Work conditions force me to switch to a 3 day split
 

Hey guys.
I recently got a promotion at work and have seen a considerable increase in the hours spent at the office. I was on a 5 day split that looked a bit like this:
Day 1: Legs
Day 2: Back / Abs
Day 3: Chest
Day 4: Shoulders / Traps
Day 5: Arms / Abs

Now i need to make a 3 day split. Considering my goal is mass gains do you think a 3 day split will be beneficial towards that goal, and if so can you guys suggest any 3 day splits i could use?

If 3 days is what you have to work with there is no reason why you can't make it beneficial to gaining mass. Ask yourself, are you more likely to gain mass working 3 days a week, or working 0 days a week? I bet you're seeing the benefits already.

I would say combine Back & Chest; Arms & Shoulders; Legs seperate.

You can do it. Many powerlifters do it based around their lifts on a 3 days split. It would look like this:
Day 1: Squats
Day 2: Bench
Day 3: Deadlifts
In powerlifting terminology, they call the other movements assistance exercises. Examples would be barbell rows etc..

Now if you did it bodybuilding style, here's how it might look:
Day 1: squats + other leg work such as stiffleged deadlifts and calf raises
Day 2: bench + other upper body work such as military presses and arm work
Day 3: deadlifts + upper back work, traps, and abs