Needle trap extraction for GC analysis of formic and acetic acids in aqueous solution

Abstract

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 6-7 times lower than the fiber at 1000 μg/mL depending on the analyte. It is, however, superior to the latter at 10 μg/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.

Determination of Aqueous Formic and Acetic Acids by Purge-and-Trap Analysis with a Needle-Type Extraction Device and Gas Chromatography Barrier Discharge Ionization Detector

“…In addition, PT extraction with a needle-type extraction device achieved a lower detection limit than SPME for the determination of FA and AA in aqueous samples. 30 Previously, we reported the extraction of FA and AA from gaseous samples with a needle-type extraction device, followed by GC-BID analysis. 31 In that study, gaseous FA and AA were sensitively determined with a simple and rapid sample preparation step and the method was successfully applied for analyzing in-door air samples.…”

Solid phase microextraction techniques used for gas chromatography: a review

“…Specifically, the ITEX system was designed for dynamic HS, followed by thermal desorption prior to GC analysis [23]. Analogously, the extraction needle (NeedlEx), introduced by Shinwa Chemical Industries Ltd (Kyoto, Japan), is made by inserting a sorbent plug inside the needle used for both sampling and injecting in the GC after thermal desorption directly in the GC inlet [25].…”

Purge-and-Trap Extraction with a Miniaturized Extraction Capillary for the Determination of Aqueous Formic Acids in Ion Chromatography

“…Therefore, the analytical method with the needle-type extraction device offers rapid and sensitive determination for several types of VOCs [17,18]. The extraction needle has also been applied to PT analysis of VOCs in aqueous samples [19][20][21][22][23]. The method does not require expensive instruments, and VOC analytes can be rapidly and sensitively determined.…”