You say you train biceps and triceps each on their own days once a week–so do you do a chest and triceps day once a week and a back and biceps day once a week or what?
My current split looks like this:
Saturday: Quads (workout 1: 45 mins - 1 hour) and Calves (workout 2 45 mins)
Sunday: Chest (45 mins)
Monday: Back (usually only takes 40 mins)
Tuesday: Shouders, Hams, Calves (1 hour)
I do deadlifts on quads day. Now… if I want to specialize a muscle, say chest (like I’m doing now), then I will do 1 exersize for it (usually bench) on a day when it has recovered from the previous workout and will be recovered for the next. This means I do that 1 exersize on biceps day. I realise this is after triceps, but if I’m careful with my technique, they don’t really get hit. You can try doing this additional 1 exersize for all body parts… but I found that after a few weeks I was slightly overtraining. So now I only do it for one special muscle that needs attention.
Another option is, rather than doing chest & triceps together, do a chest & biceps day together or a back & triceps if you’re going to pair an arm part day with either chest or back. This way you’ll still get in half of an arm workout while maximizing the arm part being worked, since you won’t have exhausted it with another part where it is a secondary player in exercises. So, an example split would be something like this:
Sunday - Chest/Biceps Monday - Off Tuesday - Legs Wednesday - Back/Triceps Thursday - Off Friday - Shoulders/abs Saturday - off
This is just an idea off the top of my head, but you can see how it would work. It is actually an idea I've seen advocated in a few places, as it allows for you to do one indirect day and one all-out day for each part of the arm while giving yourself an extra day off for rest during the week since you won't have to devote an entire day to arm workouts.