Comparison of Heated Electrospray Ionization and Nanoelectrospray Ionization Sources Coupled to Ultra-High-Resolution Mass Spectrometry for Analysis of Highly Complex Atmospheric Aerosol Samples.

Direct infusion analysis using soft ionization techniques coupled to ultra-high-resolution mass spectrometers (UHRMS) allows screening of thousands of organic species in complex samples. Despite the high analytical throughput of direct infusion, this technique is known to be prone to matrix effects caused by changes in the ionization efficiency of an analyte, ion suppression, or enhancement due to the presence of certain compounds and inorganic salts in the sample. In this study we compared two soft ionization sources, that is, heated electrospray ionization (HESI) and nano-ESI for the analysis of atmospheric aerosol samples in the negative ionization mode. In-source fragmentation tests were conducted and experiments involving sample desalting through solid-phase extraction (SPE) with a reversed phase functionalized polymeric sorbent and spiking samples with inorganic salt were performed. Both ionization sources showed specific advantages and disadvantages for the direct infusion analysis of atmospheric aerosol extracts. The mass spectra of aerosol samples analyzed using HESI contained a large number of high molecular weight homologues containing sulfur and nitrogen, suggesting that this source is prone to formation of salt adducts and noncovalent compounds in samples enriched with inorganic salts. Data from the same aerosol sample extracts analyzed using nanoelectrospray ionization (nano-ESI) show less adduct formation; however, a decrease in the number of homologues was observed, as well as loss of molecules at higher mass range, indicating that the nano-ESI source is more prone to ion suppression. Irrespective of ionization source, SPE pretreatment significantly improved ion recoveries for organic species with nonpolar and moderately polar functional groups, but lower recoveries were obtained for highly oxygenated molecules. Therefore, while SPE reduced in-source adduct formation, it also limited the range of compounds identified through a single analysis.

Mass and chemically speciated size distribution of Prague aerosol using an aerosol dryer--the influence of air mass origin.

Ambient aerosol particles dried using a diffusional aerosol dryer were sampled using a 7-stage modified Berner low pressure impactor with a back-up filter during the heating and non-heating season campaigns in 2008. The samples were analyzed for water-soluble ions and water-soluble organic carbon. Because of the drying, the aerosol size distribution was not influenced by the daily variability of ambient relative humidity. The results summarize the observations from campaigns in both the heating (11 sampling days) and non-heating (10 sampling days) seasons. The aerosols sampled on individual days were classified based on the connected air mass back trajectories into three classes: sea-influenced aerosol (SIA), continental aerosol (CA) and mixed aerosol (MA) for samples of intermediate origin. The differences between CA and SIA were substantial both when looking at the normalized mass size distributions of the particulate matter (PM) and of the individual species and when taking into account the absolute concentrations in the fine and coarse size fractions. The main differences were found in the normalized mass size distributions of the PM and of the sea-salt related ions.

Intercomparison of measurement techniques for black or elemental carbon under urban background conditions in wintertime: influence of biomass combustion.

A generally accepted method to measure black carbon (BC) or elemental carbon (EC) still does not exist. An earlier study in the Vienna area comparing practically all measurement methods in use in Europe gave comparable BC and EC concentrations under summer conditions (Hitzenberger et al., 2006a). Under summer conditions, Diesel traffic is the major source for EC or BC in Vienna. Under winter conditions, space heating (also with biomass as fuel) is another important source (Caseiro et al., 2007). The present study compares the response of thermal methods (a modified Cachier method, Cachier et al., 1989; a thermal-optical method, Schmid et al., 2001; and two thermal-optical (TOT) methods using Sunset instruments, Birch and Cary, 1996 and Schauer et al., 2003) and optical methods (a light transmission method, Hansen et al., 1984; the integrating sphere method, Hitzenberger et al., 1996; and the multiangle absorption photometer MAAP, Petzold and Schönlinner, 2004). Significant differences were found between the TOT methods on the one hand and all other methods on the other. The TOT methods yielded EC concentrations that were lower by 44 and 17% than the average of all measured concentrations (including the TOT data). The largest discrepancy was found when the contribution of brown carbon (measured with the integrating sphere method) was largest.

