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Related Concept Videos

2D NMR: Heteronuclear Single-Quantum Correlation Spectroscopy (HSQC)01:19

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Heteronuclear single-quantum correlation spectroscopy (HSQC) is a 2D NMR technique that reveals one-bond correlations between hydrogen and a heteronucleus. The HSQC experiment is similar to the heteronuclear correlation experiment (HETCOR) but is more sensitive. In the HSQC spectrum, the proton chemical shift is plotted on the horizontal F2 axis, while the 13C chemical shift is plotted on the vertical F1 axis. The corresponding proton and 13C spectra are also shown. The HSQC contour plot does...
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In an NMR sample, precise measurement of the absolute absorption frequencies of nuclei is difficult. A standard internal reference compound is added, and the frequency difference between the reference signal and sample signals is measured.
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NMR Spectrometers: Resolution and Error Correction01:14

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When magnetic nuclei in a sample achieve resonance and undergo relaxation, the signal detected in NMR is an approximately exponential free induction decay. Fourier transform of an exponential decay yields a Lorentzian peak in the frequency domain. Lorentzian peaks in an NMR spectrum are defined by their amplitude, full width at half maximum, and position, where the peak width is governed by the spin-spin relaxation time alone. In real experiments, however, the applied magnetic field is rendered...
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2D NMR: Overview of Heteronuclear Correlation Techniques01:18

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Heteronuclear correlation spectroscopy is an analytical technique that investigates the coupling between different types of nuclei, often a proton and an X-nucleus, such as carbon-13 or nitrogen-15. This method is commonly used in nuclear magnetic resonance (NMR) spectroscopy to gain insights into complex chemical compounds' structural and compositional aspects. A typical heteronuclear correlation spectrum displays X-nucleus chemical shifts on one axis and a proton spectrum on the other...
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The probability of having two carbon-13 atoms next to each other is negligible because of the low natural abundance of carbon-13. Consequently, peak splitting due to carbon-carbon spin-spin coupling is not observed in spectra. However, protons up to three sigma bonds away split the carbon signal according to the n+1 rule, resulting in complicated spectra.
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¹H NMR of Conformationally Flexible Molecules: Variable-Temperature NMR01:15

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The axial and equatorial protons in cyclohexane can be distinguished by performing a variable-temperature NMR experiment. In this process, except for one proton, the remaining eleven protons are replaced by deuterium. The deuterium substitution avoids the possible peak splitting caused by the spin-spin coupling between the adjacent protons. The remaining proton flips between the axial and equatorial positions.
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Collaborative Study to Validate Purity Determination by 1H Quantitative NMR Spectroscopy by Using Internal

Toru Miura1, Naoki Sugimoto2, Sitaram Bhavaraju3

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Summary

Quantitative 1H-NMR (1H qNMR) is a validated method for determining chemical purity. An international study confirmed 1H qNMR achieves accuracy comparable to primary measurement methods.

Keywords:
collaborative studymeasurement uncertaintymethod validationmetrological traceabilityquantitative (q)NMR

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Area of Science:

  • Analytical Chemistry
  • Metrology
  • Spectroscopy

Background:

  • Nuclear Magnetic Resonance (NMR) spectroscopy offers metrological traceability for quantifying organic molecules.
  • Quantitative 1H-NMR (1H qNMR) uses proton nucleus signals for chemical quantification and is adopted in standards.
  • Limited validation reports exist for 1H qNMR methodology.

Purpose of the Study:

  • To validate the 1H qNMR methodology using an internal calibration approach.
  • To assess the quantification performance and accuracy of 1H qNMR against primary methods.

Main Methods:

  • An international collaborative study involving thirteen laboratories.
  • Validation of 1H qNMR for purity determination of three certified reference materials (CRMs).
  • Samples included butyl p-hydroxybenzoate (JP standard), benzoic acid (CRM), and fludioxonil (CRM).

Main Results:

  • Optimized 1H qNMR experiments were performed for each sample.
  • Measured purities were equivalent to the reference values for all samples.
  • Normalized error (En-value) assessment indicated statistical equivalence to primary methods.

Conclusions:

  • The international collaborative study successfully validated the 1H qNMR method.
  • 1H qNMR demonstrates competence and accuracy comparable to conventional primary measurement methods.
  • This validates 1H qNMR as a reliable technique for chemical purity assessment.