How to calibrate ph meter without solution

How to calibrate ph meter without solution

A pH probe or a pH meter is a very useful tool for quickly determining the pH value of a sample. What is often overlooked in this statement is how to calibrate a pH meter, since an uncalibrated pH meter is practically useless. But what if there are no typical calibration procedures or solutions? This article discusses calibrating a pH meter without a solution and the possibilities that arise in this situation.

What is pH and the basics of pH calibration?

The pH value measures the concentration of hydrogen ions in an aqueous solution and defines the terms acid and base. A solution with a high ion concentration is an acid with a pH below neutral 7. As the scale ranges from 0 to 14, the opposite is true for bases with a pH above 7. In comparison, water has a neutral value of 7 on the pH scale, while coffee and lye have a pH of about 5 (acidic) and 9 (basic) respectively.

Since pH meters measure the concentration of these ions, they need a reference point, such as a zeroed bathroom scale. Generally, there are commercially available or laboratory-made calibration solutions with which several two-point and three-point calibrations can be performed, depending on the required accuracy. Typical calibration solutions are made with pH values of 4, 7 and 10, which provides a reasonable range for the most common test samples. In any case, this calibration step is necessary for reliable pH analysis of any sample.

What happens if I run out of calibration liquid?

Most pH meters are initially stored in a solution that is usually pH neutral, such as a neutral salt electrolyte solution. In theory, one point is already included in the calibration curve, but it is good practice to use two or three different points for calibration, as with two or three other calibration solutions.

However, in the first case, if you run out of calibration solutions, you can make your own buffers if you have calibrated probes on hand. If the probes are not calibrated, you cannot determine the pH of these home measurements.

Using calibrated probes and a little common sense, these buffer/calibration solutions can be made with water and various chemicals such as KOH (monopotassium phosphate, pH around 7) and citric acid (pH around 4), to name a few. You will have to do some research to find the pH solution you want and then do some experiments with calibrated probes in water, slowly adding chemicals until you reach the pH you want. However, it is possible to make normal buffer solutions with pH values of 4, 7 and 10.

Just make sure that these homemade solutions are tested repeatedly over time and stored in a dark room and in jars so that they do not spoil. This approach may be more cost effective in the long run, but it always requires more effort to develop a solution and creates much more uncertainty in the pH range than a high quality calibration solution.

What if I don't have a calibration solution?

As above, if the pH meter is not calibrated and there is no calibration solution, it cannot be calibrated and measured accurately. It may be inconvenient, but it is not recommended to try to calibrate in common household items such as bleach, as prolonged contact can damage the electrode and the pH meter housing.

It is also important to remember that these probes and pH meters should not be allowed to dry out and that a suitable storage solution should be used. If this storage solution runs out, do not store the pH meter in tap or deionized water, as this may cause unwanted diffusion and damage the pH meter.

If all this is too much for you, you can start with simple pH test strips with a color scale to show the general pH value. Or better yet, purchase a pH test kit that includes everything you need to measure pH, including calibration and storage solutions, so you don't have to worry about it.

Purchase a standard calibration solution

In conclusion, pH meters are very useful tools for quickly measuring the pH of water and soil in both industrial and consumer applications. However, the most important step in this investigation is to ensure that these probes are properly calibrated. Calibration must be performed with a known pH solution, called a buffer or calibration solution, and pH meters require at least two points.

The key to this wonderful scenario is, what if there is no calibration solution available? If you already have a calibrated pH meter, you can make your own calibration solution with water and various chemicals. This will be cheaper in the long run, but it will be more difficult to obtain an accurate pH solution that will not easily degrade over time.

On the other hand, if a calibration solution is not available and the pH meter is not calibrated, it will be necessary to purchase a calibration solution to begin proper calibration and testing. These commercially available calibration solutions will provide you with the most accurate readings for your pH meter and provide you with a more convenient procedure.