TY  - JOUR
A1  - Burger, René
A1  - Rumpf, Jessica
A1  - Do, Xuan Tung
A1  - Monakhova, Yulia
A1  - Diehl, Bernd W. K.
A1  - Rehahn, Matthias
A1  - Schulze, Margit
T1  - Is NMR combined with multivariate regression applicable for the molecular weight determination of randomly cross-linked polymers such as lignin?
JF  - ACS Omega
N2  - The molecular weight properties of lignins are one of the key elements that need to be analyzed for a successful industrial application of these promising biopolymers. In this study, the use of 1H NMR as well as diffusion-ordered spectroscopy (DOSY NMR), combined with multivariate regression methods, was investigated for the determination of the molecular weight (Mw and Mn) and the polydispersity of organosolv lignins (n = 53, Miscanthus x giganteus, Paulownia tomentosa, and Silphium perfoliatum). The suitability of the models was demonstrated by cross validation (CV) as well as by an independent validation set of samples from different biomass origins (beech wood and wheat straw). CV errors of ca. 7–9 and 14–16% were achieved for all parameters with the models from the 1H NMR spectra and the DOSY NMR data, respectively. The prediction errors for the validation samples were in a similar range for the partial least squares model from the 1H NMR data and for a multiple linear regression using the DOSY NMR data. The results indicate the usefulness of NMR measurements combined with multivariate regression methods as a potential alternative to more time-consuming methods such as gel permeation chromatography.
Y1  - 2021
U6  - http://dx.doi.org/10.1021/acsomega.1c03574
SN  - 2470-1343
VL  - 6
IS  - 44
SP  - 29516
EP  - 29524
PB  - ACS Publications
CY  - Washington, DC
ER  - 
TY  - JOUR
A1  - Lindner, Simon
A1  - Burger, René
A1  - Rutledge, Douglas N.
A1  - Do, Xuan Tung
A1  - Rumpf, Jessica
A1  - Diehl, Bernd W. K.
A1  - Schulze, Margit
A1  - Monakhova, Yulia
T1  - Is the calibration transfer of multivariate calibration models between high- and low-field NMR instruments possible? A case study of lignin molecular weight
JF  - Analytical chemistry
N2  - Although several successful applications of benchtop nuclear magnetic resonance (NMR) spectroscopy in quantitative mixture analysis exist, the possibility of calibration transfer remains mostly unexplored, especially between high- and low-field NMR. This study investigates for the first time the calibration transfer of partial least squares regressions [weight average molecular weight (Mw) of lignin] between high-field (600 MHz) NMR and benchtop NMR devices (43 and 60 MHz). For the transfer, piecewise direct standardization, calibration transfer based on canonical correlation analysis, and transfer via the extreme learning machine auto-encoder method are employed. Despite the immense resolution difference between high-field and low-field NMR instruments, the results demonstrate that the calibration transfer from high- to low-field is feasible in the case of a physical property, namely, the molecular weight, achieving validation errors close to the original calibration (down to only 1.2 times higher root mean square errors). These results introduce new perspectives for applications of benchtop NMR, in which existing calibrations from expensive high-field instruments can be transferred to cheaper benchtop instruments to economize.
Y1  - 2022
SN  - 1520-6882
U6  - http://dx.doi.org/10.1021/acs.analchem.1c05125
VL  - 94
IS  - 9
SP  - 3997
EP  - 4004
PB  - ACS Publications
CY  - Washington, DC
ER  -