title: Analysis of the stable carbon isotope composition of formic and acetic acids.
abstract: Formic and acetic acids are ubiquitous in the environment and in many biological processes. Analysis of the stable carbon isotope composition (δ(13)C) of formic and acetic acids is important to understanding their biogeochemical cycles. However, it has been faced with poor accuracy and high detection limits due to their low carbon number, high hydrophilicity, and semi-volatility. Here we developed an analytical technique by needle trap and gas chromatography-isotope ratio mass spectrometry (GC-IRMS). The organic acids in aqueous solution were extracted using a NeedlEx needle through purge-and-trap and were analyzed by GC-IRMS for δ(13)C. The procedures incur no isotope fractionation. Defined as the point at which the mean δ(13)C is statistically the same as the given value and the analytical error starts rising, the method's detection limits are 200 and 100 mg/L for formic and acetic acids, respectively, with an uncertainty of approximately 0.5‰ in direct extraction and analysis. They were lowered to 1 mg/L with precision of 0.9‰ after samples were subjected to preconcentration. The method was successfully applied to natural samples as diverse as precipitation, vinegars, ant plasma, and vehicle exhaust, which vary considerably in concentration and matrix of the organic acids. It is applicable to the organic acids in not only aqueous solution but also gaseous phase.
authors: State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang, Guizhou 550002, China. lee@mail.gyig.ac.cn
authors: Xinqing
authors: X
authors: Lee
authors: Like
authors: L
authors: Zhang
authors: Daikuan
authors: D
authors: Huang
authors: Ning
authors: N
authors: An
authors: Fang
authors: F
authors: Yang
authors: Wei
authors: W
authors: Jiang
authors: Bin
authors: B
authors: Fang
mesh_terms: D000085:Acetates / Q000032:analysis*; D000818:Animals; D001000:Ants; D002138:Calibration; D002247:Carbon Isotopes / Q000032:analysis*; D004867:Equipment Design; D005561:Formates / Q000032:analysis*; D008401:Gas Chromatography-Mass Spectrometry / Q000295:instrumentation / Q000379:methods*; D057230:Limit of Detection; D001335:Vehicle Emissions / Q000032:analysis
chemical_list: D000085:Acetates; D002247:Carbon Isotopes; D005561:Formates; D001335:Vehicle Emissions; C030544:formic acid