What are elemental analyzers?

An elemental analyzer is an instrument that can determine the elemental composition of a sample. The analyzer may simply determine which elements are present, or it may make a quantitative analysis to identify how much of each element is present. In some cases, isotopic composition may also be determined. Elemental analyzers are used in many applications including biological and medical samples such as blood and urine, soil analysis, environmental monitoring such as for drinking water quality, and the analysis of industrial materials.

Elemental analyzers often heat a sample until it combusts, and then analyze the composition of the combustion products in gaseous form. (The term elemental analysis is often used to refer to this combustion analysis.) However, there are also methods of elemental analysis which are suited to non-combustible materials, such as X-ray fluorescence spectrometry.

In organic chemistry, elemental analysis is synonymous with CHNX analysis. This determines the mass fractions of carbon, hydrogen, nitrogen and other substances, the X in CHNX. Typically, combustion analysis is used. Combustion analysis takes a small sample, often just a few milligrams, and instantaneously oxidizes it using flash combustion. The combustion products can then be separated using gas chromatography and analyzed using thermal conductivity detection or infrared spectroscopy.

There are many other techniques used for elemental analysis. Qualitative analysis methods, which simply detect which elements are present, include atomic spectroscopy, X-ray fluorescence spectrometry, and Scöhniger oxidation. Quantitative methods, which determine how much of each element a sample contains, include gravimetry, neutron activation analysis, and optical atomic spectroscopy.

X-ray fluorescence spectrometry is a non-destructive technique that excites a sample with x-rays and measures the radiation re-emitted by the sample. When a substance absorbs radiation, electrons are momentarily excited to higher energy states and then drop back to their original energy state, releasing a photon. While other forms of radiation tend to interact at the molecular level and can be used to determine chemical composition, x-rays interact with inner shell electrons and therefore give information at elemental composition. Each element has its own characteristic energy that produces a photon with a unique energy, and therefore radiation at a characteristic frequency. The frequency therefore indicates the element. Spectral analysis, using fast Fourier transforms, can identify multiple elements present in the sample.

Atomic spectroscopy also works by analyzing the energy level of radiation from the sample, but it requires the sample to be vaporized and so is a destructive test. Atomic absorption spectroscopy passes light of a known wavelength through a sample and measures how much is absorbed. Atomic emission spectroscopy measures the intensity of light at a particular frequency emitted from a flame or plasma.