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. Electronics Power supply Magnet Sample 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. FT n FID (time domain) spectrum - unphased (frequency domain) spectrum - phased (frequency domain) Processing of NMR signals

8. 1 n A 1 A FT T2 t T2 n frequency domain (spectrum) time domain (FID) 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. exponential decay character of FID  data set 1  data set 2 + 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. magnitude spectrum of resolved components FID-DECRA 40 20 0 -20 -40 n1 = 10 Hz, n2 = 12 Hz n/Hz 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. product by-product Dehydroxylation of tetrafluorohydroquinone

18. TFHQ TFB TFP TFP 19F NMR spectrum of mixture(with 10 Hz line broadening)

19. TFHQ TFB TFP TFP Magnitude spectrum of FID-DECRA resolved components

20. TFHQ concentration v FID-DECRA area

21. FID-DECRA - 1 calibration sample (PLS - 10 calibration samples) 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