focus on how the instrument itself can affect reproducibility and stability of the flame.
The samples and standards themselves can affect reproducibility - something that seems quite simple. However, it can be caused by a huge variation of different factors in play coming together.
This would be the viscosity of the solution, or the ease at which the sample flows.
What causes differences in viscosity between solutions?
One factor which can cause differences in viscosity between solutions is ambient temperature.
More energy in the liquid would increase its fluidity, and therefore the rate at which all of the mixing kinetics occurs.
This is due to the energy of the system being higher and making it easy to break the intermolecular hydrogen bonds in the solution.
What other factors can have an effect?
There is also pH, where if there are any proteins in the solution, can cause huge variations in viscosity in a sample.
This is due to the acid or alkaline causing the overall structure of the protein to contract or expand.
Another one which is similar to the mechanism of how pH and proteins work would be the total dissolved solids (TDS) of the solution.
TDS is used to describe the inorganic salts and small amounts of organic matter present in solution in water.
Obviously, a higher TDS solution would be more viscous than that of a low one.
In relation to the TDS of a solution, let's discuss the mixing chamber.
It all comes down to ensuring that as close to a fully homogeneous gas as possible is passed through the burner head for combustion.
If the gas is “chunky” and not mixed properly, there will be a nonlinear burning in the flame and therefore unstable results.
How does this relate back to the TDS of the solution?
In the mixing chamber, when high concentrations of dissolved solids are added for mixing, droplets can form on the chamber surface.
These can then grow and grow, until they then drop off into the chamber's vortex and the droplet is carried into the flame.
However, this droplet could be millions or billions of times the size of the droplets that are emitted from the nebuliser, which can then be heated by the flame.
Of course, this would emit a huge spike in emissions from the sample.
Essentially, the stability of the flame is more of an artform than a science and is a balancing act between so many different variables.