Advancing Quantitative 31P NMR Spectroscopy for Reliable Thiol Group Analysis

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 Mn 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.