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Application

Measuring pH of Pure Water & Other Low Conductivity waters

Introduction

Measuring pH in pure water may seem simple in theory. For example, pure water should be neutral- pH 7.0 and there should be no interferences.

Measuring the pH of pure water is challenging because the pH electrode response tends to drift and may be slow, non-reproducible and inaccurate. Measurements in these samples are more difficult because of the low conductivity of the sample, differences between the low ionic strength solutions and normal ionic strength buffers, changes in the liquid junction potential and the absorption of carbon dioxide into the sample. Since pure water solutions have a low conductivity, the solution will tend to act as an “antenna” and the electrode response can be noisy.

The three most common challenges when testing pH in pure water and other low conductivity waters are:

1. Electrode Drift
Low conductivity water is a high resistance sample. This may lead to noisy readings and signal drift.
2. Contamination of Sample
Due to the low concentration of ions in these waters, they are also poorly buffered and so are subject to contamination (e.g. from CO2 or ammonia absorption, and/or cross contamination from other sources, during sampling, transport, storage, handling, and testing).
3. Inaccurate Measurement
The large difference in ionic strength between the electrode filling solution inside and the sample outside the electrode may lead to significant junction potentials. This can affect accuracy, cause long stabilization times, and lead to poor precision.

By understanding the challenges associated with measuring pH in pure water and other low conductivity liquids, you can overcome them and ensure that your pH measurements are reliable and repeatable.

Ultra-Pure pH samples below 1 µSiemens

Bela Instruments recommends BI-10 pH Sensor

For low-conductivity media less than 1 µS/cm, refillable liquid electrolyte. Precise measurements due to self-cleaning junctions with high outflow of electrolyte even for media of very low conductivity.

A specialized pH System i.e. BELA Make pH Transmitter cum controller 672P series with BI-10 pH Sensor.

672p
pH Transmitter cum controler692P Series
BI-10
PH Sensor Model: BI-10

ure water pH Measurement below 10 µSiemens.

Bela Instruments recommends BI-11 pH Sensor

pH Sensor specially designed for low-conductivity media less than 10 µS/cm with built-in temperature element. The unique construction methods used allow this electrode to operate under pressures of up to 5 bar and temperature up to 80 ºC.

A specialized pH System i.e. BELA Make pH Transmitter cum controller 672P series with BI-11 pH Sensor.

672p
pH Transmitter cum controller 672P Series
BI-10
PH Sensor Model: BI-11

Introduction pH Sensor Housing available for Online Measurement.

MOC options available:
1. PVC- Polyvinyl chloride
2. PP – Polypropylene
3. TF – Teflon
4. SS – SS316