Calibrating ITC instruments: Problems with weak base neutralization

IF 4.6 Q2 MATERIALS SCIENCE, BIOMATERIALS
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引用次数: 0

Abstract

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.

Abstract Image

校准 ITC 仪器:弱碱中和的问题。
现代等温滴定量热仪精度很高,但要达到相当的精度,需要进行化学校准。对于热因子,一种推荐的方法是将盐酸转化为弱碱 TRIS。在使用 VP-ITC 和两个 Nano-ITC 研究该反应时,我们遇到了一些问题,其中最重要的是滴定剂体积不足 Δv ≈ 0.3 μL,我们将其归因于盐酸在注射器针尖的扩散损失。这一解释得到了扩散问题数学处理的支持。这种效应是通过变量-v 方案发现的,因此在任何类似的接近完成的反应中都应适当考虑这种效应。我们还发现,碳酸盐污染和弱碱水解产生的 OH- 的影响可能比以前认为的更为显著。为了便于在最小二乘法拟合数据时适当加权,我们从重复数据中估算了数据方差函数。所有三台仪器的低信号精度均为σ ≈ 1 μJ;滴定剂体积的不确定性对于 Nano-ITCs 而言比 VP-ITC 大 2 倍。最终热因子的不确定性仍然高于仪器精度的 ∼1%,并且对盐酸浓度过于敏感。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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来源期刊
ACS Applied Bio Materials
ACS Applied Bio Materials Chemistry-Chemistry (all)
CiteScore
9.40
自引率
2.10%
发文量
464
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