A metal–organic framework, consisting of Er(III) linked together by 1,4-phenylenediacetate, was synthesised by a one-pot reaction and successfully used as an affinity material for the selective capturing of phosphopeptides. An optimised protocol for loading, washing and elution was developed and the eluents were analysed via matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry. A standard protein digest (α-casein, β-casein and ovalbumin) as well as digested egg white proteins were used to test the efficiency and selectivity of the presented approach. 14 phosphopeptides could be recovered from the peptide mixture and in the case of digested egg-white, four phosphorylated peptides which could be assigned to ovalbumin were isolated. Ab initio calculations based on the affinities of various ligands to the material have provided reasonable explanations of the observed experimental properties.
