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PubMed2003

Determination of chloramphenicol residues in fish meats by liquid chromatography-atmospheric pressure photoionization mass spectrometry.

A liquid chromatography-atmospheric pressure photoionization (APPI) mass spectrometry method was developed for the determination of chloramphenicol (CAP) in fish meats (young yellowtail and flatfish). For the optimization of APPI, several APPI ion source parameters and mobile phases were investigated. CAP with APPI using the optimized parameters gave simple mass spectra and a strong signal corresponding to [M-H]- was observed. Further, APPI was compared with atmospheric pressure chemical ionization (APCI) and APPI gave similar results in terms of structural information and a better signal-to-noise ratio. The samples were extracted with acetonitrile and evaporated to dryness followed by a clean-up step using the liquid-liquid distribution between acetonitrile and n-hexane. The mean recoveries of chloramphenicol from a young yellowtail meat and a flatfish meat spiked at 0.1-2 ng/g were 89.3-102.5 and 87.4-94.8%, respectively. The limit of detection (signal-to-noise ratio = 3) of the young yellowtail meat and the flatfish meat were 0.1 and 0.27 ng/g.

Anti-Bacterial Agents↗

PubMed1999

Ion-pair liquid chromatography--atmospheric pressure ionization mass spectrometry for the determination of quaternary ammonium herbicides.

High-performance liquid chromatography coupled with atmospheric pressure ionization mass spectrometry (electrospray and atmospheric pressure chemical ionization) has been used to characterize some quaternary ammonium herbicides (quats). The separation of these compounds was carried out using ion-pair chromatography with heptafluorobutyric acid (15 mM, pH 3.3) and acetonitrile gradient elution for successful coupling to mass spectrometry. Detection limits down to 0.1-4 micrograms l-1 were obtained for spiked tap water following a preconcentration step. Good reproducibilities (day-to-day and run-to-run) were also obtained.

Atmospheric Pressure↗

PubMed1999

Poor reproducibility of in-source collisional atmospheric pressure ionization mass spectra of toxicologically relevant drugs.

The purpose of the study was to examine the intra- and interlaboratory reproducibility of mass spectra obtained with liquid chromatography-atmospheric pressure ionization mass spectrometry (LC--API-MS) both in electrospray (ESI) and atmospheric pressure chemical ionization (APCI) modes. Toxicologically relevant drugs of different polarity were selected as test substances: morphine-6-glucuronide, 6-monoacetylmorphine, codeine, lysergic acid diethylamide, methylenedioxymethamphetamine. The study was performed in two laboratories using identical instruments and in one using a slightly different instrument. Basic instrument settings and mobile phase were identical in all laboratories. Mass spectra of drugs were taken at four collision energy voltages and using mobile phase of different composition (four concentration levels of acetonitrile and of ammonium formate buffer). The experiments demonstrated that mass spectra of given drugs, obtained in identical conditions with identical instruments, may show very different degrees of fragmentation. Mass spectra obtained with different instruments differed profoundly not only in the degree of fragmentation, but also different fragments and adducts were observed. Short-term intralaboratory reproducibility of mass spectra was satisfactory. On the other hand, the long-term experiments showed different degrees of fragmentation of APCI-generated mass spectra at nominally identical fragmentation energy. The changes in the composition of the mobile phase (concentration of organic modifier or buffer molarity) did not affect the reproducibility of fragmentation to any relevant degree. The study showed that the interlaboratory exchange and use of mass spectrum library, generated by single-quadrupole (LC--API-MS instruments, is hardly feasible at the moment, even under very carefully standardized conditions.

Atmospheric Pressure↗

PubMed1999

Atmospheric pressure ionisation multiple mass spectrometric analysis of pesticides.

