Cannot Eject Passport Ultra (Mac)

I have a 2TB Passport Ultra, currently connected to a MacBook Pro (OS 10.5.8).

Ealier I was rearranging files within the drive itself and kept running into Authentication problems, needing to enter an Admin’s password nearly every time I tried to move a file or folder. I found a fix online to change the Permission settings by selecting the drive and looking under “Get Info.” I changed a couple permisson settings for the drive itself along with the content on the drive.

As far as I know the action has been completed. This was done over an hour ago and any progress bars have disappeared. Now when I try to eject the drive I receive a message that states it is in use and therefore cannot be ejected.

Long story short, how can I be sure that the drive actually is not in use and safely eject the drive?

If you have verified that any program that might be using the Passport is closed and you still get the same message, you can try turning off your Mac and then disconnecting the Passport. 

Thank you for responding. I was thinking that it might come to that, perhaps I was being overly-cautious.

I did what you suggested and shut down the MacBook, proceeding to unplug the Passport. I had wanted to see if I experienced the same issue if I were to plug the deice back in, though so far so good. Again, thank you.