You shouldnt really work a muscle goup two days in a row tbh. So biceps the day before back, triceps the day before shoulders or triceps or shoulders the day before chest as all those muscles are used secondarily in working the larger muscle group. It works the other way round too, so you dont really want to be working tris the day after chest etc etc...
If you want to work everything twice per week there are some really good routines on this site that you could perhaps look at and see if they are along the the lines of what you want to do. For me the program seems a bit 'arm heavy' but if your getting the results you want then its all good. I wouldnt tell someone to change something that is working, but i think you may get better results from perhaps having a look around the site and getting a few ideas from there. The newly created 'real results' section in the 'fullbody' section has some fantastic routines that you could look at to see how muscles are separated throughout a working week
hope this helps