Nitrogen Trace Research Articles

Efficient l-DOPA production by Stizolobium hassjoo cell culture in a two stage configuration

A medium composition which favors the growth of plant cells may be sub-optimal for the production of secondary metabolites and vice versa. A two-stage culture system was examined in the present study to overcome this problem. Efficient production of l-DOPA (3,4-dihydroxyphenylalanine) by Stizolobium hassjoo cell culture was attempted by reformulating the MS (Murashige–Skoog) medium to one more suitable for l-DOPA production. The concentrations of the carbon and nitrogen sources, inorganic nutrients, trace elements and organic supplements in the basal MS medium were optimized for l-DOPA production. Concentrations of phosphate, Ca ++ and Zn ++ corresponding to 20, 10 and 0% of the levels present in MS medium maximized l-DOPA content. Also, elimination of the organic supplements and some inorganic compounds enhanced l-DOPA production. Medium adjustment conducted in our previous work, particularly Cu ++, Co ++, IAA (indole-3-acetic acid), was also taken into consideration. A medium tailored to the efficient production of l-DOPA in the second stage of a two-stage culture system was elaborated. Validation of the medium in shake flasks resulted in 2.1–2.3 fold increases in l-DOPA content compared to the control medium. Validity tests of the production medium in large laboratory-scale bioreactors were also conducted. By adequate control in aeration and agitation rates for each bioreactor, remarkable enhancement of l-DOPA production was obtained. The l-DOPA content (% dry weight) in 1-l round bottom spinner flask increased 4-fold of the initial content. Thus, the possibility of scaling-up two stage cultures was shown.

Preparation of aligned carbon nanotubes catalysed by laser-etched cobalt thin films

Pyrolysis of 2-amino-4,6-dichloro-s-triazine over laser-etched thin films of cobalt deposited on an inverted silica substrate generates aligned bundles and films of carbon nanotubes of uniform dimensions. Scanning electron microscopy, high resolution transmission electron microscopy, energy dispersive X-ray analyses, electron energy loss spectroscopy and electron diffraction studies reveal that the aligned tubes, which usually grow perpendicular to the substrate surface, are mainly straight (length ⩽100 μm; 30–50 nm OD), contain traces of nitrogen (<5%) and exhibit a preferred helicity (e.g. armchair 25–30%). Other graphitic structures (e.g. polyhedral particles, encapsulated particles and amorphous carbon) are absent. Energised cobalt clusters/particles (⩽50 nm), ablated during laser-etching, may condense and recrystallise evenly on the surface of the substrate as cobalt and/or cobalt oxide. These crystals apparently play a key role in nanotube production.

Comparison of N2O emissions from soils at three temperate agricultural sites: simulations of year-round measurements by four models

Nitrous oxide (N2O) flux simulations by four models were compared with year-round field measurements from five temperate agricultural sites in three countries. The field sites included an unfertilized, semi-arid rangeland with low N2O fluxes in eastern Colorado, USA; two fertilizer treatments (urea and nitrate) on a fertilized grass ley cut for silage in Scotland; and two fertilized, cultivated crop fields in Germany where N2O loss during the winter was quite high. The models used were daily trace gas versions of the CENTURY model, DNDC, ExpertN, and the NASA-Ames version of the CASA model. These models included similar components (soil physics, decomposition, plant growth, and nitrogen transformations), but in some cases used very different algorithms for these processes. All models generated similar results for the general cycling of nitrogen through the agro-ecosystems, but simulated nitrogen trace gas fluxes were quite different. In most cases the simulated N2O fluxes were within a factor of about 2 of the observed annual fluxes, but even when models produced similar N2O fluxes they often produced very different estimates of gaseous N loss as nitric oxide (NO), dinitrogen (N2), and ammonia (NH3). Accurate simulation of soil moisture appears to be a key requirement for reliable simulation of N2O emissions. All models simulated the general pattern of low background fluxes with high fluxes following fertilization at the Scottish sites, but they could not (or were not designed to) accurately capture the observed effects of different fertilizer types on N2O flux. None of the models were able to reliably generate large pulses of N2O during brief winter thaws that were observed at the two German sites. All models except DNDC simulated very low N2O fluxes for the dry site in Colorado. The US Trace Gas Network (TRAGNET) has provided a mechanism for this model and site intercomparison. Additional intercomparisons are needed with these and other models and additional data sets; these should include both tropical agro-ecosystems and new agricultural management techniques designed for sustainability.

