factory with flue gasAlthough selenium is a component of many minerals, it is only the seventieth most abundant element in the earth’s crust and occurs mostly in small crystals and in small quantities. It typically only occurs at elevated concentrations in the environment as a byproduct of anthropological activity. An essential micro-nutrient, selenium becomes toxic to most eukaryotic organisms at relatively low concentrations.

Selenium testing for total recoverable concentrations by conventional ICP-MS techniques is extremely prone to mass spectral interferences. The plasma gas (argon) and constituents of the sample matrix (calcium, carbon, chloride, sulfur, etc.) can easily combine to form polyatomic ions with the same mass-to-charge ratios as the various isotopes of selenium, resulting in false-positives and elevated detection limits.

The table below lists the different isotopes of selenium and the common interferences that can affect measurements at those isotopes.

Isotope

Interference

Source

74Se

37Cl37Cl

Chlorides can be at high concentrations in many matrices

38Ar36S

Sulfides can be at high concentrations in many matrices

76Se

40Ar36Ar

Argon dimers are formed from the ICP-MS plasma gas

76Ge

Germanium is commonly used as an internal standard

77Se

40Ar37Cl

Chlorides can be at high concentrations in many matrices

78Se

40Ar38Ar

Argon dimers are formed from the ICP-MS plasma gas

78Kr

Krypton is a common contaminant in an argon gas supply

38Ar40Ca

Calcium can be at high concentrations in many matrices

80Se

40Ar40Ar

Argon dimers are formed from the ICP-MS plasma gas

32S16O3

Sulfides can be at high concentrations in many matrices

82Se

82Kr

Krypton is a common contaminant in an argon gas supply

40Ar42Ca

Calcium can be at high concentrations in many matrices

12C35Cl2

Chlorides can be at high concentrations in many matrices

34S16O3

Sulfides can be at high concentrations in many matrices

 

Without an analytical technique to eliminate the interferences that lead to elevated results, decision makers might be acting on inaccurate data.

At Brooks Applied Labs, we employ ICP-MS instruments equipped with both dynamic reaction cell (DRC) and collision cell interference reduction technologies to overcome mass spectral interferences and thereby produce highly accurate data in even complex matrices. With these types of interference reduction technologies, gas-phase reactions take place that can remove the source of the interferences or derivatize the analyte of interest to a mass that won’t be mistaken for one of the common interferences.

Selenium Speciation
While selenium’s basic biogeochemistry determines its natural distribution in the environment, historically, research on selenium has focused almost exclusively on total selenium concentrations in soils, sediments, water, and plants. Whereas such data is invaluable in establishing relative concentrations, it does very little to further understanding of how selenium cycles through the environment and the ultimate fate and effect of the rapidly increasing quantities being introduced by modern agricultural, mining, and energy generation practices. Individual inorganic selenium valence states and organic selenocompounds can exhibit entirely different characteristics. Furthermore, bioavailability and therefore toxicity are highly contingent on the selenium species in question.

An understanding of which selenium species are present in a wide range of matrices, including water, soil, sediments, wildlife, pharmaceuticals, dietary supplements, human urine, blood, and serum, and industrial wastewater streams, can be crucial when making important decisions regarding human health and the environment.

Brooks Applied Labs offers highly advanced analytical services for the determination and characterization of selected selenium species by our customized methods coupling ion chromatography (IC) with inductively coupled plasma – mass spectrometry (ICP-MS), employing optimized dynamic reaction cell (DRC) parameters. This IC-ICP-MS configuration allows for multi-element and multi-isotopic detection, high sensitivity, a wide linear dynamic range, and minimal polyatomic interferences. This allows us to separate and quantify selected selenium species (e.g., selenite, selenate, selenocynate, etc.) in even the most complex matrices while maintaining ultra-low detection limits.

Brooks Applied Labs has some of the lowest detection limits commercially available to our clients for selenium speciation. View our MDL & MRL Table.