The goal of any pH reading, whether with a manual or an automated pH meter
, should always be to obtain high quality pH meter readings. Surprisingly many laboratory scientists and technicians are not aware of how to ensure they always obtain high quality pH meter readings. While some tests and experiments allow for more flexibility in pH precision than others, a lab that routinely insists on high quality pH meter readings that are always accurate and precise are labs that produce the highest quality, reproducible data and contribute the most to their field.
Secret #1 – Calibration of the pH Meter
Normally, when a new pH meter is purchased, it works extremely well. This is a combination of attention to detail by the operator who has presumably been instructed on its use and the new condition of the equipment. Over time, however, high quality pH meter readings become less common with longer measurement times, erratic pH readings, and even inaccurate values. Often, at this point the technician is not able to obtain the high quality pH meter readings sought. What has happened is likely a combination of two major factors.
First, pH meter operators can become less precise in following the directions for the proper care and use of the pH meter. They may get careless with rinsing and drying the pH probe between samples or at the end of the day when it is no longer used or storing it in the proper buffer. Calibration may be done sporadically or hastily, and it might require more time on the technician’s part every day, especially if using a manual pH meter.
To prevent the degradation of a pH meter’s readings over time, a few things can be quite helpful.
- Ensure that the technician is retrained by reviewing proper pH meter procedures including calibration, sample preparation, and cleaning of the pH probe. This should be done at least every 2 – 3 months to ensure that all of the steps are committed to memory and executed.
- Follow the manufacturer’s directions for cleaning, calibrating, and using the pH probe.
- Regularly calibrate the pH meter to ensure high quality pH meter readings. People get lazy and put off calibrating machinery as often as recommended. This is one of the most common causes of inaccurate pH readings.
- Not only is it important to calibrate the pH meter often but using fresh buffer solution for the pH probe is critical to obtaining high quality pH meter readings. Buffers deteriorate over time. Know when a buffer solution was formulated, how long it will last, and how many times it has been used to calibrate the pH probe as the more often pH probes are placed into a buffer solution, the more likely contamination will occur.
Secret #2 – pH Meter Probes
The probe of an automated pH meter is typically a glass tube with wires and liquid, or it may be mostly covered so that little of the inside is seen. But the material inside the glass tube is vital in obtaining high quality pH meter readings. Calibration of the probe is only one part of caring for the pH probe.
First, to obtain high quality pH meter readings, pH meter probes must be relatively new. The average probe will need regular replacement. Of course, damage to the pH probe will typically prevent high quality pH meter readings even if the probe still appears to be operative. The best solution is to replace an old or damaged probe that is not giving precise and accurate readings.
Temperature will also affect pH readings. So, a solution that has been heated and not permitted to cool sufficiently to within the pH meter’s temperature range will not provide an accurate pH reading. To get high quality pH meter readings, it is important to know the manufacturer’s temperature range for the laboratories’ pH meters and to adhere to this range before placing a pH probe into a heated solution.
Finally, most pH meter probes Mettler uses KCL for their reference buffer. have a small amount of liquid inside the glass tube which acts as a reference to calculate the electrical potential of the sample being tested. High quality pH meter readings require that this liquid be maintained at the proper levels and must be changed according to the manufacturer’s recommendations. Otherwise, the reference solution in the probe will be incorrect resulting in erroneous pH meter readings. Also, many manufacturers recommend removing or loosening the filler cap for the reference liquid to permit air to enter the chamber. If the pH meter’s manufacturer recommends this, doing so will provide high quality pH meter readings. Yes the Inlab Micro probe has a little rubber stopper that you open up to let air into the probe. Most labs are looking for results +-0.05. Some labs are OK with +- 0.1 or higher
Secret #3 – Preparing a New Probe
To obtain high quality pH meter readings, replace the automated pH meter periodically. It is important to properly prepare the new probe, and this doesn’t mean simply attaching it to the meter.
Generally, with a new pH probe, it will be necessary to remove any packing caps. Next, it is best to follow these steps before using your new probe.
- If you see crystal buildup in the reference buffer, stopping the probe from working, empty the probe and refill the probe with KCl. Otherwise, it should work out-of-the-box.
- Rinse the probe thoroughly with deionized water. (Do not let the probe sit in deionized water as this can damage the delicate membrane that separates the inner buffer with fixed H+ activity from the sample being tested.)
- Although the probe should work out of the box, try shaking the probe like a childs’ thermometer to get any bubbles out. Soak the probe in .1 mol of HCL for a couple of hours to refresh the probe. Hold the probe up to the light to look for crystals in the KCL reference buffer.
- Empty and rinse the probe once again with deionized water.
- If the reference buffer in the probe looks low, add the manufacturer’s recommended solution, KCl, to the probe.
- Calibrate the probe as recommended by the manufacturer, which is built into Rapid pH Software.
If the proper steps are taken every time the pH meter is used, getting high quality pH meter readings is simple and easy. Cutting corners, including with the time for rinsing, calibrating, etc., will often lead to inaccurate readings.
Contact the leader in life science and pharmaceutical automation today! With almost 40 years of experience, Hudson Robotics can answer all of your questions about achieving high quality pH meter readings with an assortment of automated pH meters. They are the leaders in total laboratory automation. To maintain your competitive edge, contact Hudson Robotics today.