Low Mass Resolution Research Articles

Determination of elements in situ in green leaves by laser ablation ICP-MS using pressed reference materials for calibration

Laser ablation (LA) was used with double focusing sector field inductively coupled plasma mass spectrometry (ICP-MS) for direct elemental analysis of green leaves from seven species of desert plants. Pressed leaf standards (n = 7) were used as matrix matched standards for calibration and quality assurance. Nine elements (Mg, Ca, Mn, Cu, Sr, Cd, Ba, Hg and Pb) were determined in low mass resolution (m/Δm ≈ 400). Data was collected for three ablation line scans starting from near the stem to the tip of the leaf. The 213 nm laser ablation system was operated at the full energy setting (100%), with a repetition rate of 20 Hz, a spot size of 100 μm, and a scan rate of 50 μm min−1. Pressed cellulose was used for estimating detection limits, which were found to vary between 0.04 and 26 μg g−1 for Pb and Ca, respectively. Results suggest that the calibration approach is feasible for some elements (Mg, Ca, Mn, Cu, Sr, Cd, Ba) but problematic for others (Pb, Hg). Although somewhat element dependent, desert willow, autumn sage and brittle bush tended to have the highest concentrations of the elements monitored. Overall, LA-ICP-MS is a useful method for quantifying (in situ) the distribution of many elements in plant leaves.

C60 Secondary Ion Fourier Transform Ion Cyclotron Resonance Mass Spectrometry

Secondary ion mass spectrometry (SIMS) has seen increased application for high spatial resolution chemical imaging of complex biological surfaces. The advent and commercial availability of cluster and polyatomic primary ion sources (e.g., Au and Bi cluster and buckminsterfullerene (C(60))) provide improved secondary ion yield and decreased fragmentation of surface species, thus improving accessibility of intact molecular ions for SIMS analysis. However, full exploitation of the advantages of these new primary ion sources has been limited, due to the use of low mass resolution mass spectrometers without tandem MS to enable enhanced structural identification capabilities. Similarly, high mass resolution and high mass measurement accuracy would greatly improve the chemical specificity of SIMS. Here we combine, for the first time, the advantages of a C(60) primary ion source with the ultrahigh mass resolving power and high mass measurement accuracy of Fourier transform ion cyclotron resonance mass spectrometry. Mass resolving power in excess of 100 000 (m/Δm(50%)) is demonstrated, with a root-mean-square mass measurement accuracy below 1 part-per-million. Imaging of mouse brain tissue at 40 μm pixel size is shown. Tandem mass spectrometry of ions from biological tissue is demonstrated and molecular formulas were assigned for fragment ion identification.

Analysis of high-molecular-weight fructan polymers in crude plant extracts by high-resolution LC-MS.

The main water-soluble carbohydrates in temperate forage grasses are polymeric fructans. Fructans consist of fructose chains of various chain lengths attached to sucrose as a core molecule. In grasses, fructans are a complex mixture of a large number of isomeric oligomers with a degree of polymerisation ranging from 3 to >100. Accurate monitoring and unambiguous peak identification requires chromatographic separation coupled to mass spectrometry. The mass range of ion trap mass spectrometers is limited, and we show here how monitoring selected multiply charged ions can be used for the detection and quantification of individual isomers and oligomers of high mass, particularly those of high degree of polymerization (DP > 20) in complex plant extracts. Previously reported methods using linear ion traps with low mass resolution have been shown to be useful for the detection of fructans with a DP up to 49. Here, we report a method using high-resolution mass spectrometry (MS) using an Exactive Orbitrap MS which greatly improves the signal-to-noise ratio and allows the detection of fructans up to DP = 100. High-sugar (HS) Lolium perenne cultivars with high concentrations of these fructans have been shown to be of benefit to the pastoral agricultural industry because they improve rumen nitrogen use efficiency and reduce nitrous oxide emissions from pastures. We demonstrate with our method that these HS grasses not only contain increased amounts of fructans in leaf blades but also accumulate fructans with much higher DP compared to cultivars with normal sugar levels.Electronic supplementary materialThe online version of this article (doi:10.1007/s00216-011-5374-8) contains supplementary material, which is available to authorized users.

