# Blank interference custom fields

Hi, I'm trying to set up a couple of custom fields for calculation of blank interference and can't get the syntax right. I want one comparing the peak area in the blank to the average of all working standards: Blank Interference = Area*100/(Average Area of all Working Standards), and one comparing only to the first injection of the working standard: Blank Interference = Area*100/(Area of 1st injection of WS). Thanks for your help!

• For your first requirement, label all your standards starting with S, so for example S1 S2 etc or S01 S02..and label your Blank injection as B.Create a peak, real, calculated custom field, result set only, All Sample and Peak types.Formula is (B.%.(Area)*100)/S%.%..AVE(Area) and call it Blank_Interference. If you only have one active then you can substitute area for CCalRef1[Area]. And to make the result only populate for the Blank Injection add on a condition at the end (make sure All or Nothing is ticked for this to work) so your final formula for Blank_Interference becomes:

(B.%.(Area)*100)/S%.%..AVE(Area)+NEQ(Label,"B")*-1*50000.

The above CF requires a Summarize Custom Fields function as the last line of the sample set.

The second CF is another peak, real calculated field, formula is

(B.%.(Area)*100)/S%.%.(Area)

for this to work your first working standard will have to be labelled as S and some other number or symbol as above example S1 S2 etc, Or if you want to be completely specific and only return values for the first working standard, you can label your first working standard as S1 (taking into account you will need labels for calibration so don't make the syntax too complicated) then the formula becomes:

(B.%.(Area)*100)/S1.%.(Area) and call this BlankInter_FirstStd.

Hope this helps.