Response of surface microlayers to artificial acid precipitation in a meso-humic lake in Norway

A meso-humic lake was divided into two basins. One basin and its catchment area were treated with an acid solution (pH 3.0–3.5), while the other served as control. To study the influence of the treatment on the physical and chemical properties of surface microlayers (SM), samples were taken with a remotely controlled slick collector, fitted with a hydrophilic Teflon-coated rotating drum. SM of acid-treated (A) and non-treated (B) basins and respective subsurface water (SW) were compared to identify possible effects of the acid treatment. The average enrichment factor ( E f) of particulate organic carbon (POC), i.e. the quotient of SM and SW concentrations, was 16 in SM A and 18 in SM B during the 1994 investigation. The particulate fraction ( > 0.45 μm) of organic carbon constituted 25–30% of total organic carbon in SM A and 10–15% in SM B during the study. E f values of dissolved organic carbon (DOC) rarely exceeded 3 and varied little during the day-night cycle. UV 254 absorbance capacity of SM was 10–15% lower in the treated basin than in the control during the whole study. In 1992, SM B contained relatively high amounts of UV-absorbing high-molecular-weight (HMW) material, while SM A contained two distinct fractions, one of higher and one of lower molecular weight. This coincided with a higher biomass of phytoplankton in SM B than in SM A. Acetic acid was the most abundant simple organic acid detected in SM and is a common product of organic acid degradation. The volatile carboxylic acids (C 2–C 6) represented a lower fraction of the DOC than the less volatile fatty acids (C 8–C 18). Yet, these compounds contributed less than 1% of total DOC. Protein material, measured as particulate organic nitrogen, was greater in SM A than in SM B. Nitrogen fractions, base cations and trace metals concentrations in SM A were qualitatively different from SM B. This could have been an effect of the treatment, but it was probably also related to differences in hydrology and geomorphology in the catchment area. The acid treatment of the catchment and lake influenced the microlayer properties by increasing particle formation and by acid degradation of HMW organic material. The acid degradation resulted in reduced UV extinction in the SM of the treated basin.

Development of a Detector for Ultratrace Nitrogen in Argon Using Low-Pressure, Capillary Glow Discharge Molecular Emission Spectrophotometry

A highly sensitive detector was developed for determining parts per billion of nitrogen in high-purity argon. The method is based on the spectrophotometric determination of the emission intensity from the nitrogen molecule excited in the lowest vibrational transitions of the electronic C(3)Π(u) → B(3)Π(g) system. A capillary glow discharge technique was applied to excite nitrogen in an argon flow at several Torr. The low-pressure, capillary glow discharge method offered high sensitivity for detecting trace nitrogen in argon. The response of the detector was proportional in the range of nitrogen concentrations from 0.1 ppb, which correspond to S/N = 3, to 100 ppm.

Fourier Transform Infrared Emission Spectroscopy of the [6.7]2Σ+–X2Σ+System of HfN

The electronic emission spectrum of HfN has been observed in the near infrared using a Fourier transform spectrometer. HfN molecules were excited in a hafnium hollow cathode lamp operated with neon gas and a trace of nitrogen. The bands located near 5746, 5802, 6668, and 6715 cm−1have been assigned as the 0–1, 1–2, 0–0, and 1–1 bands of the [6.7]2Σ+–X2Σ+transition. The rotational analysis of these bands has been performed and the equilibrium molecular constants for the lower electronic state of180HfN are ωe= 932.7164(15) cm−1, ωexe= 4.41299(65) cm−1,Be= 0.436217(18) cm−1, αe= 0.002659(11) cm−1, andre= 1.724678(36) Å. We believe that the lower state of this transition is the ground electronic state but more experimental and theoretical work is necessary to prove this. Our work represents the first experimental observation of an electronic transition of HfN.

Improvements of a combined size exclusion chromatography and solid phase extraction approach for the clean-up of marine sediment samples for trace analysis of pesticides

Two methods based on gel permeation chromatography (GPC) [size exclusion chromatography] for the analysis of traces (ng/kg) of nitrogen and phosphorus containing pesticides (like triazines or phosphothionates) from marine sediment samples are compared: A macro GPC with Biobeads SX-3 and a chromatography on a high-performance (HP-GPC) column with UV-detection. Results for eight triazine herbicides, two triazine metabolites, the phenylurea derivative linuron, two acetanilides and two organophosphorus compounds are given. Concentrations obtained with the HP-GPC are compared with those obtained with a macro GPC approach in an earlier study.

