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Related Concept Videos

NMR Spectrometers: Resolution and Error Correction01:14

NMR Spectrometers: Resolution and Error Correction

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...
¹H NMR of Conformationally Flexible Molecules: Temporal Resolution00:52

¹H NMR of Conformationally Flexible Molecules: Temporal Resolution

At room temperature, the chair conformer of cyclohexane undergoes rapid ring flipping between two equivalent chair conformers at a rate of approximately 105 times per second. These two chair conformers are in equilibrium. The rapid ring flipping results in the interconversion of the axial proton to an equatorial proton and an equatorial to the axial proton. Such interconversions are too rapid and cannot be detected on the NMR timescale. Hence, the NMR spectrometer cannot distinguish between the...
¹H NMR of Conformationally Flexible Molecules: Variable-Temperature NMR01:15

¹H NMR of Conformationally Flexible Molecules: Variable-Temperature NMR

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.
¹H NMR: Interpreting Distorted and Overlapping Signals01:02

¹H NMR: Interpreting Distorted and Overlapping Signals

Spin systems where the difference in chemical shifts of the coupled nuclei is greater than ten times J are called first-order spin systems. These nuclei are weakly coupled, and their chemical shifts and coupling constant can generally be estimated from the well-separated signals in the spectrum.
As Δν decreases and the signals move closer, the doublets appear increasingly distorted. The intensities of the inner lines increase at the cost of those of the outer lines as the signals are slanted or...
Determination of Molar Masses of Polymers II01:27

Determination of Molar Masses of Polymers II

Polymer samples typically consist of macromolecular chains with a distribution of lengths, resulting in a range of molar masses rather than a single discrete value. Conventional descriptors such as the number-average molar mass and weight-average molar mass quantify this distribution but do not fully capture polymer behavior in solution..The viscosity-average molar mass provides a more realistic description of polymer behavior in solution because it accounts for the enhanced contribution of...
Chemical Shift: Internal References and Solvent Effects01:17

Chemical Shift: Internal References and Solvent Effects

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.
The internal reference compound generally used in NMR spectroscopy is tetramethylsilane (TMS). TMS is preferred because it is chemically inert, soluble in NMR solvents, and easily removable. Also, the highly shielded methyl protons in TMS yield an intense...

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Related Experiment Video

Updated: Jun 20, 2026

Characterization of Synthetic Polymers via Matrix Assisted Laser Desorption Ionization Time of Flight (MALDI-TOF) Mass Spectrometry
06:56

Characterization of Synthetic Polymers via Matrix Assisted Laser Desorption Ionization Time of Flight (MALDI-TOF) Mass Spectrometry

Published on: June 10, 2018

Error analysis for NMR polymer microstructure measurement without calibration standards.

XiaoHua Qiu1, Zhe Zhou, Gian Gobbi

  • 1The Dow Chemical Company, Building 1897, Midland, Michigan 48674, USA. sqiu@dow.com

Analytical Chemistry
|September 22, 2009
PubMed
Summary
This summary is machine-generated.

This study introduces a novel error analysis method for quantitative (13)C NMR spectroscopy, applicable even without calibration standards. The technique ensures accurate measurements by identifying and correcting systematic biases, optimizing NMR resource utilization.

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Atomic Scale Structural Studies of Macromolecular Assemblies by Solid-state Nuclear Magnetic Resonance Spectroscopy
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Atomic Scale Structural Studies of Macromolecular Assemblies by Solid-state Nuclear Magnetic Resonance Spectroscopy

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Characterization of Synthetic Polymers via Matrix Assisted Laser Desorption Ionization Time of Flight (MALDI-TOF) Mass Spectrometry
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Characterization of Synthetic Polymers via Matrix Assisted Laser Desorption Ionization Time of Flight (MALDI-TOF) Mass Spectrometry

Published on: June 10, 2018

MALDI-ToF MS Method for the Characterization of Synthetic Polymers with Varying Dispersity and End Groups
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MALDI-ToF MS Method for the Characterization of Synthetic Polymers with Varying Dispersity and End Groups

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Atomic Scale Structural Studies of Macromolecular Assemblies by Solid-state Nuclear Magnetic Resonance Spectroscopy
14:55

Atomic Scale Structural Studies of Macromolecular Assemblies by Solid-state Nuclear Magnetic Resonance Spectroscopy

Published on: September 17, 2017

Area of Science:

  • Analytical Chemistry
  • Spectroscopy
  • Polymer Science

Background:

  • Calibration standards are crucial for accurate analytical measurements.
  • Traditional methods for quantitative (13)C NMR analysis of copolymers like ethylene/1-octene (E/O) often require calibration standards.
  • The absence of calibration standards poses a challenge for error analysis and accuracy assessment.

Purpose of the Study:

  • To develop and validate an error analysis method for primary analytical techniques in the absence of calibration standards.
  • To apply this method to quantitative (13)C NMR analysis of E/O copolymers.
  • To demonstrate the method's ability to assess accuracy and identify systematic biases.

Main Methods:

  • A self-calibration scheme based on counting principles was employed.
  • The method was applied to quantitative (13)C NMR data of ethylene/1-octene copolymers.
  • Experimental errors and systematic biases were analyzed without external calibration.

Main Results:

  • The developed method provides a measure of accuracy, not just precision.
  • The error analysis was demonstrated to be self-consistent.
  • Previously unrecognized systematic biases in a NMR instrument were identified.
  • The method reduces the need for extensive data averaging, conserving NMR resources.

Conclusions:

  • The proposed accuracy estimation method is effective for quantitative (13)C NMR of E/O copolymers.
  • The methodology is adaptable to other measurement systems requiring accuracy assessment without calibration standards.
  • This approach enhances the reliability of analytical results and optimizes resource allocation.