Nitrogen isotope analysis of free glycine in soil using isotope dilution mass spectrometry [An article from: Soil Biology and Biochemistry]

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Description:
To enable the estimation of production and consumption rates of free glycine in soils through ^1^5N isotope dilution experiments, an isotope dilution mass spectrometric method was developed. The method, which enabled high precision N isotope ratio determination of glycine in soil extracts at @d^1^5N levels up to 4000%% and concentrations from approximately 2@mM, is based on the following steps: (i) addition of glycine spike to the soil extract, (ii) removal of humic substances and pre-concentration of glycine using solid phase extraction, (iii) derivatization of amino acids, (iv) separation of the derivatives using gas chromatography (GC), (v) their combustion to yield sample N"2 gas, and (vi) finally the use of N isotope ratio mass spectrometry (IRMS). Judging by uncertainty budget calculations, the precision obtained (SD=0.01-0.06at% ^1^5N) is sufficient for detecting differences in N isotopic ratios obtained in ^1^5N isotope dilution experiments.