Real-time single particle mass spectrometry: a historical review of a quarter century of the chemical analysis of aerosols

Elemental analysis of single ambient aerosol particles using laser-induced breakdown spectroscopy

Analysing the composition of aerosol particles is essential when studying their health effects, sources and atmospheric impacts. In many environments the relevant particles occur in very low concentrations, meaning that their analysis requires efficient single particle techniques. Here we introduce a novel method to analyse the elemental composition of single aerosol particles sampled directly from the aerosol phase using size amplification aided aerosol charging (SAAC), linear electrodynamic quadrupole (LEQ) and laser-induced breakdown spectroscopy. We present results of the charging and focusing efficiencies of the SAAC and of the LEQ, and a proof-of-concept of the analysis method. The proof-of-concept test series was conducted with particle diameters down to 300 nm, sampled directly from the aerosol phase. The method shows unprecedented performance for spectroscopic submicron particle analysis from arbitrarily low concentrations and has exceptional potential for a portable analysis platform for various applications in the field of aerosol research.

Comprehensive proteomic analysis of sea cucumbers (Stichopus japonicus) in thermal processing by HPLC-MS/MS

Thermal processing is the most frequently adopted processing technology for sea cucumbers, which can significantly affect their protein composition. In this paper, three thermal processing methods high pressure steaming (HPS), atmospheric pressure boiling (APB), and atmospheric pressure steaming (APS) were adopted and protein compositions of both body walls and cooking liquors by thermal processing stichopus japonicus were systematically analysis by proteomic strategy. The total proteins loss rates of body walls were 11.6%, 13.0%, and 14.8% for HPS, APS, and APB methods, respectively. However, the main types of protein composition were retained. Similar mechanisms of protein loss may exist even if different thermal processing were applied. The most frequent hydrolysis sites in thermal processing were phenylalanine, leucine, asparagine, and tyrosine at both C and N terminals. This study provides theoretical guidance for optimizing the industry thermal processing of sea cucumbers.

Application of Single-Particle Mass Spectrometer to Obtain Chemical Signatures of Various Combustion Aerosols

A single-particle mass spectrometer (SPMS) with laser ionization was constructed to determine the chemical composition of single particles in real time. The technique was evaluated using various polystyrene latex particles with different sizes (125 nm, 300 nm, 700 nm, and 1000 nm); NaCl, KCl, MgCO₃, CaCO₃, and Al₂O₃ particles with different chemical compositions; an internal mixture of NaCl and KCl; and an internal mixture of NaCl, KCl, and MgCl₂ with different mixing states. The results show that the SPMS can be useful for the determination of chemical characteristics and mixing states of single particles in real time. The SPMS was then applied to obtain the chemical signatures of various combustion aerosols (diesel engine exhaust, biomass burning (rice straw), coal burning, and cooking (pork)) based on their single-particle mass spectra. Elemental carbon (EC)-rich and EC-organic carbon (OC) particles were the predominant particle types identified in diesel engine exhaust, while K-rich and EC-OC-K particles were observed among rice straw burning emissions. Only one particle type (ash-rich particles) was detected among coal burning emissions. EC-rich and EC-OC particles were observed among pork burning particles. The single-particle mass spectra of the EC or OC types of particles differed among various combustion sources. The observed chemical signatures could be useful for rapidly identifying sources of atmospheric fine particles. In addition, the detected chemical signatures of the fine particles may be used to estimate their toxicity and to better understand their effects on human health.

Measuring the Chemical Evolution of Levitated Particles: A Study on the Evaporation of Multicomponent Organic Aerosol

