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Elemental analysis is a process where a sample of some material (e.g., soil, waste or drinking water, bodily fluids, minerals, chemical compounds) is analyzed for its elemental and sometimes isotopic composition. Elemental analysis can be qualitative (determining what elements are present), and it can be quantitative (determining how much of each is present). Elemental analysis falls within the ambit of analytical chemistry, the instruments involved in deciphering the chemical nature of our world.


History

Antoine Lavoisier is regarded as the inventor of elemental analysis as a quantitative, experimental tool to assess the chemical composition of a compound. At the time, elemental analysis was based on the gravimetric determination of specific absorbent materials before and after selective adsorption of the combustion gases. Today fully automated systems based on thermal conductivity or infrared spectroscopy detection of the combustion gases, or other spectroscopic methods are used.


CHNX analysis

For organic chemists, elemental analysis or "EA" almost always refers to CHNX analysis—the determination of the mass fractions of carbon, hydrogen, nitrogen, and heteroatoms (X) (halogens, sulfur) of a sample. This information is important to help determine the structure of an unknown compound, as well as to help ascertain the structure and purity of a synthesized compound. In present-day organic chemistry, spectroscopic techniques ( NMR, both 1H and 13C),
mass spectrometry Mass spectrometry (MS) is an analytical technique that is used to measure the mass-to-charge ratio of ions. The results are presented as a ''mass spectrum'', a plot of intensity as a function of the mass-to-charge ratio. Mass spectrometry is use ...
and chromatographic procedures have replaced EA as the primary technique for structural determination. However, it still gives very useful complementary information. It is also the fastest and most inexpensive method to determine sample purity. The most common form of elemental analysis, CHNS analysis, is accomplished by combustion analysis. Modern elemental analyzers are also capable of simultaneous determination of
sulfur Sulfur (or sulphur in British English) is a chemical element with the symbol S and atomic number 16. It is abundant, multivalent and nonmetallic. Under normal conditions, sulfur atoms form cyclic octatomic molecules with a chemical formula ...
along with CHN in the same measurement run.


Quantitative analysis

Quantitative analysis determines the mass of each element or compound present. Other quantitative methods include gravimetry, optical atomic spectroscopy, and
neutron activation analysis Neutron activation analysis (NAA) is the nuclear process used for determining the concentrations of elements in many materials. NAA allows discrete sampling of elements as it disregards the chemical form of a sample, and focuses solely on atomic ...
. Gravimetry is where the sample is dissolved, the element of interest is precipitated and its mass measured, or the element of interest is volatilized, and the mass loss is measured. Optical atomic spectroscopy includes flame atomic absorption,
graphite furnace atomic absorption Graphite furnace atomic absorption spectroscopy (GFAAS) (also known as Electrothermal Atomic absorption spectroscopy (ETAAS)) is a type of spectrometry that uses a graphite-coated furnace to vaporize the sample. Briefly, the technique is based on ...
, and inductively coupled plasma atomic emission spectroscopy, which probe the outer electronic structure of atoms. Neutron activation analysis involves the activation of a sample matrix through the process of neutron capture. The resulting radioactive target nuclei of the sample begin to decay, emitting gamma rays of specific energies that identify the radioisotopes present in the sample. The concentration of each analyte can be determined by comparison to an irradiated standard with known concentrations of each analyte.


Qualitative analysis

To qualitatively determine which elements exist in a sample, the methods are mass spectrometric atomic spectroscopy, such as inductively coupled plasma mass spectrometry, which probes the mass of atoms; other spectroscopy, which probes the inner electronic structure of atoms such as X-ray fluorescence, particle-induced X-ray emission, X-ray photoelectron spectroscopy, and
Auger electron spectroscopy file:HD.6C.037 (11856519893).jpg, A Hanford Site, Hanford scientist uses an Auger electron spectrometer to determine the elemental composition of surfaces. Auger electron spectroscopy (AES; pronounced in French) is a common analytical technique us ...
; and chemical methods such as the
sodium fusion test The sodium fusion test, or Lassaigne's test, is used in elemental analysis for the qualitative determination of the presence of foreign elements, namely halogens, nitrogen, and sulfur, in an organic compound. It was developed by J. L. Lassaigne. T ...
and Schöniger oxidation.


Analysis of results

The analysis of results is performed by determining the ratio of elements from within the sample and working out a chemical formula that fits with those results. This process is useful as it helps determine if a sample sent is the desired compound and confirms the purity of a compound. The accepted deviation of elemental analysis results from the calculated is 0.3%.


See also

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Dumas method of molecular weight determination The Dumas method of molecular weight determination was historically a procedure used to determine the molecular weight of an unknown substance. The Dumas method is appropriate to determine the molecular weights of volatile organic substances that ...


References

{{Branches of chemistry Analytical chemistry Materials science