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Jan-1997

Gas chromatography and the modern laboratory

Gas chromatology continues to be the most significant analytical tool used in the petrochemical and refining industries

Michael King, CDTech

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Article Summary

The evolution of the modern laboratory in most refining, petrochemical and chemical organisations has taken place against a conflict between two trends. One is downsizing, an ultimate goal in the re-engineering strategy adopted by many organisations. The other has been the increase in complexity of applications and the sophistication of laboratory instrumentation.

Many laboratories are vulnerable, since the most knowledgeable and experienced hands are generally the ones  lost in the shuffle, thereby inhibiting the advancement of knowledge of new instrumentation.

The result has been the loss of a great deal of knowledge and expertise regarding analytical method development and implementation in all areas of the laboratory, one of the most significant areas being gas chromatography.

Not so long ago, many organisations had a number of gas chromatographers capable of designing and developing new chromatography techniques. Most had acquired their skills through years of experience, working with different columns and configurations. This knowledge and experience enabled the chromatographer to make decisions regarding the proper equipment, both hardware and columns, as well as analytical techniques, to meet the needs of the process. In many cases, this meant building and applying systems after receipt of the gas chromatograph.
Like other sophisticated analytical techniques, gas chromatography requires skills beyond those taught by many universities. It has been and continues to be the most significant analytical technique to contribute to the vast requirements of petrochemical, chemical and refining industries.

Since its commercial inception in the 1950s it has had astronomical growth in analytical laboratories. The ease of use and versatility of the equipment has allowed gas chromatographs to be used for process as well as laboratory bench instruments.

There are a variety of detectors to ensure proper detection of the compounds of interest, from the standard hydrocarbon analysis to the more specific compound analysis, such as sulphur, nitrogen, halogen and organo-metallics.

Gas chromatographs have been coupled with detectors as “mundane”, as a standard flame ionisation detector, to the more exotic mass spectrophotometers, fourier-transform infrared and atomic emission detectors. Column selection has been expanded to include capillary columns, meaning that the need for knowledge in selecting the right column is more important.

Capillary columns give the chromatographer the capability to successfully measure compounds that were difficult to measure in the packed column days. In short, there is not another single instrument made for analytical measurement that has enjoyed such a long and sustained ride “at the top of the heap.”

As I sit on a jobsite writing this article while training personnel on the new equipment they have just purchased, I am reminded of how the complexion of the modern laboratory has undergone significant changes in the past 10 to 20 years.

In a similar to personal computers, the equipment in the lab has been rapidly changing, becoming more sophisticated with each generation. Many of the new models of lab equipment are now being controlled by computers with more intelligent software, capable of interpreting data at a faster rate.

While this new equipment has been developed to enable users to  make measurements more accurately, faster and at lower detection levels, a whole new set of problems arise with sample and data handling.Sample handling techniques used with new equipment has undergone redefinement. In the past, we were not as concerned about sample preparation, since sample sizes were large enough to overcome cross-contamination, that is, contamination from a poorly flushed injection valve.

Today, we must be concerned about micro levels of cross-contamination, sample cleanliness and sample volumes. Many of the new systems are capable of detecting very low quantities of components in a very short time. Where we were concerned about percent and parts-per-million levels in the past, now we are faced with lower levels of detection, parts-per-million, parts-per-billion and parts-per-trillion levels.

The trade-off of this new high tech capability is the need for exacting techniques for handling the samples. Since smaller and smaller quantities of material are required for the analysis, the significance of small levels of contamination become magnified.

The quantities of material being injected is a fraction of what it was during the packed column days. This smaller quantity compounds the effect of contamination. From the use of syringes to the use of sampling valves for injections, attention to the sample preparation has become paramount to the analysis, second only to the method/application being used to measure the components of interest. The systems used to introduce the samples have also undergone a radical transition.

All of this new sophistication falls on the shoulders of the new breed of analytical personnel, who must decide which equipment is appropriate for the process and how to handle the sample streams, from the unit into the laboratory instrument. Due to the complexity of the sample streams and the required analysis, no two sample streams can be handled the same way. There is an art to some of the techniques used in the laboratory which can only be developed over time. These techniques cannot be found in a cook book but are passed down from senior personnel to junior personnel.

Concepts of analytical techniques can be found in books and procedural manuals, but there is no substitute for hands-on experience. Decisions on calibration techniques, sampling procedures, analytical methodology, and detection levels are being made with an insufficient amount of knowledge or experience in the nuance of laboratory protocol.


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