Needs review
Source: Quintessential Elf 2

Description: Your spells remain even after you stop concentrating on them.

Prerequisites: 10 levels of arcane spells, Words of Binding

So long as you maintain more than 10 levels of available arcane spells, spells with a duration of Concentration linger for a number of rounds equal to your Intelligence modifier after you stop concentrating on them. This bonus is added to the duration of the spell, if it maintains itself for Concentration + X rounds. If casting the spell would drop you below 10 levels of stored energy, you may not use this feat.