How to ensure reliability of your pH measurements?

pH meter with reference electrode

pH meter with reference electrode

A pH meter is an indispensable commodity in any chemical laboratory irrespective of its size of scale of operation. Useful tips on correct handling and care of pH meter were provided earlier. The present article is a further elaboration on the subject to help you gain greater confidence on the observed pH readings.

Electrode should not remain dry

Often due to hurry or carelessness the electrode remains hanging on the stand and over a period of time it can dry out resulting in loss in its sensitivity, drifting values, slow response and unreliable readings. The electrode should always be kept immersed in the neutral buffered solution. Storage in deionized water is not recommended as is promotes migration of ions from inside the bulb to solution outside thereby affecting its performance. Fortunately the performance of a dried out electrode can be restored by immersion in storage solution and subsequent calibration before being put to use. Take care to replenish the immersion solution from time to time so that evaporation loss can be avoided.

Always rinse the bulb instead of wiping

It is advised to simply rinse the electrode after use with distilled or deionized water. Soak the water droplets, if any, with soft tissue and avoid rubbing as in the process a static charge is introduced which can interfere with the readings

Uniformity of observation temperature

The pH of the solution is dependent on its temperature so both calibration standard buffer and test solution should be kept at same temperature before recording the pH readings..

Replace calibration buffers before expiry date

Buffers have a shelf life. However, even before the expiry date if any solid suspensions or haziness are observed the buffer should be discarded and replaced with fresh stock.

Allow readings to stabilize

A slight drift in pH readings for a few seconds is a common observation. This is generally due to clogging of the electrode junction due to crystal deposits. The crystalline deposits can be removed by gentle flushing with warm deionized water

Choose the right bulb design

pH electrodes are commonly available with spherical or conical designs. The choice of correct geometry depends on the nature of sample and its available quantity. It is essential that the electrode should be completely dipped in the solution to be measured. Conical tipped electrodes should be referred for pH measurements of soft permeable solids or suspensions and slurries.

Replenishment of electrolyte level inside the bulb

The electrolyte level inside the bulb should not be allowed to get low as the readings can become erratic at low electrolyte levels

Timely electrode replacement

As the electrode starts ageing the response can get deteriorated. In case the observed calibration results differ significantly from known standard values it is time to replace the electrode.

Regular daily calibration schedule alongwith with careful handling ensures long time use of the pH meter along with highest reliability on results.

About Dr. Deepak Bhanot

Dr Deepak Bhanot is a seasoned professional having nearly 30 years expertise beginning from sales and product support of analytical instruments. After completing his graduation and post graduation from Delhi University and IIT Delhi he went on to Loughborough University of Technology, UK for doctorate research in analytical chemistry. His mission is to develop training programs on analytical techniques and share his experiences with broad spectrum of users ranging from professionals engaged in analytical development and research as well as young enthusiasts fresh from academics who wish to embark upon a career in analytical industry.

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