I dont really see any problem with working out any group of muscles seperate. I know my way of training is different than most because I work out everything the same day. I dont overwork myself and I'm not saying my way is better. My way is just the best for me, but I still dont think working your biceps and triceps on the same day is wrong, I mean shoot, I do one after the other... lol hope that helps.
"Blessed be the Lord my strength, who
teacheth my hands to war and my fingers to fight." - Psalm 144:1