Chromatography Forum

I’m trying to set up a method for the quantification of Diesel fuel, using an FID, over a timed range (c10-c24) using MSD Chemstation D.01. I have made a compound that extracts signal from the time of my alkane carbon markers (3.00 min to 9.480 min). The data system does a good job with the starts and stops for collecting the signal but where it applies the horizontal baseline seems to vary a lot. Sometimes the integrator skims along the top and sometimes it draws all the way down to the bottom of the Qedit window, this results in huge quanitation differences. When I go to draw a manual baseline in Qedit the window does not let me zoom out so it is difficult to know where to apply the right height for the baseline, i.e. I can’t see the whole chromatogram’s natural baseline so it is hard to follow it along. So my questions are:
1. Does anyone know how to set up MS Chemstation to reliably and consistently apply a baseline over a large timed range?
2. Does anyone know how to zoom out or scroll the x-axis in Qedit? It is easy to zoom out when looking at MS data (left click), but in GC data it is static.
Thanks in Advance

I have this problem with hydrocarbon ranges daily. Unfortunately any integration parameters I've tweaked only change integration of single peaks and not ranges...not to say it can't be done. Anyone who knows how to do this would be my hero.

As for your second question, in qedit if you go to "qedit" you should see "xpand chromatographic window". clicking this a couple times zooms you out little at a time. also if you have the command line available you can type "xpand 10" (try different values for this in minutes, 2, 10, 20 etc...)

Thanks CJM,

I'm beginning to understand just how unsuitable Chemstation is for timed ranges, that said it’s all I have to work with. Thanks for the “xpand 10â€

Mr. Ellison,

Working from memory here but I believe there is an option about which integration algorithm to use, RTE integrator or Chemstation. It sounds to me like you are using RTE and you might have more luck with the alternative integration algorithm.

(I don't have any MS's in my shop to look at, only GC's, but I can check on this later this week to clarify if you need me to.)


Best regards.

If you use the ChemStation integrator, search for an event code or command in the integrator that is "Baseline Hold" or "Baseline Forward." This will hold the baseline at a fixed value. This is available in the non-MS versions of CS, and may also be in the MS version.

baseline hold, baseline back, baseline now all work great for single peak integrations but I have not been able to affect the way hydrocarbon ranges are integrated using one of these events.

I'm sure you all know of the peakwidth parameter. Currently I can integrate all of the nonylphenols in a single bunch by setting a very large peak width in GC/MS Chemstation.

Hi,

with interest I followed your postings because I meet the same problem in my daily work.
My Agilent is featured with a thermodesorption inlet and I'm analysing unknown materials for their outgassing products. The result always includes selected peaks of interest and the so called "total amount of outgassing substances" which is nothing more but an integration from 0 min. to the end of my programme.
To be more detailed I have to integrate along the baseline after the CO2 peak at the very beginning to the end. The baseline rises significantly when the column temperature is raised. So the integration has to be some kind of "flexible".

Please let me know if you got a solution for that problem!

Thanx,

Cmdr. Keen

(sorry I have to stay anonymous because of data protection problems - our customers won't be too happy if they read this [which is quite unlikely but possible])

OK I think I actually have a solution!

1) Make sure the compound type is "H" in page 2 of the compound information screen.

2) type the word "FLAT" all capital letters in line A2 of same screen. (page 2).

3) Requant data file. It should integrate hydrocarbon range flat using lowest point on chromatogram as reference.

Note: I use column compensation runs to subtract unnecessary column bleed area from my ranges already, this in combination with the FLAT feature could prove very useful.

Please let me know if you get this to work!

Thanks for the hint.

On monday my 5973N will be upgraded and I'll try this during next week. If it worked I'll let you know.