pH measurement of dirty water sources by ISFET: addressing practical problems

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Abstract
Purpose: To expose the gate of ion‐sensitive field‐effect transistor (ISFET) to filthy and muddy water, suspended algae, etc. investigate the influence of these conditions on device performance and suggest measures for using the device in applications where suspended soil particles are present.Design/methodology/approach: In this paper, cleaning procedure to make the blocked ISFET operative has been described. The effect of dirty water on pH sensitivity factor of ISFET, after it restarted functioning, has been measured. ISFET package has been modified. A relatively simple disposable nylon mesh with openings of size 100 μm for filtering bigger particles and lower for smaller particles, has been proposed for dirty applications to minimize device failures. This sieves away any dirt and thereby avoids failure.Findings: The device action is frequently blocked by deposition of dirt on the gate. Generally, it is recoverable by proper cleaning action although with reduced sensitivity. This necessitates recalibration. But a protective filter helps in reducing failures. It is more advantageous to prevent clogging of ISFET than to revive a clogged device, sacrificing sensitivity.Research limitations/implications: After recovery, the original sensitivity of the device is not achieved, and the device has to be used with degraded sensitivity.Practical implications: Measurement of pH of actual sources of water, whether clean or dirty, is important.Originality/value: Problems of pH measurements of dirty samples have been studied. The study helps in understanding device behaviour in these samples and provides suitable corrective measures. Further, the pH survey of dirty and clean water samples provides useful information about the pH distribution and balance in nature.

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