Previous measurements of hydroxyacetone and glycolaldehyde concentrations have been made using a range of analytical techniques. The most common of these involve ambient sample collection, derivatization with a chemical agent, separation of compounds, and detection by HPLC, GC-MS, or GC-FID (Lee et al., 1993, 1995; Zhou et al., 2009; Moortgat et al., 2002; Spaulding et al., 2003; Matsunaga et al., 2003). Two shortcomings of these techniques are the intensive sample processing required and the time lag between sample collection and concentration measurement. In contrast, both single quadrupole and triple quadrupole (tandem) chemicalionizationmassspectrometry en- able online, fast, in situ measurements with no sample processing. In these techniques, the ambient sample enters the instrument directly and reaches the detector in less than one second, enabling immediate detection of these compounds. The Caltech single quadrupole and tandem chemicalionizationmass spectrometers are equally capable of quantifying hydroxyacetone, an analyte with minimal known isobaric interferences. The Caltech tandem chemicalionizationmass spectrometer enables direct separation of mass analogues glycolaldehyde and acetic acid.
trations only started to decrease at sunset (at 19:30 EDT) in this study. This suggests that there may be differences in the types and/or magnitudes of formic acid sources and sinks in these two field studies. Land cover and/or land use dif- ferences may have contributed to differences in formic acid sources and sinks at the Centreville and Yorkville field sites. The area surrounding the Yorkville field site is covered pri- marily by hardwood mixed with farmland and open pastures. In contrast, the Centreville field site is surrounded by forests comprised of mixed oak–hickory and loblolly trees (Hansen et al., 2003). It is also possible that seasonal differences con- tributed to differences in formic acid sources and sinks in the two field studies. The SOAS campaign took place in the middle of summer (1 June to 15 July 2013) when biogenicemissions are typically higher, while this field study took place in early fall when biogenicemissions are lower due to cooler temperatures. For example, the average concentration of isoprene (a formic acid source) in this study (1.21 ppb) is lower than that in SOAS (1.92 ppb; Millet et al., 2015). De- spite these differences, our overall results are similar to the formic acid measurements performed in SOAS in both mag- nitude and diurnal variability.
acid mixing ratios were observed at ∼ 1000 m; although this could arise from intercepting polluted plumes at higher al- titudes only, it may also signal the presence of a significant secondary source of formic acid within the plume. Formic acid levels as estimated by a trajectory model showed an un- derprediction of concentrations by up to a factor of 2. The model discrepancy can be resolved by the addition of 1- alkene surface emissions that are oxidised to produce formic acid in situ or by addition of a direct emission of HCOOH. Whether the source of the 1-alkene is of anthropogenic or biogenic origin is unclear. More measurements and in-depth modelling studies are needed to validate the current chem- ical transport models and help identify and quantify formic acid emission sources. This should also improve understand- ing of the role of formic acid in chemical cycling in the tro- posphere. Direct measurements of formic acid in the UK boundary layer have shown how variable formic acid lev- els can be, and that distinct plumes of formic acid can be identified in the horizontal and vertical. The inability of the model to reproduce the observations in the part of the flight before ca. 02:00 p.m. highlights that further studies must aim to improve the understanding and quantification of formic acid sources.
al., 2014). We compare the resulting sum total mass load- ings of all molecular components with the submicron or- ganic aerosol mass concentrations measured by an aerosol mass spectrometer (AMS) (DeCarlo et al., 2006). Applying the collision-limited sensitivity to all organic–iodide adducts to which we have not explicitly calibrated (vast majority of ions) results in a lower limit to mass concentrations measured by the FIGAERO HR-ToF-CIMS. Figure 5 shows the re- sult of this comparison for two different locations: (1) a pol- luted region in the southeast United States (Brent, Alabama), which is dominated by isoprene, and (2) a remote boreal for- est site (Hyytiälä, Finland) during springtime which is pre- dominantly influenced by monoterpene emissions. In both locations, the FIGAERO-HRToF-CIMS molecular composi- tion observations explain at least 50 % of the total AMS or- ganic mass. That is, based on our declustering scans and dis- tribution of binding enthalpies (e.g., Fig. 3c) from a similar chemical system (e.g., α-pinene ozonolysis in the presence of NO x ), we know that not all organic compounds are de-
al., 1995). The emission rate and the chemical composition of emitted BVOCs is a complex function of the vegetation species and the wide array of stress factors that it is exposed to (Hallquist et al., 2009; Lang-Yona et al., 2010; Zhao et al., 2017). Atmospheric oxidation of BVOCs results in the for- mation of low-volatility compounds that can lead to new par- ticle formation (Jokinen et al., 2015; Kirkby et al., 2016) and particle growth through secondary organic aerosol formation (Allan et al., 2006; Wiedensohler et al., 2009). Both of these processes impact Earth’s radiative budget by scattering so- lar radiation and/or altering cloud formation and precipita- tion (Chung et al., 2012). The contribution of different types of BVOCs (e.g., isoprene, MTs and SQTs) to secondary or- ganic aerosols (SOA) differ significantly (Zhao et al., 2017). Therefore, uncertainties in BVOCs emissions present signifi- cant issues in estimating net climate forcing (Kerminen et al., 2005; Kulmala et al., 2004). Identification of the chemical composition of the emitted BVOCs and quantification of the surface exchange rates of these compounds are essential for understanding complex and nonlinear biosphere–atmosphere interactions.
