pH meters are used in pharmaceutical, food and other industries to check or measure the pH of different materials. One key point to remember is that to measure the pH of any substance, it must be in liquid form, and we dip the electrode of the pH metre to check its pH value.
The pH metre must be calibrated before use to ensure accurate measurements, as any contamination, wear, or tear may affect the performance of the pH metre.
To calibrate the pH meter, different solutions of known pH are used, which are known as buffer solutions, and usually following pH range buffer solutions are used to calibrate the pH meter.
- Buffer solution of pH 7
- Buffer solution of pH 10
- Buffer solution of pH 4
One key point to remember while calibrating pH metres is that we always use a buffer solution of pH 7 first to calibrate the pH metre, and then we use the buffer solution of pH 4 or 10.
Now, a question comes to mind: why do we use the buffer solution of pH 7 first to calibrate the pH meter?
In this article, we will learn the logic behind the calibration of a pH metre with a buffer solution of pH 7 first.
Why should we calibrate the pH metre with a buffer solution of pH 7 first before the pH 4 or 10 buffer?
We are all well aware that the pH scale has values from 1 to 14, and 7 is the middle point. At pH 7, we have neutral pH, and above 7 is the basic pH and below 7 is acidic pH. Now let’s deep dive into the main topic.
- To set the zero point of the pH meter, we use the buffer solution of pH 7 first. Checking the zero point first means that it is working accurately to find out the neutral point or zero reference point.
- Starting with pH 7 as the standard, set the zero point of the pH meter.
- After setting the zero reference point, we use a pH 4 or pH 10 solution to create a slope for the pH meter.
- pH solution 7 is used first for calibration because it sets the zero point or the first point for calibration, and pH 4 or pH 10 buffer solution creates the slope point or second point for calibration.
- pH 7 buffer solution is used first to calibrate the pH metre for determining the asymmetry point & which is the point where mV is equal to zero, which is achieved by placing the electrode of the pH metre in buffer solution of pH 7.
- After calibrating the pH meter with a buffer solution of pH 7, we use a buffer solution of pH 4, and this is known as 2-point calibration. Some pH metres support two-point calibration, but the most accurate method is the 3 point calibration, where a third buffer solution of pH 10 is used after buffer solution of pH 4.
- If we use a buffer solution of pH 4 or 10 first, it may contaminate the electrode if not properly washed and may fluctuate the next measurements, so taking pH 7 at first ensures accuracy due to neutral pH.
- We use pH buffer solution 7 first to adjust any drift in the pH value.
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