Focus on MALDI imaging

Matrix-assisted laser desorption/ionization (MALDI) emerged in the late 1980s concomitantly with electrospray ionization and contributed substantially to the promotion of mass spectrometry as an invaluable tool for analysis of biological macromolecules. Because MALDI is based on the production of ions from solid-phase samples deposited onto a conducting surface, some researchers attempted to analyse directly biological materials without any preliminary extraction step. MALDI analysis of bacterial cultures as early as the mid-1990s illustrates this approach, the objective of these studies being to characterize and identify microorganisms on the basis of a set of characteristic peaks present in their mass spectra. Identification of bacteria by MALDI mass spectrometry is now a routine method for clinical use. The ability of MALDI mass spectrometry to obtain spectra on well-defined surfaces with a focus of approximately 50–100 μm should also enable linking of the histological characteristics of biological tissue with local molecular composition. The driving idea was that tissue heterogeneity could be correlated with a difference in the mass spectral peak patterns. MALDI “profiling” of tissue sections was then proposed by the Todd and Caprioli groups at the end of the 1990s to differentiate, on a molecular basis, healthy or pathological areas present within the same tissue section. Soon after, the Caprioli team proposed a method for systematic profiling in which mass spectra were recorded at regularly spaced points on a biological surface, leading to a global vision of the molecular composition of the sample. By translating the relative intensity values of the ion peaks into a colour code, differences in local abundances in the x–y plane of the sample were revealed as contrast changes in the generated images. Immediately, MALDI mass spectrometry imaging (MALDI–MSI) seemed to be a unique method to record simultaneously as many images as ion peaks present on the mass spectra and without any a priori information about the nature of the detected molecules. It is therefore logical that MALDI imaging has initially been developed for research on biomarkers of pathologies, in a context in which the “omics” methods, in particular proteomics, have experienced explosive growth. If MALDI imaging was originally devoted to protein analysis only, this approach quickly met its limits in this area. Measuring the protein ions at low or moderate mass resolution is, indeed, not sufficient for their straightforward identification. In this area, MALDI imaging seemed more a complementary step to conventional proteomic analysis rather than an alternative method. In this way, MALDI imaging can provide precious indications of in situ protein-expression changes, making this technique attractive as a future diagnostic tool in biomedical research (Hanrieder et al., in this special issue). Recent years have seen a growing number of methodological developments and applications of MALDI imaging in the field of “small molecules”. For such compounds, accurate mass measurements, associated or not with tandemmass spectrometry (MS–MS), are often sufficient for assignment of the structures of the detected ions. Illustrating this evolution, the analysis of lipids is now a major field of application of MALDI imaging (Fernandez et al., Garrett et al., and Hart et al., in this special issue). Published in the special issue MALDI Imaging with Guest Editor Olivier Laprevote

Combined use of medium mass resolution and desolvation introduction system for accurate plutonium determination in the femtogram range by inductively coupled plasma-sector-field mass spectrometry

Formation of a polyatomic species made of an atom of a heavy element like lead, mercury or iridium, and atoms abundant in plasma (argon, nitrogen, oxygen, and hydrogen) when using an inductively coupled plasma-sector-field mass spectrometer (ICP-SFMS) may lead to false detection of femtograms (fg) of plutonium or bias in the measured concentrations. Mathematical corrections, based on the measurement of heavy element concentrations in the sample solutions and determination of the extents of formation of the polyatomic interferences, are efficient but time-consuming and degrade detection limits. We describe and discuss a new method based on the combination of, on the one hand, medium mass resolution (MR) of the ICP-SFMS to separate plutonium isotopes physically from interfering polyatomic species, and, on the other, use of a desolvation introduction system (DIS) to enhance sensitivity, thus partly compensating for the loss of transmission due to use of a higher resolution. Plutonium peaks are perfectly separated from the major interfering species (PbO 2, HgAr, and IrO 3) with a mass resolution of ~ 4000. The resulting nine-fold transmission loss is partly compensated by a five-fold increase in sensitivity obtained with the DIS and a lower background. The instrumental detection limits for plutonium isotopes, calculated for measurements of pure synthetic solutions, of the new method (known as MR-DIS method) and of the one currently used in the laboratory (LR method), based on a low mass resolution equal to 360, a microconcentric nebulizer and two in-line cooled spray chambers, are roughly equivalent, at around 0.2 fg ml − 1 . Regarding the measurement of real-life samples, the results obtained with both methods agree and the corresponding analytical detection limits for plutonium isotopes 239Pu, 240Pu and 241Pu are of a few fg·ml − 1 of sample solution, slightly lower with the MR-DIS method than with the current LR method. Although less sensitive than other plutonium ICP-MS measurement methods described in the literature, the main advantage of the MR-DIS method is that it is robust against the risk of false plutonium detection, even in the case of relatively high concentrations of heavy elements like lead, mercury or iridium.

