Solving 1D diffusion PDE with finite quantity using pdepe/pdetoolbox

Hi,

I am trying to solve the second fick's law (simple parabolic pde) for the diffusion in 1D of a finite amount of compound (here is my problem). I am new to the resolution of pde using matlab, and I have a problem understanding how the boundary conditions are implemented for a finite source. I am looking to make a GUI to allow colleagues to use it easily so I need to do it in command lines. I just need some help for the start, the I will be settled. Any help ?

Thank you,

Best,

A