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In the field of analytical chemistry, knowing what is present in a given sample is essential for its analysis. Therefore, many different processes and types of equipment are used in this field. This article will provide an overview of elemental analysis and how one of the common technologies employed, the elemental analyzer, works.
What is Elemental Analysis?
Elemental analysis is the process where a sample of material is analyzed for its elemental composition. It can also provide information on the isotopic composition of a substance. Examples of samples that this process can analyze include chemical compounds, minerals, bodily fluids, and waste/drinking water.
Elemental analysis can be both qualitative and quantitative. Many different techniques can be employed by analytical chemists for both types of analysis. For qualitative analysis, methods include atomic spectroscopy, X-ray fluorescence, and Scöhniger oxidation. Quantitative methods include gravimetry, neutron activation analysis, and optical atomic spectroscopy.
The field of elemental analysis can be traced back to Antoine Lavoisier, who is widely considered the father of modern chemistry. At the time, elemental analysis was based on the gravimetric determination of samples before and after the adsorption of combusted gases. Today, elemental analysis can be carried out by fully automated systems.
Elemental analysis (EA) commonly refers to CHNX analysis. This is the determination of the fractions of the mass of carbon, hydrogen, nitrogen, and heteroatoms (X). Heteroatoms include halogens and sulfur. Analysis of these elements is important to tell the structure of an unknown compound or elucidate the purity and structure of a synthesized one. Other elements can be analyzed with the right equipment.
What is an Elemental Analyzer?
An elemental analyzer is a piece of equipment that provides information on the elements which make up a target sample. A sample is superheated to the point at which it instantly becomes a gas, and it is this gaseous form that passes through the analyzer’s mechanism.
While other techniques such as chromatographic procedures and mass spectrometry are now the primary techniques for structural determination, EA still gives valuable complementary information for analytical chemists. Elemental analyzers are also faster and less expensive than the alternatives. In addition, they are capable of handling a wide variety of samples, including solids, liquids, and volatile compounds.
Elemental analyzers have found use in many fields. For example, in the oil industry, they are used to regularly monitor coke build-up on refinery catalysts to ensure optimal operation parameters. In the food industry, they determine nitrogen (as protein surrogates) in foodstuffs to evaluate grain pricing and meat products.
How Does an Elemental Analyzer Work?
Elemental analyzers work by heating an element quickly to a sufficiently high temperature so that it combusts. It is then passed through the analyzer in its gaseous state. A detector detects the elements present, and the researcher reads this information on a computer screen.
Analyzers are commonly constructed in a modular form which means they can be set up to determine different elements. This modular set-up provides the flexibility of operation and the ability to use a wide range of sample weights, from a few milligrams to several grams of the target substance. For example, in CHNS (carbon, hydrogen, nitrogen, sulfur) analyzers, they can be set up to analyze N, CHN, CHNS, or any combination thereof, thanks to this modular nature.
The choice of instrumentation depends on the elements, sample type, sample size, and concentration of the analyte. For example, the sample introduction system is highly dependent on sample type and application. Solids and viscous liquid are introduced in a capsule. Liquid samples can either be sealed in individual vials or introduced via a liquid auto-sampler. A microbalancer may be required to allow automatic recording of each test portion’s weight. Ash from the combustion process must be removed along with other impurities to avoid interference with analysis results.
Two gas supplies are required: an inert carrier gas (usually helium) and high purity oxygen for combustion. Helium removes gas for the next stage in the process. They are then passed over heated high-purity copper to remove any additional oxygen and convert any nitrogen oxides to nitrogen gas. Passing the gases through absorbent traps leaves only water, nitrogen, carbon dioxide, and sulfur dioxide.
Some instruments house the combustion and reduction stages in separate furnaces, while others carry them out in a single two-tier furnace. Catalysts, copper, and absorbents are packed into exchangeable tubes made of high-quality silica or ceramics.
There are a variety of ways the detection of gases can be carried out. These include a gas chromatography (GC) separation followed by quantification using thermal conductivity detection or a series of separate thermal conductivity and infra-red cells to detect individual compounds. Calibration for quantification of each element is carried out using high-purity compounds such as benzoic acid and acetanilide.
Control of the equipment is carried out via a computer interface. This is used to set up the work program, manage the calibration procedures, and provide diagnostics information on the equipment itself. Finally, dedicated software offers readings on the level of analytes present in the sample.
Elemental analyzers are reliable, cost-effective pieces of laboratory equipment used in a wide variety of industries. As a result, they will no doubt find application in the field of analytical chemistry for many years to come. Used in conjunction with other analytical techniques, they are a cornerstone of the modern laboratory.
Further Reading and More Information
Royal Society of Chemistry (Website) AMC technical briefs – CHNS Elemental Analysers [Accessed online 21 April 2021] https://www.rsc.org/images/CHNS-elemental-analysers-technical-brief-29_tcm18-214833.pdf
Chem.libretexts.org (Website) 1:1 Introduction to Elemental Analysis [Accessed online 21 April 2021] https://chem.libretexts.org/Bookshelves/Analytical_Chemistry/Book
Chem.libretexts.org (Website) 1:3: Introduction to Combustion Analysis [Accessed online 21 April 2021] https://chem.libretexts.org/Bookshelves/Analytical_Chemistry/Book