Complex sentence: Sensitivity to isotopes also allows contrast to be greatly (and selectively) enhanced for some systems of interest using isotopic substitution, and multiple experiments that differ only by isotopic substitution can be used to resolve the phase problem that is general to scattering techniques.
Split into simpler sentences: Sensitivity to isotopes allows contrast to be greatly (and selectively) enhanced for some systems of interest. Multiple experiments that differ only by isotopic substitution can also be used to resolve the phase problem that is general to scattering techniques.