A flame photometer is an instrument used to measure the concentration of certain specific elements in a sample. This is based on the emission of characteristic light for each substance when nebulised (or atomised) so that it may be introduced into a stable flame. This conversion is required because the flame photometer analyses the metal ion concentrations only in the vapour phase rather than the liquid phase.
Once the water is evaporated by the flame those single atoms are electronically stimulated, not from solid state circuitry, of course, but in the very literal sense that their electrons are energised by the flame. This causes the electrons to ascend to a higher and unstable orbital position around the nucleus, but this state cannot be maintained so the electron drops back down to its normal position. In the process it emits a photon (to rid itself of the excess energy) of an extremely specific colour or frequency. This repeats endlessly as long as they are in the flame and can gain energy.
The substances that we analyse most often are the alkali metals and alkali earths Barium, Calcium, Lithium, Potassium, and Sodium. The nebuliser is one of the most vital components of the flame photometer that helps put the atoms into the right state so they can be introduced into the flame for analysis.
The nebuliser's primary function is to convert a liquid sample into a fine aerosol, which can then be easily vaporised in the flame. The sample is usually a Double Distilled (DD) water neutral solution alternated with solutions to be examined containing the elements of interest.
Nebulisers must be carefully designed and then engineered to produce absolute consistency; their outputs are critical for achieving accurate and precise measurements in flame photometry. Under-engineered nebulisers will never produce dependable, quantitative results, amounting to little more than guesswork!
Three Methodologies
Electrothermal Nebulisation
Just to be complete, we’ll mention all three types of nebulisation, though two rarely concern us. The least common is Electrothermal Nebulisation which is used to analyse solid materials that don’t lend themselves to dissolution in water or other liquid or gas carriers. By heating a sample (say a lump of coal) vapours can be created that can then be directed to the flame for analysis.
Ultrasonic Nebulisation
If you have observed a table top or desktop humidifier, you have probably seen ultrasonic nebulisation. A piezoelectric transducer sits beneath a layer of water, and generates ultrasonic vibrations. This creates waves that strongly interfere with one another and provides enough mechanical energy to kick loose molecules of water at the surface producing a dense mist. Since such units are enclosed, providing only a small outlet on top, the intrinsic pressure of constant solitary molecule creation drives the vapour out the top with no need for a fan or pump of any kind.
Although such a thing can be used for monitoring a flow, such as at a wastewater treatment plant, it is not used in the laboratory because the photometer would have to be purged and cleaned after each test requiring a shut down and reset. This is far too inefficient for a working laboratory.
Pneumatic Nebulisation
This is, of course, the optimal solution from testing dozens or hundreds of samples extremely rapidly. Utilising Bernoulli’s Principle, a high velocity stream of gas passes over a small capillary tube creating a low pressure area so that liquid flows up the small tube freely from its reservoir. When the sample reaches the compressed air stream, the sheering forces rip off individual molecules turning them into an ultrafine mist ideally suited for introduction into the detector flame. In many cases this ultrafine mist creation happens at the very base of the flame for maximum consistency.
The Takeaway
Ultimately, the flame photometer relies on the nebuliser for its function. Having created the perfect mist, the interaction with the flame produces consistent light, which is fed to a detector. This might be a photomultiplier tube or a photodiode array, which captures the emitted light, quantifies it to determine how much “test substance” is present (based on calibration curves) and produces a solid result that you can take to the bank.
Of course the best flame photometers are crated right here, at BWB, and we would be pleased to show you how you can make your lab better, faster, more accurate, and respected industry-wide for consistent results.
Call us today and let’s talk!