Ionization of solutions using mechanical spray in collison nebulizer: A new simple ion source for mass-spectrometric analysis

Ionization methods for mass-spectrometric analysis based on mechanical liquid spray by a high-speed gas flow (like Sonic Spray Ionization (SSI)) offer some advantages over other ionization methods. Among these one should mention the absence of electric voltage, radioactive sources and heaters. In this paper we suggest using the Collison nebulizer for solution ionization via mechanical spray. Research results into the efficiency of the Collison spray ionization of different solvents used in chemical synthesis are submitted. It is shown that an increase in dipole moment of the solvent molecules leads to increased ionization efficiency for all solvents tested, except water. This seems to result from anomaly high surface tension and vaporization enthalpy for water. High concentrations (>10⁻⁴g/ml) of both inorganic salts (NaCl, K2SO4) and organic additive (morphine) give a decrease in the total ion current at the Collison nebulizer outlet. This is assumed to be due both to an increased droplet size of aerosol produced upon spraying and a low dipole moment of an ion-solvation shell complex. Mass-spectra of aqueous K2SO4 and morphine (C17H19NO3) were obtained with the Collison nebulizer. These spectra contained non-identified background peaks along with the peaks of K⁺ and H⁺C17H19NO3 that were likely to result from the water ionization and presence of uncontrolled impurities. A relationship between the intensity of mass-spectroscopic peaks of the ions of potassium and morphine and the concentration of appropriate aqueous solution was determined. Mass-spectrometric analysis using the Collison spray ionization gave a detection limit for morphine ∼10⁻⁸g/ml and a linear response range for protonated molecular ion (H⁺C17H19NO3 with m/z=286 from 10⁻⁸g/ml to 2×10⁻⁷g/ml.