Determination of isoprene and alpha-/beta-pinene oxidation products in boreal forest aerosols from Hyytiälä, Finland: diel variations and possible link with particle formation events.

Biogenic volatile organic compounds (VOCs), such as isoprene and alpha-/beta-pinene, are photo-oxidized in the atmosphere to non-volatile species resulting in secondary organic aerosol (SOA). The goal of this study was to examine time trends and diel variations of oxidation products of isoprene and alpha-/beta-pinene in order to investigate whether they are linked with meteorological parameters or trace gases. Separate day-night aerosol samples (PM(1)) were collected in a Scots pine dominated forest in southern Finland during 28 July-11 August 2005 and analyzed with gas chromatography/mass spectrometry (GC/MS). In addition, inorganic trace gases (SO(2), CO, NO(x), and O(3)), meteorological parameters, and the particle number concentration were monitored. The median total concentration of terpenoic acids (i.e., pinic acid, norpinic acid, and two novel compounds, 3-hydroxyglutaric acid and 2-hydroxy-4-isopropyladipic acid) was 65 ng m(-3), while that of isoprene oxidation products (i.e., 2-methyltetrols and C(5) alkene triols) was 17.2 ng m(-3). The 2-methyltetrols exhibited day/night variations with maxima during day-time, while alpha-/beta-pinene oxidation products did not show any diel variation. The sampling period was marked by a relatively high condensation sink, caused by pre-existing aerosol particles, and no nucleation events. In general, the concentration trends of the SOA compounds reflected those of the inorganic trace gases, meteorological parameters, and condensation sink. Both the isoprene and alpha-/beta-pinene SOA products were strongly influenced by SO(2), which is consistent with earlier reports that acidity plays a role in SOA formation. The results support previous proposals that oxygenated VOCs contribute to particle growth processes above boreal forest.

New analytical method for the determination of levoglucosan, polyhydroxy compounds, and 2-methylerythritol and its application to smoke and rainwater samples.

Biomass burning is an important source of smoke aerosol particles, which contain water-soluble inorganic and organic species, and thus have a great potential of affecting cloud formation, precipitation, and climate on global and regional scales. In this study, we have developed a new chromatographic method for the determination of levoglucosan (a specific tracer for biomass burning particles), related polyhydroxy compounds, and 2-methylerythritol (recently identified as isoprene oxidation product in fine aerosols in the Amazon) in smoke and in rainwater samples. The new method is based on water extraction and utilizes ion-exclusion high-performance liquid chromatography (IEC-HPLC) separation and spectroscopic detection at 194 nm. The new method allows the analysis of wet samples, such as rainwater samples. In addition, aliquots of the same extracts can be used for further analyses, such as ion chromatography. The overall method uncertainty for sample analysis is 15%. The method was applied to the analysis of high-volume and size-segregated smoke samples and to rainwater samples, all collected during and following the deforestation fires season in Rondonia, Brazil. From the analysis of size-segregated samples, it is evident that levoglucosan is a primary vegetation combustion product, emitted mostly in the 0.175-1 microm size bins. Levoglucosan concentrations decrease below the detection limit atthe end of the deforestation fires period, implying that it is not present in significant amounts in background Amazon forest aerosols. The ratio of daytime levoglucosan concentration to particulate matter (PM) concentration was about half the nighttime ratio. This observation is rationalized by the prevalence of flaming combustion during day as opposed to smoldering combustion during night. This work broadens the speciation possibilities

Characterization of novel di- and tricarboxylic acids in fine tropical aerosols.

