Method for detecting alkalinity in water quality:Potentiometric titration method (automatic titrator)

1. Principle

By monitoring the pH change of the solution during titration with a pH electrode, the endpoint is determined by a potential jump, which is suitable for turbid or colored water samples.

2. Steps

Connect the automatic titrator, install the pH electrode and burette.

Take 100 mL of water sample into a titration cup and select the "Alkalinity Titration" program.

The instrument automatically adds phenolphthalein indicator (or simulates phenolphthalein endpoint pH 8.3), titrates until the potential jumps, and records P alkalinity.

Continue to add methyl orange indicator (or simulate the endpoint pH of methyl orange at 4.3), titrate until the second potential jump, and record the M alkalinity.

3. Advantages

Avoiding manual judgment of endpoint errors, resulting in more accurate results.

It can simultaneously measure P alkalinity and M alkalinity, suitable for batch testing.

Key precautions:

Reagent purity: Analytical grade reagents should be used, and standard acids should be calibrated regularly.

Indicator selection: Adjust the amount of indicator according to the alkalinity range of the water sample to avoid unclear color changes at the endpoint.

Titration speed: When approaching the endpoint, acid solution should be added dropwise to prevent excess.

Carbon dioxide interference: After collecting water samples, they should be immediately sealed and avoid vigorous shaking before testing.

Temperature control: The titration process is kept stable at room temperature (20-25 ℃), and temperature affects pH value and reaction rate.

Application Scenario:

Drinking water treatment: Monitor alkalinity to control the stability of disinfectants (such as chlorine).

Industrial circulating water: Evaluate the buffering capacity of water bodies to prevent scaling or corrosion.

Environmental monitoring: Determine the self purification capacity of water bodies and the impact of acid rain.

Boiler water: Control alkalinity to avoid steam water co distillation or metal corrosion.