You are here:
ENVIRONMENTAL APPLICATIONS OF THERMOSPRAY LCMS: QUALITATIVE ANALYSIS OF SULFONATED AZO DYES
Citation:
Flory, D., M. McLean, M. Vestal, AND L. Betowski. ENVIRONMENTAL APPLICATIONS OF THERMOSPRAY LCMS: QUALITATIVE ANALYSIS OF SULFONATED AZO DYES. U.S. Environmental Protection Agency, Washington, D.C., EPA/600/J-87/249 (NTIS PB88177084), 1987.
Description:
Thermospray mass spectra (TSMS) has been used to obtain mass spectra of several di- and tetra- sulfonated azo dyes. Commercial dye preparations were dissolved in various mobile phases and injected into the TSMS system. Mobile phases investigated included pure water and varying concentrations (0.00001 to 0.1 M) of aqueous ammonium acetate and ammonium sulfate. Negative ion mass spectra were obtained for seven di- and two tetra-sulfonated azo dyes with as little as 100 nanograms of sample injected into a pure water mobile phase. Singly and doubly charged negative ions corresponding to losses of one and two sodium atoms were generally observed. Results indicate that protonation by ammonium acetate begins to occur at concentrations between 0.001 and 2.5 x 0.001 M. At concentrations higher than 0.01 M there is suppression of the response. These results mean that anion evaporation of the analyte directly from the droplet is the major ionization process operating under these conditions and there is no significant chemical ionization contribution. The suppression of ionization at higher salt concentrations is due to the injection of the more volatile salt anion (relative to the dye) before the field strength is sufficient to eject dye anions from the evaporating droplets. (Copyright (c) Hayden + Son Limited 1987.)