Three unknown di- and tricarboxylic acids were characterized in the fine size fraction of aerosols which were collected during the wet season in the Amazon basin (Rondonia, Brazil). For the structural characterization of the methyl esters of these unknown compounds, mass spectrometry with electron ionization (EI) and tandem mass spectral techniques combined with gas chromatographic (GC) separation were employed. Fragment and parent ion spectra were recorded during elution of the GC peaks by linked scanning of the B and E sectors in combination with high-energy collision-induced dissociation. The fragmentation patterns of significant ions in the first-order EI spectra were also obtained for nonanedioic acid, which was examined as a model compound. The compounds were tentatively identified as 4-acetyloxyheptanedioic acid and cis and trans isomers of 5-hexene-1,1,6-tricarboxylic acid. Since there were indications of biomass burning during the aerosol sampling the di- and tricarboxylic acids characterized in the present work could be markers for biomass burning. Furthermore, the characterization of di- and tricarboxylic acids in the fine size fraction of atmospheric aerosols may be important for assessing the effects of organic aerosols in cloud formation.

Transport of traffic-related aerosols in urban areas.

This study was undertaken to assess the influence of traffic on particulate air pollution in an urban area, and to characterise the short-range transport of the aerosols generated by traffic. The study was conducted in Kraków, a city located in southern Poland with a population of approximately 800,000. Aerosol samples were collected using automatic sampling equipment at five sites located at different distances from the main road in Kraków, ranging from 5 to 1500 m. The sampling set-up allowed standardisation of the results due to continuous determination of the meteorological parameters (temperature, atmospheric pressure, wind speed and direction, rainfall and humidity). Aerosol particles were separated according to aerodynamic diameter into two size fractions: > 1.9 microm (coarse fraction); and 1.9-72 microm (fine fraction). The concentrations of 27 elements were measured in both size fractions (Na, Mg, Al, Si, P, S, Cl, K, Ca, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, Ga, Ge, As, Se, Br, Rb, Sr, Zr, Ba, Pb). The multielement analyses were performed by Particle-Induced X-ray Emission (PIXE) spectrometry. Traffic contribution to particulate air pollution was determined on the basis of 13 elements which were present above the detection limit in all samples (Mg, Al, Si, P, S, K, Ca, Ti, Mn, Fe, Cu, Zn, Pb). It was found that the traffic contribution in the coarse size fraction was approximately 80% up to 150 m from the road; it dropped abruptly by a factor of 2 over a distance of 150-200 m and declined further to 20% at 1500 m from the road. Traffic contribution for the fine particle concentrations of individual elements was 50-70% in the close vicinity of the road (5 m); then there was a decrease, followed by an increase at a greater distance from the road. Possible explanations for this behaviour of the fine particles are given.

Comparison between levels of trace elements in normal and cancer inoculated mice by XRF and PIXE.

Determination of Rb, Br, Se, Zn, Cu, Fe, and Br/Rb ratio in tissues of mice inoculated with colon and melanoma cancer cells is described. A group of 19 Balb/c mice inoculated with C26 colon carcinoma, 4 C57B1/6 mice inoculated with B16 melanoma, and 13 control mice of both kinds were under investigation. The study was conducted on samples of blood, liver, kidneys, colon, and skin, and the trace element levels in normal and inoculated mice were compared. The inoculation was by subcutaneous injection either at the back or intrafootpad. The blood samples were taken 1, 2, and 3 wk after inoculation, and after 4 wk all the animals were sacrificed. Two nondestructive, complementary analytical methods were used: a modified X-ray fluorescence (XRF) for solid tissue and particle-induced X-ray emission (PIXE) for blood samples. The detection limit (DL) in the PIXE method was 0.35 microg/g dry wt in 600 s counting time and in XRF, 1 microg/g dry sample for Rb, Br, Se and Zn and 2 microg/g for Cu and Fe in 200 s counting time. In all the cases studied, cancerous tissue developed at the site of the injection, and a significant difference in the trace element levels was observed between tissue samples obtained from normal and inoculated mice. The most pronounced effect was an increase in Rb level in the tumor by a factor ranging between 4 and 10 relative to normal tissue, with a corresponding decrease in the Br/Rb ratio (p < 0.05). Smaller changes were found in the Br, Se, Zn, and K levels. The changes in trace element levels in the inner organs were much smaller and seem to be influenced by the site of injection.

Br, Rb, Zn, Fe, Se and K in blood of colorectal patients by INAA and PIXE.

