I am facing an issue with how chromatograms are recorded. From time to time, on our chromatograms the peak assigned to heptane is integrated as well and this gives us wrong results. Sometimes the value of this peck is less than 0,01 %, but there are situations when it is 20 % . I made no changes for the methods. I don’t know why this problem appears randomly and what can be the cause? Do you think that it could be a bubble of air, the manual injection or may be is the column? On this GC, we have another column with automatic injection, and this problem never arrived on this one.
The user programmed method determines what the integration parameters are (not the instrument). Change the integration parameters to suit your application. *Please contact someone local with GC experience who can assist you to use the instrument.
William Letter, thank you for your replay.
The method is designed with no integration of the solvent, and even so, for the same method, in case of, lets say 5 % of the GC analyses, the heptane is integrated. Of course, I can reintegrate after analyze, but is not something I want to do each time, but rather I would like to find a solution. It can be a method problem, but I wasn't able to identify it. Furthermore, I have been using this method in a while and this issue is something new. Additionally, no one made changes to this method.
I already looked for support to our GC consultant and I am waiting for their replay.
best regards
It is your method's auto-integration settings that must be adjusted.
Methods include saved integration events. "Integration" events can not exclude a "solvent" peak per se, but they can be set to exclude any and all peaks based on a user selected time-range or specific integration event settings (e.g. peak areas, heights, widths, slope etc).
The user/operator is responsible for programming in appropriate AUTO integration events and saving them as part of the method. Once saved, these integration events can be turned 'ON' or 'OFF' in the software. You can always set your own integration events after the analysis and manually integrate the chromatogram, but the" auto" feature is optional and very useful if you run a series of samples and want the computer to perform the integration using YOUR saved settings. If the selected events do not integrate the desired peaks, then you need to re-evaluate the integration settings selected and modify them to work with your actual sample (this requires a great deal of software and instrument training to get right). If an undesired peak is included in the report (as in your case), then you should evaluate the actual data (integration results) to determine why it was included and which settings should be changed to exclude it next time. Once completed, save the new auto-integration settings (over-write) and test. Sometimes this process takes many tries to find the best settings (software training is needed). The computer is only doing what you tell it to do and will provide completely unscientific and wrong data on the report if you select events that are of poor quality.
- The reason that sometimes you see a peak integrated and sometimes you do not is because the specific peak is occasionally meeting the integration event parameters that you have programmed for some of the runs, but not others (because the 'peak's' size and shape are changing run-to-run or sample-to-sample).
These are basic fundamentals of chromatography and training is required to learn how to program the system, make modifications that follow good chromatography fundamentals and develop methods. Most users need three or more years of full-time training and experience with GC to learn these basic skills so please find and work with someone who is an experienced chromatographer. Doing so will help you acquire valid data using a valid method. The process will be less frustrating too as you will learn how very logical the whole process is.
thank you for your time in writing such a elaborate and complex answer.
Best regards
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