Fishes, salt water fishes in particular, are rich in polyun- saturated fatty acids (PUFA, mainly DHA and ei- cosapentaenoic acid (EPA)), and their worldwide con- sumption has increasingly expanded year by year be- cause of their beneficial effects in human health. Drying fish under sunlight for their preservation and flavor gen- eration is a traditional practice in many countries in the world. In this process, oxidatively vulnerable PUFA should naturally decompose to afford many degradation products including toxic aldehydic products with highly unpleasant odors. Against our expectation, dried fishes usually have appetizing flavor especially when they are baked. This apparent contradiction has long remained unexplained. Our synthetic phospholipid molecular probe 5 having docosahexaenoyl group has been used to inves- tigate this problem . The molecular probe was ap- plied on the surface of herring fillets and dried over one week under the sunlight. The lipid fraction was extracted from the surface of the dried fish and the extract was directly subjected to electrospray ionizationmass spec- trometry in precursor ion scan mode at 491 m/z as a product ion. The spectrum is shown in Figure 5. A signal at this m/z 582.7 was assigned as a hydrolytic fragment 18. Also, a signal at m/z 524.8 was assigned as another hydrolytic fragment, lyso-PC 19. In addition to these signals, a number of small signals were observed, and we tried to assign the structures based on m/z and oxidative fragmentation mechanism of DHA. The deduced struc- tures from the spectrum were given as compounds 20-23 (Scheme 5). It is well known that processed fishes have amino compounds such as those shown in Scheme 6. It is also known that the oxidation of polyunsaturated fatty acids like DHA affords various aldehydes, most of which have unpleasant odor. On the basis of chemistry, amines
The performance of the Bruker Biotyper matrix-assisted laser desorption ionization–time of flight (MALDI- TOF) mass spectrometer (MS) for the identification of dermatophytes from clinical cultures was compared to that of dermatophyte identification using 28S rRNA gene sequencing. The MALDI Biotyper library (MBL; version 3.0) was used alone and in combination with a supplemented library containing an additional 20 dermatophyte spectra (S-MBL). Acquired spectra were interpreted using both the manufacturer-recommended scores (genus, >1.7; species, >2.0) and adjusted cutoff values established by this study (genus, >1.5; species, >1.7); identifications required a minimum 10% difference in scores between the top two different organisms to be considered correct. One hundred well-characterized, archived dermatophyte isolates and 71 fresh dermato- phyte cultures were evaluated using both libraries and both sets of cutoff criteria. Collectively, the S-MBL significantly outperformed the MBL at both the genus (93% versus 37.4%; P < 0,0001) and species (59.6% versus 20.5%; P < 0.0001) levels when using the adjusted score criteria. Importantly, application of the lowered cutoff values significantly improved genus (P ⴝ 0.005)- and species (P < 0.0001)-level identification for the S-MBL, without leading to an increase in misidentifications. MALDI-TOF MS is a cost-effective and rapid alternative to traditional or molecular methods for dermatophyte identification, provided that the reference library is supplemented to sufficiently encompass clinically relevant, intraspecies strain diversity.
