A Brief Guide To The Inner Workings of a Flame Photometer.
A Flame Photometer is made up of what is primarily a main column of working parts supported by electrical control chips for the operation of the unit. A simple flame photometer consists of the following basic components:
1. A flame that can be maintained in a constant form and at a constant temperature: “The Burner”.
2. A means of transporting a homogeneous solution into the flame at a steady rate: “Nebuliser and mixing chamber”.
3. A means of isolating light of the wavelength to be measured from that of extraneous emissions: “Simple colour filters” (interference type).
4. A means of measuring the intensity of radiation emitted by the flame: “Photo detector”.
First we must overcome the difficulty in introducing the sample to the flame in a consistent and effective manner. For this a nebuliser is utilised. The nebuliser is a small bore needle in which a liquid sample is consumed by a jacket of high pressure air passed around it. This causes the liquid sample to be not only be drawn up from the sample pot using the basis of venturi but also atomised into a fine mist when passed through a small orifice at the end of the device. The process of obtaining a fine mist is quintessential to the accuracy of the instrument and is the heart of the instruments repeatability, accuracy and stability. Here at BWB Technologies we have invested hundreds of man hours and thousands of pounds in order to design one of the best nebulisers on the market.
After sample atomisation the sample passes into the mixing chamber; here the fuel gas is typically mixed into the sample mist. Again the design of the air flow within the mixing chamber is another area of paramount importance to generate results within tight specifications. A cyclone action is utilised to thoroughly mix the gases which avoid causing hot spots of higher fuel concentrations in the mixture, as these would cause greater and random emissions in the flame, thus affecting stability and repeatability. The design of the BWB Technologies mixing chamber stems back to our company foundation in 2005 and now leads the market in its construction, chemical resistance and operation.
The Burner head finally combines the mixture of gas, air and vapour sample into an emission spectra from a flame burning at approximately 1900°C. The burner assembly is another area of great design work, as it must not only warm up rapidly and maintain a constant temperature but also ensure that velocities and burn rate are such that blow back of the flame cannot occur, for operational safety. Most instruments include a viewing port allowing the operator to observe the flame conditions and set the height of flame. The BWB Technologies burner assembly is constructed from high performance grade stainless steel and expertly machined to high tolerances using CNC lathes. This ensures that every burner performs to our high standard.
The Sensor array is a collection of photodiodes. These photodiodes are what turn the physical light emission into a pulse of electrical energy which can then be processed by the instrument. Photodiodes however, cover a large range of wavelengths and so to ensure only the required wavelength is collected they are typically installed behind an inference filter. The interference filter is produced to only allow a specific range of light to pass through. Through research and experimentation BWB Technologies have put in place a set of design parameters which set our diodes to specific wavelengths to pick up samples of light emission with minimal spectral overlap between different ions spectral emissions.
Once the light has been converted to an electrical signal it needs displaying in a form appropriate for user interpretation. Typically analogue instruments convert the electrical signal into a number based on intensity. Older flame photometers then display this number for the operator to plot up on their own calibration curve, whereas other instruments may display the number as a concentration relative to a calibration curve pre-generated. However, the BWB Technologies’ range of flame photometers are microprocessor controlled. The BWB XP Plus instrument allows the operator to produce self-defined calibration curves across the 4 detectable elements with up to 10 points of calibration per Ion. Furthermore, the 4 elements can all be calibrated simultaneously using multi Ion calibration standards thus drastically reducing operation time. The employment of microprocessor technology allows the XP Plus to adjust the calibration curve automatically making allowances for changes in atmospheric conditions or sample temperatures through the use of an internal standard (Internal reference). In the XP Plus instrument this can be Lithium or the fifth channel of operation, Caesium.
For more information on the range of BWB Technologies Flame Photometers please Contact Us.