Chemical-shift referencing and resolution stability in methanol:water gradient LC–NMR

Keifer, Paul A.

doi:10.1016/j.jmr.2010.04.009

Cited by 10 publications

(10 citation statements)

References 14 publications

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“…The WET technique uses a series of variable tip-angle solvent-selective radio frequency (RF) pulses, where each selective RF pulse is followed by a dephasing field gradient pulse (Smallcombe et al, 1995). In an acetonitrile:water solvent gradient system, the relative positions of the acetonitrile and water resonances change according to the mobile-phase composition (Keifer, 2010). The scout scan technique allows us to automatically track the frequencies of the largest NMR resonances.…”

Section: Resultsmentioning

confidence: 99%

Fast identification of flavonoids in the roots of Sophora flavescens by on-flow LC-NMR

Kim¹,

Kim²,

Kim³

et al. 2010

J. Med. Plants Res.

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Sophora flavescens Ait (Leguminosae) is a Chinese herbal medicine. Sophorae radix, the dried roots of S. flavescens, has been used for various diseases including atherosclerosis and arrhythmias. For the direct identification of the compounds present in Sophorae radix, the hyphenated LC-NMR technique has been applied. WET solvent suppression and scout scan techniques were used to suppress solvent peaks in on-flow LC-NMR experiment. Six prenylflavonoids were identified successfully as kushenol U (1), kurarinone (2), sophoraflavanone G (3), leachianone A (4), kuraridin (5) and kushenol A (6).

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Section: Resultsmentioning

confidence: 99%

Fast identification of flavonoids in the roots of Sophora flavescens by on-flow LC-NMR

Kim¹,

Kim²,

Kim³

et al. 2010

J. Med. Plants Res.

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show abstract

“…The mobile phases commonly used in reversed‐phase HPLC are acetonitrile or methanol as the organic mobile phase, and water as the aqueous mobile phase. All of these solvents have protons at concentrations of 30‐100 M; although NMR has a wide dynamic range of 10 5 such strong solvent signals can overwhelm the NMR signal of low concentration analytes and add to the background noise . To reduce interference from solvent resonances, deuterated solvents are preferably used for separation but, due to cost, often only water is substituted with D 2 O (relatively inexpensive, below $0.50/mL) while the organic phase (>$1/mL) is often reported in its non‐deuterated form.…”

Section: Challenges In Integrating Lc Ms and Nmrmentioning

confidence: 99%

“…Gradient elution, which aids the separation of compounds with very different polarities in a complex sample in the LC dimension, can be problematic in NMR . Steep gradients—changes of more than a few percent per minute—can create solvent gradients in the NMR flowcell, and thus a gradient of magnetic field (magnetic inhomogeneity), which causes resonances to broaden, split, and weaken . Moreover, even when a gradient is slow enough to avoid broadening, the chemical shifts of analytes are affected.…”

Section: Online Lc‐ms‐nmrmentioning

confidence: 99%

“…Stop‐flow LC‐MS‐NMR also enables the acquisition of more time‐consuming 13 C spectra and 2D NMR spectra . An additional advantage realized through stop‐flow NMR is that conditions are static, thus solvent peaks remain constant for suppression …”

Section: Online Lc‐ms‐nmrmentioning

confidence: 99%

“…4 An additional advantage realized through stop-flow NMR is that conditions are static, thus solvent peaks remain constant for suppression. 4,6,30,31,35 Stopping the LC pump for NMR analysis can be triggered by either UV peak detection or by the MS detector. Delays between peak UV and peak NMR intensity need to be calibrated, and prior knowledge of the elution patterns of analytes and interferences is valuable.…”

Section: Stop-flow Lc-ms-nmrmentioning

confidence: 99%

See 2 more Smart Citations

The integration of LC‐MS and NMR for the analysis of low molecular weight trace analytes in complex matrices

Gathungu

Kautz

Kristal

et al. 2018

Mass Spectrometry Reviews

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This review discusses the integration of liquid chromatography (LC), mass spectrometry (MS), and nuclear magnetic resonance (NMR) in the comprehensive analysis of small molecules from complex matrices. We first discuss the steps taken toward making the three technologies compatible, so as to create an efficient analytical platform. The development of online LC-MS-NMR, highlighted by successful applications in the profiling of highly concentrated analytes (LODs 10 μg) is discussed next. This is followed by a detailed overview of the alternative approaches that have been developed to overcome the challenges associated with online LC-MS-NMR that primarily stem from the inherently low sensitivity of NMR. These alternative approaches include the use of stop-flow LC-MS-NMR, loop collection of LC peaks, LC-MS-SPE-NMR, and offline NMR. The potential and limitations of all these approaches is discussed in the context of applications in various fields, including metabolomics and natural product discovery.

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Investigation into the structural composition of hydroalcoholic solutions as basis for the development of multiple suppression pulse sequences for NMR measurement of alcoholic beverages

Monakhova

Mushtakova

Kuballa

et al. 2014

Magnetic Reson in Chemistry

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An eight-fold suppression pulse sequence was recently developed to improve sensitivity in (1) H NMR measurements of alcoholic beverages [Magn. Res. Chem. 2011 (49): 734-739]. To ensure that only one combined hydroxyl peak from water and ethanol appears in the spectrum, adjustment to a certain range of ethanol concentrations was required. To explain this observation, the structure of water-ethanol solutions was studied. Hydroalcoholic solutions showed extreme behavior at 25% vol, 46% vol, and 83% vol ethanol according to (1) H NMR experiments. Near-infrared spectroscopy confirmed the occurrence of four significant compounds ('individual' ethanol and water structures as well as two water-ethanol complexes of defined composition - 1 : 1 and 1 : 3). The successful multiple suppression can be achieved for every kind of alcoholic beverage with different alcoholic strengths, when the final ethanol concentration is adjusted to a range between 25% vol and 46% vol (e.g. using dilution or pure ethanol addition). In this optimum region, an individual ethanol peak was not detected, because the 'individual' water structure and the 1 : 1 ethanol-water complex predominate. The nature of molecular association in ethanol-water solutions is essential to elucidate NMR method development for measurement of alcoholic beverages. The presented approach can be used to optimize other NMR suppression protocols for binary water-organic solvent mixtures, where hydrogen bonding plays a dominant role.

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Chemical-shift referencing and resolution stability in methanol:water gradient LC–NMR

Cited by 10 publications

References 14 publications

Fast identification of flavonoids in the roots of Sophora flavescens by on-flow LC-NMR

Fast identification of flavonoids in the roots of Sophora flavescens by on-flow LC-NMR

The integration of LC‐MS and NMR for the analysis of low molecular weight trace analytes in complex matrices

Investigation into the structural composition of hydroalcoholic solutions as basis for the development of multiple suppression pulse sequences for NMR measurement of alcoholic beverages

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