Martinez-Lozano P.,National Research Council Italy |
Journal of the American Society for Mass Spectrometry | Year: 2010
Sarcosine, an isomer of L-alanine, has been proposed as a prostate cancer progression biomarker . Both compounds are detected in urine, where the measured sarcosine/alanine ratio has been found to be higher in prostate biopsy-positive group versus controls. We present here preliminary evidence showing that urine samples spiked with sarcosine/alanine can be partially resolved in 3 min via tandem differential mobility analysis-mass spectrometry (DMA-MS). Based on the calibration curves obtained for two mobility peaks, we finally estimate their concentration ratio in urine. © 2010 American Society for Mass Spectrometry.
Vidal-De-Miguel G.,SEADM |
De La Mora J.F.,Yale University
Aerosol Science and Technology | Year: 2012
All known multi-stage aerodynamic lenses able to focus sharply a wide range of particle sizes include decelerating regions where the flow becomes turbulent at Reynolds numbers Re typically of 100 or less. Here, we propose a design for a focusing concentrator operating laminarly at Re of many thousands. The particles are accelerated by the gas through a continuously converging ladder of smooth contractions, each designed such that: (1) the flow remains laminar at substantial Re; (2) a certain band of particle sizes is focused in each contraction, without substantial defocusing of larger particle focused in 1 or several preceding contractions; (3) the form, length, and ratio of entry to exit diameter of each contraction, as well as the number of consecutive contractions are chosen such that all particles within a given relatively wide range of sizes are focused at the end of the ladder of contractions into a relatively narrow focal region. The focusing virtual impactor formed by coupling this device to a perforated surface could provide a powerful particle concentrator. © 2012 Copyright Taylor and Francis Group, LLC.
Attoui M.,University Paris Est Creteil |
Paragano M.,Yale University |
Cuevas J.,SEADM |
De La Mora J.F.,Yale University
Aerosol Science and Technology | Year: 2013
Generation of monomobile molecular standards by electrospray (ES) followed by classification in a differential mobility analyzer (DMA) fails at diameters above ∼2 nm because many clusters in different charge states z crowd in a narrow mobility range. Use of a second DMA (DMA2) in series (tandem) with DMA1 is very helpful because, unexpectedly, many multiply charged ions selected in DMA1 undergo spontaneous transitions, appearing as pure species at different mobilities in DMA2. Remarkably, for salt clusters of composition (CA)n(C+)z carrying z elementary charges and n neutral ion pairs, (i) ion evaporation (CA)n (C +)z →(CA)n-1(C+) z-1+(CA)C+ and (ii) neutral evaporation transitions (CA)n (C+)z →(CA)n-1(C +) z+CA affect a substantial fraction of the clusters. Neutral evaporation (fueled by the Kelvin effect) is effective in isolating singly charged clusters, yielding mobility standards easily exceeding 2 nm. Ion evaporation (fueled by large electric fields) produces even larger well-resolved standards. Singly charged clusters of up to 2.5 nm rising in isolation result from metastable doubly charged parent ions (z = 2→1 transition). Isolated doubly charged ions of up to 3.5 nm arise from the z = 3→2 transition, but are harder to resolve from the products of higher initial charge states. We report tandem DMA measurements for electrosprayed nanodrops of two ionic liquids: EMI-Im and EMI-Methide, both based on the small cation EMI+ (1-Ethyl-3-methylimidazolium+) and two relatively large anions: Im- = (CF3SO2)2N-; Methide- = (CF3SO2)3C-. Some exploration on the effect of actively reducing the charge on the clusters as they pass between both analyzers is also included. © 2013 American Association for Aerosol Research.
Rawat V.K.,University of Minnesota |
Vidal-De-Miguel G.,SEADM |
Vidal-De-Miguel G.,ETH Zurich |
Hogan C.J.,University of Minnesota
Analyst | Year: 2015
Low field ion mobility spectrometry-mass spectrometry (IMS-MS) techniques exhibit low orthogonality, as inverse mobility often scales with mass to charge ratio. This inadequacy can be mitigated by adding vapor dopants, which may cluster with analyte ions and shift their mobilities by amounts independent of both mass and mobility of the ion. It is therefore important to understand the interactions of vapor dopants with ions, to better quantify the extent of dopant facilitated mobility shifts. Here, we develop predictive models of vapor dopant facilitated mobility shifts, and compare model calculations to measurements of mobility shifts for peptide ions exposed to variable gas phase concentrations of isopropanol. Mobility measurements were made at atmospheric pressure and room temperature using a recently developed transversal modulation ion mobility spectrometer (TMIMS). Results are compared to three separate models, wherein mobility shifts due to vapor dopants are attributed to changes in gas composition and (I) no vapor dopant uptake is assumed, (II) site-specific dopant uptake by the ion is assumed (approximated via a Langmuir adsorption model), and (III) site-unspecific dopant uptake by the ion is assumed (approximated via a classical nucleation model). We find that mobility shifts in peptide ions are in excellent agreement with model II, site-specific binding predictions. Conversely, mobility shifts of tetraalkylammonium ions from previous measurements were compared with these models and best agreement was found with model III predictions, i.e. site-unspecific dopant uptake. © The Royal Society of Chemistry.
Martinez-Lozano Sinues P.,National Research Council Italy |
Martinez-Lozano Sinues P.,ETH Zurich |
Criado E.,SEADM |
International Journal of Mass Spectrometry | Year: 2012
The fact that electrosprays of pure solvents can efficiently ionize gas-phase analytes has been known for decades, although this method has not been widely exploited. With the advent of ambient mass spectrometry, this approach is becoming increasingly popular. However, the mechanism by which vapors become ionized in the encounter with electrospray plumes remains largely unknown. This has been our motivation in this study in which we have exposed a set of amine vapors towards electrosprays of water, water/methanol (1/1) and methanol. The ionized vapors were characterized via ion mobility-mass spectrometry. We further tested a recently developed model to predict ionization probabilities for the encounter and charge transfer of vapors with ions or charged droplets emerging from an electrospray source. We found: (i) the highest sensitivity with water sprays and the poorest with methanol; (ii) an approximate correlation of sensitivity with vapor mass, being the heaviest species insoluble in water; (iii) different electrical mobility spectra for the same compounds ionized from the liquid phase and from the gas phase (i.e. one main feature for gas-phase and 3 features for liquid-phase); (iv) a closer agreement with the model for ion-molecule reactions than for droplet-vapor charge exchange. We conclude that the analytes could not possibly be dissolved in the droplets to be reemitted as if they were originally present in the electrospray solution. Our observations suggest that the vapors are ionized via ion-molecule reactions. © 2011 Elsevier B.V. All rights reserved.