Unexpected Materials in a Rembrandt Painting Characterized by High Spatial Resolution Cluster-TOF-SIMS Imaging

The painting materials of the Portrait of Nicolaes van Bambeeck (Royal Museums of Fine Arts of Belgium, Brussels, inv. 155) painted by Rembrandt van Rijn in 1641 has been studied using high resolution cluster-TOF-SIMS imaging. In the first step, a moderate spatial resolution (2 μm) was used to characterize the layer structure and the chemical composition of each layer on account of a high mass resolution. Then, in the second step, and despite a low mass resolution, the cluster primary ion beam was focused well below 1 μm in order to reveal smaller structures in the painting sample. The study confirmed the presence of starch in the second ground layer, which is quite surprising and, at least for Rembrandt paintings, has never been reported before. TOF-SIMS also indicated the presence of proteins, which, added to the size and shape of lake particles, suggests that it was manufactured from shearings (waste of textile manufacturing) of dyed wool, used as the source of the dyestuff. The analyses have also shown various lead carboxylates, being the products of the interaction between lead white and the oil of the binding medium. These findings considerably contribute to the understanding of Rembrandt's studio practice and thus demonstrate the importance and potential of cluster-TOF-SIMS imaging in the characterization on a submicrometer scale of artist painting materials.

Ion–molecule reactions of ammonia clusters with C60aggregates embedded in helium droplets

Helium nanodroplets are co-doped with C(60) and ammonia. Mass spectra obtained by electron ionization reveal cations containing ammonia clusters complexed with up to four C(60) units. The high mass resolution of Δm/m≈ 1/6000 makes it possible to separate the contributions of protonated, unprotonated and dehydrogenated ammonia. C(60) aggregates suppress the proton-transfer reaction which usually favors the appearance of protonated ammonia cluster ions. Unprotonated C(x)(NH(3))(n)(+) ions (x = 60, 120, 180) exceed the abundance of the corresponding protonated ions if n < 5; for larger values of n the abundances of C(60)(NH(3))(n)(+) and C(60)(NH)(n-1)NH(4)(+) become about equal. Dehydrogenated C(60)NH(2)(+) ions are relatively abundant; their formation is attributed to a transient doubly charged C(60)-ammonia complex which forms either by an Auger process or by Penning ionization following charge transfer between the primary He(+) ion and C(60). The abundance of C(x)NH(3)(+) and C(x)NH(4)(+) ions (x = 120 or 180) is one to two orders of magnitude weaker than the abundance of ions containing one or two additional ammonia molecules. However, a model involving evaporation of NH(3) or NH(4) from the presumably weakly bound C(x)NH(3)(+) and C(x)NH(4)(+) ions is at odds with the lack of enhancement in the abundance of C(120)(+) and C(180)(+). Mass spectra of C(60) dimers complexed with water complement a previous study of C(60)(H(2)O)(n)(+) recorded at much lower mass resolution.

