Uemura Ryu, Matsui Yohei, Motoyama Hideaki, Yoshida Naohiro
Research Organization of Information and Systems, National Institute of Polar Research, Itabashi, Tokyo 173-8515, Japan.
Rapid Commun Mass Spectrom. 2007;21(11):1783-90. doi: 10.1002/rcm.3022.
We describe a modified version of the equilibration method and a correction algorithm for isotope ratio measurements of small quantities of water samples. The deltaD and the delta(18)O of the same water sample can both be analyzed using an automated equilibrator with sample sizes as small as 50 microL. Conventional equilibration techniques generally require water samples of several microL. That limitation is attributable mainly to changes in the isotope ratio ((18)O/(16)O or D/H) of water samples during isotopic exchange between the equilibration gas (CO(2) or H(2)) and water, and therefore the technique for microL quantities of water requires mass-balance correction using the water/gas (CO(2) or H(2)) mole ratio to correct this isotopic effect. We quantitatively evaluate factors controlling the variability of the isotopic effect due to sample size. Theoretical consideration shows that a simple linear equation corrects for the effects without determining parameters such as isotope fractionation factors and water/gas mole ratios. Precisions (1-sigma) of 50-microL meteoric water samples whose isotopic compositions of -1.4 to -396.2 per thousand for deltaD are +/-0.5 to +/-0.6 per thousand, and of -0.37 to -51.37 per thousand for delta(18)O are +/-0.01 to +/-0.11 per thousand.
我们描述了一种平衡方法的改进版本以及一种用于少量水样同位素比率测量的校正算法。同一水样的δD和δ¹⁸O均可使用样品量低至50微升的自动平衡仪进行分析。传统的平衡技术通常需要几微升的水样。这种限制主要归因于平衡气体（CO₂或H₂）与水之间进行同位素交换时水样同位素比率（¹⁸O/¹⁶O或D/H）的变化，因此对于几微升水样的技术需要使用水/气体（CO₂或H₂）摩尔比进行质量平衡校正，以校正这种同位素效应。我们定量评估了控制因样品量导致的同位素效应变异性的因素。理论分析表明，一个简单的线性方程可以校正这些效应，而无需确定诸如同位素分馏因子和水/气体摩尔比等参数。对于δD同位素组成在-1.4‰至-396.2‰之间的50微升大气降水样品，精度（1-σ）为±0.5‰至±0.6‰；对于δ¹⁸O在-0.37‰至-51.37‰之间的样品，精度为±0.01‰至±0.11‰。
