Hanna Instruments HI 84431 User Manual
Page 6
6
The results of a titration provide a means to classify the principle forms of alkalinity.
Relationship of titrant volumes for alkalinity calculations:
According to the Standard Methods of Waters and Wastewaters Analysis, there are two options to
determine water alkalinity:
1) Strong alkalinity determination by titration of the water sample with strong acid solution
to 8.3 pH (known as phenolphtalein alkalinity).
2) Total alkalinity determination by titration of the water sample with strong acid solution
to 4.5 pH (known as bromcresol green alkalinity).
Potentiometric end point detection using a pH electrode is more objective than using visual end
point determinations with color changing indicators. The HI 84431 minititrator is a potentiometric
titrator. The instrument also can be used as a pH meter. The volume of titrant dispensed necessary
to reach the end point is then used to calculate the water alkalinity expressed in mg/L as CaCO
3
meq/L as CaCO
3
.
Interferences:
•
dissolved gases, lost or gained during samples storage or transport can modify the
alkalinity of the samples;
•
presence in the samples of the: precipitates, solid suspensions, oils, soaps can coat a pH
electrode;
To eliminate or diminish the interference effects, it is recommended:
•
to protect the samples against the atmospheric action (store in an airtight vessel);
•
to avoid vigorous shaking or mixing: stir gently;
•
maintenance of the pH electrode (see section Electrode Conditioning and Maintenance)
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