Methods have been developed and compared for the analysis of a glycerol-based polyether polyol using a low-field, medium-resolution NMR spectrometer, with an operating frequency of 29 MHz for 1 H. Signal areas in the time and frequency domains were used to calculate the ethylene oxide (EO) content of individual samples. The time domain signals (free induction decay) were analysed using a new version of the direct exponential curve resolution algorithm (FID-DECRA). Direct analysis of the H-1 NMR FF spectra gave percentage EO concentrations of reasonable accuracy (average percentage error of 1.3%) and precision (average RSD of 1.8%) when compared with results derived from high-field C-13 NMR spectrometry. The direct FID-DECRA method showed a negative bias (-0.8+/-0.12% w/w) in the estimation of percentage EO concentration, but the precision (average RSD of 0.9%) was twice as good as that of direct spectral analysis. When the 13C NMR analysis was used as a reference method for univariate calibration of the 1 H NMR procedures, the best accuracy (average percentage error of 0.5%) and precision (average RSD of 0.6%) were obtained using FID-DECRA, for EO concentrations in the range 14.8-15.5% w/w. An additional advantage of FID-DECRA is that the analytical procedure could be automated, which is particularly desirable for process analysis. (C) 2002 Elsevier Science B.V. All rights reserved.
- low-field NMR spectrometry
- process analysis
- polyether polyols
- ethylene oxide
- direct exponential curve resolution algorithm