Chromatography Forum

Work flow - GC Headspace
Results from two of the vials are used as the blank
I need to average the two peak heights between the two vials and if the average height is equal to or less than 100 then use the 100 as the blank value. Once the sample's height is corrected for the blank we multiply it against a response factor

+ There often isn't a peak for the constituent which was giving me some issues with the calculation failing completely. I found this to be due to the value being a Null(); therefore, I've creating a custom field:
Result Set Only, Real, Peak
NoNullHeight: Replace(Height,0)

This works fine returns zeros for the missing peak values

+ The issue I have now is trying to get the average height between the two blank vial results to subtract from the current sample's peak height.

I labeled the two blank samples "Blk" and following some information I've found online about inter-sample custom field calculations I've tried
Result Set Only, Real, Result
AvgBlkHeight: EQI(Name,"PeakName")*Blk...AVE(NoNullHeight)

This results in an error about peak/component fields need a SUM,MIN,MAX,AVE function; however, this equation appears to have one.

I'm at a loss at this point.

The Response factor will be entered into the processing method as CCONST2

Thank you for any help you can offer, the more I read the tutorials I could find online about the Empower Custom Fields the worse I understand them.

Hi ,

This may help :

SAME.%.SAME.AVE(Area)-B1.%.SAME.AVE(Area)

Replacing Area with Height and 'B1' with 'Blk'

or replace EQI with EQ

Thank you for the suggestion, I'll have to give that a try this morning when the workload abates a bit!

Sorry the formula does not return any values.

Should have mentioned
Empower 2 Fr5 Sp A - H w/hotfixes

When I try something like:
BLK.%.SAME.AVE(Height)
I receive an error about using peak fields; however,
BLK.%.SAME.AVE(constituent[NoNullHeight])
It doesn't error; however, there's no result.
(both CF are Field-Type Result, Real, Result Set Only, Missing Peak True)
SAME.%.SAME.AVE(constituent[NoNullHeight])
Does not return a height either

What I have now is
[AvgBlkNoNull]
Field-Type Result, Real(12,0), Result Set Only, Missing Peak True
AVE(BLK..(constituent[NoNullHeight ])

[NoNullHeight]
Field-Type Peak, Real(12,0), Result Set Only, Missing Peak True
Replace(Height,0)

This is not however returning the proper average value...
(Sample 1)(Ref) - constituent[NoNullHeight ] = 5356
(Sample 2)(Ref) - constituent[NoNullHeight ] = 6834
(Sample 3)(BLK) - constituent[NoNullHeight ] = 0
(Sample 4)(BLK) - constituent[NoNullHeight ] = 386
(Samples 5 - 10 have no labels...)
Instead of (386+0)/2 = 193
I'm getting something like 112, the other sample peak heights are between 500 to 2000 range so the average of all of the peak heights wouldn't be 112.

If I put the [AvgBlkNoNull] field on the report instead of one value I get something like
AvgBlkNoNull: 0, 386

This just has me confused...

Solved this one...
ydna1977 sent me down the right track here...

It's the simple things... after re-reading the tutorial, I discovered that was overlooking a section that talked about the "Summarize Custom Fields" function requirement for cross sample summary functions. I went back into my sample sets and added the Summarize Custom Fields and the correct sample labels to the sample information to get:

Sample set (abbreviated):


>Line 7 was/is the key to getting the summary functions to work on the result-set level.

Custom Fields:
[NoNullHeight]
Field-Type Peak, Real(12,0), Result Set Only, Missing Peak True
Replace(Height,0)

[AVG_NoNullHeight]
Field-Type Result, Real(12,0), Result Set Only, Missing Peak True
BLK...AVE(Constiutent[NoNullHeight])

There's logic to subtract the larger of 100 or [AVG_NoNullHeight] from samples, to prevent negative results, use the CCONST1 value for our response factor, and a few other minor calculations for the result.

and Bob's your Uncle.