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.
摘要：
现代等温滴定量热仪器提供了很高的精度，但对于可比的精度，他们需要化学校准。对于热因素，一种推荐的方法是HCl进入弱碱TRIS。在用一个VP-ITC和两个Nano-ITC研究这个反应时，我们遇到了一些问题，最重要的是滴定剂体积不足Δv≈0.3μL，我们将其归因于注射器尖端中HCl的扩散损失。扩散问题的数学处理支持了这种解释。效果是通过可变v协议发现的，因此，它应该被用来适当地允许它在任何类似接近完成的反应中。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显著。为了便于在数据的最小二乘拟合中进行适当的加权，我们从复制数据中估计了数据方差函数。所有这三种仪器的低信号精度均为σ≈1μJ；Nano-ITC的滴定剂体积不确定性比VP-ITC大2倍。Thefinalheatfactorsremainsuncertainbymorethanthe~1%precisionoftheinstrumentsandareundulatesensitivetotheHClconcentration.
