Characterisation of organic compounds in aerosol particles from a Finnish forest by on-line coupled supercritical fluid extraction–liquid chromatography–gas chromatography–mass spectrometry

During the European Union project Quantification of Aerosol Nucleation in the European Boundary Layer (QUEST), which began in spring 2003, atmospheric aerosol particles were collected in a Finnish Scots pine forest using a high-volume sampler. The organic compounds in the filter samples were then analysed by on-line coupled supercritical fluid extraction–liquid chromatography–gas chromatography–mass spectrometry (SFE–LC–GC–MS). The sample was first extracted by SFE. During LC the extracts were fractionated into three fractions according to polarity. The final separation was carried out by GC–MS. A fraction volume as high as 840 L was transferred to the GC, using the partial concurrent eluent evaporation technique. The same instrumentation, with an in-situ SFE derivatisation method, was used to analyse organic acids. Major compounds such as n-alkanes and PAH were analysed quantitatively. Their concentrations were lower than those usually observed in urban areas or in other forest areas in Europe. The wind direction was one of the most important factors affecting changes in the daily concentrations of these compounds. Scots pine needles were analysed with the same system to obtain reference data for identification of biogenic compounds in aerosol particles. Other organic compounds found in this study included hopanes, steranes, n-alkanals, n-alkan-2-ones, oxy-PAH, and alkyl-PAH; some biogenic products, including oxidation products of monoterpenes, were also identified.     

Poly(dimethylsiloxane) electrospray devices fabricated with diamond-like carbon-poly(dimethylsiloxane) coated SU-8 masters

This study presents coupling of a poly(dimethylsiloxane) (PDMS) micro-chip with electrospray ionization-mass spectrometry (ESI-MS). Stable electrospray is generated directly from a PDMS micro-channel without pressure assistance. Hydrophobic PDMS aids the formation of a small Taylor cone in the ESI process and facilitates straightforward and low-cost batch production of the ESI-MS chips. PDMS chips were replicated with masters fabricated from SU-8 negative photoresist. A novel coating, an amorphous diamond-like carbon-poly(dimethylsiloxane) hybrid, deposited on the masters by the filtered pulsed plasma arc discharge technique, improved significantly the lifetime of the masters in PDMS replications. PDMS chip fabrication conditions were observed to affect the amount of background peaks in the MS spectra. With an optimized fabrication process (PDMS curing agent/silicone elastomer base ratio of 1/8 (w/w), curing at 70 degree C for 48 h) low background spectra were recorded for the analytes. The performance of PDMS devices was examined in the ESI-MS analysis of some pharmaceutical compounds and amino acids.     

Photoinduced Ultrafast Dynamics of Ru(dcbpy)(2)(NCS)(2)-Sensitized Nanocrystalline TiO(2) Films: The Influence of Sample Preparation and Experimental Conditions

In most of the previous ultrafast electron injection studies of Ru(dcbpy)2(NCS)2-sensitized nanocrystalline TiO2 films, experimental conditions and sample preparation have been different from study to study and no studies of how the differences affect the observed dynamics have been reported. In the present paper, we have investigated the influence of such modifications. Pump photon density, environment of the sensitized film (solvent and air), and parameters of the film preparation (crystallinity and quality of the film) were varied in a systematic way and the obtained dynamics were compared to that of a well-defined reference sample: Ru(dcbpy)2(NCS)2-TiO2 in acetonitrile. In some cases, the induced changes in the dynamics were uncorrelated to the electron injection process. High pump photon density (not in the linear response region) and exposure of the sensitized film to air altered the picosecond-time-scale kinetics considerably, and the changes were attributed mostly to degradation of the dye. In other cases, changes in the measured kinetics were related to the electron injection processes: reducing the firing temperature of the nanocrystalline film or making the film via electron beam evaporation (EBE) resulted in a decrease of the overall crystallinity of the film, and the electron injection slowed. In the sensitized EBE films, in addition to an increased contribution of triplet excited-state electron injection, a new electron transfer (ET) process with a time constant of 200 fs was observed.     