Single-particle levitation methods provide an effective platform for probing the physical properties of atmospheric aerosol via micrometer-sized particles. Until recently, chemical composition measurements on levitated particles were limited to spectroscopy, yielding only basic chemical information. Here, we describe, benchmark, and discuss the applications of an approach for probing the physical properties and chemical composition of single levitated particles using high-resolution mass spectrometry (MS). Using a linear quadrupole electrodynamic balance (LQ-EDB) coupled to paper spray mass spectrometry, we report accurate measurements of the evolving size within 5 nm (using broadband light scattering) and relative composition (using MS) of evaporating multicomponent levitated particles in real time. Measurements of the evaporation dynamics of semivolatile organic particles containing a range of n-ethylene glycols (n = 3, 4, and 6) in various binary and ternary mixtures were made under dry conditions and compared with predictions from a gas-phase diffusion evaporation model. Under assumptions of ideal mixing, excellent agreement for both size and composition evolution between measurements and models were obtained for these mixtures. At increased relative humidity, the presence of water in particles causes the assumption of ideality to break down, and the evaporative mass flux becomes a function of the mole fraction and activity coefficient. Through compositionally resolved evaporation measurements and thermodynamic models, we characterize the activity of organic components in multicomponent particles. Our results demonstrate that the LQ-EDB-MS platform can identify time-dependent size and compositional changes with high precision and reproducibility, yielding an effective methodology for future studies on chemical aging and gas-particle partitioning in suspended particles.

Combining Mass Spectrometry of Picoliter Samples with a Multicompartment Electrodynamic Trap for Probing the Chemistry of Droplet Arrays

Single droplet levitation provides contactless access to the microphysical and chemical properties of micrometer-sized samples. Most applications of droplet levitation to chemical and biological systems use nondestructive optical techniques to probe droplet properties. To provide improved chemical specificity, we coupled a multicompartment quadrupole electrodynamic trap (QET) with single droplet mass spectrometry. Our QET continuously traps a monodisperse droplet population (tens to hundreds of droplets) and allows for the simultaneous sizing of a single droplet using its Mie scattering pattern. Single droplets are subsequently ejected into the ionization region of an ambient pressure inlet mass spectrometer. We optimized two complementary soft ionization techniques for picoliter aqueous droplets: (1) paper spray (PS) ionization and (2) thermal desorption glow discharge (TDGD) ionization. Both techniques detect oxygenated organic acids in single droplets, with signal-to-noise ratios >100 and detection limits on the order of 10 pg. Sensitivity and reproducibility across single droplets are driven by the droplet deposition location and spray stability in PS-MS and the ionization region humidity and analyte evaporation rate in TDGD-MS. Importantly, the analyte evaporation rate can control the TDGD-MS quantitative capability because high evaporation rates result in significant ion suppression. This effect is mitigated by optimizing the vaporization temperature, droplet size range, and analyte volatility. We demonstrate quantitative and reproducible measurements with a droplet internal standard (<10% RSD) and compare the sensitivity of PS-MS and TDGD-MS. Finally, we demonstrate the application of QET-MS to the study of heterogeneous chemical kinetics with the reaction of gas phase O₃ and aqueous maleic acid droplets.

An integrated instrument of DUV-IR photoionization mass spectrometry and spectroscopy for neutral clusters

We have developed an integrated instrument combining deep ultraviolet laser ionization mass spectrometry (DUV-LIMS) and infrared multiphoton dissociation (IR-MPD) spectroscopy, abbreviated as DUV-IR. The 177.3 nm DUV laser (7 eV single-photon energy) has short pulse duration (15 ps) and appropriate pulse energy (∼20 µJ), which is found to be highly efficient for low-fragment photoionization of neutral metal clusters and molecules. A home-made cluster source is designed with an adjustable formation channel suitable for the generation of different cluster series. The well-aligned components of the reflection time-of-flight mass spectrometer, as well as the coaxial design of DUV laser and molecular beam, bring forth high sensitivity and high resolution of the DUV-LIMS. Taking these advantages, well-resolved neutral V_n (n = 1-43) and (Benzene)_n (n = 1-25) clusters have been generated free of fragmentation. In addition to the generation and detection of neutral clusters, a fast-flow reaction tube is also designed downstream of the cluster source allowing to study their reactivity. In particular, a broad-range tunable IR laser (1.3-16 µm) is coupled with the DUV laser to attain IR-MPD spectroscopic analysis. This integrated system offers a general protocol to prepare various clusters to study their gas-phase reactivity and to determine their structures.

Selective C–C and C–N bond activation in dopamine and norepinephrine under deep ultraviolet laser irradiation

Selective C–C bond and C–N bond activation in dopamine and norepinephrine is analyzed utilizing deep-ultraviolet laser ionization mass spectrometry (DUV-LIMS).

