Positive and negative ion electrospray mass spectra were obtained directly from water/alcohol solutions for phosphoric acid, methylphosphonic acid and its mono(1,2,2- trimethylpropyl) ester and bis(1- methylethyl) ester. Collisional activation and tandem mass spectrometry (MS/MS) of both the cations and anions of the phosphonates resulted in hydrogen rearrangement with loss of neutral alkenes to give the respective methylphosphonic acid anion (m/z 95) and methylphosphonic acid cation (m/z 97). Solutions of this series of compounds, which comprise a neutral, mono-basic, di-basic and tri-basic ligand, were complexed with alkali and alkali earth metal ions. The peaks observed in the positive ion electrospray mass spectra, and their propensity for fragmentation under collisional activation, were found to be consistent with the predicted stabilities of the complexes.

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