The calcium displacement technique. The β-radiation emitted from 45Ca2+ ions in an aqueous subphase is shielded by the aqueous layer above the ions, yielding the β-intensity I
. (2.) A monolayer prepared on the subphase leads to the adsorption of calcium and in particular of 45Ca2+ ions to the surface, and subsequently a higher β-radiation I
can be detected. The β-intensity resulting from the monolayer can be calculated as I
. (3.) Substances having a higher affinity to the lipid monolayer as compared to Ca2+ lead to the displacement of the Ca2+ ions from the surface and a reduction of the β-intensity I
. The titration of peptides/proteins into the buffer can lead to a time trace of the β-intensity as depicted exemplarily in the lower trace.