No abstract

No abstract

Three laser wavelengths (1064, 532, and 266 nm) were employed for laser ablation at varied laser pulse energies to study the effect of irradiance and wavelength upon analytical results for laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Two important results were observed and are reported here: (1) the intensity of the MS signal came to a local minimum when the laser focal point was on the sample surface, and (2) elemental fractionation based upon laser wavelength and laser pulse energy was observed. For the waste glass simulant studied, ablation with 1064-nm (IR) and 532-nm (green) radiation produced elemental fractionation that relates to the melting point of the elemental oxide, whereas with 266-nm (UV) ablation the response was independent of the elemental oxide melting point. At high laser powers, ablation at 266 nm produced an elemental bias based upon the mass of the elements. These observations suggest the use of ultraviolet radiation at low pulse energies to obtain improved analytical results.

Addition of silver nitrate to nonpolar hydrocarbon polymer solutions prior to their analysis by laser desorption Fourier transform mass spectrometry is shown to allow efficient silver ion chemical ionization. High-quality mass spectra are thus obtained for polymers, such as polystyrene, polyisoprene, polybutadiene, and polyethylene, that previously failed to yield useful mass spectra using conventional laser desorption. Accurate mass measurement experiments and isotopic ratios verify that the spectra are those of silver-attached oligomer ion distributions. Mass measurement errors for complete oligomer distributions average between 3 and 12 ppm for oligomers with masses between 400 and 6000 D whereas unit mass resolution is maintained throughout the entire spectral range.

The first mass spectrometric analysis of a new class of hydrocarbon dendrimers that result from a convergent synthetic approach is reported. Molecular weights of a series of phenylacetylene dendrimers (715 to 14776 u MW) are characterized by ultraviolet matrix-assisted laser desorption (MALDltime-of-flight (TOF) mass spectrometry, direct and silver chemical ionization infrared laser desorption Fourier transform mass spectrometry @I'MSl, and ultraviolet matrix-assisted laser desorption silver chemical ionization Fourier transform mass spectromeby. New matrices and techniques were developed to facilitate analysis of the dendrimers. Mass measurement accuracies between 10 and 25 ppm are obtained for molecular ion species of the five dendrimers analyzed. Laser desorption time-of-flight and FI'MS techniques are shown to be complementary, with FTMS providing high mass resolution (27,000-67,000 resolving power) and accuracy for lower mass dendrimers (10-14 ppm) and MALD TOF yielding the highest resolution (1100 resolving power) and accuracy (25 ppm) for the largest dendrimer. These results are consistent with proposed empirical formulas.