Single-Particle Time-of-Flight Mass Spectrometry Utilizing a Femtosecond Desorption and Ionization Laser

Single-particle time-of-flight mass spectrometry has now been used since the 1990s to determine particle-to-particle variability and internal mixing state. Instruments commonly use 193 nm excimer or 266 nm frequency-quadrupled Nd:YAG lasers to ablate and ionize particles in a single step. We describe the use of a femtosecond laser system (800 nm wavelength, 100 fs pulse duration) in combination with an existing single-particle time-of-flight mass spectrometer. The goal of this project was to determine the suitability of a femtosecond laser for single-particle studies via direct comparison to the excimer laser (193 nm wavelength, ∼10 ns pulse duration) usually used with the instrument. Laser power, frequency, and polarization were varied to determine the effect on mass spectra. Atmospherically relevant materials that are often used in laboratory studies, ammonium nitrate and sodium chloride, were used for the aerosol. Detection of trace amounts of a heavy metal, lead, in an ammonium nitrate matrix was also investigated. The femtosecond ionization had a large air background not present with the 193 nm excimer and produced more multiply charged ions. Overall, we find that femtosecond laser ablation and ionization of aerosol particles is not radically different than that provided by a 193 nm excimer.

Airborne single particle mass spectrometers (SPLAT II & miniSPLAT) and new software for data visualization and analysis in a geo-spatial context

Understanding the effect of aerosols on climate requires knowledge of the size and chemical composition of individual aerosol particles-two fundamental properties that determine an aerosol's optical properties and ability to serve as cloud condensation or ice nuclei. Here we present our aircraft-compatible single particle mass spectrometers, SPLAT II and its new, miniaturized version, miniSPLAT that measure in-situ and in real-time the size and chemical composition of individual aerosol particles with extremely high sensitivity, temporal resolution, and sizing precision on the order of a monolayer. Although miniSPLAT's size, weight, and power consumption are significantly smaller, its performance is on par with SPLAT II. Both instruments operate in dual data acquisition mode to measure, in addition to single particle size and composition, particle number concentrations, size distributions, density, and asphericity with high temporal resolution. We also present ND-Scope, our newly developed interactive visual analytics software package. ND-Scope is designed to explore and visualize the vast amount of complex, multidimensional data acquired by our single particle mass spectrometers, along with other aerosol and cloud characterization instruments on-board aircraft. We demonstrate that ND-Scope makes it possible to visualize the relationships between different observables and to view the data in a geo-spatial context, using the interactive and fully coupled Google Earth and Parallel Coordinates displays. Here we illustrate the utility of ND-Scope to visualize the spatial distribution of atmospheric particles of different compositions, and explore the relationship between individual particle compositions and their activity as cloud condensation nuclei.

Organic constituents on the surfaces of aerosol particles from Southern Finland, Amazonia, and California studied by vibrational sum frequency generation

This article summarizes and compares the analysis of the surfaces of natural aerosol particles from three different forest environments by vibrational sum frequency generation. The experiments were carried out directly on filter and impactor substrates, without the need for sample preconcentration, manipulation, or destruction. We discuss the important first steps leading to secondary organic aerosol (SOA) particle nucleation and growth from terpene oxidation by showing that, as viewed by coherent vibrational spectroscopy, the chemical composition of the surface region of aerosol particles having sizes of 1 μm and lower appears to be close to size-invariant. We also discuss the concept of molecular chirality as a chemical marker that could be useful for quantifying how chemical constituents in the SOA gas phase and the SOA particle phase are related in time. Finally, we describe how the combination of multiple disciplines, such as aerosol science, advanced vibrational spectroscopy, meteorology, and chemistry can be highly informative when studying particles collected during atmospheric chemistry field campaigns, such as those carried out during HUMPPA-COPEC-2010, AMAZE-08, or BEARPEX-2009, and when they are compared to results from synthetic model systems such as particles from the Harvard Environmental Chamber (HEC). Discussions regarding the future of SOA chemical analysis approaches are given in the context of providing a path toward detailed spectroscopic assignments of SOA particle precursors and constituents and to fast-forward, in terms of mechanistic studies, through the SOA particle formation process.

