Sea water — Determination of total alkalinity

The REX Ti-50 Automatic Potential Titrator allows quick and simple determinations of the total alkalinity of sea water.

1. Standard Reference

ISO 22719:2008 《Water quality — Determination of total alkalinity in sea water using high precision potentiometric titration》

This International Standard specifies an open-cell potentiometric titration determination of total alkalinity in sea water. The results are expressed in moles per kilogram of sea water. The method is suitable for assaying oceanic levels of total alkalinity (2 000 µmol kg⁻¹ to 2 500 µmol kg⁻¹) for normal sea water of practical salinity ranging from 30 to 40.

2. The Principle

A known amount of sea water is placed in an open cell where it is titrated in a two stage procedure with a solution of hydrochloric acid. The acid solution also contains sodium chloride to compensate for the sodium ion concentration of the sea water and to maintain approximately constant activity coefficients during the titration. An open cell is used so that, in subsequent data processing, it can be assumed that the total dissolved inorganic carbon (and hence the residual bicarbonate ion concentration) is approximately zero between pH 3,0 and pH 3,5. The progress of the titration is monitored using a pH glass-reference cell, and the total alkalinity is computed from the titrant volume and electromotive force (EMF) measurements using a non-linear least-squares approach allowing for the reactions of hydrogen ion with sulfate and fluoride ions.

3. Recommended Configuration

1. Ti-50 Automatic Potential Titrator 

• Range：(-2000.00~2000.00) mV
• mV Accuracy：±0.03% or ±0.2mV
• 1 extra burette driver can be installed (optional).
• Replaceable burette with high-accuracy (10 ml or 20 ml selectable).
• Support acid-base titration, non-aqueous aqueous phase titration, constant titration, REDOX titration, precipitation titration, complexation titration
• Support the following titration modes: DET (dynamic equivalence point titration), MET (monotone equivalence point titration), SET (Preset Endpoint Titration) and MAT (manual titration).
• Titration methods, curves and results are displayed in detail.

• Include 231-01 pH Indicator Elecrode and 232-01 reference electrode.

2. Auxiliary titration unit 20mL
3. Burette valve device 20mL (SC5.461.057)
4. Anti-diffusion capillary
5. Electrodes

• 231-01 pH Indicator Elecrode
• 232-01 Reference electrode（Saturated KCl）

4. Titration Setting

• Acid-base titration
• Sample: DET (dynamic equivalence point titration)
• Blank Sample: MET (monotone equivalence point titration)