RESUMEN
It is demonstrated that laser desorption ion trap mass spectrometry (LD-ITMS) can be successfully applied to the chemical analysis of a monolayer of adsorbates on a solid surface. Negative ion spectra obtained from LD-ITMS of self-assembled monolayers adsorbed from solutions of alkanethiols (CH3(CH2)nSH with n=5, 9, and 15) onto polycrystalline gold surfaces displayed clear ion peaks corresponding to the sulfonate adsorbate species. Sulfonate ions with the general formula CH3(CH2)n SO3 were detected at m/z 165, 221, and 305, respectively, and were derived from the partial oxidation of the corresponding alkanethiol self-assembled monolayers. Little fragmentation and no clustering was observed in these mass spectra. These results indicate that the sensitivity of LD-ITMS is sufficient to allow its application to a wide array of problems in surface science.
RESUMEN
Polystyrene sulfate particles of 189 to 1,085 nm radius are retarded in their electrophoretic migration in solutions of methyl-hydroxypropyl-cellulose (4,000 and 15,000 cP viscosity for a 2% solution). The retardation is proportional to polymer concentration and increases inversely with particle size. This suggests a separation mechanism based on size-dependent exclusion from the polymer network, as found previously in other liquid polymer media. In the size range of approximately 200 to 600 nm radius, the 4,000 cP polymer exhibits a steeper decrease of retardation with particle size than the 15,000 cP polymer, but fails to exhibit any size dependent retardation beyond that range.