元素分析計-同位体比質量分析計による有機物試料の炭素・窒素・酸素安定同位体比分析の試験所間比較

摘要

The elemental analyzer-isotope ratio mass spectrometer (EA-IRMS) has become increasingly important as a potential powerful tool for food authenticity. However, the lack of a reliable technique for the isotope ratio measurement, and limited availability of adequate international references are significantly regrettable, and should be improved immediately. Here we present results of an inter-laboratory test on the EA-IRMS determination of stable carbon, nitrogen and oxygen isotopic compositions (δ~(13)C, δ~(15)N and δ~(18)) in organic compounds. Three organic compounds (L-alanine for δ~(13)C and δ~(15)N, and 1,2,3,4,6-penta-O-acetyl-α-D-glucopyranose and Dimethyl aminoterephthalate for δ~(18)O) were distributed and analyzed by a total of 25 laboratories. The results show that the 1σ standard deviation among laboratories is -11.9 ±0.2 ‰ (for δ~(13)C), -2.6±0.3‰ (for δ~(15)N), +32.3 + 1.0 ‰ (for δ~(18)O of the glucopyranose derivative), and + 25.9 ± 2.3 ‰ (for δ~(18)O of Dimethyl aminoterephthalate). Although the variations of the standard deviations for δ~(13)C, δ~(15)N and δ~(18)O (glucopyranose derivative) among laboratories are not so large compared to the instrument uncertainties, δ~(18)O of Dimethyl aminoterephthalate, which contains nitrogen, shows a large variation among laboratories. This may have been caused by much contamination of N_2 to the CO peak on the EA-IRMS chromatogram, and may be improved by using a longer GC column (1.0 ～ 1.5 m) for chromatographic separation.%軽元素（水素・炭素・窒素・酸素・硫黄）の安定同位体比は，関与する物理化学・化学・生化学反応によって変動する．すなわち，その差（変動）には，起源物質と反応過程・反応量が記録されているということであり，それを測定することで，物質循環の解明や食物網の構造解析，動物の食性解析といった地球化学・生態学・環境化学・考古学などの分野の様々な研究課題を解くことができる．