Liquid chromatography-multiple mass spectrometry (LC-MS") has been investigated for analysis of polar pesticides in water using an ion-trap instrument and atmospheric pressure ionisation. Carbamate, triazine and phenylurea pesticides were best ionised as positive ions with atmospheric pressure chemical ionisation, while phenoxy acid herbicides, nitrophenols and bentazone yielded stronger signals as negative ions with pneumatically assisted electrospray. The ion fragmentation processes and pathways were studied in detail by MS, MS2, MS3 and MS4. All compounds were observed as their protonised or deprotonised molecular ions by MS and in the successive fragmentation by MS" the structures of typical (diagnostic) product ions were tentatively identified for each class of pesticide. Phenylureas yield an ion at m/z 72 by MS2, corresponding to O=C=N+(CH3)2. Carbamates produce [M+H-CONCH3]+ fragments by MS2 from neutral loss of methylisocyanate. Characteristic fragmentation pathways for triazine pesticides are [M+H]+-->m/z 174-->m/z 146-->m/z 110 and [M+H]+-->m/z 174-->m/z 132-->m/z 104 by MS-MS2-MS3-MS4 from cleavage of lateral chains in the triazine ring followed by ring opening. Phenoxy acid herbicides produce peculiar fragments by MS2 from loss of the acidic group possibly as the corresponding lactone. Nitrophenols are subject to loss of both *OH radical and NO groups thereby forming the correspondent phenols and quinones. The performance of the method with respect to quantitation compares favourably with traditional methods. With the ion-trap run in a time scheduled single ion monitoring mode, typical limits of detection (LODs) are in the low pg range and the repeatability standard deviations are between 3 and 15%. Assuming extraction of 1-l water samples and 1 ml final volumes the injection of 50-microl aliquots corresponds to LODs well below the requirement for the European Union water directive (EC/80/778).

Atmospheric Pressure↗

PubMed1997

Calculated hydroxyl A2 sigma --> X2 pi (0, 0) band emission rate factors applicable to atmospheric spectroscopy.

A calculation of the A2 sigma --> X2 pi (0, 0) band emission rate factors and line center absorption cross sections of OH applicable to its measurement using solar resonant fluorescence in the terrestrial atmosphere is presented in this paper. The most accurate available line parameters have been used. Special consideration has been given to the solar input flux because of its highly structured Fraunhofer spectrum. The calculation for the OH atmospheric emission rate factor in the solar resonant fluorescent case is described in detail with examples and intermediate results. Results of this calculation of OH emission rate factors for individual rotational lines are on average 30% lower than the values obtained in an earlier work.

Atmosphere↗

PubMed2002

Atmospheric phase distribution of oxidized and reduced nitrogen at a forest ecosystem research site.

Atmospheric concentrations of gaseous NH3 and HNO3 and of particulate NH4+ and NO3- were measured during various seasons at a forest ecosystem research site in the "Fichtelgebirge" mountains in Central Europe. Air masses arriving at this site were highly variable with respect to trace compound concentration levels and their concentration ratios. However, the distributions of NH4+ and NO3- within the aerosol particle size spectra exhibited some very consistent patterns, with the former dominating the fine particle concentrations, and the latter dominating the coarse particles range, respectively. Overall, the particulate phase (NH4+ + NO3-) dominated the atmospheric nitrogen budget (particulate and gas phase, NH4+ + NO3- + NH3 + HNO3) by more than 90% of the median total mixing ratio in winter, and by more than 60% in summer. The phase partitioning varied significantly between the winter and summer seasons, with higher relative importance of the gaseous species during summer, when air temperatures were higher and relative humidities lower as compared to the winter season. Reduced nitrogen dominated over oxidized nitrogen, indicating the prevailing influence of emissions from agricultural activity as compared to traffic emissions at this mountainous site. A model has been successfully applied in order to test the hypothesis of thermodynamic equilibrium between the particulate and gas phases.

Atmosphere↗

PubMed2003

Ageing of chromium(III)-bearing slag and its relation to the atmospheric oxidation of solid chromium(III)-oxide in the presence of calcium oxide.

