Calculating %Recovery, accounting for pre-existing amount in sample

I have a question regarding the calculation of recovery when there is a pre-existing amount of analyte in the sample. We have two schools of thought on how to calculate this…wondering what the general consensus is…

  1. %Recovery= ((Actual calculated amount in recovery sample)/(Amount Spiked into the recovery sample+ calculated theoretical pre-existing amount (determined from unspiked sample evaluation)) )x 100%

  2. %Recovery=((Actual calculated amount in recovery sample - Calculated theoretical pre-existing amount)/ (Amount Spiked into the recovery sample)) x 100%


In my opinion,

Actually the recovery study must produce the real time acceptable results.

In above mentioned case sample contain = pre amount + spiked amount…so at real time the calculation must be done on the similar way.

Here I am bidding for Option-1.

both the approaches gives the same result