Formic and acetic acids are ubiquitous in the environment, food, and most of the natural products. Extraction of the acids from aqueous solution is required for their isotope analysis by the gas chromatography-isotope ratio mass spectrometry. To this objective, we have previously developed a purge-and-trap technique using the dynamic solid-phase microextraction technology, the NeedlEX. The extraction efficiency, however, remains unexamined. Here, we address this question using the flame ionization detector and isotope ratio mass spectrometer while comparing it with that of the CAR/PDMS fiber. The results show that the NeedlEX is applicable at a wide range of concentration through coordination of purge volume given the minimum amount 3.7 ng and 1.8 ng of formic and acetic, respectively, is extracted. The efficiency of NeedlEX was 67 times lower than the fiber at 1000 mu g/mL depending on the analyte. It is, however, superior to the latter at 10 mu g/mL or less owing to its lower detection limit. The extraction efficiency of both acids is equivalent in molar amount. This is, however, disguised by the different response of the flame ionization detector. The isotope ratio mass spectrometor overcomes this problem but is compromised by relatively large errors. These results are particularly useful for isotopic analysis of carboxylic acids.

Publication name	JOURNAL OF SEPARATION SCIENCE　Volume: 35 　Issue: 13 　Pages: 1675-1681　 Published: JUL 2012
Author(s)	Lee, Xinqing; Huang, Daikuan; Lou, Dawei; Pawliszyn, Janusz
Corresponding author	LEE Xingqing  lee@mails.gyig.ac.cn  Chinese Acad Sci, State Key Lab Environm Geochem, Inst Geochem, Guiyang 550002, Peoples R China.

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