12/06/2021 | Industrial Wastewater | 8 MINUTE READ

How to Calibrate a pH Meter and What Solutions You Need

When measuring a sample of water or any aqueous sample, it’s often important to determine the sample’s pH; essentially how acidic or alkaline a solution is. The reading you obtain will provide you with a number ranging from 0-14. A sample with a pH of 7.0 is considered to be neutral. Anything below 7.0 is acidic. At the other end of the scale, readings above 7.0 are considered alkaline. While measuring pH is useful in a wide range of different applications, these measurements are especially important in industrial applications. Typical applications where pH measurements are used include:
-Food quality control
-pH neutralization in effluent
-Paper manufacturing
-Odor scrubbers
-Environmental monitoring
-Boiler and cooling tower control
-Blood-gas analysis for various medical devices
-Water pre-treatment
-Swimming pool control
These processes can’t be completed without understanding the impact of pH at various stages of the process. You can also determine the quality of water by measuring its pH. When the pH is excessively acidic or alkaline, this may indicate that the water contains a high level of contaminants. If you want to measure the pH of water or a aqueous sample, the most accurate method is to use a pH sensor.
When you measure pH with an electrode and pH meter, the most important tool that you should have on hand is a set of pH calibration solutions, often referred to as pH buffer. Even though it’s possible to create a homemade pH buffer, doing so can lead to inaccurate results. Professional-grade pH calibration solutions are highly stable and are formulated to resist change, ensuring consistent and accurate results. For most accurate results with your pH meter and sensor, it’s recommended that you calibrate the device with at least two calibration solutions before every use.

By calibrating the device, you can ensure that the electrode has not drifted or become damaged over time. Every electrode two-point calibration will check both the offset and slope. However, each electrode will change as it ages, which can make pH measurements less accurate. When you calibrate your pH meter, the issues with an electrode will be diminished since the calibration determines the actual offset and slope. This determination is then sent to your pH meter as an update.
If you find that the offset and slope of your pH meter’s electrode are substantially different than what they should be, this indicates that your pH electrode may be dirty or damaged. Keep in mind that there are several different solutions that can be used to calibrate a pH meter, all of which you should be aware of. This article goes into detail about the calibration solutions at your disposal.

How Can You Calibrate a pH Meter?

When you want to calibrate your pH meter, there are two separate buffer solutions that you should use, which include the pH4 and pH7 solutions. These specific solutions make it easier for you to obtain the correct pH values. Before you calibrate your pH meter, make sure that the solutions you’re using are fresh. If you opt for the pH4 and pH7 solutions, you should begin with the pH7 buffer solution before following it up with the pH4 solution. The steps involved with calibrating a pH meter are simple and straightforward.

Steps to Calibrate Your pH Meter

calibrating your pH meter
Place your pH sensor’s electrode directly into the pH7 solution. The measurement will reach stability after 60 seconds. The meter should provide you with a pH value of 7.0 because of the solution you’re using. If the reading is lower or higher, the pH meter should be established at this value.
The electrode should then be rinsed thoroughly with demineralized water before the electrode is placed directly in the pH4 solution.
At this point, the first step should be repeated until you obtain the correct measurement. You should obtain a reading with your pH meter of 4.0. A different reading means that your meter should be calibrated to take this difference into account.

Why Do You Need to Calibrate a pH Meter?

pH meter calibration sensor
As touched upon previously, there are many reasons why you should calibrate your pH meter on a regular basis. Regardless of your pH meter’s quality, all electrodes will worsen over time. When an electrode worsens, the pH measurements you obtain will be less accurate, which can pose a problem if you require pH measurements for industrial applications. If you need to have precise pH measurements, calibrating your pH sensor is essential and highly recommended.
The offset of an electrode is the reading that occurs when the electrode is placed in a pH7 solution. As for the slope, it’s determined by measuring the difference the pH4 and pH7 solutions. Keep in mind that these readings will be displayed as millivolts or mV. Even though every electrode has a base offset and slope, these readings will change over time. Calibrating your pH meter allows you to identify how much these readings have changed, after which you can input the results into your pH meter.
With the right calibration solutions, you can identify if your pH meter is damaged and needs to be replaced. If the readings that you obtain when calibrating your pH meter don’t align with what the readings should be, it’s possible that your pH meter will need to be replaced entirely.

Solutions to Calibrate a pH Meter

There are three separate solutions that can be used to calibrate a pH meter, which include standard, millesimal, and technical solutions.
Standard calibration solutions come with a guaranteed accuracy of plus or minus 0.01 on the pH scale. These solutions are also available in seven distinct pH values, which extend from 1.68-10.01. The most common buffers have pH values of 401, 7.01, and 10,01. You’ll find that standard calibration solutions can be used for practically any application. Make sure that the sample you’re measuring is around 77 degrees Fahrenheit to obtain an accurate reading.
Millesimal solutions are available in many different pH ranges. The main benefit in using a millesimal solution is that this particular solution is extremely precise. When you use a standard or technical solution, the accuracy is around plus/minus 0.01 on the pH scale. In comparison, millesimal solutions have an accuracy of plus/minus 0.002 on the pH scale, which is considerably better. Such precise measurements are necessary in settings like medical research facilities, municipal drinking water plants, and science labs.
As for technical solutions, their accuracy and specifications are the same as standard solutions. The main difference is that technical solutions are available in a much wider range of pH values. You can find a technical solution on almost every point of the pH scale. The solution you decide to use depends on how precise you need your readings to be.

How Often Should You Calibrate Your pH Meter?

scientist in lab for pH meter
The rate at which you calibrate your pH meter depends on how much you believe the device has been contaminated and how often you use it. If you use the pH meter on a frequent basis, it should be calibrated frequently. The same is true if you find that your pH meter is highly contaminated. If you want to avoid notable measuring errors, consider calibrating your pH meter twice per month. The pH meter should also be calibrated when:
-You’re using a completely new electrode
-You decide to clean the electrode
-When the electrode or meter hasn’t been used for a lengthy period of time
-When you need to obtain a precise measurement
-After you’ve measured a strong solution
The amount of time that you should soak an electrode when attempting to calibrate your pH meter depends on what condition the electrode is in. If the electrode has been dry for a lengthy amount of time or is brand new, you should soak the electrode in a cup that contains additive fluid for four hours or more. If the electrode is used on a regular basis, it only needs to be soaked in tap water for around 15 minutes.

Final Thoughts of pH Calibration Solutions

If you require accurate pH readings for any type of application, it’s important that the measurements you obtain are accurate. You can identify the accuracy of your pH meter with pH calibration solutions. By going through this process, you’ll be able to calibrate your sensor and make sure that the readings you obtain are precise. There are several different types of solutions at your disposal, which include standard, millesimal, and technical solutions.
Even though the process itself can be lengthy, it’s necessary because of how imprecise readings can become as an electrode ages. When you follow the three steps mentioned earlier, you should be able to properly calibrate your pH meter. Over time, the calibration process will become simpler as you get used to it. Check out products for pH sensor calibration with Sensorex here: !

Posted by Sensorex on December 6, 2021

Sensorex is a global leader in the design and manufacture of quality sensors for water quality and process applications. The company offers more than 2000 sensor packages for pH, ORP, conductivity, dissolved oxygen, free chlorine, chlorine dioxide, UV transmittance and other specialty measurements, as well as a full line of sensor accessories and transmitters. Its expert technical support engineers solve analytical sensor challenges with custom designs and off the shelf products.

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