In the interest of a more thorough understanding of the relationship between sample deposition technique and the quality of data obtained using matrix-assisted laser desorption/ionization (MALDI) mass spectrometry, details of the electrospray (ES) process of sample deposition are investigated using a number of techniques. Sample morphology was observed with scanning electron microscopy (SEM) and atomic force microscopy (AFM), while matrix-enhanced secondary ion mass spectrometry (MESIMS) monitored surface coverage. Electrospray deposition reduces the analyte segregation that can occur during traditional dried droplet deposition for MALDI. We attribute statistically significant improvements in the reproducibility of signal intensity and MALDI average molecular mass measurements to the ES sample deposition technique.
Size exclusion chromatography (SEC) is shown to be an effective method to characterize single-wall carbon nanotube (SWNT) dispersions. SEC separates nanotube dispersions by size, and an on-line viscosity detector gives intrinsic viscosity as a function of hydrodynamic size, as is determined by universal calibration. The scaling contains information about the shape of the dispersed particles. This characterization method was tested on three representative dispersions, octadecylamine functionalization (SWNT-ODA) in tetrahydrofuran (THF), butyl group functionalization (SWNT-butyl) in THF, and DNA wrapping (SWNT/DNA) in aqueous solution. Significant differences between the dispersions were found. Small-angle neutron scattering (SANS) and atomic force microscopy (AFM) produced results consistent with the SEC method.
Recent attention has focused, for example, on reports of biological (3,4) and abiotic (5) formation of volatile tetramethyllead in aquatic media with its apparent large-scale transport into the atmosphere (6). Tin's chemical similarities to lead also imply its widespread environmental formation and gaseous transport as hydrophobic tetramethyltin (Me4Sn). Biogenesis of this molecule, though not heretofore detected in the aquatic environment, seems reasonable on the basis of recent evidence for in vitro methylation of various inorganic tin and organotin compounds by microbes isolated from the Chesapeake Bay (7-9) and by viable sediments from San Francisco Bay (10) or Canadian freshwater lakes (11).fThis work was presented in part at the 15th Middle Atlantic
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.