Simulation modeling of nitrogen trace gas emissions along an age gradient of tropical forest soils

Applications of a process simulation model for ecosystem production and soil nutrient cycling were carried out to test hypotheses concerning the controls on nitrogen trace gas fluxes in tropical forests. Assuming that emissions of trace gases (N 2O and NO) can help characterize patterns in N cycling among forests of different age and nutrient status, we applied a new daily time step version of the CASA (Carnegie-Ames-Stanford approach) model in an attempt to reproduce soil biophysical conditions previously measured in three forest stands that comprise a soil age gradient (ranging from 200 to 185 000 years old) on the island of Hawaii. We compared model-predicted soil moisture, temperature, N mineralization, and N trace gas emission rates to measurements at forest sites made during 1990 and 1991. Results showed that predicted water filled pore space (WFPS) in the soil is consistently lower than measured WFPS, possibly due to incomplete understanding of moisture holding capacity, drainage properties, and small scale variability of these volcanic soils. Simulations correctly predicted the observed difference of an order of magnitude between N 2O emission fluxes in the youngest and the oldest forest soils. Nevertheless, specific day-by-day comparison of predicted and measured N 2O fluxes reveal only occasional agreement within an order of magnitude tolerance level. Although soil moisture conditions appear favorable for emission on NO at these sites, as predicted by the generalized model design, lack of observed NO emissions from the previous field and laboratory studies suggest that: (1) our hypothesized NO emission levels as a function of WFPS should be truncated at lower levels of soil moisture availability; and/or (2) nitrification potentials of natural forest soils should be considered in revised versions of the model.

Colloidal trace metals, organic carbon and nitrogen in a southeastern U.S. estuary

We have used cross-flow ultrafiltration on eleven 0.45-μm-filtered samples taken across the salinity gradient in the Ochlockonee Estuary. We sequentially ultrafiltered the samples using 10- and 1-kD filters (1 kD = 1000 daltons). The results indicate that total Fe and Mn behave nonconservatively in the estuary and that the removal is from the high-molecular-weight (HMW; > 10 kD) fraction although Mn is removed at lower salinity than Fe. For Ni, Cu and Cd, the HMW fraction is very important in the river but these elements are quickly converted from HMW to low-molecular-weight (LMW) species with increasing salinity. Carbon in the HMW fraction is strongly correlated with Fe but only weakly correlated with Fe in the smaller size fractions. The two important processes controlling the behavior of metals, carbon and nitrogen in the estuary are colloid aggregation and desorption or dissociation.

Pesticide residue analysis in foodstuffs applying capillary gas chromatography with atomic emission detection State-of-the-art use of modified multimethod S19 of the Deutsche Forschungsgemeinschaft and automated large-volume injection with programmed-temperature vaporization and solvent venting

Atomic emission detection (AED) provides high element-specific detection of all compounds amenable to gas chromatography (GC). The heteroatoms nitrogen, chlorine, phosphorus, sulfur, bromine and fluorine, which are important elements in pesticide residue analysis, are of major interest. A main drawback of AED is its lower sensitivity with respect to other selective detection methods used in pesticide residue analysis such as electron-capture and nitrogen-phosphorus detection. This holds true especially for the important nitrogen trace. For this reason, more sensitive detection can be achieved by injection of larger volumes or higher concentrations of sample extracts, because matrix compounds were usually registered only in the carbon, hydrogen and oxygen traces. This paper focuses on recent developments from the authors' laboratory in order to demonstrate the feasibility of screening analyses with the identification of pesticide residues down to the 0.01 ppm concentration level in plant foodstuffs. This has been achieved by means of automated large volume injection with programmed-temperature vaporization and solvent venting as well as careful optimization of make-up and reactant gases with AED. Clean up follows the principle of multimethod S19 of the Deutsche Forschungsgemeinschaft in a reduced procedure. After elimination of lipids and waxes by gel permeation chromatography, extracts from 10 g of the food samples were concentrated to 200 μl, of which 12.5 μl were introduced into the GC-AED system. Two analyses were usually performed with the element traces of sulfur, phosphorus, nitrogen and carbon in the first run and chlorine and bromine in the second run. Fluorine and oxygen were not detected in any screening analyses. The method has proved to be of great value especially with “problem foodstuffs”. The limits of detection were determined for 385 pesticides and are presented together with their retention data.

