ISO 18191:2015 specifies a spectrophotometric determination of the pHt of sea water on the total hydrogen ion concentration pH scale using the indicator dye m-cresol purple. The total hydrogen ion concentration, [H+]t, is expressed as moles per kilogram of sea water. The method is suitable for assaying oceanic levels of pHt 7,4 to 8,2 for normal sea water of practical salinity ranging from 20 to 40.
GSO ISO 18191:2021 history
2021GSO ISO 18191:2021 Water quality — Determination of pHt in sea water — Method using the indicator dye m-cresol purple