National Physical Laboratory

About: National Physical Laboratory is a facility organization based out in London, United Kingdom. It is known for research contribution in the topics: Dielectric & Thin film. The organization has 7615 authors who have published 13327 publications receiving 319381 citations.

The effect of electrospray solvent composition on desorption electrospray ionisation (DESI) efficiency and spatial resolution

Abstract: In desorption electrospray ionisation (DESI) the interaction between the electrospray and the surface is key to two important analytical parameters, the spatial resolution and the sensitivity. We evaluate the effect of the electrospray solvent type, organic solvent fraction with water, analyte solubility and substrate wettability on DESI erosion diameter and material transferral into useful ion signal. To do this five amino acids, glycine, alanine, valine, leucine and phenylalanine are prepared as thin films on three substrates, UV/ozone treated glass, glass and polytetrafluoroethylene (PTFE). Four different solvents, acetonitrile (ACN), methanol (MeOH), ethanol (EtOH) and propan-2-ol (IPA), are used with organic solvent fractions with water varying from 0.1 to 1. These model systems allow the solubility or wettability to be kept constant as other parameters are varied. Additionally, comparison with electrospray ionisation (ESI) allows effects of ionisation efficiency to be determined. It is shown that the DESI efficiency is linearly dependent on the solubility (for these materials at least) and for analytes with solubilities below 1.5 g kg−1, additional strategies may be required for DESI to be effective. We show that the DESI erosion diameter improves linearly with organic solvent fraction, with an organic solvent fraction of 0.9 instead of 0.5 leading to a 2 fold improvement. Furthermore, this leads to a 35 fold increase in DESI efficiency, defined as the molecular ion yield per unit area. It is shown that these improvements correlate with smaller droplet sizes rather than surface wetting or ionisation.

Synthesis of silicon carbide through the sol-gel process from different precursors

Abstract: Silicon carbide (SiC) was synthesised from silicon alkoxides and various carbon sources. Tetraethoxysilane (TEOS), methyltriethoxysilane (MTES) and a mixture of TEOS and MTES were hydrolysed in the presence of phenolic resin, ethylcellulose, polyacrylonitrile (PAN) and starch to incorporate the gel into the carbon source in the silica network. The gel thus obtained was carbonized at 800°C in an argon atmosphere to obtain the mixture of silica and carbon which when heated to 1550°C in argon yielded silicon carbide. The characterization of the product by X-ray, FTIR and SEM showed it to be β SiC with different crystallite and grain sizes. The difference in the crystallite and grain sizes is attributed to the nature of the carbon source. The density of the SiC obtained by the sol—gel process was found to be lower than the values reported for SiC and this is ascribed to the porous nature of the products generally obtained by this process.