Atomic fluorescence spectroscopy (AFS) is an interesting wrinkle on atomic absorbance spectroscopy (AA), a much more common technique. AFS has certain advantages for measuring trace amounts of particular elements that allow the technique to flourish in some niche applications.

As their names indicate, AFS and AA differ in the kind of light measurements they make. In AA, the amount of light absorbed by the sample is measured, while in AFS, the fluorescent signal is measured. In both cases, the sample is ionized by a flame, and then a light source (typically a hollow cathode lamp, which are commonly manufactured to select a particular element of interest) is directed into the energized sample. Depending on their electronic structure, atoms absorb light at very specific wavelengths corresponding to quantum transitions to excited states. When the energized atoms release this energy, this process results in the fluorescent light that is the measured signal.

One advantage of AFS is that the detector can be placed out of the path of the original light source, so that the only light reaching the detector comes from the fluorescent signal, allowing trace detection in a straightforward manner without the complication of the bright incident light. The strength of the fluorescent signal is essentially linearly correlated with the concentration of the selected element in the sample, providing the means of measurement. While many instruments are single channel, others can be upgraded to measure 2 or 3 elements simultaneously, or to perform speciation analysis.

AFS is nearly always used in concert with a hydride generation apparatus. This is a sample treatment step that forms gaseous hydride compounds of certain elements. Elements that form hydrides include a number that are important for environmental applications, including arsenic, mercury, cadmium, antimony and others. The combination of hydride generation and AFS can enable these instruments to detect trace quantities of some of the elements in the parts per trillion range, rivaling the limits for more expensive techniques, such as ICP-MS. Because of its affordability, AFS appeals to customers that have particular interests in the hydride-forming elements, or who otherwise cannot afford or obtain access to ICP-MS technology.

The known human health hazards posed by many of these hydride-forming elements results in the use of the technique in many areas that have, broadly speaking, an environmental focus. Probably the most common use is for detecting trace amounts of these hazardous elements in food samples. General environmental testing is also common, and there are also uses in mining not only for environmental safety, but for quantifying precious metals in ore and other metallurgical applications. Safety of water and pharmaceutical products are also common applications.

There are many vendors of dedicated mercury analyzers that are based on AFS, but there are few vendors of the more general purpose AFS systems considered here. Aurora Biomed is the leading vendor. Because of the low-cost aspect, the Chinese market is quite substantial and many of the other players in the market are Chinese firms, including the next two largest vendors. In addition to lab systems, Beijing Beifen-Ruili Analytical Instrument (under its Rayleigh brand) offers a portable AFS system, as well as a chromatography-AFS system. Titan Instruments is the third most significant vendor. Other market participants include Angstrom Advanced, Hunan Xiangnan Chemicals and PG Instruments.  The total market demand for general purpose AFS was about $15 million in 2018.

Atomic Fluorescence at a Glance:

Leading Suppliers

• Aurora Biomed
• Beijing Beifen-Ruili Analytical Instrument
• Titan Instruments

Largest Markets

• Food and Agriculture
• Environmental
• Metals and Mining.

Instrument Cost

• $10,000–$40,000