Measurement of pHT values of Tris buffers in artificial seawater at varying mole ratios of Tris:Tris·HCl

Measurements of total pH, pHT, in Harned cells are reported for 2-amino-2-hydroxymethyl-1,3-propanediol (Tris) buffers in artificial seawater (ASW) of salinity 35 at three molality ratios of Tris to Tris·HCl: 0.03:0.05, 0.04:0.04, and 0.05:0.03. The ASW formulation was derived from the 2008 International Association for the Physical Sciences of the Oceans (IAPSO) composition of seawater (Millero et al., 2008). The pHT value of each buffer was measured at 288.15 K, 298.15 K, and 308.15 K (15 °C, 25 °C, and 35 °C). Measurement uncertainties compliant with the ISO GUM (JCGM, 2008) are provided for each buffer. These new formulations extend the available data for Tris buffers in ASW to pHT values that bracket the pHT range of natural surface seawaters at 298.15 K. The data provide a framework for future multiple-point calibrations of spectrophotometric and potentiometric pHT measurements traceable to these new buffers.