Flame Photometry and Temperature
How flame temperature affects your samples.
We have written about the mechanism of photon emission from Ions in a previous segment, however, we wanted to give this grounding and show how it is effected by physical parameters that you can control, here’s a quick refresher. The process of excitation is a constant “flickering” effect where the ion is excited and relaxed. During the excitation stage the ion takes in ambient energy to promote the ion to a higher energy state and then at relaxation the ion releases the energy as a photon of light equivalent to the drop in energy states.
The temperature of the flame is essential to promote the excitation of the ions and therefore emit a photon; this is where the energy for the excitation process comes from. As flame temperature is increased, it is not that the emission of the single photon is given a more energy from the flame, or the electron is excited to a higher energy state than a lower one. This is because atoms and ions have set energy states that they can achieve.
Therefore, the intensity of the flame emission is not a “larger” jump but a higher ratio of ions that are in the excited state compared to the relaxed state thus resulting in a greater quantity of the relaxation process emitting more photons for the photodiode to detect. In short – a hotter flame means greater emission spectra.
An increase in flame temperature can also help reduce contaminants and interfering species that alter the ion’s energy quantum levels and therefore the wavelength of emission. Let’s look at Calcium Phosphate for example. Calcium Phosphate is known to give a much lower reading of calcium in a sample, however, is very strongly bonded together. The energy given from a standard air and propane flame is not sufficient to break the Calcium to Phosphate ionic bond. Let’s say theoretically we were to use a mixture of an oxidiser and acetylene gas, this would burn at a much greater temperature and would break the ionic bond and eliminate the reduction of the emission caused by the phosphate interference.
Other suitable means of increasing flame temperature whilst using an air and propane flame are through the introduction of organic solvents which burn in the flame and boost the flame temperature. This is a huge reason why matrix correction in samples is vital. Having a sample of wine and not treating your standards with the same % of alcohol that is found in the wine would result in the flame temperature being higher in the sample than that of the standards. Hopefully having read through this you’ll now have an understanding as to why this would impact on the accuracy of results obtained.
For further information on matrix solutions or application specific advice please get in touch with the BWB team who will be more than happy to help - Contact Us.