Which pH calibration solution should you use?

pH calibration solutions, also referred to as pH buffers, are an integral part of the pH measuring process. Hanna pH buffers are stable and resistant to change, providing you with peace of mind that your results are precise. Using a high-grade buffer to calibrate your pH meter before each use helps to maintain a high level of accuracy.

Why calibrate your pH meter?

Calibrating is key in pH measurement, as calibration helps to keep your readings reliable and accurate. pH electrodes are based on slope percentage and offset - the Nernst equation - but the electrode won’t behave exactly in line with this equation every time.

Calibration provides an effective solution to achieve accurate results as the electrode ages, determining its actual slope and offset with the use of known buffers. The algorithm in the pH meter is then updated to match this change.

In addition, pH calibration solutions can provide an early indicator of damage to your electrode through the sloping and offset. Unexpected numbers during calibration can suggest that the probe is dirty, damaged or in need of replacement due to age.

Hanna manufactures three types of pH calibration solution in-house: standard, technical and millesimal. We cover all three of these options below to help you determine which solution is the ideal choice for you.

1. Standard pH calibration solutions

Standard pH calibration solution has an accuracy of +/- 0.01 pH at 25°C, and is available in seven different pH values ranging from 1.68-10.01. The most popular and commonly used pH buffers in the Hanna range, 4.01, 7.01 and 10.01, are available with red, green and purple colouring for easy visual identification in addition to a clear option.

Like all Hanna calibration buffers, these standard solutions are manufactured in accordance with ISO standards in our European facility, are NIST traceable, and are available in a range of sizes from one-litre bottles to single-use sachets.

Standard pH calibration solution is an ideal choice for a wide variety of applications and meters. From measuring the pH of cheese with a HALO2 wireless pH tester to testing water samples using a benchtop meter in a laboratory, standard pH buffers are the best fit for many requirements.

2. Technical pH calibration solutions

Technical solutions are as accurate as standard solutions and follow the same specifications. They also come with certificates. The primary difference in technical solutions is the wider range they cover, including nearly every point on the pH scale to allow you to bracket for calibrations to a specific measurement.

Bracketing is the process of calibrating to two pH points, also known as two-point or multi-point calibration. Bracketing involves calibration to one above and one below your required pH range. If you were to measure the pH of lemon juice, which is around 2 pH, you could use technical buffers 1.00 and 4.01 for two-point calibration.

Tip: For greater accuracy, we recommend introducing a third calibration of pH 7.01 as a way to accurately determine the offset. pH 7.01 calibration provides valuable information to diagnose issues such as a broken or contaminated probe, helping to avoid any measurement errors.

3. Millesimal pH calibration solutions

Millesimal pH buffers cover a wide selection of pH ranges, more than standard calibration solution but less than technical. These pH buffers also include certificates. Millesimal solutions are unique in their greater accuracy, to +/- 0.002 in comparison to the +/- 0.01 accuracy of standard and technical solutions.

Millesimal calibration solutions are suitable for use in environments where accuracy down to three decimal places is required. For example, in drinking water treatment facilities, science labs and for medical research.

Maintaining your pH buffers

Our pH bottles and sachets should be kept away from direct sunlight for accurate readings. pH calibration solution is affected by UV light, which can reduce the lifespan of your buffer if it is not stored appropriately.

To prevent contamination, it’s important that you do not soak your electrode in the bottle itself. Instead, pour out the correct amount into a clean container that has been rinsed with deionised water, and use that for calibration. Once used, the pH buffer should be disposed of appropriately and never returned to the original bottle.

While we recommend daily calibration, we understand it’s not always feasible. If high accuracy is not key to your requirements, calibrating once or twice a week is a good middle ground for pH testing. If you are calibrating less frequently, choosing single-use sachets may be the better option to ensure your buffer remains fresh.

The shelf life of pH calibration solution is shortened once the bottle is opened, while single-use products are packaged individually to maintain a longer lifespan.

If you’d like advice on the best pH calibration solution for your requirements, speak to our expert team directly via email or by calling us on 01525 850 855.

We can advise on the best pH buffers and offer training and demonstration on our comprehensive range of pH instruments, including the HI-6221 Advanced pH Meter.