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Product Name: Spectrophotometric Seawater pH Analyzer

model AS-spec-pH1


1. Precision: better than 0.001 pH units.

2. Accuracy: better than 0.005 pH units.

3. Wavelengths for pH analysis: 434 nm, 578 nm, and 730 nm.

4. Indicator for pH: m-cresol purple.

5. Spectrophotometer: Agilent 8453 or 8454

6. Digital Pump: Kloehn V6 pump equipped with a 12-port valve and a 25 mL syringe

7. Spectrophotometric cell: 10 cm with thermostatic water jacket.

8. Precision of temperate-control system: 0.01°C

9. Automated: run 8 samples sequentially

10. Typical sample volume: 60 mL per analysis

11. Time consumption: ~4 minutes per analysis

12. Working environment: Both land and shipboard laboratories


The Apollo SciTech’s AS-spec-pH1 Analyzer has been developed for high precision and accuracy, automated 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 (434 nm, 578 nm, and 730 nm) 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 Carter et al. (2013) with improvements. A high-quality Agilent spectrophotometer (model 8453 or 8454) is used for the colorimetric determination and a high precision Kloehn digital pump is used for the delivery of pH indicator and the sample. An innovative thermostated spectrophotometric flow cell is built in-house which effectively controls all sample temperatures to a describable constant temperature in the analytical cell. 

Sample Analysis Results

Differences in pH between repeat analyses in the same sample.



Carter, B. R., J. A. Radich, H. L. Doyle, and A. G. Dickson. 2013. An automated system for spectrophotometric seawater pH measurements. Limnol. Ocean. Methods, 11: 16–27.

Clayton, T. D., and R. H. Byrne. 1993. Spectrophotometric seawater pH measurements: total hydrogen ion concentration scale calibration of m-cresol purple and at-sea results. Dee-Sea Res., 40: 2315–2329.

Liu, X., M. C. Patsavas, and R. H. Byrne. 2011. Purification and Characterization of meta-Cresol Purple for Spectrophotometric Seawater pH Measurements. Environ. Sci. Technol., 45: 4862–4868. doi:10.1021/es200665d


Manufacturer: Apollo, USA

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