A Microcoil NMR Probe for Coupling Microscale HPLC with On-Line NMR Spectroscopy

Subramanian, Raju; Kelley, Wayne P.; Floyd, Philip D.; Tan, Zhixin Jessica; Webb, Andrew; Sweedler, Jonathan V.

doi:10.1021/ac990876s

Cited by 58 publications

(46 citation statements)

References 39 publications

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“…18 In terms of cLC-NMR applications, two are described here. In the first, 24 analysis of submicrogram to microgram quantities of alanine and two dipeptides was reported using a C 18 (150 ð 0.5 µm i.d.) column and a 1.1 µl observe volume solenoidal probe at 500 MHz.…”

Section: Clc-nmr Hyphenationmentioning

confidence: 99%

Nuclear magnetic resonance coupled microseparations

Webb¹

2005

Magnetic Reson in Chemistry

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The increased separation efficiency afforded by reducing the size of the separation column has resulted in 'microseparations' becoming an important component in many chemical and biochemical applications. The coupling of microseparations with NMR detection is an area of increasing interest owing to the high structural information of NMR. In order to couple efficiently with the separation, the NMR detector must be reduced in size to correspond to that of the separation peak. This paper summarizes some of the approaches used in coupling NMR detection with pressure-driven and electrophoretic microseparations, the design of small NMR detectors and applications of this technology.

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Section: Clc-nmr Hyphenationmentioning

confidence: 99%

Nuclear magnetic resonance coupled microseparations

Webb¹

2005

Magnetic Reson in Chemistry

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“…However, the main potential of microcoils is in their combination with microflow liquid Review 799 chromatography, resulting in capillary HPLC-NMR [67], [68], [69], [70], [71], [72], [73], [74]. Stopped-flow capillary HPLC-NMR was recently used for the identification of isoflavonoids in plant material [75].…”

Section: Other New Trends In Nmr Hyphenationmentioning

confidence: 99%

Untitled

2005

Planta Med

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IntroductionIn the first part of this review [1], the use of direct NMR hyphenation in natural products research has been discussed. The direct HPLC-NMR methods were defined as methods in which the NMR data acquisition is performed on the HPLC column eluate [1]. This implies either a direct connection between the NMR spectrometer and the HPLC apparatus, or use of storage capillaries in which the HPLC eluate is temporarily stored prior to acquisition of NMR data.Many useful results related to natural products have been obtained using direct HPLC-NMR methods [1] [30]. However, the direct combination of state-of-the-art separation technology with the most powerful and versatile tool for structure elucidation of organic molecules in solution suffers from various practical problems. In short, these practical limitations are due to somewhat contradictory requirements of HPLC and NMR with respect to solvents and time-scale of the experiment, and thus compromises are necessary in order to hyphenate these two techniques. For example, 1 H-NMR spectra are preferably acquired in deuterated solvents, but use of deuterated solvents for HPLC is expensive and the selection is limited. Some useful HPLC eluents, such as buffers with high ionic strengths, are directly undesirable in direct HPLC-NMR hyphenation. Gradient elution of HPLC columns, required in most separations, implies constantly changing magnetic susceptibility and field homogeneity in the NMR flowprobe, not to mention variations of analyte chemical shifts with solvent composition. Hyphenated NMR Methods in Natural Products AbstractThis review describes the principles and performance of a novel and highly promising hyphenated technique, HPLC-SPE-NMR, which is based on post-column analyte trapping by solid-phase extraction. The analytes are subsequently eluted from the SPE cartridges using deuterated solvents. This indirect HPLC-NMR hyphenation offers numerous advantages compared to direct HPLC-NMR methods. Multiple trapping leads to a dramatic increase of analyte amounts available for NMR, enabling acquisition of high-quality 2D NMR data within a short time. Other new developments, including combination of solenoidal coil capillary flow-probes with microflow HPLC, are also discussed. Fast extract dereplication using these techniques enables focusing of isolation efforts on truly novel and promising natural products, based on precise structural data obtained with crude extracts or fractions.

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“…Due to these benefits, many different applications for NMR with microfluidics have been proposed. For example, NMR has been coupled with μTAS HPLC and capillary electrophoresis [14][15][16] , used to image cells in a capillary 17 , and to study protein folding 18 as well as chemical reactions on a microscale 19 . These studies were entirely conducted in capillaries, around which a highly sensitive solenoidal microcoil was wrapped.…”

Section: Introductionmentioning

confidence: 99%

NMR Analysis on Microfluidic Devices by Remote Detection

et al. 2005

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We present a novel approach to perform high-sensitivity NMR imaging and spectroscopic analysis on microfluidic devices. The application of NMR, the most information rich spectroscopic technique, to microfluidic devices remains a challenge because the inherently low sensitivity of NMR is aggravated by small fluid volumes leading to low NMR signal, and geometric constraints resulting in poor efficiency for inductive detection. We address the latter by physically separating signal detection from encoding of information with remote detection. Thereby, we use a commercial imaging probe with sufficiently large diameter to encompass the entire device, enabling encoding of NMR information at any location on the chip. Because large-diameter coils 1 are too insensitive for detection, we store the encoded information as longitudinal magnetization and flow it into the outlet capillary. There, we detect the signal with optimal sensitivity using a solenoidal microcoil, and reconstruct the information encoded in the fluid. We present a generally applicable design for a detection-only microcoil probethat can be inserted into the bore of a commercial imaging probe. Using hyperpolarized 129 Xe gas, we show that this probe enables sensitive reconstruction of NMR spectroscopic information encoded by the large imaging probe while keeping the flexibility of a large coil.

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A Microcoil NMR Probe for Coupling Microscale HPLC with On-Line NMR Spectroscopy

Cited by 58 publications

References 39 publications

Nuclear magnetic resonance coupled microseparations

Nuclear magnetic resonance coupled microseparations

Untitled

NMR Analysis on Microfluidic Devices by Remote Detection

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