# Advancing Quantitative 31P NMR Spectroscopy for Reliable Thiol Group Analysis

## TL;DR

A new 31P NMR method using TMDP enables accurate and reliable thiol group analysis across various substrates.

## Contribution

A novel phosphitylation reagent (TMDP) extends 31P NMR for thiol quantification with high specificity and stability.

## Key findings

- The TMDP-based 31P NMR method shows superior selectivity and resolution compared to Ellman’s assay and 1H NMR.
- The method is effective for substrates ranging from small molecules to polymers with molecular weights up to 8000 g·mol–1.
- It provides simultaneous insights into hydroxy and carboxyl functionalities alongside thiol quantification.

## Abstract

Accurate thiol quantification is essential for advancing
thiol–X-ligation
strategies in polymer and materials synthesis. Conventional assays,
most notably Ellman’s test, are limited in scope, particularly
for hydrophobic or multifunctional thiols. Here, we introduce a straightforward
and broadly applicable 31P NMR spectroscopy method for
thiol quantification, using 2-chloro-4,4,5,5-tetramethyl-1,3,2-dioxaphospholane
(TMDP) as a phosphitylation reagent. The approach extends established 31P NMR protocols for hydroxyl and carboxyl group analysis
to thiols, offering high specificity and stability in readout. The
method demonstrates applicability across a wide range of substrates,
from small organic molecules to polymeric multi thiols with M
n up to 8000 g·mol–1.
Comparative validation against Ellman’s assay and 1H NMR spectroscopy reveals superior selectivity and resolution of
the TMDP-based 31P NMR protocol, particularly for technical-grade
thiols, where conventional methods fail to distinguish degradation
products. This study establishes the TMDP-enabled 31P NMR
as a reliable, information-rich tool for thiol quantification, giving
simultaneously insights on hydroxy and carboxyl functionality patterns.