A preliminary study was conducted on blood samples and blood fractions of 11 colorectal patients and 10 healthy subjects (controls) in Belgium, in order to determine the concentration of some vital trace elements. Two non destructive analytical methods were used for the determination: INAA and PIXE. The agreement between PIXE and INAA was within about +/- 10% for plasma, but for Rb, Se and Fe in whole blood and red cells a difference of +/- 20% was noted; part of the discrepancy may be due to self absorption problems in PIXE, and for Rb, spectral interferences also may have contributed. The precision of the INAA method for the elements studied was found to be +/- 3% for whole blood and red cells and +/- 5% for plasma; the accuracy for Br, Rb and Zn was better than +/- 10% and +/- 17% for Se. The ratios of the concentrations in whole blood to red cells and whole blood to plasma were not significantly different for normals and cancer cases and, therefore, in future studies analysis of whole blood only may be sufficient. The mean values for Br, Rb, Br/Rb ratio, K, Fe and Se were significantly lower for cancer cases than for healthy individuals, and this might be applicable as an additional parameter for differentiating normals from malignant cases.

Effect of neurotropin on cerebral edema, calcium and other elements in mice subarachnoidally injected with carrageenan.

Neurotropin, an inhibitor of the kallikrein-kinin system, was therapeutically i.p. administered to mice with brain inflammation induced by subarachnoidal injection of carrageenan. Brain water content was determined by the wet/dry weight ratio. The concentrations of cerebral Ca, K, Mn, Fe, Cu, Zn, Se, Rb, and Sr were measured by particle-induced X-ray emission. It was found that neurotropin dose dependently reduced brain water content. The mean concentration of cerebral calcium was significantly lower in the neurotropin-treated group than that in the non-treated group, suggesting less cell damage. Since it has been reported that dexamethasone and some prostaglandin inhibitors have no effect on brain swelling in this model and that, in contrast to these drugs, neurotropin has only a weak inhibiting activity on carrageenan-induced paw swelling, it is hypothesized that the kallikrein-kinin system is differently implicated in cerebral and peripheral inflammation.

Trace element alterations in rat tissues induced by the hepatotoxic agent CCl4.

An acute or chronic intoxication by i.p. injection of CCl4 was used to induce liver injuries (liver necrosis, steatosis and cirrhosis) in rats. Liver, kidneys and blood serum were collected from the experimental animals and from controls. The tissues were analyzed by particle-induced X-ray emission analysis (PIXE) for up to 12 elements (i.e., K, Ca, Mn, Fe, Cu, Zn, As, Se, Br, Rb, Sr and Mo). The acute intoxication (leading to necrosis and steatosis) caused definite alterations of many trace element levels. The alterations were most pronounced in the liver, as expected. In this organ, Ca exhibited a strongly increased concentration. Important alterations for the elements K, Zn and Se were also observed.

Applicability of microwave acid digestion to sample preparation of biological materials for analysis by particle-induced X-ray emission (PIXE).

A microwave acid digestion method for the preparation of biological samples for PIXE analysis is presented. The precision and accuracy of the entire PIXE analytical procedure, including the microwave digestion step, were evaluated by analyzing eight certified reference materials. For elements heavier than K, and for concentration levels from 2 micrograms/g upward, the total random error of a single analysis is in the range of 2-5%. The accuracy is better than 5%. The detection limits are down to 0.3 micrograms/g.

Multielement analysis of biological materials by particle-induced X-ray emission (PIXE).

An analytical particle-induced X-ray emission (PIXE) procedure for the multielement analysis of biological materials consists of various stages. These include sample and specimen preparation, specimen bombardment, spectral data processing, quantification and correction for matrix effects. Critical aspects of the procedure are contamination and/or losses during sample and specimen preparation and the danger of radiation or heat-induced losses during specimen bombardment. With optimized PIXE procedures precisions of 1-2% and an accuracy of better than 5% are obtainable, whereas the detection limits are down to 0.1 microgram/g. Because of its inherent characteristics, PIXE offers great potential for trace element analysis in the biological and medical fields, and this is demonstrated through selected examples of applications.

Regional distribution of potassium, calcium, and six trace elements in normal human brain.

