Measurement of pHT Values of Tris Buffers in Artificial Seawater at Varying Mole Ratios of Tris:Tris·HCl

Abstract

Measurements of total pH, pHT, in electrochemical cells without transference are reported for 2 amino-2-hydroxymethyl 1,3-propanediol (‘Tris’) buffers in synthetic seawater (SSW) 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 SSW formulation was derived from the 2008 International Association for the Physical Sciences of the Oceans (IAPSO) composition of seawater [ ]. 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). The measured pHT value of the equimolal formulation at 298.15 K agrees with published data to within the measurement uncertainty. These new formulations extend the available data for Tris buffers in SSW to two new pHT reference values that bracket the pHT range of natural surface seawaters and provide measurement uncertainties compliant with the ISO GUM [ ]. The data provide a framework for multiple-point calibrations of spectrophotometric and potentiometric pHT measurements traceable to these buffers.