Guide to Elemental Analyzers

Laboratories worldwide use elemental analyzers for measuring the carbon, hydrogen, nitrogen, sulfur, oxygen, and halogen content in samples such as chemical-reaction products, soil, bodily fluids, and waste or drinking water. Benchtop elemental analyzers come in a variety of types for specific applications: total organic content (TOC), total organic halogens (TOX), nitrogen, nitrogen concentration relative to protein (nitrogen derived from protein molecules), and CHN analyzers, named after the three most common elements they measure—carbon (C), hydrogen (H), nitrogen (N).

This purchasing guide presents models of benchtop elemental analyzers currently available for the laboratory.

TOC analyzers
TOC instruments indirectly measure organic molecules in water, a popular choice for testing water quality and validating cleaning procedures. These instruments oxidize carbon in a sample and then measure the carbon dioxide produced.

A typical TOC analysis measures both the total carbon present and the inorganic carbon from dissolved carbon dioxide and carbonic acid salts. Subtracting inorganic carbon from the total carbon yields the TOC. Another common instrument version removes the inorganic carbon portion first and then measures the leftover carbon.

TOX analyzers
Common for environmental work, TOX analyzers measure total organic halogens (chlorine, fluorine, bromine, and iodine) in surface water, groundwater, wastewater, and soils to determine contamination from sources such as chlorinated pesticides and industrial solvents.

TOX analyzers are often converted to analyze absorbable organic halogen (AOX), extractable organic halogen (EOX), and purgeable organic halogen (POX).

Nitrogen analyzers
Nitrogen analyzers—instrumental alternatives to manual Kjeldahl digestion methods—feature two types: total nitrogen analyzers (TN) and nitrogen relative to protein content analyzers (N-Protein).

Monitoring the total nitrogen content (TN) from nitrates, nitrites, and ammonia is common in biological and oxygen level studies of waters and wastewaters, such as determining the effects of fertilizer runoff.

Since proteins are 16 percent nitrogen on average, measuring nitrogen content relative to protein (N-Protein)—common in food analysis—indicates protein level.

CHN analyzers
CHN analyzers determine the elemental composition of solids, liquids, and gases by measuring the carbon dioxide, water, and nitric oxide produced after sample combustion.

Beyond carbon, hydrogen, and nitrogen, some instruments also measure sulfur (S), oxygen (O), and chlorine (Cl); others specialize in identifying only one or two elements, such as H and CS analyzers. CHN analysis has traditionally determined the empirical formula of unknown organic compounds in biology and synthetic chemistry labs.

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