Chromatography Forum

Hello everyone,

I have a problem with peak identification calculation in Empower. Our method says that identity is confirmed if unknown retention time / standard average retention time is within 0.99-1.01. I tried to calculate that with peak custom field

[RetentionTime] /STD... AVE(RetentionTime)

and it seems to work fine for 1 API only. In case of 2 or more APIs it gives no result. I did something wrong but I cannot figure it out. Maybe my whole idea of this calculation was wrong from the very beginning.

I'll be very grateful for any help or advice you can give me.

Regards,
Anna

Your syntax is off slightly. You don't need square brackets for the first part, you also need a % for the injection part of the Label.Injection.Channel.SummaryFunction(Field) equation. This is because you presumably have multiple injections of standard and the % includes all of them. Leave it out and Empower will only calculate all injections except the last one, giving you an inaccurate value. Are all of your standards labelled simply as STD in the sample set? If so, here is the correct formula:

Retention Time/STD.%..AVE(Retention Time)

Make sure Peak Type is set to All and more important Sample Type to All. If you have set Sample Type to Unknowns Only, and the equation references standard injections, you are not going to get anything in the custom field. Search Order is also very important. "Result Set Only" is the best setting for this to ensure the average retention time of standards only includes those standards labelled as STD in that sample set and not all the data sets in the project with standards labelled as STD. If you make these changes it will work.