The 10 Most Common Process Chromatographs Mistakes

The 10 Most Common Process Chromatographs Mistakes

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The 10 Most Common Process Chromatographs Mistakes

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Sharing knowledge gained over several years! This first e-book has been designed to demonstrate the top 10 most mistakes in process chromatography and help mainly professionals whose main expertise is not analytical instrumentation field. We know that an analytical team is not common in every industry, sometimes leadership team doesn't realize this importance. The main purpose is to help you to prevent and fix the common mistakes, support you in solving some problems for analyzers that you are liable and help to increase reliability, and improve the reputation for our discipline.


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FULL Tips To Increase your pH Skills

Our latest expert advice, best practices, and professional tips.

An experienced and passionate Product Manager with a long history of working in the Industrial Automation industry. Skilled in Process Optimization, Process Control and Chemical Engineering Strong and Creative product management professional. I'm talking about Miranda de Bruijn, European Product Manager - Yokogawa. Specialized in Analytical Instrumentation. She is from Utrecht Area, Netherlands

The effect on Total Cost of Ownership (TCO) by extending pH Sensor Lifetime


Top 4 Factors That Determine The Lifetime Of Your pH Sensor.

The lifetime of a pH sensor has a significant impact on the overall annual costs of a pH measuring loop. Optimizing four key factors will decrease these costs and optimize process control and overall plant efficiency.

These four key factors are :


Although Calibration itself does not influence the life time of a pH sensor, improper calibration might result in replacement of a sensors, without it being necessary.


The measurement results obtained from dirty sensor can be anything from slow response, to a completely wrong reading. Therefor correct Maintenance is very important.

Engineer Skillset

A pH sensor is a highly technical, precision instrument. Sensors like these often require a specific Engineering skillsets in order to get the most out of the measurement.

Sensor Selection

The most important factor in obtaining the highest performance possible is Sensor Selection. Selecting the wrong pH sensor for your application can lower the lifetime significantly.

Download this free guide directly from Yokogawa Library

Free Guide

The lifetime of a pH sensor has a significant impact on the overall annual costs of a pH measuring loop. Optimizing four key factors will decrease these costs and optimize process control and overall plant efficiency.

Download the "pH Sensor Lifetime eBook" and learn more about:

  • How calibration, maintenance, engineering skillset, and process conditions influence the lifetime of your sensor;
  • The total cost of ownership of a pH measurement loop;
  • Typical problems that cause a shorter sensor lifetime;
  • How to extend the lifetime of your pH sensor;
  • 15+ pages of educational content.

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Recommended practices to extend your pH sensor lifetime

Extending pH sensor lifetime

The lifetime of a pH sensors has a significant impact on the overall costs of the entire pH measuring loop. Optimizing four key factors - maintenance, operator skill-set, sensor selection, and calibration - will lower costs and optimize process control and overall plant efficiency. In this 2/5 blog we will look into calibration.

The role of calibration

There often is a misinterpretation of the meaning of calibration and maintenance.

Basically, maintenance activities will focus on "CHANGEABLE effects", for example: cleaning a dirty sensor. Calibration on the other hand will compensate UNCHANGEABLE effects.

These are:

Aging of the pH glass, usually caused by chemicals in the process or high temperatures

Poisoning or depletion of the reference chamber

Calibration itself won’t extend the life of your sensor, but a sensor that is not calibrated properly can cause unreliable measurements. In some cases, that even results in unnecessary replacements. Don't underestimate the importance of calibration!


Yokogawa has directories and websites which give access to a wealth of freely available, high quality, online resources. Take a look!


The lifetime of a pH sensor has a significant impact on the total costs of onwnership and performance of the entire pH measuring loop. Improving four key areas will lower costs and optimize process control and overall plant efficiency. These four key area's are:

maintenance & storage,

operator skill-set,

sensor selection, and




Cleaning and calibration will always involve some amount of maintenance.

So, where should you pay attention to?

A clean reference should have a potential difference of 0 mV across the junction (it has open pores). On the other hand, dirty references will have a potential difference across the junction. Why is this important?

When measuring pH, the potential difference generated by the process across the pH sensitive glass membrane is a measure for the pH of the process. This value needs to be compared to the reference, which should of course be approximately 0 mV.

However, when the reference sensor is dirty, a potential difference is generated across the junction resulting in the measurement having a slower response-rate. In fact, total blockage of the reference will result in a non-responsive measurement. This is what we call a “changeable effect”. Luckily, by regular cleaning of the reference sensor, this effect is easily reversed, increasing the sensor lifetime.

A dirty pH sensitive glass bulb will result in a slow measurement. This - again - is a changeable effect, and by regularly cleaning the sensor, the sensor lifetime will increase, and the response rate of the sensor will be at its best.