Mass spectrometry of atmospheric aerosols--recent developments and applications. Part II: On-line mass spectrometry techniques

Many of the significant advances in our understanding of atmospheric particles can be attributed to the application of mass spectrometry. Mass spectrometry provides high sensitivity with fast response time to probe chemically complex particles. This review focuses on recent developments and applications in the field of mass spectrometry of atmospheric aerosols. In Part II of this two-part review, we concentrate on real-time mass spectrometry techniques, which provide high time resolution for insight into brief events and diurnal changes while eliminating the potential artifacts acquired during long-term filter sampling. In particular, real-time mass spectrometry has been shown recently to provide the ability to probe the chemical composition of ambient individual particles <30 nm in diameter to further our understanding of how particles are formed through nucleation in the atmosphere. Further, transportable real-time mass spectrometry techniques are now used frequently on ground-, ship-, and aircraft-based studies around the globe to further our understanding of the spatial distribution of atmospheric aerosols. In addition, coupling aerosol mass spectrometry techniques with other measurements in series has allowed the in situ determination of chemically resolved particle effective density, refractive index, volatility, and cloud activation properties.

Detecting nanoparticulate silver using single-particle inductively coupled plasma-mass spectrometry

The environmental prevalence of engineered nanomaterials, particularly nanoparticulate silver (AgNP), is expected to increase substantially. The ubiquitous use of commercial products containing AgNP may result in their release to the environment, and the potential for ecological effects is unknown. Detecting engineered nanomaterials is one of the greatest challenges in quantifying their risks. Thus, it is imperative to develop techniques capable of measuring and characterizing exposures, while dealing with the innate difficulties of nanomaterial detection in environmental samples, such as low-engineered nanomaterial concentrations, aggregation, and complex matrices. Here the authors demonstrate the use of inductively coupled plasma-mass spectrometry, operated in a single-particle counting mode (SP-ICP-MS), to detect and quantify AgNP. In the present study, two AgNP products were measured by SP-ICP-MS, including one of precisely manufactured size and shape, as well as a commercial AgNP-containing health food product. Serial dilutions, filtration, and acidification were applied to confirm that the method detected particles. Differentiation of dissolved and particulate silver (Ag) is a feature of the technique. Analysis of two wastewater samples demonstrated the applicability of SP-ICP-MS at nanograms per liter Ag concentrations. In this pilot study, AgNP was found at 100 to 200 ng/L in the presence of 50 to 500 ng/L dissolved Ag. The method provides the analytical capability to monitor Ag and other metal and metal oxide nanoparticles in fate, transport, stability, and toxicity studies using a commonly available laboratory instrument. Rapid throughput and element specificity are additional benefits of SP-ICP-MS as a measurement tool for metal and metal oxide engineered nanoparticles.

Advances in mass spectrometry for the identification of pathogens

Mass spectrometry (MS) has become an important technique to identify microbial biomarkers. The rapid and accurate MS identification of microorganisms without any extensive pretreatment of samples is now possible. This review summarizes MS methods that are currently utilized in microbial analyses. Affinity methods are effective to clean, enrich, and investigate microorganisms from complex matrices. Functionalized magnetic nanoparticles might concentrate traces of target microorganisms from sample solutions. Therefore, nanoparticle-based techniques have a favorable detection limit. MS coupled with various chromatographic techniques, such as liquid chromatography and capillary electrophoresis, reduces the complexity of microbial biomarkers and yields reliable results. The direct analysis of whole pathogenic microbial cells with matrix-assisted laser desorption/ionization MS without sample separation reveals specific biomarkers for taxonomy, and has the advantages of simplicity, rapidity, and high-throughput measurements. The MS detection of polymerase chain reaction (PCR)-amplified microbial nucleic acids provides an alternative to biomarker analysis. This review will conclude with some current applications of MS in the identification of pathogens.

