Selected ion flow tube study of ion-molecule reactions of N(+)(3P) and Kr+ with C3 hydrocarbons propane, propene, and propyne

Reactions of (14)N(+)((3)P), (15)N(+)((3)P), and Kr(+) with propane, propene, and propyne were studied using the selected ion flow tube, SIFT, technique. Thermal rate constants in all N(+)/C(3) systems were k = (2 ± 0.4) × 10(-9) cm(3) molecule(-1) s(-1), close to the collisional rate constants. With propane and propene, only hydrocarbon ions were found among the products of reactions with N(+); in propyne about 15% of the products were N-containing ions (C(3)H(2)N(+), C(2)H(4)N(+), C(2)H(3)N(+), C(2)H(2)N(+)), and the rest were hydrocarbon ions. A comparison with product ions from electron transfer between Kr(+) (of recombination energy similar to that for N(+)((3)P)) and the C(3) hydrocarbons and further analysis of the results led to an estimation of an approximate ratio of electron transfer vs hydride-ion transfer reactions leading to the hydrocarbon product ions: in propane the ratio was 2:1, in propene 3:1, and in propyne 5:1. A fraction of product ions resulted from reactions leading to the excited neutral product N*.     

Thermal characterization of aminium nitrate nanoparticles

Amines are widely used and originate from both anthropogenic and natural sources. Recently, there is, in addition, a raised concern about emissions of small amines formed as degradation products of the more complex amines used in CO(2) capture and storage systems. Amines are bases and can readily contribute to aerosol mass and number concentration via acid-base reactions but are also subject to gas phase oxidation forming secondary organic aerosols. To provide more insight into the atmospheric fate of the amines, this paper addresses the volatility properties of aminium nitrates suggested to be produced in the atmosphere from acid-base reactions of amines with nitric acid. The enthalpy of vaporization has been determined for the aminium nitrates of mono-, di-, trimethylamine, ethylamine, and monoethanolamine. The enthalpy of vaporization was determined from volatility measurements of laboratory generated aerosol nanoparticles using a volatility tandem differential mobility analyzer set up. The determined enthalpy of vaporization for aminium nitrates range from 54 up to 74 kJ mol(-1), and the calculated vapor pressures at 298 K are around 10(-4) Pa. These values indicate that aminium nitrates can take part in gas-to-particle partitioning at ambient conditions and have the potential to nucleate under high NO(x) conditions, e.g., in combustion plumes.     

Why ultra high performance liquid chromatography produces more tailing peaks than high performance liquid chromatography, why it does not matter and how it can be addressed

The purpose of this study is to demonstrate, with experiments and with computer simulations based on a firm chromatographic theory, that the wide spread perception of that the United States Pharmacopeia tailing factor must be lower than 2 (T(f)<2) is questionable when using the latest generation of LC equipment. It is shown that highly efficient LC separations like those obtained with sub-2 μm porous and 2.7 μm superficially porous particles (UHPLC) produce significantly higher T(f)-values than the corresponding separation based on 3 μm porous particles (HPLC) when the same amount of sample is injected. Still UHPLC separations provide a better resolution to adjacent peaks. Expressions have been derived that describe how the T(f)-value changes with particle size or number of theoretical plates. Expressions have also been derived that can be used to scale the injection volume based on particle size or number of theoretical plates to maintain the T(f)-value when translating a HPLC separation to the corresponding UHPLC separation. An aspect that has been ignored in previous publications. Finally, data obtained from columns with different age/condition indicate that T(f)-values should be complemented by a peak width measure to provide a more objective quality measure.     

Slow excited state injection and charge recombination at star-shaped ruthenium polypyridyl compounds--TiO2 interfaces

The excited states of two star-shaped nanometre-sized ruthenium polypyridyl compounds were largely unchanged when anchored to nanocrystalline TiO(2) thin films due to a highly symmetrical and rigid ligand structure that isolated the chromophoric core from the semiconductor. Interfacial electron transfer occurred on unusually slow time scales.     