Each application is different, and optimizing the maintenance cycle is not always straightforward.. In some case, cleaning once a week is sufficient, but when a lot of dirt builds up, or the deposits are very heavy, it can be necessary to clean as often as every 8 hours! To complicate things further the type of cleaning liquid required can be different for each application.


Don't forget to download your free e-Book for more information on do’s and don’ts for pH sensor maintenance and storage.

Let's improve the pH measurement maintenance cycle and start increasing the lifetime of your pH sensor now!

Engineering Skills

The lifetime of a pH sensor has a significant impact on the total costs of ownership and performance of the entire pH measuring loop. Improving four key areas will lower costs and optimize process control and overall plant efficiency.

These four key areas are:

Maintenance & Storage


Engineering Skill-set

Sensor Selection

Ms. Miranda told that one of the most rewarding tasks of her job as a Product Manager is visiting customers. Together with their service engineers, She enjoys helping customers who run into problems with their pH measurement. This can range from an unstable measurement, deviating pH readings or problems related to the sensor’s lifetime.

She emphasizes, the ultimate problem with pH measurements is often: no or limited process control. In each of these cases, the main question is: "How can I make sure I have a reliable pH measurement and extend the lifetime of my pH sensor?"

She wants to share with us many valuable lessons, so, welcome aboard and let's go. The four most important lessons related to engineering skills were:

1 - Use step by step approach on how to do the trouble shooting

2 - Patience

3 - Understand what the Slope and Zero of a pH sensor is

4 - Understand how temperature effects the lifetime of a pH sensor

The first two lessons apply in many situations, but are especially important in pH troubleshooting.

Lesson 1: Use Step by step approach

A systematic step-by-step approach is the most effective way for identifying the cause of the problem. This helps to make your troubleshooting procedures as efficient as possible.

First of all, following a logical structure in case of trouble shooting will help drill down the cause of the problem systematically. The sequence of this step-by-step approach is :


To increase the accuracy it is important to be patient and wait a few seconds longer.

Lesson 2: Patience

The second important lesson is patience. Hasty conclusions may not always be correct conclusions. For example, if a pH cable looks dirty, it might be tempting to blame it on a faulty cable. But, after following the 4 step-structure mentioned above patiently, another cause may become visible.

Proper calibration also requires patience. Regularly, Ms. Miranda told that she was at a customer sites with the service engineer performing calibrations on new sensors or older sensors. When the analyser would give the stable signal, she wanted to move it to the second buffer but the service engineer waited a bit longer to make sure it was really stable. This is important because an analyser is a computer and will only give the stable signal when the mV value has not changed for 5 seconds (standard setting). Sensors that have been installed for some time become slower. To increase the accuracy it is important to be patient and wait a few seconds longer.

So she alerts: The pH measurements always involve some time pressure but be patient when calibrating and troubleshooting. It will improve the accuracy of the measurement and will help you find the problem in the measurement easier.

Replace sensor WHEN...

Lesson 3: Understand what the Slope and Zero of a pH sensor is

Understanding what the Slope and Zero of a pH sensor means, will already give you an indication of the health of the sensor. When the sensor ages, it will become slower and the slope will go down. When process comes into the sensor (poisoning) the zero will shift.



Slope < 80 %

Zero higher or lower (> +40mV or < -40mV)

How does temperature affect a sensor a sensor lifetime

Lesson 4: Understand how temperature affects the lifetime of a pH sensor

Temperature affects the lifetime of a pH sensor. Every 10°C decrease in temperature will double the lifetime of the sensor. Just look at he below chart:


Step-by-step approach


Slope and Zero of a pH sensor

Temperature Effects

Learning these four lessons have helped me improve my engineering skills and most importantly helped me improve the pH sensor lifetime of our customers. I hope sharing my own experiences will help you increase your pH Engineering Skills.

Miranda de Bruijn


To learn more about how pH measurements, in general, we recommend you this pH handbook:

Type: Adobe Acrobat Document  |  Pages: 72  |   Size: 7,87 MB 


Measuring pH/ORP is a common procedure, but taking a true measurement and making the correct interpretation of the results is not always easy or simple. Part of achieving accurate and reliable pH/ORP measurements requires sufficient and correct maintenance and storage conditions.

From this handbook, you will gain a comprehensive understanding of pH/ORP measurements, the construction of the sensing elements, how to achieve reliable results, and use cases in process applications.

Besides a frequently asked questions and answers section, this handbook also includes a variety of other resources, such as a Chemistry Compatibility Table and a Liquid-Application data sheet.

Download the "Back to the pHuture - pH and ORP Handbook" and learn:

-The opportunities and challenges associated with pH and ORP measurement control;

-How to optimize hardware operation and life with proper maintenance;

-Typical problems that cause poor performance;

-Insights from various applications and solutions.

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