Norm % (Amount or Area) when not all peaks are present.

[AMNangle]

I am changing over to Clarity from a different GC software for doing headspace. With the old software I was able to get a % area normalization even when "not all compounds are found in sample." I think I have worked this problem out, but I do not always have the same amount of air going into the GC and I need the % norm to adjust based on the peaks that are in the sample. Another way to put it is my injection volumes change. How would I go about always having 100% total rather than 105% or 33%?

[Daniel Mentlik]

Dear Ariel,
"not all compounds are found in sample" warning was an error introduced somewhere around Clarity 8.1, will be partially fixed in Clarity 8.2. NORM calculation type is in fact just an ESTD calculation type with added data consistency checks, and by error Clarity expected the check of compounds between calibration and chromatogram in both ways (not only checking that all compounds found in the chromatogram have representation in the calibration, but also checking that all peaks as defined in the calibration are also found in the sample).

The area% calculation is done by dividing the area of the given peak by the total area. This works in all cases to have 100% area totals except the case when there are groups defined in the sample, and where some of the peaks used as a part of the group are calibrated both as an individual compound and also as the group. I would suggest reading the appropriate user guide entry: https://www.dataapex.com/documentation/ ... lation.htm

If you want to calibrate based on the area% values (using area% as a calibration response base), it is also possible, calibration must be set accordingly.

For some specific calculation patterns, you can also use the User Columns - when setting the User Column formula, you can use a "Special Value" option containing for example area total.

Please describe in more details what exactly you want to set and how in order for us to advise better.

Best Regards,
Daniel

[AMNangle]

After I posted I got the user calculation to work for what we are doing. I'm using the following calculation:

[Amount]/([Amount]sum/100)

If there was a way to do this without the user column that would be great!

[Daniel Mentlik]

Hi Ariel,
this may be even easier then - I haven't considered Amount%, talk was about Area%.
Clarity calculates the Amount% natively too, there is a special column (not user column) for this calculation. Instead or "Amount(sum)" part in your equation the formula for Amount% uses Amount column Total value, which in most cases calculates as Amount(sum). However, if you fill in Sample Amount field to anything other than 0, either in the Single Analysis/Sequence dialog or in the measured chromatogram, the value entered will be used instead of Amount(sum). This is probably what gets you to totals different from 100%.
Easy remedy here is not enter anything into the Sample Amount field, you will always get 100% total results. If you definitely need to pass some value through from Single Analysis/Sequence to the chromatogram, you may use various diferent fields to do so, for example the User Variables fields. Sample Amount is specific field which also influences the Total Amount display, other than that the User Variables fields are equivalent in usage.

Best Regards,
Daniel

[AMNangle]

That works!

Thank You!!!

[AMNangle]

So, the Amount% works if all the peaks are on the chromatogram, but most/all of our samples only have 1-3 peaks on the chromatogram. Is there a way to force the Amount% to calculate every time?

[Daniel Mentlik]

I may not understand the question. mount% is calculated every time, even when not all peaks are in the chromatogram. Please see following screenshot:

Calibration contains additional peaks which are not present in the sample, yet the Amount% column is still calculated. It is just not visible for the peaks not found (result there would obviously be 0%).
Display of the peaks not found in the sample but present in the calibration can be switched on by selecting the All Peaks in Calibration display option.

[AMNangle]

I noticed that you had the calibration as ISTD. I was using NORM. Once I switched to ESTD the amount% worked. Thank you.

[Daniel Mentlik]

Yes, ESTD or ISTD should work easily.
NORM calculation is basically ESTD with several added validity checks. In case some of the checks fails, no results are displayed and the reason for failure is visible above the Result Table.

Best Regards,
Daniel