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Summer is just around the corner and as you plan for vacations or upcoming events, remember that Infometrix' October training course
is not too far away. Register now by completing an application form
and sending it to firstname.lastname@example.org
to save a spot. You don't want to miss the opportunity to gain valuable tips and information.
Recent Happenings at Infometrix
Infometrix is much more than just a chemometrics software vendor. We are a solutions provider. For example, over the past several years the oil industry has experienced a boom in upstream production. Infometrix has been there, working with producers to help map oil reserves by characterizing samples using GC and GC/MS data. The LineUp
software product and Pirouette
chemometrics software, when used together, have made it possible to effectively use chromatography with a multivariate analysis approach to determine how oil reserves may be associated with each other through migration, which is a key factor on where to drill.
Being successful in production has it's ups and downs through the supply and demand curve. With the drop in price for a barrel of oil this past few months profits are down for the big producers. The need to add to their bottom line becomes even more evident and the way to that goal is on the down stream side. Infometrix is a key solutions provider to refining operations
. We are helping to optimize output through better assessments in blending operations. Knowing the energy values of what's coming off the line equals less giveaway at the pump. With our software and technical staff we are customizing solutions for refineries to achieve best practices with the potential to save billions of dollars every year in giveaways. In coming news letters we will explore some of these problems in more detail. Stay tuned!
Comparing Different Approaches to Chromatographic Alignment
There are three mechanisms for dealing with changes in retention time that are being used in various software systems. The three approaches in common use are:
Manual Graphical Tools
- Manual graphical tools (present in most, but not all, instrument control software);
- Method modification tools (Agilent's Retention Time Locking is an example); and
- Retention matching tools (Infometrix' LineUp software is the leader in this field).
- This is the least useful of all the techniques and is primarily just for display and printing reports. The mechanism is to allow the user to interact with the time axis and link peaks in a standard to a sample causing the chromatogram to redraw. The problem here is that the mechanism is usually only for display so the chromatogram is 'fixed' only for as long as the view stays on the screen. Peak areas and possibly heights are likely affected and are a function of the redraw algorithm used. There should be a mechanism to turn this display into a chromatographic file (.cdf), which would at least allow the chromatogram to be reprocessed, but at best this would require a lot of manual intervention. The prime disadvantage is that this cannot be automated, it is unsuitable for process settings, and likely not practical for routine QC.
Method Modification Tools
- By method modification, I mean that the parameters of the chromatographic instrument itself are altered to cause peaks to shift back into their expected retention windows. The most common here is electronic control of pressure (GC only) to compensate for column changes. Even though Agilent claims to have the exclusive in this technology, it is effectively present in many GC systems. This is a good idea and should be used (of course, we think it should be used in concert with the next item). The main disadvantage is that it does not allow you to do post-run processing to change the retention times of any legacy file; it only works for future runs. And, as we look to keep a laboratory’s worth of chromatographs in common alignment, the mechanism becomes unwieldy.
Retention Matching Tools
- This is an approach that is both the oldest and the newest way to handle retention time variability in an automated fashion. There are two ways to handle this: the use of retention markers, relying on peaks that are present in every run; or treating the chromatogram as if it were a spectrum and doing a series of stretches or compressions on a sequence of short time segments (think of an accordion).
Retention markers are 100 years old and work to recast the x-axis to a scale that is independent of time. In hydrocarbon analysis, the approach is commonly referred to as an application of Kovats indices. The underlying reference peaks are the n-alkanes, assigning a value of 10 to decane, 11 to undecane, etc. With this assignment, we linearly interpolate between these fence posts to get a position marker for all intervening peaks. This approach is also common in fatty acid analysis.
Approaches like Correlation Optimized Warping (COW) do the accordion thing and work by maximizing the correlation between a gold-standard example chromatogram and the sample. The advantage here is that the algorithm will work as part of the data acquisition process and can be integrated into the chromatography system method. It also allows us to correct the retention times for previously-collected traces, and can be deployed in as many instruments as needed. This enables comparison year-in and year-out, across chromatographs spanning the entire company, even an entire industry. You need to keep the method as consistent as possible, but injection-startrun timing, column changes, and laboratory temperature are not critical.
The Infometrix LineUp software will handle both retention markers and the correlation approach. LineUp will work with any chromatographic system (ChromPerfect, EZChrom, ChemStation, TotalChrom, Chromeleon, Siemens Maxum EZChrom, ...). LineUp also allows you to process the aligned chromatogram enabling accurate identification of peaks. Disadvantages are similar to anything that has to stretch or shrink the baseline: peak areas and heights (less so) can be affected if the movement is too extreme (i.e., chromatograms are too dissimilar).
After Further Review...
When I first learned about Infometrix, it was 1980 and I was a Research Scientist running the chromatography lab at an oil company in Tulsa, Oklahoma. I had just completed installing a lab automation system (the first for the company) to standardize and archive the files we were creating. I also added autosamplers, and this combination of sample and file management eliminated our persistent backlog in less than a week.
What became instantly obvious was that the new lab system was absolutely great at managing data acquisition and it was very efficient at storing chromatograms. What was equally obvious was that my new toy was incredibly poor at retrieving the information content of these chromatograms. Sure, if you knew the file name or acquisition date, you could retrieve an old file. But if I was faced with an unusual sample, I wanted to know if my lab had processed such a file in the past and, if so, where the heck it is. Unfortunately, there was no mechanism in place to explore the contents of the file, only the metadata.
Little has been done in the intervening 35 years on this automated interpretation front by the major players. However, chemometrics can be used to categorize samples based on the chromatographic features of the file and has evolved into a general set of software tools that can be adapted to any evaluation and has a 20+ year, time-tested approach (in chemicals, pharmaceuticals, clinical, food, and the oil industries). The automated alignment of the chromatogram is absolutely critical to effective, hands-off interpretation. Achieving higher levels of consistency in the chromatograms from run-to-run, year-to-year, and instrument-to-instrument must be done if there is to be any hope of generating a core interpretive capability with any degree of efficiency. LineUp is a near-universal solution to this consistency problem.
Brian G. Rohrback
To leave comments or questions on any of the topics presented in this newsletter, please visit the Discuss page on our website and look under the title of this newsletter.
Thank you for your support and continued readings.