Preparation of 2-amino-2-hydroxymethyl-1,3-propanediol (TRIS) pHT buffers in synthetic seawater

Buffers of known quality for the calibration of seawater pH(T)measurements are not widely or commercially available. Although there exist published compositions for the 0.04 mol kg-H(2)O(-1)equimolar buffer 2-amino-2-hydroxymethyl-1,3-propanediol (TRIS)-TRIS center dot H(+)in synthetic seawater, there are no explicit procedures that describe preparing this buffer to achieve a particular pH(T)with a known uncertainty. Such a procedure is described here which makes use of easily acquired laboratory equipment and techniques to produce a buffer with a pH(T)within 0.006 of the published pH(T)value originally assigned by DelValls and Dickson (1998), 8.094 at 25 degrees C. Such a buffer will be suitable for the calibration of pH measurements expected to fulfil the weather uncertainty goal of the Global Ocean Acidification Observation Network of 0.02 in pH(T), an uncertainty goal appropriate to identify relative spatial patterns and short-term variation.