Rapid determination of the acidity, alkalinity and carboxyl content of aqueous samples by 1H NMR with minimal sample quantity

Matthew Wallace, Kevin Lam, Agne Kuraite, Yaroslav Z. Khimyak

Research output: Contribution to journalArticle

1 Downloads (Pure)

Abstract

The titratable acidity, alkalinity, and carboxylate content are fundamental properties required for the understanding of aqueous chemical systems. Here, we present a set of new methods that allow these properties to be determined directly by 1H NMR without the labor, cost, and sample quantity associated with running separate potentiometric or conductometric titrations. Our methods require only the measurement of the pH-sensitive 1H chemical shifts of indicator molecules and do not require the tedious titration of reagents into a sample. To determine the titratable acidity, an excess of 2-methylimidazole (2MI) is added to a sample and the quantity of protons absorbed by 2MI is determined from its 1H chemical shifts. The titratable alkalinity of a sample can be similarly determined using acetic acid. To determine the concentration of deprotonated carboxylates, a sample is acidified with HCl, and the quantity of H+ absorbed is determined from the 1H chemical shift of methylphosphonic acid. We validate our methods by demonstrating the measurement of the acidity of fruit-flavored drinks, the alkalinity of tap water, and the carboxylate content of nanocellulose dispersions.

Original languageEnglish
Pages (from-to)12789–12794
Number of pages6
JournalAnalytical Chemistry
Volume92
Issue number19
Early online date8 Sep 2020
DOIs
Publication statusPublished - 6 Oct 2020

Cite this