A comparison of ten different methods for the analysis of saturates, olefins, benzene, total aromatics, and oxygenates in finished gasolines

The Technical Committee 19 of the European Committee for Standardization (CEN/TC19) in the "Lisbon resolution" requested to evaluate replacement methods to the fluorescent indicator absorption (FIA) (American Standardization for Testing and Material D 1319) method for the determination of aromatics and olefins in gasolines. In the same resolution it was requested to review the two existing methods for the determination of benzene content of gasolines, anticipating lower limit values in future European gasoline specifications. As a result of this request, a round robin (RR) was organized in which 8 gasoline samples are analyzed using 10 different methods in 33 laboratories. The methods used in the RR include, apart from the FIA method, one-dimensional gas chromatography (GC) and multidimensional GC, with and without specific detectors and spectroscopic analysis methods. This study describes these methods in short, gives an evaluation of the results of the RR, and draws a conclusion on the outcome.     

Comparison of negative and positive ion electrospray ionization mass spectra of calmodulin and its complex with trifluoperazine

The protein calmodulin (apoCaM) undergoes a conformational change when it binds calcium. This structure of the protein (Ca4CaM) is a dumbbell-shaped molecule that undergoes a further profound conformational change on binding of the antipsychotic drug trifluoperazine (TFP). Experimental conditions were developed to prepare samples of apoCaM, Ca4CaM and Ca4CaM/TFP that were substantially free of sodium. The effects of the conformational changes of calmodulin on the charge-state distributions observed in positive ion and negative ion electrospray ionization (ESI) mass spectra were examined. Conversion of apoCaM into Ca4CaM was concomitant with a change in the negative ion ESI mass spectrum whereby the 16- ion was the most abundant ion observed for the apo form and the 8- ion was the most abundant for the complex. In contrast, in the positive ion ESI mass spectra of apoCaM and Ca4CaM, the most abundant species in each case was the 8+ ion. When a complex of Ca4CaMwith TFP was prepared, the most abundant species was the 5+ ion. This is consistent with a conformational change of Ca4CaM that rendered some basic sites inaccessible to ionization in the ESI process. Using the same Ca4CaM/TFP mixture, no complex with TFP was observed in negative ion ESI mass spectra. These observations are discussed in the context of the structural changes that are known to occur in calmodulin, and suggestions are made to explain the apparently conflicting data. The results reported here reflect on the validity of using differences in charge-state distributions observed in ESI mass spectra to assess conformational changes in proteins.     

Multiphoton-Excited Visible Emission by Serotonin Solutions

Nonlinear excitation of the neurotransmitter serotonin (5HT) in aqueous solution is shown to generate a blue-green-emitting photoproduct in addition to UV fluorescence characteristic of native 5HT. The visible emission rate in diffusional steady-state measurements scales as the sixth power of excitation intensity, demonstrating that absorption of six near-IR photons is required to generate emission of one visible photon. Transient measurements reveal that this process is composed of two sequential nonlinear steps, the first excited by four photons and the second by two photons. These results, in combination with measurements of multiphoton-excited serotonin UV fluorescence, support a model in which 5HT is photochemically transformed as a consequence of four-photon absorption (E_tot?6 eV) to a photoproduct that then emits in the visible region via two-photon excitation. A minimum bound of ?10^-51 cm⁴ s photon^-1 is observed for the two-photon emission action cross section at 830 nm. Photoionization, rather than reaction with a dissolved oxygen species, appears to be the primary mechanism for generation of the blue-green-emitting photoproduct. The peak intensities required to generate significant blue-green emission (?5 times 10¹¹ W cm^-2 from 80 MHz 150 fs titanium: sapphire laser pulses) are approximately five-fold higher than are typically used in two-photon laser scanning microscopy but are still substantially lower than the estimated intensity needed to induce dielectric breakdown of water.     

Speciation analysis of arsenic in groundwater from Inner Mongolia with an emphasis on acid-leachable particulate arsenic

Arsenic in drinking water affects millions of people around the world. While soluble arsenic is commonly measured, the amount of particulate arsenic in drinking water has often been overlooked. We report here determination of the acid-leachable particulate arsenic and soluble arsenicals in well water from an arsenic-poisoning endemic area in Inner Mongolia, China. Water samples (583) were collected from 120 wells in Ba Men, Inner Mongolia, where well water was the primary drinking water source. Two methods were demonstrated for the determination of soluble arsenic species (primarily inorganic arsenate and arsenite) and total particulate arsenic. The first method used solid phase extraction cartridges and membrane filters to separate arsenic species on-site, followed by analysis of the individual arsenic species eluted from the cartridges and filters. The other method uses liquid chromatography separation with hydride generation atomic fluorescence detection to determine soluble arsenic species. Analysis of acidified water samples using inductively coupled plasma mass spectrometry provided the total arsenic concentration. Arsenic concentrations in water samples from the 120 wells ranged from <1 to ∼1000 μg L⁻¹. On average, particulate arsenic accounted for 39 ± 38% (median 36%) of the total arsenic. In some wells, particulate arsenic was six times higher than the soluble arsenic concentration. Particulate arsenic can be effectively removed using membrane filtration. The information on particulate and soluble arsenic in water is useful for optimizing treatment options and for understanding the geochemical behavior of arsenic in groundwater.     

The adamantane-derived bananins are potent inhibitors of the helicase activities and replication of SARS coronavirus

Bananins are a class of antiviral compounds with a unique structural signature incorporating a trioxa-adamantane moiety covalently bound to a pyridoxal derivative. Six members of this class of compounds: bananin, iodobananin, vanillinbananin, ansabananin, eubananin, and adeninobananin were synthesized and tested as inhibitors of the SARS Coronavirus (SCV) helicase. Bananin, iodobananin, vanillinbananin, and eubananin were effective inhibitors of the ATPase activity of the SCV helicase with IC50 values in the range 0.5-3 microM. A similar trend, though at slightly higher inhibitor concentrations, was observed for inhibition of the helicase activities, using a FRET-based fluorescent assay. In a cell culture system of SCV, bananin exhibited an EC50 of less than 10 microM and a CC50 of over 300 microM. Kinetics of inhibition are consistent with bananin inhibiting an intracellular process or processes involved in SCV replication.     

Unintegrated parton distributions and inclusive jet productionat HERA

We describe how unintegrated parton distributions can be calculated from conventional integrated distributions. We extend and improve the last-step evolution approach, and explain why doubly unintegrated parton distributions are necessary. We generalise k _t-factorisation to (z,k _t)-factorisation. We apply the formalism to inclusive jet production in deep-inelastic scattering, mainly at leading order, but we also study the extension to next-to-leading order. We compare the predictions with recent HERA data.Received: 19 June 2003, Published online: 19 September 2003