Abstract. Volatilization and subsequent processing in the at- mosphere are an important environmental pathway for the transport and chemical fate of pesticides. However, these pro- cesses remain a particularly poorly understood component of pesticide lifecycles due to analytical challenges in measuring pesticides in the atmosphere. Most pesticide measurements require long (hours to days) sampling times coupled with offline analysis, inhibiting observation of meteorologically driven events or investigation of rapid oxidation chemistry. Here, we present chemicalionization time-of-flight massspectrometry with iodide reagent ions as a fast and sensi- tive measurement of four current-use pesticides. These semi- volatile pesticides were calibrated with injections of solu- tions onto a filter and subsequently volatilized to generate gas-phase analytes. Trifluralin and atrazine are detected as iodide–molecule adducts, while permethrin and metolachlor are detected as adducts between iodide and fragments of the parent analyte molecule. Limits of detection (1 s) are 0.37, 0.67, 0.56, and 1.1 µg m −3 for gas-phase trifluralin, meto- lachlor, atrazine, and permethrin, respectively. The sensitivi- ties of trifluralin and metolachlor depend on relative humid- ity, changing as much as 70 and 59, respectively, as relative humidity of the sample air varies from 0 to 80 %. This mea- surement approach is thus appropriate for laboratory experi- ments and potentially near-source field measurements.
where m SBSE is the mass of analyte in the sorbent and m o is the mass of the analyte in solution. For a speciﬁc sample in a known volume with a stable value for β, the extraction eﬃciencies of an analyte are positively correlated with the K o/w values, which are constant to speciﬁc compounds . Nonetheless, equation (E1) is only valid when the equilib- rium has been reached and it is diﬃcult to reach the theo- retical extraction eﬃciency in equation (E1) for a complex solution containing several analytes due to their diﬀerent equilibrium times. Therefore, extractions under equilibrium conditions are not always possible and compromise condi- tions have to be set. For the SBSE technique, extraction time, stirring rate, pH value, ionic strength, desorption solvent, and desorption time can aﬀect the equilibrium and extraction eﬃ- ciency. To achieve optimal extraction eﬃciency, the above factors have been investigated and optimized based on the performances in the dominant carbonyls in rainwater includ- ing GLY, MGLY, formaldehyde, ethanal, acetone, 2-hydroxy ethanal, and isobutenal.
Aminoglycosides are broad-spectrum antibiotics often employed to combat Gram-negative bacterial infections. A technique based on electrospray-ionizationmassspectrometry (ESI-MS) was developed for rapid determination of aminoglycosides. This method, which does not require prior chromatographic separation, or derivatization and extensive sample preparation steps, was deployed to estimate gentamicin, tobramycin, and amikacin in pharmaceutical formulations. Upon gas-phase collisional activation, protonated gentamicin, tobramycin, and amikacin undergo a facile loss of their respective “ C ” ring moiety to produce characteristic ions of m/z 322, 324, and 425, respectively. The mass spectral peak intensities for these specific product ions were monitored either by a flow-injection analysis selected-ion monitoring (FIA-SIM) time-intensity method or by a mass spectrometric internal- standard method. The linear dynamic ranges of detection for both methods were evaluated to be 10 – 1000 ng/mL for gentamicin, 25 – 2500 ng/mL for tobramycin, and 10 – 1000 ng/mL for amikacin. The internal-standard mass spectrometric method afforded lower intra-day and inter-day variations (2.3 – 3.0% RSD) compared to those from FIA-SIM method (4.5 – 5.0% RSD). This method was applied as a potential alternative procedure to determine gentamicin in commercial pharmaceutical samples and to monitor the release of gentamicin from “ self-defensive ” tannic acid-based layer-by-layer films into phosphate buffer solutions at different pHs.
The multi-sprayer nESI experiments were conducted using a home-built source consisting of two nESI sprayers secured to an X-Y-Z translational stage. The sprayers were each at an angle of 5° with respect to and ~ 1.5 mm off of the axis of the flared inlet capillary. For clarity, the names left sprayer and right sprayer will be used throughout the paper to refer to the side of the transfer capillary that the sprayer is situated on when looking down onto the XZ-plane. A positive x-position will refer to the right side of the transfer capillary. Both sprayers were immobilized on the translational stage such that any movement of the staging mechanism resulted in both sprayers being repositioned concurrently. The sprayers are constructed from Swagelok 1/4” to 1/16” reducing unions which accept 0.060” O.D. x 0.045” I.D. glass capillaries (Drummond Scientific Company, Broomall, PA) that were pulled at one end to ~ 4 µm using a Narishige model PP-830 dual stage glass electrode puller (Narishige International USA, Inc., Easy Meadow, NY). nESI solutions were injected into the pulled sprayer through the non-tapered end. Electrical contact is made with the nESI solution via a platinum wire inserted into the open end of the sprayer which is in contact with the Swagelok body; spray is initiated and maintained through the applied voltage without any pneumatic assistance. Separate, independent EMCO supplies are connected to the Swagelok reducing unions such that the sprayers were electrically isolated from each other. Both sprayers were positioned 1-2 mm from the entrance of the flared inlet capillary and its metal mesh-cap.
