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

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Wallace, Matthew ORCID: https://orcid.org/0000-0002-5751-1827, Lam, Kevin, Kuraite, Agne and Khimyak, Yaroslav Z. ORCID: https://orcid.org/0000-0003-0424-4128 (2020) Rapid determination of the acidity, alkalinity and carboxyl content of aqueous samples by 1H NMR with minimal sample quantity. Analytical Chemistry, 92 (19). 12789–12794. ISSN 0003-2700

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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.

Item Type: Article
Faculty \ School: Faculty of Science > School of Pharmacy (former - to 2024)
UEA Research Groups: Faculty of Science > Research Groups > Pharmaceutical Materials and Soft Matter
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Depositing User: LivePure Connector
Date Deposited: 10 Sep 2020 23:57
Last Modified: 04 Dec 2024 01:33
URI: https://ueaeprints.uea.ac.uk/id/eprint/76834
DOI: 10.1021/acs.analchem.0c02594

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