Proton transfer reaction ion trap mass spectrometer

Proton transfer reaction mass spectrometry is a relatively new field that has attracted a great deal of interest in the last few years. This technique uses H(3)O(+) as a chemical ionization (CI) reagent to measure volatile organic compounds (VOCs) in the parts per billion by volume (ppbv) to parts per trillion by volume (pptv) range. Mass spectra acquired with a proton transfer reaction mass spectrometer (PTR-MS) are simple because proton transfer chemical ionization is "soft" and results in little or no fragmentation. Unfortunately, peak identification can still be difficult due to isobaric interferences. A possible solution to this problem is to couple the PTR drift tube to an ion trap mass spectrometer (ITMS). The use of an ITMS is appealing because of its ability to perform MS/MS and possibly distinguish between isomers and other isobars. Additionally, the ITMS duty cycle is much higher than that of a linear quadrupole so faster data acquisition rates are possible that will allow for detection of multiple compounds. Here we present the first results from a proton transfer reaction ion trap mass spectrometer (PTR-ITMS). The aim of this study was to investigate ion injection and storage efficiency of a simple prototype instrument in order to estimate possible detection limits of a second-generation instrument. Using this prototype a detection limit of 100 ppbv was demonstrated. Modifications are suggested that will enable further reduction in detection limits to the low-ppbv to high-pptv range. Furthermore, the applicability of MS/MS in differentiating between isobaric species was determined. MS/MS spectra of the isobaric compounds methyl vinyl ketone (MVK) and methacrolein (MACR) are presented and show fragments of different mass making differentiation possible, even when a mixture of both species is present in the same sample. However, MS/MS spectra of acetone and propanal produce fragments with the same molecular masses but with different intensity ratios. This allows quantitative distinction only if one species is predominant. Fragmentation mechanisms are proposed to explain the results.     

Stochastic properties of the Laplacian on Riemannian submersions

Based on ideas of Pigolla and Setti (2010), we prove that isometrically immersed submanifolds with bounded mean curvature into Cartan–Hadamard manifolds are Feller. We consider Riemannian submersions π : M → N with compact minimal fibers and prove that the total space M is Feller, parabolic or stochastically complete if, and only if, the base manifold N is, respectively, Feller, parabolic or stochastically complete.     

An iron-57 Mössbauer spectroscopy and EXAFS study of the hydrogen pretreatment of titania-supported iron-ruthenium catalysts

The changes in composition and structure which are induced in a titania-supported iron-ruthernium catalyst following treatment in hydrogen have been investigated in situ by⁵⁷Fe Mössbauer spectroscopy and by EXAFS. The results show that ruthenium dioxide is readily reduced at temperatures below ca. 500°C to ca. 20 Å clusters of metallic ruthenium whilst α-Fe₂O₃ is partially reduced at 130°C to Fe²⁺ and Fe⁰. The Fe³⁺ which is formed by the reoxidation of Fe²⁺ under the reducing conditions at 500°C segregates to the interface of the bimetallic phase and the titania support. It is suggested that continued treatment at 700°C produces a high dispersion of iron which is coordinated to oxygen atoms of the support. The ca. 20 Å clusters of metallic ruthenium may be envisaged as being anchored to the support via iron-ruthenium bonds     

An iron-57 Mössbauer spectroscopic study of titania-supported iron- and iron-iridium catalysts

⁵⁷Fe Mössbauer spectroscopy shows that titania-supported iron is reduced by treatment in hydrogen at significantly lower temperatures than corresponding silica- and alumina-supported catalysts. The metallic iron formed under hydrogen at 600°C is partially converted to carbide by treatment in carbon monoxide and hydrogen. In contrast to its alumina- and silica-supported counterparts, the remainder of the titania-supported iron is unchanged by this gaseous mixture. The⁵⁷Fe Mössbauer spectra and EXAFS show that iron and iridium in the titania-supported iron-iridium catalysts are reduced in hydrogen at even lower temperatures and, after treatment at 600°C, are predominantly present as the iron-iridium alloy. The treatment of these reduced catalysts in carbon monoxide and hydrogen is shown by Mössbauer spectroscopy and EXAFS to induce the segregation of iron from the iron-iridium alloy and its conversion to iron oxide.     

Stack Domination Density

There are infinite sequences of graphs {G _n } where |G _n | = n such that the minimal dominating sets for G _i × H fall into predictable patterns, in light of which γ (G _n × H) may be nearly linear in n; the coefficient of linearity may be regarded as the average density of the dominating set in the H-fibers of the product. The specific cases where the sequence {G _n } consists of cycles or path is explored in detail, and the domination density of the Grötzsch graph is calculated. For several other sequences {G _n }, the limit of this density can be seen to exist; in other cases the ratio ${\frac{\gamma (G_n \times H)}{\gamma (G_n)}}$ proves to be of greater interest, and also exists for several families of graphs.