Help with Chemstation integration for GCMS?

[ardee]

I am using Chemstation vE.02.00.493 and am a little confused with integrating my analytes. I have set up my calibration via external standards using the AutoQuant feature, and also using SIM quant (set up manually, not with AutoSIM).

The ‘response’ section of my Edit Compounds table has all been filled in automatically which is great and I can see that the calibration curve has plotted concentration vs response.

This mysterious ‘response’ is totally different to the result (peak areas) I get if I use Chromatogram>Integrate from the main menu. If I then view the results by selecting Chromatogram>Integration Results, the result shown is peak area. However, selecting Quantitate>Calculate from the main menu returns a result calculated via this quantity called ‘response’.

I’m using Chemstation Integrator, not RTE.

So I guess my question is – what is ‘response’ and how is this different from peak area? And can/should I change my calibration to calculate results based on peak area rather than ‘response’?

Thanks in advance for any replies

[ardee]

Just wanted to add that response is not peak height either

[carl.nott]

Okey, so you're not 'Measuring Response by Peak Height', you're 'Measuring Response by Area'? Just confirming. Are you using any sort of area correction?

[ardee]

yes that's right, measuring response by area. I'm not using any correction that I am aware of.

[carl.nott]

I'm not familiar with your version of Chemstation but I would check if there is some sort of 'mass correction' or something like it which is being applied to your response number. What do the numbers look like compared to the area count? 5.5 vs. 14120 / 11341 vs. 14120, etc.?

[ardee]

I don't recall seeing a mass correction option anywhere in my travels, although it does seem like the most likely cause.

I'm looking at roughly double for response compared to peak area. My lowest standard is ~53000 for response, ~21000 peak area...

[carl.nott]

Again, I don't think I'm familiar with your Chemstation, but in G1701DA D.01 you can pull up the inital cal and look at each compound and on page 3, where the list of calibration points and responses are, there are options for different corrections.

Just for trouble-shooting is the response value consistently different than the area for the entire calibration? Consistent per compound? Varies per calibration point?

If it's consistent over the entire calibration there may be an option that is checked to adjust response based on injection/purge amount. If it's consistent per compound I'd think it's a compound MW correction or, perhaps, some sort of blank subtraction. If it's not consistent per compound... I dunno, heh, but I'd think that your calibration would be bad.

Actually, that's probably a good question: Does the calibration look good except for the weird response value?

[ardee]

Ok, so I have found the options of Area Correction Mass and Correction factor but these are both currently set to zero.

The response is consistently ~2 times the peak area, not varying between compounds or concentrations but I am reluctant to just apply a 0.5 correction factor without really knowing why...

And yes, my calibrations are very nice >0.999

I am getting to the point where I will probably just go with what I have for the time being and just ask our Agilent rep about it next time he's around. I don't think this project is worth spending a lot more time on unfortunately. Oh well, thank you Carl for trying to help!

[AICMM]

ardee,

How many ions are you looking at in SIM mode? In the chromatogram, when you integrate (if I am not mistaken, it has been a while) you are looking at the total ion current for all of the ions monitored. When you are looking at your calibration curve you are looking at just the quantitation ion. If you want to see, just pull up an extracted ion profile and then integrate and look at the areas....

Bit rusty on my MS Chemstation so I could be way off, but I don't think so.

Best regards.

[ardee]

Thanks AICMM, you're absolutely correct. Seems obvious now that you have said it!