# How to find the largest peak?

<p>Hi,</p><p></p><p>Is there a way to have Empower identify the largest peak in the chromatogram? This is a rather typical situation with impurities, I usually need to quantify some known ones, impurities in total and then the single largest unknown.  Ideally I would like to access this from custom calculation similarly as in interpeak calculations, such as "largest peak"[Area] or something like that, but of course if that's not possible, other solutions will do. Any ideas?</p>

• There is a "MAX" function.  Of course if you do MAX(Area) you would get the area of the main peak, not the largest impurity.

I don't have access to create custom fields, so I am sort of winging it.  Something like below should work

You can use one of the CConst variables (entered in processing method) to define which peak is the main peak

e.g. CConst2 = 0 for main peak

Also, CCalRef1 peak could be defined as the main peak

Then you can create a field "Impurity_Area" which is = Area except if CConst2=0 where you would set to zero

Impurity_Area = NEQ(CConst2,0)*Area  (if CConst2 is not equal to zero this equals Area, if CConst2=0, this would be zero)

Then you can do MAX(Impurity_Area) and SUM(Impurity_Area) to get MAX and TOTAL as separate fields.

Even simpler (though less elegant and perhaps less effective if you are using downstream systems - e.g. LIMS) would be to use reports.

You can create a table which excludes peaks with Area% greater than (e.g.) 90%, then use the Summary functions TOTAL and MAX to get these values.

Hope this helps,

Kevin

• Hi

A really easy solution, which might work for you, is to create a new component called "Largest Peak" then use the Component table to set this as the largest area peak in a (wide) defined window. You should then be able to use this component name for custom fields, without disturbing your normal quanitation routines using the real peak name.

Heather

• Thank you both, combination of your answers helped me out and got this report automated.