Study of mechanisms of light-induced dissociation of Ru(dcbpy)(CO)2I2 in solution down to 20 fs time resolution

Mechanisms of the light-induced ligand exchange reaction of (trans-I) Ru(dcbpy)(CO)2I2 (dcbpy = 4,4'-dicarboxylic acid-2,2'-bipyridine) in ethanol have been studied by transient absorption spectroscopy. Ultraviolet 20 fs excitation pulses centered at 325 nm were used to populate a vibrationally hot excited pi bipyridyl state of the reactant that quickly relaxes to a dissociative Ru-I state resulting in the release of one of the carbonyl groups. Quantum yield measurements have indicated that about 40% of the initially exited reactant molecules form the final photoproduct. A 62 fs rise component in the transient absorption (TA) signal was observed at all probe wavelengths in the visible region for the ongoing reaction, while the rise for the photoproduct was pulse limited (20 fs). We assign the observed 62 fs time component to the depopulation of the repulsive CO dissociative state. Vibrational coherences of the TA signals were observed at a wavenumber of 90 cm(-1). The resolved frequency, typical of I-Ru-I vibrational modes, is assigned to trans-cis isomerization of the iodines of the five-coordinated intermediate and damping of this oscillation in 500 fs to simultaneous solvent coordination. Cooling of the hot reactant and the product molecules occurs on a much slower time scale from 4 to 270 ps (Lehtovuori, V.; Aumanen, J.; Myllyperki?, P.; Rini, M.; Nibbering, E. T. J.; Korppi-Tommola, J. J. Phys. Chem. A 2004, 108, 1644).     

Integration of a contactless conductivity detector into a commercial capillary cassette. Detection of inorganic cations and catecholamines

A contactless conductivity detector integrated into the capillary cassette of Agilent ^3DCE equipment is described. The detector is user-friendly, compact and easily modified. The UV detector of the ^3DCE equipment is available parallel with the contactless conductivity detector increasing the detection power. Two electrolyte solutions, 2-(N-morpholino)ethanesulfonic acid–histidine solution (20 mM, pH 6.0) and ammonium acetate (10 mM, pH 4.0), were used as the separation media for inorganic cations and organic catecholamines, respectively. The detection limit for all metal cations except barium was under 0.5 mg/l, and that for four catecholamines was ca. 10 mg/l. This last value was the same order of magnitude as achieved with parallel UV detection.     

A study of electron transfer in Ru(dcbpy)2(NCS)2 sensitized nanocrystalline TiO2 and SnO2 films induced by red-wing excitation

Excited state dynamics and electron transfer from the Ru(dcbpy)2(NCS)2 (RuN3) sensitizer to semiconductor nanoparticles were studied using time-resolved femtosecond absorption spectroscopy. We found that excitation of the red wing of the absorption spectrum of the sensitizer populates the (3)MLCT state directly, both in solution and attached on semiconductor nanoparticle films. Electron injection is slowed down and becomes gradually less efficient as excitation moves towards red from the absorption maximum at 535 nm. At 675 nm the injection is non-exponential and characterized by 5, 30 and 180 ps time constants. The non-exponential electron injection observed is assigned to injection from a distribution of triplet states with energies below the semiconductor conduction band edge.     

X-ray Raman scattering at the Si LII,III-edge of bulk amorphous SiO

X-ray Raman spectra of bulk amorphous SiO have been measured at energy losses around the Si L_II,III-edges for different momentum transfers at beamline ID16 of ESRF. The spectra are compared with measurements of the L_II,III-edges of Si powder and with results of first-principles calculations for Si and α-quartz SiO₂. Indications of sub-oxidic contributions to the L_II,III-edges are found in the experiment and discussed with respect to the model of interface clusters mixture in bulk amorphous SiO.     

An efficient high-yield synthesis of D-ribo-phytosphingosine

[Structure: see text] [4R-[4alpha(S),5alpha]]-2,2-Dimethyl-4-(2-oxo-5-vinyl[1,3]dioxolan-4-yl)oxazolidine-3-carboxylic acid tert-butyl ester 5a, obtained in excellent yield and diastereoselectivity by the alpha-hydroxyallylation of the Garner aldehyde (4), is exploited in a novel high-yield synthesis of D-ribo-phytosphingosine (8), using microwave-enhanced cross metathesis as the key step in the chain elongation.