Basicity is a important criteria to measure the catalytic effect of many solids like zeolites. So it is necesary to qualitative and quantitative analysis of it.
Using IR spectroscopy with probe molecules is a common way for acidity or basicity measurements of zeolites.
Which probe molecule is suitable for your experiment is depending on several issues. One important point to consider is the zeolite structure.
A overview could be found in literature. For example have a look at this paper:
J.C. Lavalley, Infrared spectrometric studies of the surface basicity of metal oxides and zeolites using adsorbed probe molecules, Catalysis Today, Volume 27, Issues 3–4, 1996, Pages 377-401, http://dx.doi.org/10.1016/0920-5861(95)00161-1.