Spectrophotometric Seawater
pH Analyzer

Model AS-spec-pH1

Apollo SciTech’s AS-spec-pH1 Analyzer has been developed for high precision and accuracy, automated and fast determination of seawater pH. It is based on the principle of colorimetric determination of the relative color intensity using a pH indicator (m-cresol purple) at three wavelengths (434nm, 578nm, 730nm) with the first two absorptions as a known function of pH, and the third one serves as a baseline correction (Clayton and Byrne 1993; Liu et al. 2011). The automated analyzer is designed according to that of Carter et al. (2013) with improvements. A high quality Agilent spectrophotometer (model 8453) is used for the colorimetric determination and a high precision Kloehn digital pump is used for the delivery of pH indicator and the sample. 


  • Precision: better than 0.001 pH units
  • Accuracy: better than 0.005 pH units
  • Wavelengths for pH analysis: 434nm, 578nm, 730nm
  • Indicator for pH: m-cresol purple
  • Spectrophotometer: Agilent 8453
  • Digital Pump: Kloehn V6 pump equipped with a 12-port valve and a 25 mL syringe
  • Spectrophotometric cell: 10 cm with thermostated
  • Precision of Temperate-control system:   0.01oC
  • Automated: run 8 samples sequentially
  • Typical sample volume: 60 mL per analysis
  • Time consumption: ~4 minutes per analysis
  • Working environment: Both land and shipboard laboratories