Chromatography Forum

Is there a field in Empower2 that calculates the peak area ratio of an analyte peak to an internal standard peak? For example, I have an LC-MS method that collects two data channels: one SIR at the m/z for the analyte and another SIR at the m/z for the IS. Generating the calibration curve using built in features and getting the final results (e.g. concentration and percent recovery calculations) works fine, but I also need to evaluate the variability in the peak area ratio for QC's, SSTs and PC injections and was wondering if there is a built in field that does this calculation for each sample?

Off the cuff....

Set your ISTD as CCalRef1 in your processing method.

Create a peak type custom field: area/CCalRef1[area]

Though it would seem to me that there ought to be a built in equation for this. However, if you don't want to spend hours finding it, then just use what I have above...

There are two different data channels, The custom field works for the channel that collects the m/z for the IS and, as expected, I get a peak area ratio of 1.00. It does not calculate the area ratio for the analyte as it appears to be looking for the IS in the same data channel.

I was afraid you were going to respond with that...

How about we change that custom field to:

..ChannelA(Area)/..ChannelB(CCalRef1[area])

where channel A will be the SIR for your analyte and channel B will be the SIR for your ISTD.

Note: I have not actually tested this custom field because I don't have any MS data, or dual channel data, available to me at the moment, but this really ought to work.

If you need that to only run on standards, then use the sample label in the sample set method to help out with that. Say you use SS1, SS2, SS3, etc. for your standard labels. That equation above then becomes:

SS?..ChannelA(area)/SS?..ChannelB(CCalRef1[area])

I have been able to get it to work by a simillar approach. My reservation, however, is that the channel for the SIR response in Empower2 is specified as part of the instrument method and the channel name is automatically assigned (e.g.: ZQ F1 SIR 423.50). If I have a method with a different MW for the internal standard this field would cease to work, I would need to rewrite the custom field to specify the new channel name for each new method I find.

If I were to have the instrument acquire a scan of m/z and then extract the single masses as part of the methodset, I could get it to work, however, this would not provide equivalent data quality.

You could also create a sample type custom field that is available in the sample set where you manually type in our channel name. You might be able to then use that custom field for your channel information.

Not fully automated, but it gets you around the new field for every new weight...

Okay, figured out how to derive a channel from the parent ZQ SIR channel (you can't extract it like you would from a pda or TIC, you need to click on the channel itself and derive your channel from there).

I also found, that I could not get the CCalRef1 to work in this calculation. It works fine if I used the following : Area/..B(IS[Area])

Where B is the name of the extracted channel and where "IS" is the peak name given to the internal standard. It would be nice if I could get the CCalRef1 to work so we could use whatever peak name we want with the custom field. It is likely that it isn't working because the analyte peak is missing in the data for channel B.

(I also tried using ..A(Area)/..B(IS[Area]) but that didn't work either)

I guess I could get by with what I have for now. Thanks for your help shaun78.