Slag arising in ferrochromium and stainless steel production is known to contain residual levels of trivalent chromium. As the chromium is normally bound in the slag matrix in various silicate or spinel phases, and hence not easily mobilised, utilisation or controlled disposal of such slag is generally considered unproblematic. Experimental test work with a number of slag materials indicates, however, that very gradual oxidation of trivalent to hexavalent chromium does occur when the slag is exposed to atmospheric oxygen, rendering a quantifiable but small portion of chromium in this much more mobile and toxic form. Mechanisms and rates of the oxidation reaction were investigated in a number of long-term studies using both original slag materials and artificial mixes of chromium and calcium oxides. Powders of these materials, some of them rolled into balls, were left to age under different conditions for periods of up to 12 months. In the slag samples, which contained between 1 and 3 wt.% chromium, 1000-10000 microg Cr(VI) were found per gram of chromium within 6-9 months of exposure to an ambient atmosphere. The rate of the oxidation reaction decreased exponentially, and the reaction could generally be said to have ceased within 12 months. In mixtures of calcium and chromium oxides the oxidation reaction is presumed to occur at the boundaries between chromium oxide and calcium oxide phases through diffusion of oxygen along the grain boundaries and of Cr(3+) across the boundaries, resulting in the formation of calcium chromate. In the slags, where calcium and chromium oxide can form a solid solution, the oxidation is likely to occur at the exposed surface of grains containing this solution.

Atmosphere↗

PubMed2002

Trace determination of caffeine in surface water samples by liquid chromatography--atmospheric pressure chemical ionization--mass spectrometry (LC-APCI-MS).

A new method based on liquid-liquid extraction (LLE) coupled to reverse phase liquid chromatography and atmospheric pressure chemical ionization mass spectrometry (LC-APCI-MS) has been applied to determine trace amounts of caffeine (1,3,7-trimethylxanthine) in surface water samples from a near coastal ecosystem such as Biscayne Bay, Florida. The rational behind the development of such method will be to evaluate the use of unmetabolized caffeine as a potential dissolved phase tracer of human waste contamination. The method allows for the determination of caffeine at levels as low as 4.0 ng/l (ppt) in both salt and freshwater by extracting and concentrating a 1-1 water sample to a final volume of 500 microl and using HPLC separation coupled to an atmospheric pressure chemical ionization mass spectrometry (APCI-MS) system operated in selected ion monitoring (SIM) for the protonated molecular ions (M + H(+)). Samples from different portions of Biscayne Bay and the Miami River, one of its major tributaries, were analyzed and caffeine was detected in those areas previously identified for consistently exceeding the water quality criteria for fecal coliform bacteria contamination. The caffeine concentration in the samples with positive detection was generally low at levels equal or lower than 41 ng/l. However, there is a marked difference between samples collected in open bay areas and those collected from the Miami River.

Atmospheric Pressure↗

PubMed2001

EXOCAM: Mars in a box to simulate soil-atmosphere interactions.

We present the principle of the EXOCAM chamber, devoted to the study of physical-chemical interactions between the atmosphere and the surface and subsurface in Mars conditions. The purpose of this experiment is to reach a better knowledge of the physical and chemical processes that altered the atmosphere-soil coupled system. We describe the scientific goals of EXOCAM, the multiple fields that will benefit from this experiment and the instrumentation that is devoted to the analysis of the results. We also give a description of the chamber and its main devices.

Astronomy↗

PubMed2001

Production of hydrocarbons and nitriles by electrical processes in Titan's atmosphere.

Although lightning has not been observed in Titan's atmosphere, the presence of methane rain in the troposphere suggests the possibility of electrical activity in the form of corona and/or lightning discharges. Here we examine the chemical effects of these electrical processes on a Titan simulated atmosphere composed of CH4 in N2 at various mixing ratios. Corona discharges were simulated in two different experimental arrays. For the detection of reactive intermediates we used a mass spectrometer to study the main positive ions arising by bombarding low-energy electrons from a hot filament into low-pressure methane. The final stable products, generated by applying a high voltage in a coaxial reactor with either positive or negative polarity, were separated and detected by gas chromatography-Fourier transform infrared spectroscopy and electron impact mass spectrometry (GC-FTIR-MS). Lightning discharges were simulated by a hot and dense plasma generated by a Nd-YAG laser and the final products were separated and detected by GC-FTIR-MS. Corona discharges produce linear and branched hydrocarbons as well as nitriles whereas lightning discharges generate mainly unsaturated hydrocarbons and nitriles. Lightning discharges are about 2 orders of magnitude more efficient in product formation than corona discharges.

