While they are both based on similar physical principles, atomic fluorescence spectroscopy (AFS) is far less common a technique than atomic absorption spectroscopy (AA). Both provide elemental composition information and rely on the specific wavelengths of light that serve to identify particular elements corresponding to the lines in their atomic spectra. In both, the sample is separated into individual atoms by a flame, and then a light source is directed into the sample. Atoms in their ground state absorb light at very specific wavelengths corresponding to quantum leaps to excited states. In an AA instrument, the detector is placed opposite the light source and directly measures how much of the incident light is absorbed, providing a measure of how much of that element is present. One difficulty of AA is that if the element of interest is only present in trace amounts, the amount of absorption is small, and it is hard to distinguish the difference between the bright incident beam and the slightly diminished beam after having passed through the sample.

In contrast, AFS is excellent for measuring trace amounts, occasionally even down to quantities in the parts per trillion range. In AFS, the detector is placed at right angles, so that it does not pick up the incident light at all. Instead of measuring the absorbance, the detector picks up the fluorescence signal due to the excited atoms jumping back down to the ground state. For trace amounts, the strength of the fluorescence signal is linearly related to the amount of the element present, making trace measurement quite accurate.

Commonly used with AFS, hydride generation is a sample preparation step that converts elements in the sample into gaseous hydrogen compounds. Using the techniques together provides the best results, but not all elements form hydrides. Although this limits the applications of AFS, many hydride-forming elements, such as arsenic and mercury, are of interest as hazards in food or the environment. Thus, the common applications for AFS include the detection of trace amounts of these elements in food and agricultural samples, environmental samples, geological samples and even clinical samples drawn from patients.

AFS inhabits a narrow market niche, with competition from inductively coupled plasma–MS (ICP-MS), which is a more widely applicable technology for trace analysis. AFS has some success with customers with very specific applications or those without access to ICP-MS.

There are many vendors of dedicated mercury analyzers that are based on AFS, but there are few vendors of general purpose AFS systems. Aurora Biomed is the leading vendor, followed closely by several Chinese or Chinese-manufactured brands: Beijing Beifen-Ruili Analytical Instrument, PG Instruments and Beijing Titan Instruments. US-based Angstrom Advanced is another participant in the AFS market. The total market demand in 2012 for general purpose AFS was less than $10 million.

Handheld and Portable NIR at a Glance:

Leading Suppliers

• Aurora Biomed

• Beijing Beifen-Ruili Analytical Instrument

• PG Instruments

Largest Markets

• Food and Agriculture

• Environmental

• Clinical

Instrument Cost

• $15,000–$40,000