First of all I have a problem with you doing 12 sets of Chest and then 12 sets for the shoulders. If you are doing Barbell Bench Presses you are already working your front delts enough. With an additional 12 sets for the shoulders you are asking for shoulder trouble…and you don’t want shoulder trouble.
The best routine that I have ever used for my arms was to train with a few sets, perhaps six to seven at the most, three times per week. Only go to failure on one day per week!
The theory is that the arms get a a decent workout every other day or so. This is better than blasting them with 12 sets one time per week, (I have found).
A good routine:
Chin-ups (palms facing you) Two sets-do a negative on the way down and blast up as fast as possible. Rest :90 between sets.
Rest only :90 and do one set of Straight Barbell Curls with a weight that you can do 12 strict reps with. No cheating! Final reps should be hard but you might have one or two more in the tank.
Lying Tricep Extensions-three sets 8 to 12 reps. All strict. :90 rest between sets.
Standing Dumbbell extensions-12 reps or so…again make sure they are strict.
When I worried about arm size I would use the above routine for six weeks and it worked well. Usually I would not perform the Lying Barbell Extension as I don’t think it is great for the elbow joint. However, since you want to specialize, and it is no more than 6 weeks, I wouldn’t worry about it.