Thermal Nitridation of SiO2 Films in Ammonia: Isotopic Tracing of Nitrogen and Oxygen in Further Stages and in Reoxidation

We investigated the transport of oxygenic and nitrogenic species during thermal nitridation of silicon dioxide films in ammonia in a resistance heated furnace, as well as during subsequent reoxidation of the resulting oxynitride films. Isotopic tracing of oxygen and nitrogen was used, showing that the thermal nitridation of films during long time intervals (around 1 h) is driven by essentially the same mechanisms as in the initial stages: the transport of by interstitial diffusion toward the oxynitride silicon interface reacting with the silicon network as well as toward the surface where it desorbs. There is a general enhancement of the effects previously observed in the initial stages of nitridation, namely, the amount of nitrogen accumulated in the interface is greatly enhanced. Thermal reoxidation in dry of the oxynitride films implies an increase of the film thickness. The isotopic tracing of oxygen and nitrogen during thermal reoxidation shows the incorporation of freshly arriving oxygen mainly in the surface and in the oxynitride/silicon interface regions. Nitrogen atoms near the surface and near the interface are exchanged for oxygen atoms introduced during the reoxidation. A general discussion of the mechanisms of thermal nitridation of films in and the symmetry between the mechanisms of thermal nitridation and of thermal reoxidation in dry of the resulting oxynitride films is presented.

Effect of carbon dioxide on the performance of biogas/diesel duel-fuel engine

Methane and carbon dioxide are the two main constituents of biogas. Biogas also contains traces of nitrogen, hydrogen, oxygen and hydrogen sulphide. When diesel engine runs on biogas, the combustion is poor as compared to diesel fuel. One of the reason of poor combustion is the presence of carbon dioxide in the biogas. Percentage of methane and carbon dioxide in biogas varies with the maturities of feed stock, temperature, water content, loading rate of raw material and bacterial actions. This paper examines the effect of variations of carbon dioxide in biogas on the performance of the engine to simulate the performance of the engine running with biogas from different sources (varying proportion of methane and carbon dioxide).

Thermal Nitridation of SiO2 Films in Ammonia: Isotopic Tracing of Nitrogen and Oxygen in the Initial Stages

We investigated the transport of oxygenic and nitrogenic species during the initial stages of thermal nitridation of silicon dioxide films in ammonia by means of isotopic tracing of oxygen and nitrogen. The total amounts of the different isotopes incorporated during oxidations and nitridations under , or were determined by nuclear reaction analyses, which are highly sensitive and selective. The depth profiles of the different isotopes were determined using methods based on very narrow resonances existing in the nuclear reaction cross sections at low energies. These methods lead to high depth resolution, especially near the surface, where most of the other available methods fail in providing acceptable depth resolutions. The results here reported show that during the initial stages of thermal nitridation, both oxygenic and nitrogenic species are transported toward the oxynitride/silicon interface as well as toward the surface. Oxygen atoms are lost from the oxynitride film surface, exchanged for the incorporated nitrogen atoms. A strong exchange between the nitrogen atoms incorporated into the oxynitride film and those from the ammonia gas is also observed. The dependence of the nitrogen profiles on the ammonia pressure and on the nitridation time in the initial stages indicates that the overall nitridation process is governed by diffusion mechanisms.

N-process-level regulation of nitrogen trace gas flux in Hawaiian montane rainforest

Nutrient amendments and inhibition experiments were used to evaluate factors controlling the production of N trace gases in soils. Sampling was conducted at five sites which form a 200−4.5 × 10 6 y chronosequence in Hawaiian montane rainforest. The pattern of nitric oxide (NO) and nitrous oxide (N 2O) flux from soils in the laboratory was similar to that observed in the field, with emissions of NO + N 2O increasing with soil age. Autoclaving of soils indicated that there was little or no abiological production of N 2O. The response of N 2O and NO flux to sieving and acetylene addition is consistent with N trace gas production being primarily denitrification-based in all but the oldest site, where nitrification-based production is significant. All the soils had increased emissions of N 2O in response to additions of N. Soils from the 185,000-y-old Kohala site, however, had the lowest proportional N 2O response, did not have elevated NO emissions in response to addition of N, and had a small, but significant NO response to addition of carbon. This intermediate-age site represents a transition stage in soil development in which N trace gas production is the least limited by N-availability.

