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Quantitative analysis of process NMR signals in the time domain

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Quantitative analysis of process NMR signals in the time domain Alison Nordon,1 Colin A. McGill,1 Paul J. Gemperline2 and David Littlejohn1 1 Department of Pure ... – PowerPoint PPT presentation

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Title: Quantitative analysis of process NMR signals in the time domain


1
Quantitative analysis of process NMR signals in
the time domain
  • Alison Nordon,1 Colin A. McGill,1 Paul J.
    Gemperline2 and David Littlejohn1

1 Department of Pure Applied Chemistry/CPACT,
University of Strathclyde, Glasgow, UK 2
Department of Chemistry/MCEC, East Carolina
University, Greenville, NC, USA
2
Process NMR
  • Low-resolution NMR has been used to determine
    moisture and fat content
  • However, chemical shift information is required
    to obtain chemical composition
  • High-field NMR spectrometer not suited to the
    process environment
  • Use low-field NMR spectrometer employing a
    permanent magnet which provides medium resolution

3
NMR spectrometer
  • Resonance Instruments MARAN Ultra
  • 1H, 19F, 31P
  • Permanent magnet (29 MHz for 1H)
  • Small, robust instrument (53 x 50 x 30 cm3)
  • Suitable for on-line and at-line measurements
  • Additional features
  • shim coils
  • lock channel

4
Resonance Instruments MARAN Ultra spectrometer
5
1H NMR spectrum of a sample from a benzene
production process
6
Quantitative analysis
  • Overlapping signals
  • multivariate, e.g. PLS, analysis of spectra
  • Construction of calibration model
  • reference technique
  • simulate samples
  • Validation and testing of model
  • Model maintenance and update

7
Processing of NMR signals
8
Data analysis - Analysis of FIDs
9
Analysis of FIDs
  • Eliminate data processing steps that are
    difficult to automate, e.g. phasing
  • Potential for model-free analysis
  • Methods investigated
  • continuous wavelet transform (CWT)
  • modification of generalised rank annihilation
    method (FID-GRAM)
  • modification of direct exponential curve
    resolution algorithm (FID-DECRA)

10
FID-DECRA
  • Construction of Hankel matrix, H, from FID
  • Create 2 sub matrices, H1 and H2, from H
  • Obtain individual components from solution to
    generalised eigenproblem
  • Calculate amplitude, area and T2 for resolved
    signals

11
Example
12
Applications of FID-DECRA
  • Quality control
  • determination of ethoxy chain length in nonyl
    phenol ethoxylates (1H NMR)
  • Reaction monitoring
  • dehydroxylation of tetrafluorohydroquinone (19F
    NMR)

13
Determination of ethoxy chain length in nonyl
phenol ethoxylates
14
Magnitude spectrum of FID-DECRA resolved
components
15
FID-DECRA results
16
Conclusions - nonyl phenol ethoxylates
  • Results obtained using FID-DECRA comparable to
    those obtained from univariate analysis of
    spectral data
  • However, with FID-DECRA the FID is analysed
    directly and no phase correction is required ?
    could be automated

17
Dehydroxylation of tetrafluorohydroquinone
18
19F NMR spectrum of mixture (with 10 Hz line
broadening)
19
Magnitude spectrum of FID-DECRA resolved
components
20
TFHQ concentration v FID-DECRA area
21
FID-DECRA v PLS
22
Conclusions - fluorocarbons
  • Possible to analyse quantitatively 19F NMR FIDs
    using FID-DECRA with a single calibration sample
  • Accuracy and precision of FID analysis using
    FID-DECRA (1 calibration sample) comparable to
    that of spectral analysis using PLS (10
    calibration samples)

23
Overall conclusions
  • Quantitative results can be obtained from a
    single FID using FID-DECRA
  • No phase correction needed
  • Insensitive to solvent effects
  • FID-DECRA analysis could be automated ? useful in
    process NMR spectrometry

24
Acknowledgements
  • Resonance Instruments
  • ICI
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