How to increase the detectors' lifetime and ensure the best accuracy of the process chromatographs?

Before explaining to you how to increase your detector's lifetime, I would like to share with you this history to understand one of our Analyzers Experts purposes:

There once was a farmer who grew award-winning corn. Each year he entered his corn in the state fair where it won a blue ribbon. One year a newspaper reporter interviewed him and learned something interesting about how he grew it. The reporter discovered that the farmer shared his seed corn with his neighbors.

How can you afford to share your best seed corn with your neighbors when they are entering corn in competition with yours each year? the reporter asked.


"Why sir," said the farmer, "didn't you know? The wind picks up pollen from the ripening corn and swirls it from field to field. If my neighbors grow inferior corn, cross-pollination will steadily degrade the quality of my corn. If I am to grow good corn, I must help my neighbors grow good corn."



He is very much aware of the connectedness of life. Our professional life can't improve unless our friend's and companies also improve. So it is very simple to understand. Old minds, like companies that get talented people but try to block his development, thinking like the slavery's time where that talent never had the courage to leave his post and forget that this professional will find new opportunities also. So where this company will find another one to replace him? We must create conditions for personal development even it is to go away, but always we'll have the chance to get another talented professional wishing to work there.

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The day of change is today, we are free to innovate and make better and simpler forms of learning and exchange of knowledge so that the experience of each one is easily accessible to the entire community and people interested in using analytical instrumentation for control and process optimization. We can't waste time!

That's why I shared last week my first e-book about the top 10 most common mistakes in process chromatographs for all community, on page 11 and 12, I discussed a little about this subject that we will deal with in more detail here. To get your free copy, just click here!

So here we go!

HOW to increase the detectors' lifetime and ensure the best accuracy of the process chromatographs?

Tips and cautions

Let's talk here about some tips and cautions, simple attitudes that can make a big difference in the life of the thermal conductivity detectors of process chromatographs, ensuring accuracy and repeatability for much longer and obviously increasing the replacement interval decreasing maintenance cost and higher availability of the analyzer.

Basically, the Thermal Conductivity Detector (TCD) is a metallic filament (resistance) which is heated through a small electric current (regular) and coated with a very thin layer of glass to prevent its rapid corrosion due to contact with the carrier gas (Hydrogen, Argon, Nitrogen, etc.). This circuit basically consist a Wheatstone bridge that connected to a preamplifier unit, will oscillate according to the composition of the sample, where the temperature of the filament is changed (loses heat) and consecutively, the resistance oscillates causing a change in the balance of the Wheatstone bridge ratio, proportional to the concentration of the molecules that are hitting with the detector.

Types of detectors

The thermal conductivity of the gas is related to the size of the molecule, the smaller the gas molecule, the higher its velocity and the higher the thermal conductivity. Hydrogen gas is the molecule that has the highest thermal conductivity and is widely used as carrier gas in process chromatographs, as it is easy to manufacture and relatively low cost.

It is important to look out that in the market we have several types of detectors, and many are not aware of the detector with a double coating (thin layer of glass) to increase its useful life, especially when we use hydrogen as the carrier gas. Check the difference, look the glass layer in some detectors at the left picture.

How to Increase the Life of Your Detectors:

Small actions are required so that you get greater durability of the detectors. The main problem is the contamination of the carrier gas line or problems in the sample conditioning to be injected. Below is a short checklist containing the key actions to manage to significantly increase the life of detectors:

1) Avoid contamination of the detector during the carrier gas (cylinder) replacement:

Carrier gas replacement (routine for cylinders) is the time when the team needs to be more observant and careful. While depressurizing of the pressure regulator valve and tubbings, contamination with atmospheric air occurs and it must be purged out to the atmosphere, Do not allow this air to travel to the detectors and columns. The presence of moisture and oxygen in the detector causes a notable loss of sensitivity and a reduction in the life of the detector, occurring oxidation in the filaments and drastically reduces the sensitivity, also causing deviations in the baseline.

2) Install an automatic change-over carrier gas switching system

When we have several people responsible for the routine and maintenance of process chromatographs, some additional care must be taken to avoid negligence and possible contamination of the detectors with humidity during the replacements of the drag gas cylinders.

I recommend installing a change-over system which is responsible for automatic switching when the main cylinder loses its pressure, which immediately aligns the backup (spare) cylinder avoiding contamination with atmospheric air and also increases the availability of analyzer for the process, because at any time the system will transit without the intervention of the maintenance team!

Basically, this automatic maneuver allows the replacement of empty cylinders without interruption in the operation of the analyzer. Attention should be paid to the cylinder replacement procedure (removal of the empty cylinder) since during the installation of a new (full) cylinder the technician must purge the atmospheric contamination (oxygen, dust, moisture, etc.) before performing the final alignment.