Interfacing microchip electrophoresis to a growth tube particle collector for semicontinuous monitoring of aerosol composition

Semicontinuous monitoring of aerosol chemical composition has continually increased in demand because of the high spatial and temporal variability of atmospheric particles and the effects these aerosols have on human health and the environment. To address this demand, we describe the preliminary development of a semicontinuous aerosol composition analyzer consisting of a growth tube particle collector coupled to a microfluidic device for chemical analysis. The growth tube enlarges particles through water condensation in a laminar flow, permitting inertial collection into the microchip sample reservoir. Analysis is done by electrophoresis with conductivity detection. To avoid hydrodynamic interference from the sampling pressure, the microchip was operated isobarically by sealing the buffer reservoirs from the atmosphere and interconnecting all the reservoirs with air ducts. The collector samples at 1 L min(-1) and deposits particles into 30 microL of solution. Sample accumulates with time, and sequential injections are performed as aerosol concentration increases. For extended analyses, a sample rinsing system flushes the sample collection reservoir periodically. For inorganic anions, temporal resolution of 1 min and estimated detection limits of 70-140 ng m(-3) min were obtained. The system was used to measure sulfate and nitrate, and results were compared to a particle-into-liquid-sampler running in parallel. Results indicate that the prototype growth tube-microchip system (termed aerosol chip electrophoresis, ACE) could provide a useful complement to existing aerosol monitoring technologies, especially when less expensive and/or rapid analyses are desired.

An editor's view of analytical chemistry (the Discipline)

The author recounts progress observed in analytical chemistry (the discipline) from the vantage point of a 20-year editor of Analytical Chemistry (the journal). The recounting draws liberally from the journal's monthly editorials. A complete listing of the editorials can be found in Supplemental Material .

A superconducting NbN detector for neutral nanoparticles

We present a proof-of-principle study of superconducting single photon detectors (SSPD) for the detection of individual neutral molecules/nanoparticles at low energies. The new detector is applied to characterize a laser desorption source for biomolecules and allows retrieval of the arrival time distribution of a pulsed molecular beam containing the amino acid tryptophan, the polypeptide gramicidin as well as insulin, myoglobin and hemoglobin. We discuss the experimental evidence that the detector is actually sensitive to isolated neutral particles.

Measurements of hygroscopicity and volatility of atmospheric ultrafine particles during ultrafine particle formation events at urban, industrial, and coastal sites

The tandem differential mobility analyzer (TDMA) technique was applied to determine the hygroscopicity and volatility of atmospheric ultrafine particles in three sites of urban Gwangju, industrial Yeosu, and coastal Taean in South Korea. A database for the hygroscopicity and volatility of the known compositions and sizes of the laboratory-generated particles wasfirst constructed for comparison with the measured properties of atmospheric ultrafine particles. Distinct differences in hygroscopicity and volatility of atmospheric ultrafine particles werefound between a "photochemical event" and a "combustion event" as well as among different sites. At the Gwangju site, ultrafine particles in the "photochemical event" were determined to be more hygroscopic (growth factor (GF) = 1.05-1.33) than those in the "combustion event" (GF = 1.02-1.12), but their hygroscopicity was not as high as pure ammonium sulfate or sulfuric acid particles in the laboratory-generated database, suggesting they were internally mixed with less soluble species. Ultrafine particles in the "photochemical event" at the Yeosu site, having a variety of SO2, CO, and VOC emission sources, were more hygroscopic (GF = 1.34-1.60) and had a higher amount of volatile species (47-75%)than those observed at the Gwangju site. Ultrafine particle concentration at the Taean site increased during daylight hours with low tide, having a higher GF (1.34-1.80) than the Gwangju site and a lower amount of volatile species (17-34%) than the Yeosu site. Occasionally ultrafine particles were externally mixed according to their hygroscopicity and volatility, and TEM/EDS data showed that each type of particle had a distinct morphology and elemental composition.

Microorganism characterization by single particle mass spectrometry

In recent years a major effort by several groups has been undertaken to identify bacteria by mass spectrometry at the single cell level. The intent of this review is to highlight the recent progress made in the application of single particle mass spectrometry to the analysis of microorganisms. A large portion of the review highlights improvements in the ionization and mass analysis of bio-aerosols, or particles that contain biologically relevant molecules such as peptides or proteins. While these are not direct applications to bacteria, the results have been central to a progression toward single cell mass spectrometry. Developments in single particle matrix-assisted laser desorption/ionization (MALDI) are summarized. Recent applications of aerosol laser desorption/ionization (LDI) to the analysis of single microorganisms are highlighted. Successful applications of off-line and on-the-fly aerosol MALDI to microorganism detection are discussed. Limitations to current approaches and necessary future achievements are also addressed.

