Evaluation of crown ether complexation for elemental electrospray mass spectrometry

Formation of various solvent clusters under mild source conditions and the loss of charge state information and lack of sensitivity under harsh source conditions are the major problems encountered in elemental electrospray mass spectrometry (ESI-MS). In this work, the use of crown ether complexation as a means of alleviating and solving these problems was evaluated. The crown ether (18-crown-6) was added postcolumn to the now injection analysis of various metals including alkali, alkaline earth, and transition metals. In most cases, greatly simplified mass spectra that are free from solvent cluster interference could be obtained under suitable in-source collision-induced dissociation conditions. Oxidation state information of singly and doubly charged metals was retained in the metal-crown ether complex ions. Alkali metals were detected by two modes: (i) metal-ether complex ions and (ii) metal ions dissociated from the complexes using in-source collision-induced dissociation. Alkaline earth and transition metals were detected by monitoring the metal-ether complexes. Signal improvements in the range of 5-20 times were achieved for the metals studied. Slight improvements in the dynamic range were also observed.