Eight elements (i.e. K, Ca, Mn, Fe, Cu, Zn, Se, and Rb) were measured in 50 different regions of 12 normal human brains by particle-induced X-ray emission (PIXE) analysis. The dry weight concentrations of K, Fe, Cu, Zn, Se, and Rb were consistently higher for gray than for white matter areas. The K, Zn and Se concentrations for the regions of mixed composition and, to some extent, also the Rb concentrations, were intermediate between the gray and white matter values, and they tended to decrease with decreasing neuron density. The mean dry weight concentrations of K, Ca, Zn, Se, and Rb in the various brain regions were highly correlated with the mean wet-to-dry weight ratios of these regions. For Mn, Fe, and Cu, however, such a correlation was not observed, and these elements exhibited elevated levels in several structures of the basal ganglia. For K, Fe, and Se the concentrations seemed to change with age. A hierarchical cluster analysis indicated that the structures clustered into two large groups, one comprising gray and mixed matter regions, the other white and mixed matter areas. Brain structures involved in the same physiological function or morphologically similar regions often conglomerated in a single subcluster.

Application of PIXE analysis to the study of the regional distribution of trace elements in normal human brain.

A particle-induced X-ray emission (PIXE) analysis method is presented, which allows measurement of eight elements (i.e., K, Ca, Mn, Fe, Cu, Zn, Se, and Rb) in human brain samples of only a few mg dry weight. The precision and accuracy of the method were investigated by analyzing animal brain matter with both PIXE and instrumental neutron activation analysis (INAA). The method was applied to measure the 8 elements in 46 different regions of 3 human brains. The sections analyzed originated from either the left or the right cerebral hemisphere, brain stem, and cerebellum. For one of the brains, sections were also analyzed from 26 corresponding regions of both hemispheres. For all elements, similar concentrations were found in the corresponding areas of the left and right sides of the brain. The concentrations (in µg/g dry weight) of the elements K, Fe, Cu, Zn, Se, and Rb were consistently higher in cortical structures than in white matter. Deep nuclei and brain stem, which have a mixed composition, showed intermediate values for K, Zn, Se, and Rb. A hierarchical cluster analysis indicated that the various brain regions clustered into two large groups, one comprising gray and mixed matter regions and the other, white and mixed matter brain areas.

Internal mixture of sea salt, silicates, and excess sulfate in marine aerosols.

Individual aerosol particles from the remote marine atmosphere were investigated by scanning electron microscopy and electron microprobe analysis. A large fraction of the silicate mineral component of the aerosol was found to be internally mixed with sea-salt aerosol particles. This observation explains the unexpected similarity in the size distributions of silicates and sea salt that has been observed in remote marine aerosols. Reentrainment of dust particles previously deposited onto the sea surface and collision between aerosol particles can be excluded as possible source mechanisms for these internally mixed aerosols. The internal mixing could be produced by processes within clouds, including droplet coalescence. Cloud processes may also be responsible for the observed enrichment of excess (nonsea-salt) sulfate on sea-salt particles.

Selenium, zinc, and copper changes with valproic acid: possible relation to drug side effects.

Side effects of treatment with the anticonvulsant valproic acid (VPA) suggested the possibility of alteration of trace metal status. Administration of VPA for 1 week produced significant depletion of zinc and selenium in plasma of rats and a one-third reduction of hepatic selenium. Patients who were treated chronically, with VPA as the sole anticonvulsant medication, had decreased plasma selenium levels. Most cases of VPA-associated hepatotoxicity occur in children. This could be due to decreased selenium concentrations when mechanisms for protection against peroxidative damage are not fully developed.

Variance analysis of error in selected ion monitoring assays using various internal standards. A practical study case.

This study contains a practical application of variance analysis for the evaluation of precision in selected ion monitoring using stable isotope variants or chemically related compounds as internal standards. Variance analysis is applied to determine the relative contributions of the errors due to long-term and short-term effects of instrument stability. The technique allows the resolution of variance due to sample manipulation from that introduced by the gas chromatography mass spectrometry instrumentation. This provides an objective measure of potential internal standards. Evaluation of the dependency of these errors upon concentration indicates appropriate weighing factors to be applied for regression analysis.