Preparation of 2‐amino‐2‐hydroxymethyl‐1,3‐propanediol (TRIS) pHT buffers in synthetic seawater Limnology and Oceanography: Methods

Buffers of known quality for the calibration of seawater pHT measurements are not widely or commercially available. Although there exist published compositions for the 0.04 mol kg‐H2O−1 equimolar buffer 2‐amino‐2‐hydroxymethyl‐1,3‐propanediol (TRIS)‐TRIS · H+ in synthetic seawater, there are no explicit procedures that describe preparing this buffer to achieve a particular pHT 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 pHT within 0.006 of the published pHT value originally assigned by DelValls and Dickson (1998), 8.094 at 25°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 pHT, an uncertainty goal appropriate to “identify relative spatial patterns and short‐term variation.” Grant no. NA15OAR4320071