Snickers had a little bit of separation anxiety when I first got him, he would bark and whine and just not want to be left alone. Do you usually watch t.v. with him? Do you have a certain channel you like to watch? Maybe leave the t.v. on for some noise to distract him a little while you're gone.
What I did to stop it was that I would walk outside for a few minutes, leave him in there barking up a storm, come back in, say no bark, walk back out. I had his favorite treat ready for him when he didn't bark and now the times get longer when we are gone out shopping and I usually have a treat for him, if I remember. He still barks some but then he quiets down. This also reinforces that when you leave you are coming back.
It's probably a little scary for your pup all alone in your apartment without you there, maybe just a little backround sound will do the trick. Good luck
