Chromatography Forum

Hi Guys,

I am really stuck with my data analysis at the moment. I have run some samples containing poly aromatic hydrocarbons through a GC-FID. I want to get rid of the background compounds so my chromatograms look cleaner. Does anyone know how to delete unwanted peaks from the chromatogram? I have tried right clicking on the chromatogram in report mode and selecting properties. I then changed some of the settings to only give me a certain range of values and ran the sequence again but nothing changed! I hope this is making sense to someone and I can get some help because it is desperately needed! I would appreciate any advice you guys can give me because I am really stuck at the moment!

Cheers,

mrgb89

I should have mentioned I am using Agilent ObenLab software!

From the chromatogram itself, or from the report?

If the peaks are small then increase the scale of the chromatogram and the tiny peaks will shrink.

From the report, increase the minimum peak size and the peak report will be shorter with only the larger peaks being reported.

Otherwise, whiteout or an eraser works best.

best wishes,

Rod

Hi Rod,

Thanks so much for the quick reply. I have used intelligent reporting and then displayed my data in excel by ticking the XLS box. I want to remove all of the background "noise" from this report and just show the larger peaks. I ultimately would like to diplay the chromatogram in a pdf format too. Can you give me any more advice about this?

Cheers,

mrgb89

In your manual integration parameters set an area or height reject so only the large peaks are integrated/displayed in report.

Would that work for you?

edit: you can also set integration to on or off for periods of time.

Aldehyde,

Thanks for the reply. Where do I reset the manual integration parameters? Is that in report mode. Could you possibly give me a set of instructions?

Cheers,

mrgb89

Yeah sure. You don't actually change it in the report itself, think of that as just the formatting that the data is being placed into.

Here is a screenshot of my openlab chemstation data analysis window: http://i.imgur.com/cYROG.png

Please excuse the crappy placement of the red numbers, just a quick mspaint.

Step 1: open your method, notice that I have the Def_LC.M method open. There are a bunch of different methods you COULD edit (your main acquisition method, the data-file-specific da.m method, a sequence-specific method etc. The one you want is likely in c:\chem32\1\data\[methodname.m]. If you have multiple instruments configured that '1' could be 1, 2, 3, or 4.) If you want this change to occur for all the reports you create for this type of analysis then edit the main method (and if you only want to change the parameters for a specific data file open the da.m in that data file.) You can always re-integrate data, just keep printed or backed up copies of your methods in case you want to restore the original settings. It is always good to keep printed copies of your methods, service engineers and new employees will love you when they can look through historical records of your analysis when problems crop up.

(Step 1.5: open an applicable data file)

Step 2: Click on the integration button.

Step 3: Click on the icon of the pencil writing on the chromatogram OR use the menu at the top of the screen Integration > Integration events

Step 4: Change or add the integration event to the table. To change an area or height reject just change the number next to area reject in the table. For example, if your peaks of interest have area counts of 150 and the noise is like 20 or 30 set the area reject to 75. If you want to add an event, like "turn integration off from 0 to 5 minutes, then turn integration on from 5-15 minutes then turn integration back off' look at the row of buttons near the '5' I placed in the image.

One of the buttons is a row being added, another is being removed. If you mouse over the buttons it will tell you what each one does at the bottom of the screen. Add a couple lines and click the drop down box and look for the parameter called integration, set it to "off" and then set a time. Add another line and repeat until you've set it up the way you would like.

Once you've done this press the button near the '5' in the image that looks like a check mark, that will save the table.

Next you should check to make sure the way you've set things up works. Go to the integrate menu and tell it to integrate, then go to the report menu and print a report. If you need to adjust things refine them until you are happy and then save your changes. To truly save your changes you need to go up to the method menu at the top of the screen and save method.

Let me know if you need any more explanation .

Aldehyde, Thanks for the very clear explanation in excruciating detail!