An Automated Procedure for Laboratory and Shipboard Spectrophotometric Measurements of Seawater Alkalinity: Continuously Monitored Single-step Acid Additions

Building on the spectrophotometric procedure of Yao and Byrne (1998), an automated analysis system has been developed for laboratory and shipboard measurements of total alkalinity at a rate of 6 samples per hour. The system is based on single-point hydrochloric acid (HCl) titrations of seawater samples of a known volume with bromocresol purple as an indicator. The titration is continuously monitored using visible spectroscopy to guide the titration rate according to the real-time pH of the samples. Each titration is terminated just below the equivalence point to achieve a precision and accuracy near 1 μmol kg−1