Test for mass conservation

Hello,

i am not sure how to test my solution for a compressible sediment during centrifguation.

I do not use mass but concentration instead. If i then integrate the resulting concentration profile i do get more than 100 % recovery compared to the area of my initial profile.

Test(end,:)=cumtrapz(sol(end,1:end))./cumtrapz(ustart(1:end))

Where sol = time x space

Should i convert to mass before i do that ? It would cancel out i guess, so using concentrations should be fine. Or am i wrong with that and just too tired.

Thanks