This British Standard is an adoption of an ISO standard. You can access the ISO version here.
This document specifies a spectrophotometric determination of the pHT of seawater on the total hydrogen ion concentration pH scale. The total hydrogen ion concentration, [H+]T, is expressed as moles per kilogram of seawater. The method is suitable for assaying oceanic levels of pHT from 7,4 to 8,2 for normal seawater of practical salinity ranging from 20 to 40.