H 2 production from reactions between water and small molybdenum suboxide cluster anions

Reactions between molybdenum suboxide cluster anions, Mo(x)O(y)(-) (x=1-4; y < or = 3x), and water (H(2)O and D(2)O) have been studied using mass spectrometric analysis of products formed in a high-pressure, fast-flow reactor. Product distributions vary with the number of metal atoms in the cluster. Within the MoO(y)(-) oxide series, product masses correspond to the addition of one water molecule, as well as a H/D exchange with MoO(4)H(-). Within the Mo(2)O(y)(-) oxide series, product evolution and distribution suggest sequential oxidation via Mo(2)O(y)(-)+H(2)O/D(2)O-->Mo(2)O(y+1)(-)+H(2)/D(2) reactions for y<5, while for Mo(2)O(5)(-), Mo(2)O(6)H(2)/D(2)(-) is produced. Mo(2)O(6)(-) does not appear to be reactive toward water. For the Mo(3)O(y)(-) oxide series, sequential oxidation similarly is suggested for y<5, while Mo(3)O(5)(-) reactions result in Mo(3)O(6)H(2)/D(2)(-) formation. Mo(3)O(6)(-) appears uniquely unreactive. Mo(3)O(7)(-) and Mo(3)O(8)(-) react to form Mo(3)O(8)H(2)/D(2)(-) and Mo(3)O(9)H(2)/D(2)(-), respectively. Lower mass resolution in the Mo(4)O(y)(-) mass range prevents unambiguous mass analysis, but intensity changes in the mass spectra do suggest that sequential oxidation with H(2)/D(2) evolution occurs for y<6, while Mo(4)O(y+1)H(2)/D(2)(-) addition products are formed in Mo(4)O(6)(-) and Mo(4)O(7)(-) reactions with water. The relative rate constants for sequential oxidation and H(2)O/D(2)O addition for the x=2 series were determined. There is no evidence of a kinetic isotope effect when comparing reaction rates of H(2)O with D(2)O, suggesting that the H(2) and D(2) losses from the lower-oxide/hydroxide intermediates are very fast relative to initial reaction complex formation with H(2)O or D(2)O. The rate constants determined here are two times higher than those determined in identical reactions between W(2)O(y)(-)+H(2)O/D(2)O.

CO 2 reduction by group 6 transition metal suboxide cluster anions

Reactions between small group 6 transition metal suboxide clusters, M(x)O(y)(-) (M = (98)Mo or (186)W; x = 1-4; y < or = 3x) and both CO(2) and CO were studied in gas phase using mass spectrometric analysis of high-pressure, fast flow reaction products. Both Mo(2)O(y)(-) and W(2)O(y)(-) show evidence of sequential oxidation by CO(2) of the form, M(2)O(y)(-)+CO(2)-->M(2)O(y+1)(-)+CO for the more reduced species. Similar evidence is observed for the trimetallic clusters, although Mo(3)O(6)(-) appears uniquely unreactive. Lower mass resolution in the M(4)O(y)(-) range precludes definitive product mass assignments, but intensity patterns suggest the continued trend of sequential oxidation of the more reduced end of the M(4)O(y)(-) oxide series. Based on thermodynamic arguments, cluster oxidation by CO(2) is possible if D(0)(O-Mo(x)O(y)(-)) > 5.45 eV. Although simple bond energy analysis suggests that tungsten oxides may be more reactive toward CO(2) compared to molybdenum oxides, this is not born out experimentally, suggesting that the activation barrier for the reduction of CO(2) by tungsten suboxide clusters is very high compared to analogous molybdenum suboxide clusters. In reactions with CO, suboxides of both metal-based oxides show CO addition, with the product distribution being more diverse for Mo(x)O(y)(-) than for W(x)O(y)(-). No evidence of cluster reduction by CO is observed.

STAR FORMATION AND FEEDBACK IN SMOOTHED PARTICLE HYDRODYNAMIC SIMULATIONS. II. RESOLUTION EFFECTS

We examine the effect of mass and force resolution on a specific star formation (SF) recipe using a set of N-body/Smooth Particle Hydrodynamic simulations of isolated galaxies. Our simulations span halo masses from 10^9 to 10^13 solar masses, more than four orders of magnitude in mass resolution, and two orders of magnitude in the gravitational softening length, epsilon, representing the force resolution. We examine the total global star formation rate, the star formation history, and the quantity of stellar feedback and compare the disk structure of the galaxies. Based on our analysis, we recommend using at least 10^4 particles each for the dark matter and gas component and a force resolution of epsilon approximately equal to 10^-3 R_vir when studying global SF and feedback. When the spatial distribution of stars is important, the number of gas and dark matter particles must be increased to at least 10^5 of each. Low mass resolution simulations with fixed softening lengths show particularly weak stellar disks due to two-body heating. While decreasing spatial resolution in low mass resolution simulations limits two-body effects, density and potential gradients cannot be sustained. Regardless of the softening, low-mass resolution simulations contain fewer high density regions where SF may occur. Galaxies of approximately 10^10 solar masses display unique sensitivity to both mass and force resolution. This mass of galaxy has a shallow potential and is on the verge of forming a disk. The combination of these factors give this galaxy the potential for strong gas outflows driven by supernova feedback and make it particularly sensitive to any changes to the simulation parameters.

