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

1994 Fiscal Year Final Research Report Summary

• Project/Area Number: 05554014
• Research Category: Grant-in-Aid for Developmental Scientific Research (B)
• Allocation Type: Single-year Grants
• Research Field: 地球化学
• Research Institution: Hokkaido University
• Principal Investigator: TSUNOGAI Shizuo Hokkaido University, Graduate School of Environmental Earth Science Professor, 大学院・地球環境科学研究科, 教授 (00001587)
• Co-Investigator(Kenkyū-buntansha): WATANABE Shuichi Hokkaido University, Graduate School of Environmental Earth Science Instructor, 大学院・地球環境科学研究科, 助手 (00167131)
• Project Period (FY): 1993 – 1994
• Keywords: Seawater / pH / Spectrophotometory / Carbon Dioxide / Alkalinity / pH Indicator / Dissolved Inorganic Carbon / Precise Determination of pH

Research Abstract

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 1994-199
Alkalinity 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