Peak broadening is the effect that a product is not staying concentrated in its injection volume, but is diffusing while passing through the bio purification system. This effect can impair the resolution of your separation. The reason behind peak broadening is that the flow rate in the middle of the tubing is higher than at the tubing walls, which is visible for low concentrated peaks most. One can avoid peak broadening by shortening the tubing length of the overall system and reducing inner tubing diameter. But keep in mind, that smaller inner tubing diameters are also increasing the system pressure.