Improved δ13C analysis of amino sugars in soil by ion chromatography-oxidation-isotope ratio mass spectrometry

RATIONALEAmino sugars build up microbial cell walls and are important components of soil organic matter. To evaluate their sources and turnover, C-13 analysis of soil-derived amino sugars by liquid chromatography was recently suggested. However, amino sugar C-13 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. METHODSAfter acid hydrolysis of soil samples, the extract was purified from salts and other components impeding chromatographic resolution. The amino sugar concentrations and C-13 values were determined by coupling an ion chromatograph to an isotope ratio mass spectrometer. The accuracy and precision of quantification and C-13 determination were assessed. RESULTSInternal 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 C-13 values. This correction improved the accuracy of the determination of C-13 values to <1.5 and the precision to <0.5 parts per thousand for basic and acidic amino sugars in a single run. CONCLUSIONSThis method enables parallel quantification and C-13 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 (c) 2014 John Wiley & Sons, Ltd.