CATION ATTACHMENT IN THE ANALYSIS OF POLYSTYRENE AND POLYETHYLENE-GLYCOL BY LASER-DESORPTION TIME-OF-FLIGHT MASS-SPECTROMETRY

Al+, Cr+, Fe+ and Cu+ gas-phase ions have been found to attach efficiently to two polymers, polystyrene and polyethylene glycol (PEG) in laser-desorption time-of-flight experiments, and are shown to be viable alternatives to the commonly used Na+, K+ and Ag+ ions. At high laser powers, in the range 8.0 x 10(7) to 2.0 X 10(8) W/cm2, ions can be attached by desorption from a support made of the appropriate metal. An alternative method is to add the metal ion in the form of a salt containing the metal in the + 1 oxidation state, when such salts are available. This method requires lower laser powers, in the range 2.0 x 10(7) to 8.0 x 10(7) W/cm2. The two desorption/attachment methods are characterized by different optimal time-delay values for recording of spectra. Polystyrene has been found to have a higher affinity for attachment to Al+, Cr+, and Cu+ than to K+, while PEG has been found to have a higher affinity for K+ than for Al+, Cr+ and Cu+. These preferential attachments are discussed in terms of the hard and soft acids and bases principle.