Dataset: CRM raw absorbance

The temperature dependence of spectrophotometric pH measurements was determined and compared to values calculated from total alkalinity and dissolved inorganic carbon using different combinations of the required dissociation constants. Spectrophotometric measurements were made on two batches of CRMS (179 and 189) between -1.7 and 40 ˚C.

A custom designed spectrophotometric pH system was used similar to the system described in Carter et al. (2013). It consists of an Agilent 8454 UV-Vis spectrophotometer with a Kloehn v6 syringe pump to rinse, fill, and add the indicator dye to a 10 cm quartz microvolume spectrophotometer cell. A batch of ~2 millimolar Purified meta-cresol purple indicator dye (provided by Robert H. Byrne, University of South Florida) prepared in ~0.7 molar NaCl was used. The pH on the total scale was calculated using the equations of Liu et al. (2011). The dye perturbation was accounted for by making 20 measurements at each temperature with varying amounts of dye and extrapolating to zero dye added. Both the final pH values and the raw absorbances are available from BCO-DMO. Further details of the methods can be found in Woosley (2020).