Spectrophotometric determination of pH and alkalinity in seawater using pH indicator dyes.

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In the study of the oceanic carbon system, the precise determination of pH is essentially necessary. The method using a pH electrode is insufficient for the purpose. We have considered to use a dye method for the pH measurement. Recent development in the spectrophotometer makes possible the application. We have made further improvement for the spectrophotometer system. The system can measure the adsorbance curve within 2.5 sec. with an accuracy of 0.0001 of absorbance. Using the system and seawater sample of 70ml, we have the precision of <plus-minus>0.001 pH unit. The method have been successfully applied to the actual seawater samples on board the research vessel, Hakuho Maru in 1994-199Alkalinity determination is improved by combining a single-step titration and the spectrophotometric pH determination using Bromophenol Blue. We have the precision of <plus-minus>0.001mue