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Liquid Chromatography-Nuclear Magnetic Resonance (LC-NMR)

Liquid Chromatography-Nuclear Magnetic Resonance (LC-NMR)

High performance liquid chromatography (HPLC) is the most powerful tool in the separation of complex mixtures. By combining HPLC with various detectors such as ultraviolet absorption detectors, fluorescence detectors, electrochemical detectors, etc., structural information of some compounds can be obtained, but the amount of information is very limited. Therefore, some detection techniques with richer structural information, such as IR, MS, NMR, etc., are also needed. Among them, nuclear magnetic resonance (NMR) is a powerful tool for obtaining detailed structural information of organic substances.

NMR can provide a large amount of structural information and is one of the most powerful spectroscopy techniques for analyzing unknown structures. NMR can provide a wealth of compound structure information, including stereochemical information (in terms of configuration and optical isomers), and is simple, accurate, highly specific, and does not damage the sample. However, the samples analyzed by NMR are pure substances. Because the NMR signals of each component of a complex mixture will cover each other and influence each other, it is usually difficult to obtain the analysis results of the mixture by using NMR. Therefore, it is necessary to separate and purify the mixed sample before using NMR detection. Among them, HPLC has been widely used for the separation of complex samples. By adjusting the chromatographic conditions, it can be used to separate different samples. If chromatographic technology is combined with NMR, the separation and detection process of samples can be greatly simplified.

The attempt of liquid chromatography-nuclear magnetic resonance (LC-NMR) technology began in the 1970s, and it was not developed until the mid-to-late 1990s and was widely used. At present, HPLC-NMR has become a relatively mature analysis method, which is widely used in the structural identification of mixtures, especially unknowns.

Principle of LC-NMR

The general configuration of LC-NMR includes a conventional HPLC system, coupling interface and NMR system equipped with a flow probe. The liquid chromatograph of the LC-NMR system is responsible for the separation of the components in the sample and can be regarded as the NMR sampling device. The interface injects the components flowing out of the liquid chromatography into the NMR instrument, which plays a role in adapting HPLC and NMR. NMR analyzes the components sequentially introduced into the interface and can be regarded as a detector of HPLC.

The sample is injected into the high-performance liquid chromatography system, and the components are separated under the impetus of the high-pressure pump. The separated components sequentially pass through a conventional detector (such as a DAD detector). The effluent is then injected into the NMR instrument through a suitable interface device. Therefore, the combined use of LC-NMR is realized.

LC-NMR instrument structure diagramLC-NMR instrument structure diagram

The direct connection of HPLC and NMR will encounter a series of problems related to hardware and software, such as the suppression of NMR signal peaks by the elution solvent of LC, and the low detection sensitivity of NMR. With the improvement of the magnetic field intensity of NMR instruments, the improvement of NMR probe design, and the development of pulse sequence technology, many problems have been basically solved, making the LC-NMR combined technology more practical and widely used.

Operation mode of LC-NMR

At present, HPLC-NMR has two main operating modes to choose from, namely continuous flow mode and stopped flow mode.

Application of LC-NMR

Frequently Asked Questions

What is the LC–NMR technique?

LC–NMR combines liquid chromatography (LC) separation with nuclear magnetic resonance (NMR) spectroscopy, enabling the direct structural elucidation of compounds as they elute from the chromatographic system without the need for prior isolation.

What is liquid-state NMR in analytical chemistry?

Liquid-state NMR is a spectroscopic method used to study molecules dissolved in solution, providing detailed structural, dynamic, and conformational information at the atomic level.

What is LC in chromatography?

In chromatography, LC refers to liquid chromatography, a separation technique in which a liquid mobile phase passes through a stationary phase to separate compounds based on their chemical interactions.

What is solution-state NMR and how is it applied?

Solution-state NMR is used to investigate the structure, purity, and interactions of molecules in solution. It is widely applied in organic chemistry, natural product research, metabolomics, and pharmaceutical development.

What LC–NMR capabilities does BOC Sciences provide?

BOC Sciences offers advanced LC–NMR analysis for direct structural identification of complex mixtures, impurity profiling, metabolite characterization, and confirmation of novel compounds. Our platform integrates high-resolution chromatographic separation with state-of-the-art NMR spectroscopy for comprehensive molecular analysis.

LC–NMR integration expertise from BOC Sciences

We combine liquid chromatography with nuclear magnetic resonance for comprehensive structural elucidation. BOC Sciences delivers unparalleled insight into molecular composition.

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References

  1. Zhang H., et al. Advances of liquid chromatography coupled with nuclear magnetic resonance spectrometer. Chemical analysis and meterage. 2017, 26(3): 117-122.
  2. Yang T.T., et al. Application of LC-NMR in pharmaceutical analysis. Drugs & Clinic. 2012, 27(6): 635-641.

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