|Title||Metrology for pH measurements in brackish waters-Part 1: Extending electrochemical pH(T) measurements of TRIS buffers to salinities 5-20|
|Publication Type||Journal Article|
|Year of Publication||2018|
|Authors||Muller J.D, Bastkowski F., Sander B., Seitz S., Turner D.R, Dickson AG, Rehder G.|
|Journal||Frontiers in Marine Science|
|Type of Article||Article|
|Keywords||baltic; brackish water; concentration scale; constant; dissolved organic-matter; Environmental Sciences & Ecology; Harned cell; m-cresol purple; Marine & Freshwater Biology; ph; primary standard; sea; seawater; total scale; Traceability; TRIS|
Harned cell pH(T) measurements were performed on 2-amino-2-hydroxymethyl-1,3-propanediol (TRIS) buffered artificial seawater solutions in the salinity range 5-20, at three equimolal buffer concentrations (0.01, 0.025, 0.04 mol.kg-H2O-1), and in the temperature range 278.15-318.15 K. Measurement uncertainties were assigned to the pH(T )values of the buffer solutions and ranged from 0.002 to 0.004 over the investigated salinity and temperature ranges. The pH(T) values were combined with previous results from literature covering salinities from 20 to 40. A model function expressing pH(T) as a function of salinity, temperature and TRIS/TRIS center dot H+ molality was fitted to the combined data set. The results can be used to reliably calibrate pH instruments traceable to primary standards and over the salinity range 5-40, in particular, covering the low salinity range of brackish water for the first time. At salinities 5-20 and 35, the measured dependence of pH(T) on the TRIS/TRIS center dot H+ molality enables extrapolation of quantities calibrated against the pH(T) values, e.g., the dissociation constants of pH indicator dyes, to be extrapolated to zero TRIS molality. Extrapolated quantities then refer to pure synthetic seawater conditions and define a true hydrogen ion concentration scale in seawater media.