Characterization of complex assemblages of organic acids in geological samples by negative electrospray ionization mass spectrometry using a double‐focusing magnetic sector field mass spectrometer

Four different geological sample types (a crude oil, a crude oil asphaltene, a reservoir core extract and a reservoir core asphaltene) have been characterized by negative ionization electrospray mass spectrometry at low and high mass resolution using a double-focusing magnetic sector field mass spectrometer. The mass range, shape of the spectra and the signal distribution of the acidic constituents as well as the average molecular weights, the total ion abundance and signal intensity in the spectra were compared for the different sample types. Nominal mass classes have been evaluated and Kendrick mass plots were generated in order to identify homologous series. For the crude oil sample, accurate mass assignments were made by high-resolution double-focusing magnetic sector field mass spectrometry (DFMSFMS) and were compared with those obtained by negative ion electrospray ionization (ESI) Fourier transform ion cyclotron resonance mass spectrometry (FTICRMS). With both instrument types, compounds with the molecular composition C(n)H(2n+z)O(2), among which carboxylic acids predominated, were the main acidic compound class detectable in negative ESI mass spectra. Good agreement was achieved for the double bond class distribution and the carbon number distribution of the O(2) class. In addition, minor compound classes could be identified using FTICRMS.

High‐Resolution LA‐ICP‐MS for Accurate Determination of Low Abundances of K, Sc and Other Trace Elements in Geological Samples

Laser ablation‐inductively coupled plasma‐mass spectrometry (LA‐ICP‐MS) was used to determine K, Sc, Ti, V, Cr, Mn, Co, Ni and Zn in geological samples. Because the isotopes of these elements and the internal standard element (Ca) often have interferences from molecular ions when determined using quadrupole or sector‐field ICP‐MS in low mass resolution mode, ion intensities were measured at a high mass resolution of 4000. We investigated dynamic element fractionation, type and abundance of molecular ions using different geological reference materials. Highly resolved mass spectra were especially important for accurate low‐abundance measurements. As a result, maximum “critical” concentration limits for each isotope were obtained, where a mass resolution of 4000 was necessary for reliable LA‐ICP‐MS analysis. To test the LA‐ICP‐MS technique, different international reference material glasses and powdered rock reference materials were analysed. Rock powders were fused to glass beads using an Ir‐strip heater. Nearly all concentration values for the reference materials agreed with the reference values at the 95% confidence level. To demonstrate routine LA‐ICP‐MS analysis at a mass resolution of 4000, trace element data for Hawaiian basalts are also presented.

A high resolution and high sensitivity proton-transfer-reaction time-of-flight mass spectrometer (PTR-TOF-MS)

Proton-transfer-reaction mass spectrometry (PTR-MS) developed about 10 years ago is used today in a wide range of scientific and technical fields allowing real-time on-line measurements of volatile organic compounds in air with a high sensitivity and a fast response time. Most instruments employed so far use quadrupole filters to analyze product ions generated in the reaction drift tube. Due to the low mass resolution of the quadrupoles used this has the disadvantage that identification of trace gases under study is not unambiguous. Here we report the development of a new version of PTR-MS instruments using a time-of-flight mass spectrometer, which is capable of measuring VOCs at ultra-low concentrations (as low as a few pptv) under high mass resolution (as high as 6000 m/Δm in the V-mode) with a mass range of beyond 100 000 amu. This instrument was constructed by interfacing the well characterized and recently improved Ionicon hollow cathode ion source and drift tube section with a Tofwerk orthogonal acceleration reflectron time-of-flight mass spectrometer. We will first discuss the set-up of this new PTR-TOF-MS mass spectrometer instrument, its performance (with a sensitivity of several tens of cps/ppbv) and finally give some examples concerning urban air measurements where sensitivity, detection limit and mass resolution is essential to obtain relevant data.

