I was doing curls tonight and I switched up a little. Instead of doing the entire pull in one motion, I split the curls into two exercises. I did 3x10 from rest position to 90 degrees, then another 3x10 from 90 degrees to full curl. Is this effective or am I better off just doing full bicep curls?

It's similar to 21's with barbell curls.......

- 7 reps from bottom to half way up

- then, 7 reps from half way up to the top half of your motion

- then for the last 7 you do a full range of motion ( bottom to top )

...it's O.K. If you feel you must do isolation exercises for biceps during your training session , I wouldn't rely on this alone. I'd just use it as one of many exercises you could possibly do to target biceps.