雪冰中生物有机酸的测试分析方法研究

Determination of Organic Acids in Snow and Ice from Mountain Glaciers

生物有机酸是构成酸雨的组分类别 ,对地表环境有着重要影响 .由于其来源与生物界关系密切 ,因此 ,对其在雪冰中记录的研究是从历史的角度认识C、H、O等生源元素生物地球化学循环 ,认识过去生态和环境变化的途径之一 .但是 ,由于其含量较低、易遭受污染等原因 ,雪冰中有机酸含量的定量测定一直是困扰研究人员的一个问题 .在对目前有机酸测试分析现状、测试分析的难点和问题调研的基础上 ,文章提出了一种利用DX - 30 0离子色谱测试山地冰川雪冰中生物有机酸含量的方法 .该方法利用AS4A分析柱 ,AG4A保护柱 ,TAC - 2样品富集柱和ATC - 1阴离子捕集柱 ,以梯度淋洗方式 ,在 14min内可分离检测出甲酸、乙酸、丙酮酸、甲烷磺酸、草酸等有机酸根离子及氟、氯、亚硝酸 ,硝酸、溴、磷酸和硫酸等常见无机阴离子 .上述有机、无机离子的测试分析相对标准误差分别为 :氟(2 0 % )、乙酸 (4 5 % )、甲酸 (2 0 % )、甲烷磺酸 (16 9% )、氯 (3 1% )、亚硝酸 (3 9% ) ,硝酸 (2 2 % )、溴 (4 9% )和硫酸 (2 4% )

Organic acids are major chemical species in acidic precipitation. This is especially true for light carboxylic acids in precipitation in remote areas. Thus, they play a significant part in acidification of environment. Because organic acids are closely related to the biosphere in terms of their sources, their records in snow and ice provide ways for learning changes of paleoenvironment and paleoecosystem, as well as biogeochemical cycles of C, H, O or S. However, they are very difficult to determine for their trace concentration and susceptibility to contamination. For samples from a specific place and with a specific Ion Chromatography (IC), use of the conventional instrument must take into consideration the following aspect: 1) The IC used should have advanced pump system that enables gradient elution; 2) Pre concentrator columns and anion trap columns should be added to the system; 3) The gradient elution should eluent and separate both organic and inorganic anions present in a sample in a single run; 4) Weak chemical reagent should be used for separation of monovalent analyses with similar affinity. Accordingly, a method for determining organic acids together with inorganic anions in snow and ice from mountain glaciers is provided in this paper. Based on a DX300 Ion chromatography, the method uses AS4ASC and AG4ASC as separator and guard column, respectively, TAC2 as a concentrator column, which is installed in place of sample loop, and ATC1 as a contaminant trap column that is installed before injection valve. ASRSⅡ suppressor column and chemical suppression mode is employed. The suppression solution is 25 mM H 2 SO 4 with a flow rate of 5 mL·min -1 . The eluent is prepared from Na 2 B 4 O 7 ·10H 2 O in 18 2 MΩ water. In order to analyze like species Fluoride, Acetate, Formate, Pyruvate and Methanefulfonate that are closely related in affinity thus prone to be co eluented, and to separate and quantitate in the same run all anions present in samples, gradient elution is adopted with a constant eluent rate of 2 00 mL·min -1 . In the first 6 min, the eluent is kept in 2.0 mM for elution of F - , monovalent organic acids and Pyruvate; in the next 5 min, the concentration increases from 2 mm to 31 5 mm for elution and separation of Cl - , NO - 2, Br - , NO - 3 and PO 3- 4; and in the last 3 min, the eluent is hold at 31.5 mM until SO 2- 4 and (CO) 2- 2 is eluented. The method resolves and quantitates in a single run over 10 analyses both organic and inorganic species from Fluoride, Acetate to Phosphate, Sulfide and finally Oxalate. The relative standard errors for some anions are: 2 0% for Fluoride, 4.5% for Acetate, 2.0% for Formate, 16.9% for Methanesulfonate, 3 1% for Chloride, 3 9% for Nitrite, 2 2% for Nitrate, 4 9% for Bromide and 2 4% for Sulfate.