In‐line Bragg magnifier based on V‐shaped germanium crystals

In this work an X‐ray imaging system based on a recently developed in‐line two‐dimensional Bragg magnifier composed of two monolithic V‐shaped crystals made of dislocation‐free germanium is presented. The channel‐cut crystals were used in one‐dimensional and in two‐dimensional (crossed) configurations in imaging applications and allowed measurement of phase‐contrast radiograms both in the edge‐enhanced and in the holographic regimes. The measurement of the phase gradient in two orthogonal directions is demonstrated. The effective pixel size attained was 0.17 µm in the one‐dimensional configuration and 0.5 µm in the two‐dimensional setting, offering a twofold improvement in spatial resolution over devices based on silicon. These results show the potential for applying Bragg magnifiers to imaging soft matter at high resolution with reduced dose owing to the higher efficiency of Ge compared with Si.     

Column comparison and method development for the analysis of short‐chain carboxylic acids by zwitterionic hydrophilic interaction liquid chromatography with UV detection

Short‐chain carboxylic acids are relevant in pharmaceutical, food quality control, and biomedical analysis. In this study, 11 acids commonly found in drugs and in food products were selected. Wine was chosen as matrix for testing the method. The test compounds were used for comparing the selectivity of four 150 × 2.1 mm zwitterionic hydrophilic interaction LC (HILIC) columns (ZIC‐HILIC 5 μm, 200 Å, and 3.5 μm, 100 Å, ZIC‐pHILIC 5 μm, ZIC‐cHILIC 3 μm, 100 Å) while varying the conditions to optimize for low UV wavelength detection and achieve high sensitivity. Retention using potassium phosphate and ammonium carbonate as mobile‐phase components at pH 6.0, 7.5, and 8.5–8.9 was studied considering recent hypotheses on HILIC mechanism‐related with the Hofmeister series effect and ion hydration. An isocratic method with UV detection at 200 nm and mobile phase consisting of 75% acetonitrile and 10 mM potassium phosphate at pH 6.0 applied to a ZIC‐cHILIC column was found provisionally optimal and partially validated for the 11 analytes. Satisfactory results (R² from 0.9940 to >0.9999), and recoveries from 93–106% for all analytes evidenced the method as suitable for wine analysis. To the best of our knowledge, no previous study has reported on the direct ZIC‐HILIC separation and UV detection of the acids considered here in wine.     

Hydrogenated Anatase: Strong Photocatalytic Dihydrogen Evolution without the Use of a Co‐Catalyst

The high‐pressure hydrogenation of commercially available anatase or anatase/rutile TiO₂ powder can create a photocatalyst for H₂ evolution that is highly effective and stable without the need for any additional co‐catalyst. This activation effect cannot be observed for rutile; however, for anatase/rutile mixtures, a strong synergistic effect can be found (similar to results commonly observed for noble‐metal‐decorated TiO₂). EPR and PL measurements indicated the intrinsic co‐catalytic activation of anatase TiO₂ to be due to specific defect centers formed during hydrogenation. These active centers can be observed specifically for high‐pressure hydrogenation; other common reduction treatments do not result in this effect.     

Determination of fluoroquinolones in bovine milk samples using a pipette‐tip SPE step based on multiwalled carbon nanotubes prior to CE separation

A simple CE–UV method was developed for the simultaneous determination of ciprofloxacin, norfloxacin, and ofloxacin in milk samples. The optimum separation was obtained using a 20 mM ammonium dihydrogenphosphate solution with 2 mM cetyltrimethylammonium bromide at pH 3.0 as the BGE. Satisfactory resolution for structurally very similar analytes, like norfloxacin and ciprofloxacin, was achieved without including any organic solvent. Milk samples were prepared using a simple/extraction procedure based on acidic protein precipitation followed by an SPE step using only 5 mg of multiwalled carbon nanotubes as the sorbent material. The LODs for the three compounds were between 7.5 and 11.6 μg/L and the RSDs for the peak areas were between 2.6 and 4.9%. The complete method was applied to spiked real milk samples with satisfactory recoveries for all analytes (84–106%).