实验室同位素较为贫化水标准样品的配制及光谱法线性验证  

Calibration and preparation of isotopically depleted water standards for spectroscopy

作　　者：唐晓爽 庞洪喜[1] 张王滨 Tang Xiaoshuang;Pang Hongxi;Zhang Wangbin(School of Geography and Ocean Science,Nanjing University,Nanjing 210023,China)

机构地区：[1]南京大学地理与海洋科学学院,江苏南京210023

出　　处：《极地研究》2022年第3期311-316,共6页Chinese Journal of Polar Research

基　　金：国家自然科学基金(41771031,41622605)资助。

摘　　要：由于温度低,南极内陆地区的降水和水汽中稳定同位素都较为贫化(例如对流层顶附近水汽中δ^(18)O可达–150‰),显著低于国际标准南极降水(SLAP)的δ^(18)O值(–55.50‰)。质谱测试过程中采用的线性校正方法要求待测样品的水同位素值落在标准样品水同位素值的范围区间内,因此有必要配制实验室同位素较为贫化水标准样品,以满足测试需求。此外,近年来激光光谱水稳定同位素测试方法已得到广泛的应用,但光谱法测试同位素较为贫化水样品是否和质谱一样存在线性校正问题,目前还未得到实验结果的验证。为此,本文选用富含^(16)O的Aldrich水,与已知同位素值的实验室二级标准水样进行配比,根据同位素质量守恒原理,精确计算出所用批次Aldrich水的δ^(18)O值为–940.40‰。利用Aldrich水和实验室标准水样进行不同比例的配比,精确配制了4种氧同位素较为贫化的实验室标准水样,其δ^(18)O值分别为–76.53‰、–97.08‰、–117.93‰和–137.50‰。利用光谱法对上述氧同位素较为贫化的水样进行了测试,发现测试的线性良好,测试结果具有微小的正偏差(平均为0.14‰)。本文实验结果可为南极内陆地区的降水和水汽(尤其是对流层顶附近水汽)的同位素高精度测试提供方法参考。Because of very low air temperatures, precipitation and water vapor over continental Antarctica and water vapor near the tropopause are depleted in ^(18)O isotopes. For instance, the ratio of the ^(18)O isotope (δ^(18)O) in water vapor near the tropopause can reach −150‰, which is considerably lower than that in Standard Light Antarctic Precipitation (SLAP;−55.50‰). In mass spectrometry, the calibration of isotopic measure-ments based on linear interpolation is only valid if the isotopic ratios of the samples fall within the ratio range of reference samples. To meet the needs of high-precision measurements of isotopically depleted water samples, it is necessary to prepare laboratory reference standards that are isotopically depleted. Laser spec-troscopy has also been widely used for isotopic measurements of water but the validity of linear interpola-tion for calibration still needs to be validated by experimental results. We used the principle of mass con-servation to determine the δ^(18)O value of ^(16)O-enriched water produced by Sigma-Aldrich ( −940.40‰). We used different mixing ratios of laboratory water standard and ^(16)O-enriched water to prepare four solutions with δ^(18)O values of −76.53‰, −97.08‰, −117.93‰, and −137.50‰, respectively. We measured the isotopic ratios of the solutions using the L2140-i isotope and gas concentration analyzer from Picarro. Results sup-port the validity of calibration based on linear interpolation;mean deviation is only 0.14‰. In this paper, we provided a method for high-precision measurements of stable isotopes in precipitation and water vapor over continental Antarctica and water vapor near the tropopause.

关 键 词：水稳定同位素 同位素贫化 极区降水 标准样品配制 同位素测试的线性 

分 类 号：P435[天文地球—大气科学及气象学] P426