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  • The BWB Team

Flame Photometer or Spectrophotometer: What is the difference?

Flame Photometers and Spectrophotometers are both analytical instruments used in the process of chemical analysis. They differ significantly in their principles of operation, and the type of measurements they can make. Each, however, has its particular niche to fill, and both are great at what they do!

The Flame Photometer

This instrument is used to measure the concentration of some specific metal ions in a solution. It is specifically designed to analyse the

concentration of alkali metals (such as sodium, potassium, and lithium) and alkaline earth metals (such as calcium and barium) in a given sample. The principle behind a Flame Photometer's operation is based on the characteristic emission of light by these metal ions when they are heated in a Flame. This is also known as the principle of atomic emission spectroscopy.

How it works

A sample is introduced, suspended in a liquid carrier via an extremely fine tube encircled by a high pressure airstream, to a tightly controlled Flame. The liquid sample is atomised by the sheering forces of the airstream. The heat produced by the Flame instantly evaporates the carrier and the metal atoms are left to absorb the resultant heat, exciting the atom’s electrons.

This raises the valence electrons to higher energy levels and they jump to a higher energy state (orbital). Since this excited state is unnatural, they drop back down to the ground state and emit a photon to rid themselves of the excess energy.

This photon produces visible light at very specific wavelengths characteristic of each metal. Every substance has a different and unique pattern of emissions.

A set of filters (or a monochromator) is used to isolate the strongest and most uniquely identifying wavelengths of interest for each metal. The intensity of the emitted light at that selected wavelength is directly proportional to the concentration of the metal ion in the sample.

Consequently, by comparing the intensity of the emitted light to a set of known standards, the concentration of the metal ion can be determined, correlating it (quantitatively) to the amount of the metal ion concentration in the sample.


Flame Photometers are regularly used in clinical laboratories, for wastewater and environmental monitoring, and for agricultural testing to measure the soil or growing medium concentration of specific metal ions.

The Spectrophotometer

A Spectrophotometer, on the other hand, is a more versatile instrument used to measure the absorption or transmission of light by a sample at different wavelengths. Its samples need not be in a liquid state like a Flame Photometer. In fact, it can analyse a wide range of substances, including coloured compounds, biomolecules, and even chemical reactions that involve light absorption or emission.

How it works

The Spectrophotometer consists of a light source, a monochromator, a sample holder (cuvette), and a detector. Its light source emits a broad spectrum of light including ultraviolet, visible, or infrared.

Similar to some models of Flame Photometer, the Spectrophotometer uses a monochromator to isolate a very specific wavelength of light to illuminate the sample. The sample absorbs some of the incident light at the selected wavelength, and the remaining light passes through the sample to reach the detector.

The detector “knows” the value of the original source light and after measuring the intensity of the transmitted light, determines the value of the absorbed light. This data is subsequently used to calculate the overall absorbance or transmittance of the sample. This can be repeated with many different frequencies of light to create a detailed map of the sample’s qualities.

Spectrophotometers are widely used in analytical chemistry to determine the concentration of a substance by measuring the absorption or transmission of light by the sample at a specific wavelength. The relationship between the concentration and the amount of light absorbed is governed by the Beer-Lambert law.

It can also be used to identify substances based on their characteristic absorption spectra. As noted, different compounds have unique absorption patterns, allowing scientists to identify unknown substances in a sample.

As a result, Spectrophotometers lend themselves to be used in both qualitative and quantitative analysis, depending on the needs or application.


Spectrophotometers enjoy extensive applications in a number of fields, including chemistry, physics, DNA and protein analysis, biochemistry, biology, environmental science for pollution and water quality, molecular biology, pharmaceuticals, and numerous other scientific areas.

They are also useful in industrial applications, such as the textile industry, paints, and the food industry to measure the colour of substances and products. They are frequently used to determine the concentration of various analytes, to study the kinetics of chemical reactions, in enzyme-catalysed reactions to measure enzymatic activity, and to classify or identify unknown compounds—and the list goes on and on… Surprisingly, they are even used in astronomy to assess how far light has travelled to get to Earth.

The Takeaway

Flame Photometers are widely used in various fields, including environmental analysis, agricultural research, clinical chemistry, and industrial quality control. They are especially valuable in laboratories for rapid and accurate measurement of metal ions, and they offer a cost-effective alternative to more complex and expensive analytical techniques for these specific elements. Flame Photometers excel in biomedical applications and uses where fast (and often “bulk”) identification is needed for a very specific range of substances.

Spectrophotometers, on the other hand, are more useful for identifying a much broader range of solid substances or things that don’t lend themselves to being in a liquid state. While this application could be useful in a hospital setting, for example, finding excessive lead concentration in a bone sample, it is a comparatively slow process designed for diagnostics over an extended period.

In comparison, Flame Photometers offer virtually instant results which, in that scenario, could save lives when time is of the essence. What we can conclude is that both Flame Photometers and Spectrophotometers are useful; both are necessary; and, in fact, they do not conflict in function.

In essence, the main difference between the Flame Photometer and the Spectrophotometer is in how they are used and the types of measurements of which they are capable.

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