Work

Systematic errors in isothermal titration calorimetry: The role of feedback power and effects of mixing and diffusion on concentrations

Year: 2025

Type: article

Abstract: Using experiments based on the NaCl dilution calibration method, we examine several previously unstudied instrumental effects that can lead to systematic errors in isothermal titration calorimetry (ITC). We confirm earlier results that power feedback can affect estimated heats and find further that it can also affect cell temperature and introduce temperature “noise.” To estimate effects from loss of titrant from the syringe through diffusion, and concentration changes in the cell from mixing with the overflow volume, we conduct experiments with injections separated by time intervals Δ t from 8 to 60 minutes, giving run durations from 6 hrs to over 2 days. Because the effects are small, we have developed a global least-squares fitting algorithm to analyze 20 datasets simultaneously, from which three parameters governing diffusion and mixing (“leakage”) are estimated, along with calibration parameters for heat and cell volume. Expressed as an effective volume loss from the syringe, Δ v dif is found to be of order ∼0.03 μL per injection for NaCl into water. Its effect is predicted to be negligible in many ITC applications. The effects from leakage are more significant but their neglect is still predicted to affect both NaCl calibration and 1:1 binding results by ∼1%, which is marginally significant for calibration but seldom so for 1:1 binding. The calibration results for the cell volume V 0 are particularly sensitive to temperature and to the literature source for the relative molar enthalpy function for NaCl( aq ). • Likely ITC instrumental sources of systematic error examined in VP-ITC. • Feedback power affects measured heats. • Diffusion from syringe and mixing with overflow volume alter concentrations. • Problems studied using variable injection volumes v and intervals up to 60 min. • Global analysis of 20 datasets → both effects at 1% level in typical experiments.

Source: Analytical Biochemistry

DOI: 10.1016/j.ab.2025.116010

Authors: Žiga Medoš, Marija Bešter-Rogač, Epameinondas Leontidis, Joel Tellinghuisen

Institutions: University of Ljubljana, University of Cyprus, Vanderbilt University

Language: English

Topic: thermodynamics and calorimetric analyses

Subfield: Physical and Theoretical Chemistry

Field: Chemistry

Domain: Physical Sciences

Open Access status: hybrid

Estimated APC paid: $3,540

Funder: Javna Agencija za Raziskovalno Dejavnost RS