# 1H NMR Quantification of Aromatic Monomers from Reductive Catalytic Fractionation

## TL;DR

This paper shows that 1H NMR spectroscopy can quickly and accurately measure aromatic monomers from lignin in RCF oils, reducing the need for complex methods.

## Contribution

The study introduces 1H NMR as a reliable and convenient method for quantifying RCF aromatic monomers without liquid–liquid extraction.

## Key findings

- 1H NMR showed good agreement with UHPLC for 96 RCF oils with deviations of 0.5–1.1 wt%.
- S-type monomers like 4-ethylsyringol were reliably quantified, while G-type monomers had selectivity issues due to peak overlap.
- The method works on crude RCF oils without requiring extraction, simplifying the quantification process.

## Abstract

Reductive catalytic
fractionation (RCF) can produce high
yields
of aromatic monomers from lignin in native biomass. Quantification
of these aromatic monomers is a well-known but demanding task, in
part due to the lack of commercially available standards. Here, we
demonstrate 1H NMR spectroscopy as a complementary method
to rapidly quantify aromatic monomer concentrations in RCF oils. The
method exhibited good agreement with measurements from ultrahigh pressure
liquid chromatography (UHPLC) for 96 RCF oils with varying monomer
selectivity, with average absolute deviations of individual monomer
yields between 0.5 and 1.1 wt % (relative 11–17%) and R2 values above 0.9 compared to conventional UHPLC quantification.
Quantification of S-type monomers, including for 4-ethylsyringol and
4-propenylsyringol, was generally reliable. The validity of G-type
monomer quantifications depended on reaction selectivity due to overlap
between peaks of 4-ethylguaiacol and 4-(3-hydroxypropyl)-guaiacol.
The method could be applied on crude RCF oils without needing to perform
the liquid–liquid extraction typically done for RCF reactions,
thereby providing a convenient way to quantify lignin extraction and
aromatic monomer yield. Overall, 1H NMR spectroscopy can
serve as a rapid primary quantification or secondary validation method
for RCF monomer yield and selectivity measurements.