Be very careful: even though it is an extremely useful and practical system, it is necessary to purge the cylinder during the changeover (connection at the regulator inlet), never forget it! Otherwise it may cause a possible process disturbance after switching due to the presence of moisture, and this would be a "shot" in the foot, because it would generate an emergency call at any time, for example, in the middle of the night ...

This device is supplied by several manufacturers, that is, item of easy purchase and installation.

3) Installation of a filter system (drier) in the carrier gas circuit.

Another widely used practice is the installation of silica pipes, dryers installed in series in the carrier gas circuit. These prevent moisture from flowing through the detector, so special care must be taken to avoid major disturbances.

When it gets saturated, a huge amount of moisture is trapped internally, and this can cause much more damage, as a volume of liquid will be drawn which can damage the detector at once, imagine on the separation columns and possible sample loop obstruction.

We must periodically replace the dryers according to their saturation, depending on the size of the dryer, it is estimated a few years of operation, but it is necessary to check the flow through it and estimate an average time for replacement, anticipate replacement and avoid troubles. Generally, this system remains efficient for several years, control is needed to avoid generating problems in teams with high turnover.

4) Carrier Gas - High Quality Needed

Knowing that "paper does not refuse ink", we must always make sure that the contaminants reported by the carrier gas manufacturer are actually within the parameters and concentrations required.

The presence of contaminants in pure gas cylinders is not impossible as we know that the decontamination process of the empty cylinders must be very well performed to ensure the purity of the gas.

If you have any suspicions or if the detectors has poor durability, be wary of the carrier gas that is supplied. A good test to be performed to observe the purity of the gas is to use the gas with flame ionization detectors, these are very sensitive and brutally oscillate the baseline, so you will easily notice that the contaminant content is above the reported.

5) Pressure regulator valve replacement

Never reuse a pressure regulator valve for the carrier gas circuit. Always use a new one, fully decontaminated, dust and moisture-free valve. Very careful at the time of installation to avoid the entry of contaminants and particulates such as dust or filings from the connections and tubbings.

Share your knowledge with us!

Briefly, this is what I prepared today to share with you, to talk a little about my experience and to make something available to colleagues who are entering this area of analytics that is multidisciplinary and engaging. I enjoy teaching, and I am immensely grateful to colleagues who dedicate and spend a little of precious time helping others.

I would love to learn from you too and if possible receive information content to disseminate in our Analytical Instrumentation community, share best practices and success stories in a collaborative way of learning, connecting experts with the general public by promoting knowledge and generating opportunity for all.

Final considerations

The lack of information and interest to improve analyzer's routines, in general, is primarily responsible for the "labeling" and "trivialization" that the analytical instrumentation discipline currently receives. Very accurate equipment and technology are underestimated and lose credibility due to the small details and actions that the maintenance team could easily solve.

For this same lack of knowledge on the part of some teams, more and more online analyzers are being replaced by "virtual analyzers" after all, for some professionals, it's all the same ... And when they realize it does not work, it's too late ...

The interest in the discipline of analytical instrumentation, its dedication and commitment to the final result is the key to success and a total guarantee of customer satisfaction.

Discipline, focus, dedication, quality, and teamwork all the time!

As a specialist in the discipline, I am pleased to explain and demonstrate the value and usefulness that an online analyzer has and, mainly, to share knowledge contributing with the professionals who work in this area creating together a good reputation of the discipline that is good for all of us, valuing our work and contributing to the quality assurance of the final product with cost and safety reduction. So, let's change this scenario and start sharing success cases and posting what's the difference that's process analyzers really do!

Remember that your attitude and behavior are as valuable as your professional baggage. Being supportive is something immense and sharing knowledge and experience makes us feel better and more and more human. I invite you to participate with us, the proposal is so that we can exchange knowledge with each other, help and share with people knowledge and professional experience and allow our colleagues to continue on this journey in a more productive way and to discover new solutions and generate more results.

Make every week of your life with extra learning and useful for people. The little knowledge we share can save the employment of many colleagues or even be the first step to forming a great professional for the job market.

Let's make a difference!

Publish an article as well, share your knowledge and help us to disseminate and promote value knowledge and success stories for the entire Analytical Instrumentation and Automation community, really focusing on what results in saving our precious time by investing assertively in to delivery big results for all.

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About the Author

Rogerio Matos ()

Experience in petrochemical industries, siderurgy, maintenance of process analysis system specializes in the design of sample conditioning, installation & commissioning of process gas analyzers, training analyzer technicians and technical support since 1998. System Information Bachelor - Founder of Analyzers Experts


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