well the bicep is a small muscle, and you really cannot isolate the inside or the outside.
I can tell you that with the quadriceps, which do have separate heads, that a wide stance works the inner quads, and a narrow stance hits the outer quads.
but i'm not a physiologist so I don't know if the same holds tru for the arms. my advice would just be to use a variety of grip widths, including a shoulder width grip. use barbells and dumbbels, and don't forget hammer curls...do those often.
for chest, the wider the grip, the more pecs and the less triceps. the narrower the grip, the more triceps, less pecs (hence why close grip bench press is considered a triceps exercise, with pecs assisting).
unless you have disproportional strength between pecs and triceps, I'd stick to mostly shoulder width + a couple inches grip, and keep wide grips for 'a change of pace'.
i feel close grip bench is a core triceps builder.
