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 lo7 to 2.0 X lo8 Wlcm', 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 +,l oxidation state, when such salts are available. This method requires lower laser powers, in the range 2.0 X 10' to 8.0 X lo7 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.The determination of molecular-weight distributions of synthetic polymers is an important analytical task because the properties of a particular polymer, and therefore its suitability for a particular application, are directly linked to its molecular-weight distribution. The most commonly used methods for determining molecular weights of polymers provide some sort of average molecular weight: either a number-average molecular weight, M,, (osmometry, cryoscopy, ebulliometry, endgroup titration) or a weight-average molecular weight, M , (light scattering) where M , and M , are defined by Eqns (1) and (2)
