Abstract
The apparent molal volumes and compressibilities of Tris and Tris–HCl have been determined in water (5–45°C) and 0.725m NaCl (5–25°C). The changes in the volume (ΔV) and compressibility (Δκ) for the dissociation of Tris–H+
Tris-H+=Tris+H+
as functions of temperature in water and 0.725m NaCl have been determined from these measurements. The values of ΔV and Δκ have been used to determine the effect of pressure on the dissociation constant for Tris–H+ (KP/K0).
ln(KP/K0)=-∆V/(RT)P+0.5∆k/(RT)P2
These results will be useful in the calibration of pH systems making in-situ measurements at high pressure in seawater. In 0.725m NaCl at 5°C and a pressure of 2000bar, the dissociation constant is reduced by 29%.
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•Tris buffers are used to calibrate pH electrodes and indicators.•Volumes and compressibilities for Tris–H+ dissociation were measured.•The effect of pressure on the dissociation constant (KP/K0) was determined.•In 0.725m NaCl at 5°C and 2000bar, (KP) is reduced by 29%.•Results will enable direct calibration of pH sensors at high pressure in seawater.