Probing the limits of liquid droplet laser desorption mass spectrometry in the analysis of oligonucleotides and nucleic acids

In the present work we demonstrate the advantages of LILBID mass spectrometry (laser-induced liquid bead ion desorption) in the analysis of nucleic acids and large oligonucleotides. For established methods like matrix-assisted laser desorption/ionization (MALDI) and electrospray ionization (ESI), the mass analysis of oligonucleotides or of noncovalent oligonucleotide-protein complexes, in particular of very large ones, still represents a considerable challenge either due to the lack of native solutions or nonspecific adduct formation or due to a reduced salt tolerance or a high charge state of the ions. With LILBID, oligonucleotides, solvated in micro-droplets of aqueous buffer at certain pH and ion strength, are brought into the gas phase by laser ablation. We show that our method is able to detect single- and double-stranded oligonucleotides with high softness, demonstrated by the buffer dependence of the melting of a duplex. The absolute sensitivity is in the attomole range concomitant with a total analyte consumption in the femtomole region. The upper mass limit of oligonucleotides still detected with good signal-to-noise ratio with LILBID is the 1.66 MDa plasmid pUC19. With DNA ladders from short duplexes with sticky ends, we show that LILBID correctly reflects the relative thermodynamic stabilities of the ladders. Moreover, as an example for a specific DNA-protein complex we show that a NF-kappaB p50 homodimer binds sequence specifically to its match DNA. In summary we demonstrate that LILBID, although presently performed only with low mass resolution, due to these advantages, is an alternative mass spectrometric method for the analysis of oligonucleotides in general and of specific noncovalent nucleic acid-protein complexes in particular.

Unusual products observed in gas-phase WxOy−+H2O and D2O reactions

Addition of H(2)O and D(2)O to small tungsten suboxide cluster anions W(x)O(y)(-) (x = 1-4; y < or = 3x) was studied using mass spectrometric measurements from a high-pressure fast flow reactor. Within the WO(y)(-) mass manifold, which also includes WO(4)H(-), product masses correspond to the addition of one to three H(2)O or D(2)O molecules. Within the W(2)O(y)(-) cluster series, product distributions suggest that sequential oxidation W(2)O(y)(-) + H(2)O/D(2)O --> W(2)O(y+1)(-) + H(2)/D(2) occurs for y < 5, while for W(2)O(5)(-), W(2)O(6)H(2)(-)/W(2)O(6)D(2)(-) is primarily produced. W(2)O(6)(-) does not appear reactive. For the W(3)O(y)(-) cluster series, sequential oxidation with H(2) and D(2) production occurs for y < 6, while W(3)O(6)(-) and W(3)O(7)(-) produce W(3)O(7)H(2)(-)/W(3)O(7)D(2)(-) and W(3)O(8)H(2)(-)/W(3)O(8)D(2)(-), respectively. Lower mass resolution in the W(4)O(y)(-) mass range prevents definitive product assignments, but intensity patterns suggest that sequential oxidation with H(2)/D(2) evolution occurs for y < 6, while W(4)O(y+1)H(2)(-)/W(4)O(y+1)D(2)(-) products result from addition to W(4)O(6)(-) and W(4)O(7)(-). Based on bond energy arguments, the H(2)/D(2) loss reaction is energetically favored if the new O-W(x)O(y)(-) bond energy is greater than 5.1 eV. The relative magnitude of the rate constants for sequential oxidation and H(2)O/D(2)O addition for the x = 2 series was determined. There are no discernable differences in rate constants for reactions with H(2)O or D(2)O, suggesting that the H(2) and D(2) loss from the lower-oxide/hydroxide intermediates is very fast relative to the addition of H(2)O or D(2)O.

