Hyphenation of Gas Chromatography to Microcoil ¹H Nuclear Magnetic Resonance Spectroscopy

Abstract

Whereas the hyphenation of gas chromatography (GC) with mass spectrometry is of great importance, little is known about the coupling to nuclear magnetic resonance spectroscopy (NMR). The investigation of this technique is an attractive proposition because of the valuable information given by NMR on molecular structure. The experiments shown here are to our knowledge the first hyphenating capillary GC to microcoil NMR. In contrast to liquids, gases have rarely been investigated by NMR, mainly due to the experimental difficulties in handling gases and the low signal-to-noise-ratio (SNR) of the NMR signal obtained at atmospheric pressure. With advances in NMR sensitivity (higher magnetic fields and solenoidal microprobes), this limitation can be largely overcome. In this paper, we describe the use of a custom-built solenoidal NMR microprobe with an active volume of 2 microL for the NMR detection of several compounds at 400 MHz, first in a mixture, and then with full coupling to capillary GC to identify them separately. The injected amounts of each analyte in the hyphenated experiments are in the range of 15-50 micromol, resulting in reasonable SNR for sample masses of 1-2 microg.

Simple preparative gas chromatographic method for isolation of menthol and menthone from peppermint oil, with quantitative GC‐MS and 1H NMR assay

“…Some desirable spectroscopic identification methods including nuclear magnetic resonance (NMR) are not Abbreviations: DFS, deactivated fused-silica; 1,4-DMB, 1,4-dimethoxybenzene; EO, essential oil; EPC, electronic pressure control; IS, internal standard; MDGC, multidimensional GC; prep-GC, preparative gas chromatography; TMS, tetramethylsilane; xTA, external trapping assembly readily available hyphenated directly (online) with GC, and while online GC with NMR has been little reported, Albert's group [3] showed that, provided sufficient material can be introduced into the capillary column, NMR spectra can be successfully acquired in the online GC-NMR experiment. By contrast preparative GC (prep-GC) is a viable approach that can give access to such methods.…”

An efficient approach for the isolation, identification and evaluation of antimicrobial plant components on an analytical scale, demonstrated by the example of Radix imperatoriae

“…Nowadays, microtechniques like microcoil 1 H NMR spectroscopy are much more sensitive and allow measurements of sample amounts in the low nmol range. They can also be coupled with capillary HPLC (highperformance liquid chromatography) or GC (gas chromatography) systems [19][20][21]. The HPLC-NMR or even HPLC-NMR-MS capillary technique offers a reliable analysis of unstable, light-or air-sensitive compounds in the continuous-or stopped-flow mode, and the wasteful collection of HPLC fractions, the time-consuming removal of almost nonvolatile solvents and the risk of contamination can be avoided.…”

Online coupling of enantioselective capillary gas chromatography with proton nuclear magnetic resonance spectroscopy

“…1,15 In one of their applications they isolated 8.6 lg geraniol from a complex essential oil matrix using MDGC and recorded remarkable 1 with a 800 MHz NMR spectrometer equipped with a cryoprobe within an acquisition time of 1 hr. 15 The second direct approach was published also quite recently and demonstrated the feasibility of an online coupling of gas chromatography and NMR spectroscopy 16,17 based on earlier reports of the direct combination of packed column and NMR instrumentation. 18,19 In a recent work, the successful capillary gas chromatographic separation and online identification of the stereoisomers of E,Z-2-pentene and of E,Z-2-hexene using a Chirasil-b-Dex stationary phase and a 400 MHz NMR spectrometer equipped with a custom-built, double resonant solenoidal microprobe was described.…”

“…18,19 In a recent work, the successful capillary gas chromatographic separation and online identification of the stereoisomers of E,Z-2-pentene and of E,Z-2-hexene using a Chirasil-b-Dex stationary phase and a 400 MHz NMR spectrometer equipped with a custom-built, double resonant solenoidal microprobe was described. 17 Both methods benefit from newer developments in the field of NMR such as microprobes 16,17,20,21 or cryoprobes [22][23][24][25] and stronger magnets, which dramatically improved the sensitivity of the relatively insensitive spectroscopic method so that the largest sample amounts, which can be separated by capillary GC are getting closer to the detection limit of NMR spectroscopy. Thus it is to be expected that many applications using a combined method of GC and NMR (offline as well as online) will emerge in the future especially if a high purity isolation is required for an unequivocal identification.…”