(n = 0,1) ions (PTR-MS). The instrument is a modified ver- sion of the PTR3 with a helical tripole reaction chamber and a long-time-of-flight mass spectrometer (Tofwerk AG, Switzerland), and it can be used for measurements of organic molecules in both gas and particle phases. Here we discuss the performance of the new instrument and compare the two detection modes. We demonstrate a mass spectrometric volt- age scanning procedure which is based on collision-induced dissociation that allows for the determination of the stabil- ity of detected ammonium–organic clusters. With this tech- nique, we can experimentally estimate sensitivities of the NH + 4 CIMS to the vast array of oxygenated organic com- pounds without their direct calibration in a matter of minutes. Finally, we present how this procedure can be applied to the measurement of organic aerosol composition in laboratory experiments.
(HNCO). While HONO and HNCO are pyrolysis and com- bustion products of emerging interest, all four of these acid species present a challenge for atmospheric chemical anal- ysis (Sipin et al., 2003). Calibrations and inlet tests were performed under varied water vapor concentrations in order to assess the response of the method to this important param- eter. The system was used to measure acids emitted from burning biomass under laboratory conditions. The inlet sys- tem used for those measurements was tested for transmis- sion/loss of species and the attendant equilibration time con- stants were measured. Possible interferences from secondary ion chemistry were estimated for high concentration condi- tions encountered in some experiments. The HONO mea- surements were compared with open-path FTIR measure- ments made at the same time.
surements were performed at an urban site 2 m above the ground level. b The Georgia Tech-CIMS was also used for the ANARChE and intercomparison with the early version of NOAA-CIMS was made. c This upgraded NOAA-CIMS for aircraft measurements was used in the New England Air Quality Study–Intercontinental Transport and Chemical Transformation (NEAQS-ITCT) mission. d The CIMS instrument was used at 1.2 m above a grass field treated with fertilizer in Oensingen, Switzerland. e This CIMS instrument was used in southern Scotland during the intercomparison experiments with a large number of NH 3 instruments. f The KSU-CIMS was used in ambient NH 3 measurements in Kent, Ohio (this study) and in Northern Michigan forests in summer 2009 (Kanawade et al., 2010). g Straight sampling occurred when the flow path from the tip of the inlet (where ambient air enters) through the 3-way valve and to the CIMS was all straight and no bending occurred. Bent sampling occurred when the ambient air enters the 3-way valve perpendicular to the flow that went into the CIMS as shown in Fig. 1b. h Heating was only performed for the fall measurements. i 100 cm was the total length when taking ambient measurements (including the depth of the wall, 50 cm). j This time was estimated based on the flow rate through the inlet and the inlet tubing dimensions (inner diameter and length). k Residence time for the ambient measurement mode. l This time was estimated based on the flow rate through the CIMS flow tube and the CIMS inlet dimensions (inner diameter and length).
Rondo, L., Ehrhart, S., Kürten, A., Adamov, A., Bianchi, F., Breitenlechner, M., Duplissy, J., Franchin, A., Dommen, J., Donahue, N. M., Dunne, E.M., Flagan, R. C., Hakala, J., Hansel, A., Keskinen, H., Kim, J., Jokinen, T., Lehtipalo, K., Leiminger, M., Praplan, A., Riccobono, F., Rissanen, M. P., Sarnela, N., Schobesberger, S., Simon, M., Sipilä, M., Smith, J. N., Tomé, A., Tröstl, J., Tsagkogeorgas, G., Vaatto- vaara, P., Winkler, P. M., Williamson, C., Wimmer, D., Bal- tensperger, U., Kirkby, J., Kulmala, M., Petäjä, T., Worsnop, D. R., and Curtius, J.: Effect of dimethylamine on the gas phase sulfuric acid concentration measured by ChemicalIonizationMassSpectrometry, J. Geophys. Res. Atmos., 121, 3036–3049, doi:10.1002/2015JD023868, 2016.