Determination of polar 1H-benzotriazoles and benzothiazoles in water by solid-phase extraction and liquid chromatography LTQ FT Orbitrap mass spectrometry

A sensitive, reliable and robust method for the trace determination of six polar 1H-benzotriazoles and four benzothiazoles in drinking and surface water was developed. These compounds were extracted from water by solid-phase extraction and analyzed by Liquid Chromatography–Electrospray Mass Spectrometry using a linear ion trap-Orbitrap hybrid instrument at high resolution of 30,000 FWHM in the full-scan acquisition mode. At least one product ion was simultaneously detected in the linear ion trap at low mass resolution and was used for confirmation of compound identity. The compounds studied are soluble in water, resistant to biodegradation, only partially removed in wastewater treatment and they may pass the water treatment processes in the production of drinking water. The analytes and four internal standards were preconcentrated by solid-phase extraction at low pH. Positive electrospray ionization resulted in protonated molecular ions for all the 1H-benzotriazoles and benzothiazoles. The mass accuracy was between −5 ppm at m/ z 120 and −0.1 ppm at m/ z 182 and did not change for more than 2 ppm over a sample sequence of 8 days of analysis time. The optimized method allowed quantifying six benzotriazoles and four benzothiazoles in samples of drinking and surface water down to method detection limits of 0.01 μg/L. The recoveries ranged between 45 and 125% in ultrapure, drinking and surface water at a spiking level of 0.2 μg/L; the repeatability was between 2 and 13%. All analytes showed a linear response between 0.01 and 1.0 μg/L. No significant matrix effect was observed in drinking and surface water, except for the compounds 2-aminobenzothiazole (signal enhancement about 50%) and 2-hydroxybenzothiazole (signal suppression about 25%). In Dutch drinking water samples, the compounds 1H-benzotriazole, 4- and 5-methyl-1H-benzotriazole, 5,6-dimethyl-1H-benzotriazole, 5-chloro-1H-benzothiazole and benzothiazole were detected. The concentration levels ranged from 0.01 to 0.2 μg/L. In surface waters, eight out of ten compounds tested were found to be present in concentration levels ranging between 0.1 and 1.0 μg/L. In addition, in effluents of two sewage treatment plants, eight out of ten compounds tested were present with maximum concentrations for 1H-benzotriazole of 8 μg/L and for methyl-1H-benzotriazole of 3 μg/L (summed concentration of two isomers). This work demonstrates the excellent suitability of the LTQ FT Orbitrap mass spectrometer for this type of analysis.

Extending the capabilities of electrothermal vaporization-inductively coupled plasma mass spectrometry (ETV-ICPMS): Coupling the graphite furnace to a sector field instrument

This paper reports on the capabilities of the combination of an electrothermal vaporization (ETV) unit and a state-of-art single-collector sector field inductively coupled plasma mass spectrometer (SF-ICPMS). The basic analytical characteristics of this set-up were evaluated and compared to those of the more traditional combination of ETV and quadrupole-based (Q) ICPMS instrumentation. ETV-SF-ICPMS seems capable of providing a superior performance in terms of sensitivity (15- to 20-fold improvement in low resolution mode) and, also in terms of selectivity, as in medium resolution mode significantly lower LODs were achieved, especially for some low-mass elements, for which the most abundant nuclide suffers from spectral overlap as a result of the occurrence of carbon-containing polyatomic ions (e.g., 52Cr, 28Si) at low mass resolution. No deterioration was established in terms of stability, linear dynamic range or tolerance to matrix effects in comparison with ETV-Q-ICPMS. Also the possibilities for multi-element monitoring were studied and shown to be similar (monitoring of up to approximately 20 nuclides during the same tube firing is feasible), owing to the enhanced scanning speed and reduced magnet settling time that current SF-ICPMS displays when compared to older SF instrumentation. It is demonstrated that this instrumentation still preserves the most relevant advantages of the ETV technique, such as i) the potential for temporal separation of overlapping isobaric signals (e.g., 102Ru and 102Pd; 192Os and 192Pt; 130Te and 130Ba) under optimum vaporization conditions, and ii) the ability to analyze solid samples directly, as shown by the determination of Cr and Si in biological reference materials. By operating the instrument at higher mass resolution (4000), interference-free conditions could be realized for several isotopes of the target elements and, thus, isotope dilution could be deployed for their quantification, enabling the matrix effects observed to be overcome.

