Calibrating ITC instruments : problems with weak base neutralization

Medoš, Žiga (author), Bešter-Rogač, Marija (author), Leontidis, Epameinondas (author), Tellinghuisen, Joel (author)

Modern isothermal titration calorimetry instruments give great precision, but for comparable accuracy they require chemical calibration. For the heat factor, one recommended process is HCl into the weak base TRIS. In studying this reaction with a VP-ITC and two Nano-ITCs, we have encountered some problems, most importantly a titrant volume shortfall Δv ≈ 0.3 μL, which we attribute to diffusive loss of HCl in the syringe tip. This interpretation is supported by a mathematical treatment of the diffusion problem. The effect was discovered through a variable-v protocol, which thus should be used to properly allow for it in any reaction that similarly approaches completion. We also find that the effects from carbonate contamination and from OH− from weak base hydrolysis can be more significant that previously thought. To facilitate proper weighting in the least-squares fitting of data, we have estimated data variance functions from replicate data. All three instruments have low-signal precision of σ ≈ 1 μJ; titrant volume uncertainty is a factor of ∼2 larger for the Nano-ITCs than for the VP-ITC. The final heat factors remain uncertain by more than the ∼1 % precision of the instruments and are unduly sensitive to the HCl concentration.

• Language: English
• Keywords: calorimetry, isothermal titration calorimetry, calibration, acid-base reaction, diffusion
• Work type: Article
• Typology: 1.01 - Original Scientific Article
• Organization: FKKT - Faculty of Chemistry and Chemical Technology
• Publication status: Published
• Publication version: Version of Record
• Year: 2024
• Number of pages: 9 str.
• Numbering: Vol. 694, art.115602
• PID: 20.500.12556/RUL-160001
• UDC: 543.57:536.6
• ISSN on article: 0003-2697
• DOI: 10.1016/j.ab.2024.115602
• COBISS.SI-ID: 201903875
• Publication date in RUL: 07.08.2024

Record is a part of a journal

• Title: Analytical biochemistry
• Shortened title: Anal. biochem.
• Publisher: Elsevier
• ISSN: 0003-2697
• COBISS.SI-ID: 6506759

Licences

• License: CC BY-NC 4.0, Creative Commons Attribution-NonCommercial 4.0 International
• Link: http://creativecommons.org/licenses/by-nc/4.0/
• Description: A creative commons license that bans commercial use, but the users don’t have to license their derivative works on the same terms.

Secondary language

• Language: Slovenian
• Keywords: kalorimetrija, izotermna titracijska kalorimetrija, kalibracija, kislinsko-bazna ravnotežja, difuzija

Projects

• Funder: ARIS - Slovenian Research and Innovation Agency
• Project number: P1-0201
• Name: Fizikalna kemija

• Funder: ARIS - Slovenian Research and Innovation Agency
• Project number: N1-0186
• Name: Metalcarborani kot edinstveno izhodišče za pripravo funkcionalnih nanostrukturiranih in polimernih materialov