Anubhav Diwan

Improved efficiency of reversed-phase carbon/nanodiamond/polymer core-shell particles for HPLC using carbonized poly(divinylbenzene) microspheres as the core materials.

Here, we report efficiencies up to 112,000 plates per meter (a reduced plate height, h, of 2.22) for RP, carbon/nanodiamond/aminopolymer particles using conventional injection conditions in HPLC. This efficiency greatly exceeds our best previously reported value of 71,000 N/m (h = 3.52). The carbon cores used in this study were derived from carbonized poly(divinylbenzene) spheres that were either made in-house by a two-step polymerization procedure or obtained commercially. The resulting particles showed good uniformity and were oxidized in nitric acid to increase their dispersability. X-ray photoelectron spectroscopy confirms particle oxidation and subsequent aminopolymer deposition. Layer-by-layer (LbL) growth of poly(allyamine) and nanodiamond was demonstrated to produce core-shell particles. After LbL growth, the particles were functionalized, sieved, and packed into columns. The column functionalization and packing were reproducible. Van Deemter curves indicated that the commercially obtained poly(divinylbenzene) spheres outperformed those synthesized in our laboratory. The columns appear to be stable at 120°C in a pH 11.3 mobile phase. Longer columns (2.1 × 50 mm) than previously reported were packed. Four essential oils were separated by gradient elution.

Porous, High Capacity Coatings for Solid Phase Microextraction by Sputtering

We describe a new process for preparing porous solid phase microextraction (SPME) coatings by the sputtering of silicon onto silica fibers. The microstructure of these coatings is a function of the substrate geometry and mean free path of the silicon atoms, and the coating thickness is controlled by the sputtering time. Sputtered silicon structures on silica fibers were treated with piranha solution (a mixture of concd H2SO4 and 30% H2O2) to increase the concentration of silanol groups on their surfaces, and the nanostructures were silanized with octadecyldimethylmethoxysilane in the gas phase. The attachment of this hydrophobic ligand was confirmed by X-ray photoelectron spectroscopy and contact angle goniometry on model, planar silicon substrates. Sputtered silicon coatings adhered strongly to their surfaces, as they were able to pass the Scotch tape adhesion test. The extraction time and temperature for headspace extraction of mixtures of alkanes and alcohols on the sputtered fibers were optimized (5 min and 40 °C), and the extraction performances of SPME fibers with 1.0 or 2.0 μm of sputtered silicon were compared to those from a commercial 7 μm poly(dimethylsiloxane) (PDMS) fiber. For mixtures of alcohols, aldehydes, amines, and esters, the 2.0 μm sputtered silicon fiber yielded signals that were 3-9, 3-5, 2.5-4.5, and 1.5-2 times higher, respectively, than those of the commercial fiber. For the heavier alkanes (undecane-hexadecane), the 2.0 μm sputtered fiber yielded signals that were approximately 1.0-1.5 times higher than the commercial fiber. The sputtered fibers extracted low molecular weight analytes that were not detectable with the commercial fiber. The selectivity of the sputtered fibers appears to favor analytes that have both a hydrophobic component and hydrogen-bonding capabilities. No detectable carryover between runs was noted for the sputtered fibers. The repeatability (RSD%) for a fiber (n = 3) was less than 10% for all analytes tested, and the between-fiber reproducibility (n = 3) was 0-15%, generally 5-10%, for all analytes tested. The repeatabilities of our sputtered fibers and the commercial 7 μm PDMS fiber are essentially the same. Fibers could be used for at least 300 extractions without loss of performance. More than 50 compounds were identified in a gas chromatography-mass spectrometry headspace analysis of a real world botanical sample with the 2.0 μm fiber.

Self-termination in the gas-phase layer-by-layer growth of an aza silane and water on planar silicon and nylon substrates

The authors report the gas phase, layer-by-layer deposition of an organosilane (N-n-butyl-aza-2,2-dimethoxysilacyclopentane, 1) and either water or aqueous ammonium hydroxide onto two substrates: Si/SiO2 and nylon. This process results in smooth, water resistant, inorganic-organic barrier layers. The layer-by-layer deposition of 1 appears to be self-limiting to a few nanometers, which may make it useful where ultrathin films of controllable dimensions and uniformity are desired. The authors are unaware of another thin film system that has these properties. Films were characterized by spectroscopic ellipsometry, water contact angle goniometry, x-ray photoelectron spectroscopy, and atomic force microscopy. Interestingly, film thicknesses on nylon were much higher than on silicon, and films prepared in the presence of the ammonia “catalyst” were thinner than those prepared with water. Test circuits coated only with a fluorosilane showed higher penetration of water compared to those coated with a barrier layer of 1/H2O and the fluorosilane.

New Data Analysis Tools for X-ray Photoelectron Spectroscopy (XPS) and Spectroscopic Ellipsometry (SE): Uniqueness Plots and Width Functions in XPS, and Distance, Principal Component, and Cluster Analyses in SE

Uniqueness plots are widely used in the SE community for identifying correlation between fit parameters [5]. They are easily interpreted. However, they appear not to have been employed for XPS data analysis. And certainly better tools are needed to identify inappropriate peak fits to XPS narrow scans because (i) XPS is now receiving in excess of 10,000 mentions in the literature each year [6], and (ii) with the proliferation of the technique, the number of untrained users that are collecting and fitting data has significantly increased. In a number of reported peak fits, too many fit parameters have been introduced into the data modeling, which has reduced or eliminated the statistical meaning of these parameters.