Improved δ¹³ C analysis of amino sugars in soil by ion chromatography-oxidation-isotope ratio mass spectrometry

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. Copyright © 2014 John Wiley & Sons, Ltd.