Particle-fluorescence spectrometer for real-time single-particle measurements of atmospheric organic carbon and biological aerosol

A particle-fluorescence spectrometer (PFS) for real-time measurements of single-particle UV-laser-induced fluorescence (UV-LIF) excited with a pulsed (263-nm) laser is reported. The dispersed UV-LIF spectra are measured by a 32-anode PMT detector with spectral coverage from 280-600 nm. The PFS represents a significant improvement over our previous apparatus [Pinnick et al., Atmos. Environ. 2004, 38, 1657] and can (1) measure fluorescence spectra of bacterial particles having light-scattering sizes as small as 1 microm (previously limited to about 3 microm) and so can measure particles with size in the range of 1-10 microm, (2) measure each particle's elastic scattering which can be used to estimate particle size (not available previously), (3) measure single-particle fluorescence spectra with a laser and detector that can record spectra as fast as 90,000/s, although the highest rates we have found experimentally in atmospheric measurements is only several hundred per second (previously limited by detectors to only 25/s), and (4) provide a time stamp for a data block of spectra with time resolution from 10 ms to 10 min. In addition, the PFS has been modified to be more robust, transportable, and smaller. The use of an aerodynamic-focusing sheath inlet nozzle assembly has improved the sample rate. The PFS has been employed to measure UV-LIF spectra from individual atmospheric particles during October-December 2006 and January-May 2008 in New Haven, CT, and during January-May 2007 in Las Cruces, NM.

Detection and assessment of co-association in inhalable drug particles using aerosol time-of-flight mass spectrometry

Aerosol Time-of-Flight Mass Spectrometry (AToFMS) was used to examine co-association between two inhaled drugs, fluticasone propionate (FP) and salmeterol xinofoate (SX), in fine aerosolised particles emitted from Seretide(R)/Advair(R) inhaled combination products. Principal Component Analysis (PCA) was used to identify fragmentation patterns indicative of either pure or co-associated particles (particles containing both drugs). A third component of the particles emitted from dry powder inhalers (DPIs), lactose, gave only a very weak mass spectral signal and no interpretable data was acquired for this compound; however, it was not found to interfere with the detection of the two drug substances. High levels of co-association were found in the emitted doses from both pressurised metered dose inhaler (pMDI) and dry powder inhaler (DPI) products.

Recent Advances in Real-time Mass Spectrometry Detection of Bacteria

The analysis of bio-aerosols poses a technology challenge, particularly when sampling and analysis are done in situ. Mass spectrometry laboratory technology has been modified to achieve quick bacteria typing of aerosols in the field. Initially, aerosol material was collected and subjected off-line to minimum sample treatment and mass spectrometry analysis. More recently, sampling and analysis were combined in a single process for the real-time analysis of bio-aerosols in the field. This chapter discusses the development of technology for the mass spectrometry of bio-aerosols, with a focus on bacteria aerosols. Merits and drawbacks of the various technologies and their typing signatures are discussed. The chapter concludes with a brief view of future developments in bio-aerosol mass spectrometry.

Single particle X-ray diffractive imaging

In nanotechnology, strategies for the creation and manipulation of nanoparticles in the gas phase are critically important for surface modification and substrate-free characterization. Recent coherent diffractive imaging with intense femtosecond X-ray pulses has verified the capability of single-shot imaging of nanoscale objects at suboptical resolutions beyond the radiation-induced damage threshold. By intercepting electrospray-generated particles with a single 15 femtosecond soft-X-ray pulse, we demonstrate diffractive imaging of a nanoscale specimen in free flight for the first time, an important step toward imaging uncrystallized biomolecules.

