It is possible that there is a coupling between the spin and gravitation, for instance by an adaptation of the Hamiltonian with an additional termH=k/c (gvec.Svec) where gvec is the gravitational acceleration and Svec is the spin vector, c is the light speed and k is a coupling constant. We propose to perform further measurements of the quantum gravitational effect for OffSpec. We will investigate the spin gravity coupling and find a first estimate of the coupling constant k. Another possible outcome could be an upper limit of k in case of neutrons. Accurate measurements of the phase plot need to be performed in vertical-splitting geometry of the instrument for several inclination angles. The measurements with and without the gravitational component will give us the accurate absolute result for the separation of the eigenstates which is a measurement of the difference in potential.