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Abstract

RATIONALE: Amino sugars build up microbial cell walls and are important components of soil organic matter. To
evaluate their sources and turnover, δ13C analysis of soil-derived amino sugars by liquid chromatography was recently
suggested. However, amino sugar δ13C determination remains challenging due to (1) a strong matrix effect, (2) CO2-
binding by alkaline eluents, and (3) strongly different chromatographic behavior and concentrations of basic and acidic
amino sugars. To overcome these difficulties we established an ion chromatography–oxidation–isotope ratio mass
spectrometry method to improve and facilitate soil amino sugar analysis.
METHODS: After acid hydrolysis of soil samples, the extract was purified from salts and other components impeding
chromatographic resolution. The amino sugar concentrations and δ13C values were determined by coupling an ion
chromatograph to an isotope ratio mass spectrometer. The accuracy and precision of quantification and δ13C
determination were assessed.
RESULTS: Internal standards enabled correction for losses during analysis, with a relative standard deviation <6%. The
higher magnitude peaks of basic than of acidic amino sugars required an amount-dependent correction of δ13C values.
This correction improved the accuracy of the determination of δ13C values to <1.5‰and the precision to <0.5‰for basic
and acidic amino sugars in a single run.
CONCLUSIONS: This method enables parallel quantification and δ13C determination of basic and acidic amino sugars in
a single chromatogram due to the advantages of coupling an ion chromatograph to the isotope ratio mass spectrometer.
Small adjustments of sample amount and injection volume are necessary to optimize precision and accuracy for
individual soils.