I got to a similar point about 2-3 years ago. Whenever I have a task that I need to focus on I go into what I call "5 minute mode". From :00-:05 of the hour I am free to check email/twitter, call someone back, find articles to mark for reading later, etc (Dopamine hits). Then :06-:59 = "in the zone" time.

This gets harder in an office environment, but usually some headphones, a don't bother sign, and shutting down all communication channels get's it into other people's heads.