Interference of organic signals in highly time resolved nitrate measurements by low mass resolution aerosol mass spectrometry

Highly time resolved measurements of nitrate in ambient aerosols were conducted by an Aerodyne Quadrupole Aerosol Mass Spectrometer (Q‐AMS or simply AMS) and a particle‐into‐liquid sampler (PILS) coupled to ion chromatography from field intensives at two sites: an urban site in New York City (Queens College; QC) for wintertime (22 January to 5 February 2004) and a rural site in southwestern New York state (Pinnacle State Park; PSP) for summertime (18 July to 6 August 2004). In this study, we report that in rural atmospheres the inorganic nitrate signal from Q‐AMS may contain significant interferences from organic signals. Analysis of the QC data indicates a good agreement between the PILS‐nitrate and AMS‐nitrate measurements (R2 = 0.94; linear regression slope = 1.05). In addition, the m/z 30 and m/z 46 (two dominant ion fragments in nitrate mass spectrum) signals tightly correlate at QC (R2 = 0.98) and have an average ratio similar to that determined in the laboratory for NH4NO3 (m/z 30/m/z 46 = 2.4). In contrast, at the PSP site the correlation between PILS‐ and AMS‐nitrate was poor (R2 = 0.34), the AMS reported nitrate values were substantially higher, and the m/z 30 to m/z 46 ratios were generally much larger than 2.4. These observations, together with evaluations by aerosol phase ion balance, indicate that the AMS m/z 30 signals at PSP have been strongly influenced by organic compounds that also produce signals at m/z 30, e.g., organic nitrates (NO+), oxygenated organics (CH2O+), hydrocarbon‐like organics (C2H6+), and nitrogen‐containing organic compounds (CH4N+).

Angular momentum transport and disc morphology in smoothed particle hydrodynamics simulations of galaxy formation

We perform controlled N-body/smoothed particle hydrodynamics simulations of disc galaxy formation by cooling a rotating gaseous mass distribution inside equilibrium cuspy spherical and triaxial dark matter haloes. We systematically study the angular momentum transport and the disc morphology as we increase the number of dark matter and gas particles from 10 4 to 10 6 , and decrease the gravitational softening from 2 kpc to 50 pc. The angular momentum transport, disc morphology and radial profiles depend sensitively on force and mass resolution. At low resolution, similar to that used in most current cosmological simulations, the cold gas component has lost half of its initial angular momentum via different mechanisms. The angular momentum is transferred primarily to the hot halo component, by resolution-dependent hydrodynamical and gravitational torques; the latter arising from asymmetries in the mass distribution. In addition, disc particles can lose angular momentum while they are still in the hot phase by artificial viscosity. In the central disc, particles can transfer away over 99 per cent of their initial angular momentum due to spiral structure and/or the presence of a central bar. The strength of this transport also depends on force and mass resolution - large softening will suppress the bar instability, and low mass resolution enhances the spiral structure. This complex interplay between resolution and angular momentum transfer highlights the complexity of simulations of galaxy formation even in isolated haloes. With 10 6 gas and dark matter particles, disc particles lose only 10-20 per cent of their original angular momentum, yet we are unable to produce pure exponential profiles due to the steep density peak of baryons within the central kpc. We speculate that the central luminosity excess observed in many Sc-Sd galaxies may be due to star formation in gas that has been transported to the central regions by spiral patterns.

Measurement of charm flow with the STAR Heavy Flavour Tracker

In order to understand the partonic EOS of matter created at RHIC, one needs to study both the collectivity of the produced matter and the degree of thermalization. Anisotropic flow measurements have already demonstrated the development of partonic collectivity at RHIC (Ackermann K et al 2001 Phys. Rev. Lett. 86 402), and now it is necessary to address the issue of quark thermalization. Since the masses of the heavy flavour quarks are larger than the possible excitations of the system created in the collision, their collective motion could be used to indicate the degree of thermalization of the light flavour quarks (u, d, s). The Heavy Flavour Tracker (HFT), a tracking upgrade of the STAR experiment, is being designed to provide an unambiguous measurement of charm quark flow through the direct reconstruction of the D0. The current design of our detector uses a novel CMOS-based sensor, allowing for a low mass and high resolution detector element.