The history of the flame photometer – from invention to modern-day use
Updated: Sep 18
Before the Instrument: 1556 to 1854
Long before anyone built a flame photometer, a German metallurgist named Georgius Agricola commented on "the colour of fumes" from different types of ores in a paper published in 1556, a qualitative analysis of flame colour to work out what an ore contained.
The idea wasn't picked up again for two centuries, until Isaac Newton began investigating light and its properties in the early 1700s, and a further century passed before scientists began investigating the spectral lines in light from the sun, in the 1800s.
William Herschel studied the emissions of an alcohol lamp in 1823, the first time a lamp's own light emission had been studied this way - more on his specific contribution in our dedicated piece on Herschel. Around the same period, early chemical analysis had roots in biology too; colorimetry, a related technique for analysing coloured chemicals, was originally designed by a biologist to study flowers.
It then took Foucault to make the first link between sodium emissions from a lamp and sodium emissions from the sun. The major breakthrough came from Kirchhoff, who established that the relationship between a body's powers of emission and absorption, for rays of the same wavelength, is constant for all bodies at the same temperature.
In 1854, Bunsen, inventor of the Bunsen burner, and Kirchhoff collaborated on this idea and are credited with founding analytical spectrometry, work that went on to reveal new elements on the periodic table.
1873: The First Instrument
Chemists analysing concentration in this period were largely limited to titration, a method that struggled with certain metal ions, sodium among them. Pierre Jules César Janssen, the first scientist to identify helium from his solar observations, proposed a method to detect other elements, including sodium. Three years later, in 1873, that proposal inspired Paul Champion, Henri Pellet and Jean Charles Marie Grenier to build the first instrument specifically designed for quantitative analysis using flame excitation.
Their method used two ethanol lamps side by side. One was fed a sample of sodium plant ash, dissolved in water and nitric acid and then filtered. The other was fed a series of calibration standards, made by dissolving solid sodium into water. The two flames were compared, using a spectroscope with visual photometry, the spectra displaced so both could be observed at the same time.
It couldn't report a precise parts-per-million figure, but it could reliably show a detectable difference between samples, and the authors reported an accuracy of two to five per cent for sodium in plant ash, a genuine, if imprecise, quantitative method.
1877: Solving the Accuracy Problem
The 1873 method had one serious flaw; there was no way to accurately judge the intensity of light emitted, beyond the naked eye, and no one had yet realised that the quantity of sample introduced to the flame had as much influence on the result as its concentration did.
In 1877, Louis Georges Gouy identified this problem and solved it, designing a pneumatic atomiser that introduced a set, controlled quantity of sample and standard into the flames at the same time. This was the first instrument for the quantitative analysis of sodium in water samples. Gouy also developed an early mathematical model showing that the intensity of radiation from a flame is directly proportional to the size and concentration of the sample, improving accuracy to consistently better than two per cent. The method was still tedious, done by eye and requiring standards to be remade often, but it was, for its time, a real leap forward.
1946 to 1963: The Modern Instrument Takes Shape
It took until 1946 for the technology to catch up. Barnes, Richardson, Berry and Hood developed a reasonably modern version of the flame photometer, capable of measuring both sodium and potassium with good reliability. Material shortages at the close of the Second World War meant only a handful of test machines were ever built. The design already had the now-familiar atomiser, a colourless flame, pressurised air, reference calibration samples, and filters, reporting results via a galvanometer reading the voltage produced by filtered light reaching a photocell, a surprisingly accurate method for its time.
Progress continued quickly from there. By 1950, J.W. Severinghaus and J.W. Ferrebee had worked out how to determine calcium levels in biological materials including urine, blood and serum. By 1953, barium could be detected fairly precisely. By 1962, a good method existed for identifying strontium down to as little as 0.001 parts per million. By 1963, a reliable method for detecting lithium had been developed too, along with an amplification technique capable of similarly low concentrations.
Today
Modern instruments use photomultiplier tubes and photodiode arrays to capture emitted light at very specific frequencies, quantify several substances at once, and report them all simultaneously, a long way from a pair of ethanol lamps and the naked eye. Nearly 150 years after Champion, Pellet and Grenier's first working instrument, this invention is still being developed further; at BWB Technologies we continue to push the boundaries with our Origin and Flash series flame photometers.
