A method to quantitatively trap volatilized organoselenides for stable selenium isotope analysis

Area of Science:

• Environmental Chemistry
• Geochemistry
• Microbiology

Background:

• Accurate analysis of stable selenium (Se) isotope composition in volatile organoselenides is crucial for understanding their sources and formation pathways.
• Quantitative trapping of organoselenides is essential to prevent artificial Se isotope fractionation during analysis.
• Existing methods, such as activated charcoal, have shown limitations in quantitative recovery of organoselenides.

Purpose of the Study:

• To develop and validate an efficient trap for volatile organoselenides for use in microcosm studies.
• To determine the Se isotope fractionation occurring during the microbial transformation of inorganic Se to volatile organoselenides.
• To assess the reliability of the developed trap for quantitative Se isotope analysis.

Main Methods:

• Tested the recovery efficiency of volatile dimethyldiselenide (DMDSe) using activated charcoal and alkaline peroxide solutions.
• Conducted microcosm experiments with a Se-methylating fungus, employing the alkaline peroxide trap.
• Assessed mass balances of total Se and calculated stable Se isotope values (δSe) for the supplied inorganic Se and trapped organoselenides.

Main Results:

• Activated charcoal traps recovered less than 64% of volatilized DMDSe, indicating inefficiency.
• The alkaline peroxide trap achieved a mean recovery of 96 ± 11% for volatilized DMDSe.
• Microcosm experiments using the alkaline peroxide trap yielded high Se mass balances (96-102%) and comparable δSe values between supplied inorganic Se and produced organoselenides.

Conclusions:

• The alkaline peroxide trap is a reliable method for quantitative trapping of volatile organoselenides.
• This method minimizes artificial Se isotope fractionation, enabling accurate analysis of Se isotope composition.
• The developed trapping technique facilitates the study of microbial Se cycling and the elucidation of organoselenide origins.