The chemistry and antioxidant properties of tocopherols and tocotrienols.

This article is a review of the fundamental chemistry of the tocopherols and tocotrienols relevant to their antioxidant action. Despite the general agreement that alpha-tocopherol is the most efficient antioxidant and vitamin E homologue in vivo, there was always a considerable discrepancy in its "absolute" and "relative" antioxidant effectiveness in vitro, especially when compared to gamma-tocopherol. Many chemical, physical, biochemical, physicochemical, and other factors seem responsible for the observed discrepancy between the relative antioxidant potencies of the tocopherols in vivo and in vitro. This paper aims at highlighting some possible reasons for the observed differences between the tocopherols (alpha-, beta-, gamma-, and delta-) in relation to their interactions with the important chemical species involved in lipid peroxidation, specifically trace metal ions, singlet oxygen, nitrogen oxides, and antioxidant synergists. Although literature reports related to the chemistry of the tocotrienols are quite meager, they also were included in the discussion in virtue of their structural and functional resemblance to the tocopherols.

Dry oxidation mechanisms of thin dielectric films formed under N2O using isotopic tracing methods

We investigated the mechanisms of thermal reoxidation in dry O2 of silicon oxynitride films prepared by processing Si(100) wafers in a rapid thermal furnace in a pure nitrous oxide (N2O) ambient, using isotopic tracing of oxygen and nitrogen. Standard nuclear reaction analyses for the measurement of the total amounts of the different isotopes, and very narrow resonant nuclear reactions for high resolution (1 nm) depth profiling of these elements were used. The silicon oxynitride films grown in pure 15N216O were 8-nm thick, with a small amount of nitrogen localized near the interfacial region. Under reoxidation in dry 18O2, the thickness of the dielectric film increased while a pronounced isotopic exchange took place between the 18O from the gas and the 16O from the film, as well as a significant loss of 15N. This is in contrast with the reoxidation in dry O2 of pure SiO2 films, where the oxygen exchange is rather small as compared to that observed in the present case.

Quick External Leakage Inspection Method for Gas Supplying System in Semiconductor Facility Using Atmospheric Pressure Ionization Mass Spectrometer.

Semiconductor fabrication field requires screening technology, for external air leakage inspection in a clean room gas delivery system which can inspect all inspection points in one gas line in one process. Recent advances in welding technology have meant that the occurrence of a leak at welding point is now extremely uncommon. Inspection costs of a gas delivery system can therefore be decreased by applying such a screening process. The detection sensitivity required for screening of the air component is ppt level or below.The atmospheric pressure ionization mass spectrometer (APIMS) was applied to the screening process using the argon carrier gas. Trace nitrogen which previously could not be detected by the APIMS, could be detected by mixing hydrogen in the argon gas. The detection sensitivity was increased over 100 times compared to the oxygen detection since there is a large amount of nitrogen in air and the proton transfer reaction for nitrogen ionization having a larger rate constant than the charge transfer reaction for oxygen ionization. N2H+ intensity shows a sudden increase with H2 concentration because the rate constant, in the rate-determining step for N2H+ formation in higher H2 concentrations, is larger than that in the lower H2 concentrations. The optimum H2 concentration is 3-10% for obtaining the higher sensitivity.It is expected that the application of APIMS technique will greatly reduce the costs associated with the leak inspection.

