ISTD, surrogates and recoveries

First time using MassHunter (version 12.0). I am trying to set a method for dioxin EPA 1613 and have doubts about surrogates, ISTD and how to calculate standard recoveries.

I have defined the standard added before sample extraction as ISTD, correct? and these are used to calculate native (target) concentrations.

But what about the standards added before injection? Are they surrogates? With these- I would like to obtain the recoveries of the standards added before injection, but I don´t know how 

Thanks a lot for your help!

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