the calculated detection limit, we report the 3 σ uncertainty of 23 pptv for the collection of all background determina- tions made over the course of a 24 h sampling period. In most cases, uncertainty in the background count rate varies slowly in time and an accurate representation of the uncer- tainty can be taken as the 3 σ uncertainty of successive zero determinations. To illustrate this point, we sample UHP zero air for 5 min and calculate the 3 σ uncertainty in the zero de- termination, from a Gaussian fit to the observations. At the background count rate measured here (3 × 10 4 ions s −1 ), the variability in the background can be assessed using Gaus- sian statistics, as there is little difference between Gaussian and Poisson statistics at high count rates. For measurements made during CalNex, we calculate a 3 σ and 10 σ value of 4 pptv and 13 pptv, respectively (for 1-s averages). The 3 σ value of 4 pptv is representative of our measurements dur- ing CalNex, and indicates that if we were to characterize the background at five-minute intervals during field obser- vations, a detection limit of 4 pptv (with 1-s averaging) can be achieved. For comparison, the distribution of measured count rates for five minutes of sampling in both remote and polluted air masses are shown in Fig. 5, indicating that the detection limit is well below the atmospheric abundance of formic acid even in pristine conditions. The concentrations reported in Fig. 5, for clean marine air (50–100 pptv) and off- shore pollution (650–850 pptv) are within the range of val- ues reported in the literature for measurement of formic acid concentrations in urban areas (1–10 ppbv) and remote con- tinental and marine areas (<1 ppbv) (Grosjean et al., 1990; Keene et al., 1989; Paulot et al., 2011; Veres et al., 2008). At present, the formic acid detection limit is limited by the magnitude and variability in the background. We are focus- ing our current efforts on reducing this and expect that future versions of the instrument will have significantly improved detection limits as a result.
electrospray carrier solvent in the positive ion mode. The mass spectrometer was calibrated using sodium iodide (NaI). Settings: scan = 500-4000 m/z; rolling average = 2; nebulizer = 2 bar; dry gas = 180°C @ 6.0 L/min; capillary = 4000 v; end plate offset = -500 V; capillary exit = 175 V; Skimmer 1 = 30.0 V; Skimmer 2 = 23.5 V; Hexapole RF = 800 V. The flow rate of the protein solution was 10 µL/min. ESI-MS spectra were recorded for two minutes and the Maximum Entropy application of the Bruker Compass Data Analysis software package was used to deconvolute the spectra.
A new Thermal IonizationMass Spectrometer (TIMS) analytical procedure was developed to measure with high accuracy the zirconium isotope abundance and concentration without molybdenum correction in nuclear samples. A zirconium selective separation using UTEVA column was used before the TIMS measurement in order to remove all possible isobaric interferences (Mo, Y, Nb and Ru) in the solution. The separated solution was then deposited onto a filament previously outgassed for 4 hours to reduce the molybdenum traces in the filament. Then, the filament was introduced into the TIMS source and was maintained for 4 hours at a current of 5 A (ionization filament) and 1.2 A (evaporation filament) in order to eliminate all molybdenum trace present in the filament and in the sample. This methodology allowed the zirconium isotope abundance determination without using the molybdenum interference correction equation. The analytical results obtained with a natural solution after separation is in good accordance with the reference values: bias lower than 0.16 % for the 90 Zr,
putative metabolite allocation to ESI-TOF-MS outputs can enable visualisation of metabolic blocks in C. jejuni amino-acid metabolism mutants (1). ESI-TOF-MS techniques are advantageous over other techniques such as NMR when attempting a non- targeted analysis, due to their far higher sensitivity; however the absence of a chromatographic step makes unambiguous metabolite identification impossible. Li et al. (6), has since built on the DIMS fingerprinting techniques in (1) by separating and identifying the key metabolites of antibiotic resistant mutants of C. jejuni using UHPLC-MS. For this reason it is important that DIMS techniques are used as a Ôfirst stepÕ for hypothesis formation towards the function of putative metabolic genes before rigorous metabolite identification or phenotypic analysis is performed. The potential for analysing altered metabolic fluxes as organisms experience different conditions, such as changes to temperature or growth phase, also exists (7).