Acetylene↗

PubMed2001

IR and UV spectroscopic data for polyynes: predictions for long carbon chain compounds in Titan's atmosphere.

A better understanding of the complex organic chemistry occurring in the methane rich atmosphere of Titan can be achieved via the comparison of observations with results obtained by theoretical models. Available observations are still few but their analysis requires the knowledge of a large set of data, namely frequencies and absolute band intensities. Cross sections are also needed to develop the chemical schemes of photochemical models, in particular the schemes leading to the formation of haze particles visible on Titan. Unfortunately, some of these parameters are not well known, especially if one takes into account the extreme physical conditions of the studied object. This lack of data is particularly enhanced for polyynes because these compounds are highly unstable at the usual pressure and temperature conditions of a laboratory and therefore are very difficult to study. We have developed UV and IR studies, coupling experimental and theoretical approaches, in order to extrapolate the parameters available for short polyynes to longer carbon chains. In the mid-UV range, when the length of the chain increases, the absorption system of polyynes is shifted to longer wavelength and its oscillator strength increases linearly. In the IR range, with the increase of the number of carbon bonds, the positions of the CCC and CCH bending modes shift to lower energy, the latest converging rapidly to a fixed value of 620.5 cm-1 for an infinite length polyyne. Implications for detection and evolution of polyynes in Titan's atmosphere are emphasised.

Acetylene↗

PubMed2002

Radiation-induced health effects on atmospheric flight crew members: clues for a radiation-related risk analysis.

There are few human data on low-dose-rate-radiation exposure and the consequent acute and late effects. This fact makes it difficult to assess health risks due to radiation in the space environment, especially for long-term missions. Epidemiological data on civilian flight personnel cohorts can provide information on effects due to the low-dose and low-dose rate mixed high- and low-LET radiation environment in the earth's atmosphere. The physical characteristics of the radiation environment of the atmosphere make the results of the studies of commercial flight personnel relevant to the studies of activities in space. The cooperative international effort now in progress to investigate dose reconstructions will contribute to our understanding of radiation risks for space exploration.

Aerospace Medicine↗

PubMed2003

Increase of atmospheric CO2: response patterns of a simple terrestrial man-made ecosystem.

Simple models of terrestrial ecosystems with a limited number of components are an efficient tool to study the main laws of functioning of populations, including microbial ones, and their communities, as components of natural ecosystems, under variable environmental conditions. Among other factors are the increase of carbon dioxide in the atmosphere and limitation of plants' growth by biogenic elements. The main types of ecosystems' responses to changes in environmental conditions (a change in CO2 concentration) have been demonstrated in a "plants-rhizospheric microorganisms-artificial soil" simple experimental system. The mathematical model of interactions between plants and microorganisms under normal and elevated atmospheric CO2 and limitation by nutrients (nitrogen and phosphorus) yielded a qualitative agreement between calculated and experimental values of limiting substances concentrations and release rates of exudates.

Atmosphere↗

PubMed2003

A new dynamical atmospheric ionizing radiation (AIR) model for epidemiological studies.

