DRO integration question

Discussions about GC and other "gas phase" separation techniques.

5 posts Page 1 of 1
I'm using a pretty simple integration file for my DRO analysis...
Running Chemstation D.02.01...
Initial Area Reject 0
Initial Peak Width 0.040
Shoulder Detection OFF
Initial Threshold 10
Time[min] Integration Event Name
------------------------------------
0.200 Baseline Now
0.200 Baseline Hold ON
0.200 Negataive Peak ON
0.200 Solvernt Peak ON
2.420 Solvent Peak OFF
3.200 Integrator ON
3.200 Area Sum ON
13.00 Area Sum OFF
13.00 Integrator OFF

Now I realize that invoking "Negative Peak ON" negates the solvent Peak and baseline hold commands.

So, if I have both "Baseline Hold ON" and "Negative Peak ON" I get a baseline that works very well for the upper end of the calibration but has enough excess area that the lower end of the calibration is biased high. This version also works very well for samples that have a rising baseline due to heavy oil range contamination that affects the high temperature end of the DRO range.

If I drop "Baseline Hold ON" I get the same good fit overall but a better fit in the low end of the detection range. However, its at the expense of not quite handling a rising baseline due to heavy contaminants. For example M, MD with ~350 ppm heavy DRO and an MS, MSD reading only 950ppm instead of 1300 ppm for a 1000 ppm spike. If I take out the "Negative Peak ON" command, I get M, MD of ~350ppm and MS, MSD of ~1300ppm.

My lowest standard is 50 ppm and I set that as my RDL. My 50 ppm level is 47ppm with Negative Peak ON and 62 ppm with Baseline Hold ON. Solvent blanks give me 9-11 with Negative Peak on and 18-22 with Baseline Hold ON.
Ottowa Sand method blanks rise from ~30ppm to ~60ppm because of the baseline hold. I really do need to soxlet extract that sand.

So, is using "Baseline Hold ON", the best way to fit DRO or am I missing a clue?

Edit: I had to fix my wording. Dropping "Negative Peak ON" makes it completely messed up. Apparently setting the baseline before the solvent peak makes "Baseline Hold" go nuts.
I assume you're doing FID detection of environmental (soil/water) extracts in methylene chloride and you're trying to optimize the software to integrate properly for the hydrocarbon range C10-C28? If so I'll let you know what I've been doing for years.

In chemstation, DRO is defined with an "H" on page 2 for compound type. Then in user defined fields, A2 is FLAT. This forces the range integration to be flat. Before all this we run a column compensation run to ensure our baseline is as flat as possible before calibration.

As far as integration parameters, not much is needed unless you're having trouble properly integrating a surrogate peak amidst the humpogram of #2 fuel oil.
Regards,

Christian
cjm wrote:
I assume you're doing FID detection of environmental (soil/water) extracts in methylene chloride and you're trying to optimize the software to integrate properly for the hydrocarbon range C10-C28? If so I'll let you know what I've been doing for years.

In chemstation, DRO is defined with an "H" on page 2 for compound type. Then in user defined fields, A2 is FLAT. This forces the range integration to be flat. Before all this we run a column compensation run to ensure our baseline is as flat as possible before calibration.

As far as integration parameters, not much is needed unless you're having trouble properly integrating a surrogate peak amidst the humpogram of #2 fuel oil.

The solvent is hexane because this is primarily an 8260 VOC lab. Yes, I am already using the "H" compound type as well as the A2 "FLAT". But the integration file still makes a difference. I have tried to optimize my temp/flow program to be flat from the baseline preceding the solvent peak to at least between C10-C25 then it rises just a bit.

I have not yet tried using a column compensation run to subtract out column bleed. I will read the documentation and see how to do that. I suppose it is best done using a full run without a solvent injection.
For proper column compensation you would first run a series of blanks and overlay the chromatography. If all runs look very consistent, then a compensation run can be made. If the chromatography suggests column bleed is decreasing every run, then you should continue running blanks until it's as consistent as possible.

You'll want to run the compensation run as soon as the GC is at start conditions immediately after a blank run, i.e. not idle for any length of time. Close software down. On instrument find comp run, start comp run, and then hit start (or enter...i can never remember). It should collect data. When it's done, start software back up, and choose "signal 1 - col comp 1" if using front detector. Run a blank run with new parameters and compare results.

The compensation run does wonders for integrating ranges in C20-C36. It's imperative when we run MA EPH.

Our current DRO parameter file:

Initial Area Reject: 0
Initial Peak Width: 0.010
Shoulder Detection: OFF
Initial Threshold: 10.0
Baseline All Valleys ON: 2.0 (just after solvent peak)
Regards,

Christian
Thank you for the quick tutorial for setting up column compensation. I will be using it directly.
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