Process modeling of controls on nitrogen trace gas emissions from soils worldwide

We report on an ecosystem modeling approach that integrates global satellite, climate, vegetation, and soil data sets to (1) examine conceptual controls on nitrogen trace gas (NO, N2O, and N2) emissions from soils and (2) identify weaknesses in our bases of knowledge and data for these fluxes. Nitrous and nitric oxide emissions from well‐drained soils were estimated by using an expanded version of the Carnegie‐Ames‐Stanford (CASA) Biosphere model, a coupled ecosystem production and soil carbon‐nitrogen model on a 1° global grid. We estimate monthly production of NO, N2O, and N2 based on predicted rates of gross N mineralization, together with an index of transient water‐filled pore space in soils. Analyses of model performance along selected climate gradients support the hypothesis that low temperature restricts predicted N mineralization and trace gas emission rates in moist northern temperate and boreal forest ecosystems, whereas in tropical zones, seasonal patterns in N mineralization result in emission peaks for N2O that coincide with wetting and high soil moisture content. The model predicts the annual N2O:NO flux ratio at a mean value of 1.2 in wet tropical forests, decreasing to around 0.6 in the seasonally dry savannas. Global emission estimates at the soil surface are 6.1 Tg N and 9.7 Tg N yr−1 for N2O and NO, respectively. Tropical dry forests and savannas are identified by using this formulation as important source areas for nitrogen trace gas emissions. Because humans continue to alter these ecosystems extensively for agricultural uses, our results suggest that more study is needed in seasonally dry ecosystems of the tropics in order to understand the global impacts of land use change on soil sources for N2O and NO.

Isotopic compositions of C, N, O, Mg, and Si, trace element abundances, and morphologies of single circumstellar graphite grains in four density fractions from the Murchison meteorite

We report ion microprobe determinations of carbon, nitrogen, oxygen, magnesium-aluminum, and silicon isotopic compositions and trace element (H, N, O, Al, Si) concentrations of individual graphite grains (0.8–28 pm) from the Murchison CM2 chondrite. The analyzed grains exhibit large variations of their isotopic compositions: 12C/ 13C ratios vary by a factor of 3500, 14N/ 15N ratios by a factor of 24, and 16O/ 18O ratios by a factor of 14. Most grains have isotopically light carbon and heavy nitrogen and excesses in 18O are positively correlated with excesses in 15N. According to their carbon isotopic composition and density we distinguish between four different groups of graphite grains. Many grains show large 26Mg excesses with inferred 26Al/ 27Al ratios ranging up to 0.1. Highest 26Al/ 27Al ratios are found in grains with close-to-normal carbon isotopic composition. Most grains have normal Si but some have large silicon isotopic anomalies. One of these grains has isotopic characteristics similar to those of the rare SiC grains of type X. Nitrogen contents are roughly correlated with the contents of other trace elements. Grains with isotopically heavy carbon tend to have higher trace element contents than grains with isotopically light carbon. Most graphite grains (∼ -92%) are round and dense. These grains either have smooth surfaces or appear to consist of dense aggregates of small scales. These surface morphologies are reflected in the internal structure of the grains. The morphology of graphite grains correlates with isotopic properties as only round grains have carbon isotopic anomalies, although small nitrogen anomalies are present in both round and nonround grains, and as morphologic subtypes of round grains are distributed differently over the range of 12C/ 13C ratios. Combining both carbon isotopic compositions and morphologies we distinguish between six different groups of round graphite grains. The isotopic characteristics of most graphite grains strongly differ from those of circumstellar SiC, suggesting that these two types of circumstellar grains originate from distinct stellar sources. Wolf-Rayet stars and Type II supernovae seem to account for the isotopic properties of most (>60%) circumstellar graphite grains. The presence of Ne E (L) with 20Ne/ 22Ne < 0.087, the lower limit for He-shell Ne, and isotopically heavy carbon together with heavy nitrogen indicate that some grains (<I%) originate from novae. Evidence for an AGB star origin comes from Kr S, but only few grains have isotopically heavy carbon and light nitrogen, expected from present stellar and nucleosynthetic models of these stars.

Atomic transport during thermal growth of silicon nitride

By means of isotopic tracing of nitrogen and hydrogen we studied the atomic transport mechanisms during the thermal growth of silicon nitride films in ammonia ( 14NH 3, 15NH 3 and 14ND 3). The total amounts and the depth profiles of the different isotopes were determined by nuclear reaction analyses and step-by-step chemical etching of the nitride films. A pronounced exchange between hydrogen atoms in the silicon nitride films and those in the nitriding gas was observed, as well as an exchange between the nitrogen atoms on a smaller scale. The results of the present investigation indicate that the atomic transport through the growing nitride film occurs via nitrogenous species that include hydrogen. Silicon atoms or ions can also take part in the growth process but they cannot be the only mobile species.