[Lawsen Lew]

This problem might be a first order reaction. I am not sure how to use the 50 micro liters. It appears to be the same volume in starting, initial and ending, final. I think it is to affirm that there is not loss in the volume or mass, to confirm to the law of mass conservation, a closed system. The insulin might be in solution, but degradation within the solution medium. The solution is an inert medium to store it for delivery, use, and storage. I am not sure. Only you know about what is the 50 micro liters' purpose.