Determination of Organic Acids in Snow and Ice from Mountain Glaciers
LI Xin qing (LEE Xin qing), QIN Da he, ZHOU Hui (Laboratory of Ice Core and Cold Regions Environment, CAREERI, CAS, Lanzhou Gansu 730000, China)
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.