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  • The BWB Team

Flame Photometer vs. Colorimeter: What’s the difference?

Flame photometers are wonderful devices, as you almost certainly know if you’re reading this. Colorimeters preceded them and were one of the very first techniques for spectroscopic analysis. In fact, the Duboscq colorimeter was invented by Jules Duboscq in 1870, more than 150 years ago, and it was a surprisingly accurate device.

For those of a more technical mind (though it is not necessary to understand the operation), it operated by using Beer’s Law (A=ebc, where “A” represents absorbance, “e” the molar absorptivity of a solution, “b” the path length of the light, and “c” the molar concentration).

In more pedestrian terms, it compares the colour of two solutions by matching ones visual appearance with a solution of known properties. Although it resembles a microscope, its function is different. It shows (visually) through a single eyepiece half an image of both solutions backlit by a uniform light source.

The samples sit on independent stages that can be moved up and down by the two knobs on either side. The investigator adjusts the distance of the test substance until the colour of the two samples match, and then by calculation (or a built in scrolling chart of common tests carried out) can determine the overall concentration of the test substance.

The final determination, measured in millimetres and all made by eye, looks at purity, brightness, and hue. Despite this, it only has an uncertainty of 0.1 mm per 50mm, or effectively, a 0.2% error rate! That is utterly astonishing considering the basic technology that they were working with…

Not satisfied with being amazing for their time, colorimeters could be modified to become pH meters, haemoglobinometers (to quantify haemoglobin in blood), and nephelometers (to measure light scattered by aerosols). As colorimeters however, since standard samples had to be prepared for each test, it became popular to use glass filters of known density in place of a standard solution to speed the whole process up.

Eventually spectrometers using visible light, and digital spectrophotometers, using everything from infrared (IR) to ultraviolet (UV) arrived on the scene, helping to eliminate even the modest human error factor. As discussed in earlier articles, this is accomplished with the use of monochromators, prisms, and grids to isolate one specific identifying trait (colour) or a narrow band of selected wavelengths to uniquely identify a specific substance.

All-in-all, the methods of Flame Photometry, Spectrophotometry, and Colorimetry give acceptable results in bioassays. Notably, Flame photometry is less prone to calibration drift (essentially negligible), electrode protein contamination (noted in Ion Selective Electrode, or ISE methods), slow response times, insensitivity, costliness, or complexity. Flame Photometry’s key words are often cited as fast, easy, quick-to-learn, cheap, accurate, and simple.

Colorimetry is involved with colour determination in innumerable industries, from determining the colour of the labelling on your chocolate bars or soda pop cans all the way up to transmissivity through a liquid medium to determine what chemicals are present, and in what amounts.

Of course this all involves filters and preparing standard samples and is limited to checking a single substance in a sample per sample run. Furthermore, it is only really useful for coloured substances. Putting salt in water does not imbue it with any noteworthy colouration, so good luck detecting sodium!

Strictly speaking, of course, you can detect sodium with colorimetry, but it requires special preparation. This might include (for example) adding β-galactosidase to create an intermediate product that when combined further with a “developer” results in a measurable colour.

Obviously this added effort makes the advantages of Flame Photometry abundantly clear. Just as importantly, however, is the limitation of “one test for each substance” which can really slow the process down. The most modern Flame Photometers from BWB are capable of testing for all five of the alkali and alkali-earth metals simultaneously, significantly streamlining the process.

The portability of a flame photometer is a useful trait, too. Our robust field units like the BWB SOIL actually end up in fields—farmer’s fields—taking in situ readings on the back of a pickup truck to give much more specific appraisals for the changing chemical topography of farmland. Hilltops having more sun and lowlands having copious amounts of water mean significant variations in soil nutrients.

Similarly, portable units can be brought to effluent waters from treatment plants, or to any stage of treatment before the water is returned to the environment. All that is required is mains power and gaseous fuel, both of which can be produced or carried in a typical vehicle, meaning you can use out flame photometers just about anywhere.

The Takeaway

Colorimetry is a scientific technique used for substances (even solids) where light can pass though, compared with another known source, and the results extrapolated. By seeing which frequencies of light are absorbed compared to a plain sample, it can be determined which substance is present and its quantity.

It needs, by definition, to have some colour to it. That often involves extra steps for the detection of liquid bioassay type substances containing things like sodium and potassium.

Spectrophotometry’s biggest advantage is that you don’t need to destroy the sample in order to test it. This can be useful where only tiny irreplaceable samples are available, but that is not particularly common.

Flame Photometry, once again has its watchwords: fast testing, easy to accomplish & quick-to-learn, inexpensive with few consumables, highly accurate, simple, and reliable.


Combined with its low investment cost and inexpensive upkeep, flame photometers are a long term asset, cheap enough to have multiple units in a single lab. Similarly, portable units in your fleet of sales or maintenance vehicles can provide convenient and loyalty-winning on-the-spot testing for your customers.


You can really set yourself apart from the rest of the sales crowd. Whether you’re marketing seeds and fertiliser, water quality testing, or testing sugar milling quality, that instant result, right in front of your customer’s eyes will keep them coming back to you for a level of service they cannot obtain elsewhere!

Be better than your competitors! Give us a call today and let our BWB Flame Photometry experts make you stand head and shoulders above the crowd. We’d love to hear from you!


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