A new Atmospheric Ionizing Radiation (AIR) model is currently being developed for use in radiation dose evaluation in epidemiological studies targeted to atmospheric flight personnel such as civilian airlines crewmembers. The model will allow computing values for biologically relevant parameters, e.g. dose equivalent and effective dose, for individual flights from 1945. Each flight is described by its actual three dimensional flight profile, i.e. geographic coordinates and altitudes varying with time. Solar modulated primary particles are filtered with a new analytical fully angular dependent geomagnetic cut off rigidity model, as a function of latitude, longitude, arrival direction, altitude and time. The particle transport results have been obtained with a technique based on the three-dimensional Monte Carlo transport code FLUKA, with a special procedure to deal with HZE particles. Particle fluxes are transformed into dose-related quantities and then integrated all along the flight path to obtain the overall flight dose. Preliminary validations of the particle transport technique using data from the AIR Project ER-2 flight campaign of measurements are encouraging. Future efforts will deal with modeling of the effects of the aircraft structure as well as inclusion of solar particle events.

Aerospace Medicine↗

PubMed2003

The atmospheric radiation response to solar-particle-events.

High-energy solar particles, produced in association with solar flares and coronal mass ejections, occasionally bombard the earth's atmosphere. resulting in radiation intensities additional to the background cosmic radiation. Access of these particles to the earth's vicinity during times of geomagnetic disturbances are not adequately described by using static geomagnetic field models. These solar fluxes are also often distributed non uniformly in space, so that fluxes measured by satellites obtained at great distances from the earth and which sample large volumes of space around the earth cannot be used to predict fluxes locally at the earth's surface. We present here a method which uses the ground-level neutron monitor counting rates as adjoint sources of the flux in the atmosphere immediately above them to obtain solar-particle effective dose rates as a function of position over the earth's surface. We have applied this approach to the large September 29-30, 1989 ground-level event (designated GLE 42) to obtain the magnitude and distribution of the solar-particle effective dose rate from an atypically large event. The results of these calculations clearly show the effect of the softer particle spectra associated with solar particle events, as compared with galactic cosmic rays, results in a greater sensitivity to the geomagnetic field, and, unlike cosmic rays, the near-absence of a "knee" near 60 degrees geomagnetic latitude.

Atmosphere↗

PubMed1995

Titan's atmosphere composition: certainties and speculations.

Firm results concerning the thermal structure, the composition, the seasonal effects of the atmosphere of Titan, as well as the superotation of its stratosphere are reviewed. The nature of the surface of the satellite, the possible presence of argon in the atmosphere and the structure and composition of clouds and aerosols are, among other topics, still speculative. The implications of the observed deuterium enrichment on the origin of ices in the outer part of the nebula are controversial.

Argon↗

PubMed1995

Isotopic ratios in planetary atmospheres.

Recent progress on measurements of isotopic ratios in planetary or satellite atmospheres include measurements of the D/H ratio in the methane of Uranus, Neptune and Titan and in the water of Mars and Venus. Implications of these measurements on our understanding of the formation and evolution of the planets and satellite are discussed. Our current knowledge of the carbon, nitrogen and oxygen isotopic ratios in the atmospheres of these planets, as well as on Jupiter and Saturn, is also reviewed. We finally show what progress can be expected in the very near future due to some new ground-based instrumentation particularly well suited to such studies, and to forthcoming space missions.

Atmosphere↗

PubMed2001

Modelling aerosol processes related to the atmospheric dispersion of sarin.

We have developed mathematical models for evaluating the atmospheric dispersion of selected chemical warfare agents (CWA), including the evaporation and settling of contaminant liquid droplets. The models and numerical results presented may be utilised for designing protection and control measures against the conceivable use of CWA's. The model AERCLOUD (AERosol CLOUD) was extended to treat two nerve agents, sarin and VX, and the mustard agent. This model evaluates the thermodynamical evolution of a five-component aerosol mixture, consisting of two-component droplets together with the surrounding three-component gas. We have performed numerical computations with this model on the evaporation and settling of airborne sarin droplets in characteristic dispersal and atmospheric conditions. In particular, we have evaluated the maximum radii (r(M)) of a totally evaporating droplet, in terms of the ambient temperature and contaminant vapour concentration. The radii r(M) range from approximately 15-80 microm for sarin droplets for the selected ambient conditions and initial heights. We have also evaluated deposition fractions in terms of the initial droplet size.

Aerosols↗