Thermal vaporization of biological nanoparticles: fragment-free vacuum ultraviolet photoionization mass spectra of tryptophan, phenylalanine-glycine-glycine, and beta-carotene

A simple, new way to introduce fragile biomolecules into the gas phase via thermal vaporization of nanoparticles is described. The general utility of this technique for the study of biomolecules is demonstrated by coupling this source to tunable synchrotron vacuum ultraviolet radiation. Fragment-free photoionization mass spectra of tryptophan, phenylalanine-glycine-glycine, and beta-carotene are detected with signal-to-noise ratios exceeding 100. The 8.0 eV photoionization mass spectrum of tryptophan nanoparticles vaporized at 373 K is dominated by a single parent ion peak that exhibits a 20-fold enhancement over the methylene indole fragment ion. The degree of dissociative photoionization of tryptophan can be precisely controlled either by the thermal energy imparted into the neutral tryptophan molecule or by the energy of the ionizing photon. The results reveal how approximately 0.5 eV changes in internal energy affect both the photoionization mass spectrum of tryptophan and the appearance energy of the daughter ion fragments. This method allows the ionization energies of glycine (9.3 +/- 0.1 eV), tryptophan (7.3 +/- 0.2 eV), phenylalanine (8.6 +/- 0.1 eV), phenylalanine-glycine-glycine (9.1 +/- 0.1 eV), and beta-carotene (<7.0 eV) molecules to be determined directly from the photoionization efficiency spectra.

Single-Particle Aerosol Mass Spectrometry for the Detection and Identification of Chemical Warfare Agent Simulants

Single-particle aerosol mass spectrometry (SPAMS) was used for the real-time detection of liquid nerve agent simulants. A total of 1000 dual-polarity time-of-flight mass spectra were obtained for micrometer-sized single particles each of dimethyl methyl phosphonate, diethyl ethyl phosphonate, diethyl phosphoramidate, and diethyl phthalate using laser fluences between 0.58 and 7.83 nJ/microm2, and mass spectral variation with laser fluence was studied. The mass spectra obtained allowed identification of single particles of the chemical warfare agent (CWA) simulants at each laser fluence used although lower laser fluences allowed more facile identification. SPAMS is presented as a promising real-time detection system for the presence of CWAs.

Single particle fluorescence: a simple experimental approach to evaluate coincidence effects

Real-time characterization of the chemical and physical properties of individual aerosol particles is an important issue in environmental studies. A well-established way of accomplishing this task relies on the use of laser-induced fluorescence or laser ionization mass spectrometry. We describe here a simple approach aimed at experimentally verifying that single particles are indeed addressed. The approach has been tested with a system consisting of a series of aerodynamic lenses to form a beam of dye-doped particles aerosolized from a solution of known concentration with a medical nebulizer. Two independent spectral detection channels simultaneously measure the fluorescence signals generated in two different spectral regions by the passage of a mixture of two dye-doped particles through a focused laser beam in a vacuum chamber. Coincidence effects, arising from the simultaneous observation of both fluorescence emissions, can then be directly observed. Both dual-color fluorescence and pulse height distribution have been analyzed. As expected, the probability of single- or multiple-particle interaction strongly depends on the particle flux in the chamber, which is related to the concentration of particles in the nebulized solution. In our case, to achieve a two-particle coincidence smaller than 10%, a particle concentration lower than 1.2x10(5) particles/mL is required. Moreover, it was found that the experimental observations are in agreement with a simple mathematical model based on Poisson statistics. Although the results obtained refer to particle concentrations in solution, our approach can equally be applicable to experiments involving direct air sampling, provided that the number density of particles in air can be measured a priori, e.g., with a particle counter.

Instrumentation, data evaluation and quantification in on-line aerosol mass spectrometry

On-line micro- and nanoparticle mass spectrometry has evolved into a prominent analytical method for the characterization of airborne particles, particle populations and aerosols over the recent years, driven by essential developments in instrumentation, data evaluation and validation. In this tutorial, the fundamental aspects of the technology and methodology for qualitative and quantitative on-line aerosol particle analysis are discussed. Specific properties of the on-line mass spectrometric instrumentation for particle analysis are described, combined with a discussion of basic differences of the instruments and demands for future improvements of instruments and data analysis techniques. Optimized technology and methodology in particle analysis is expected to lead to essential growth of the knowledge and to quality improvement of the description of atmospheric processes and health effects in the future.

The design of single particle laser mass spectrometers

This review explores some of the design choices made with single particle mass spectrometers. Different instruments have used various configurations of inlets, particle sizing techniques, ionization lasers, mass spectrometers, and other components. Systematic bias against non-spherical particles probably exceeds a factor of 2 for all instruments. An ionization laser tradeoff is the relatively poor beam quality and reliability of an excimer laser versus the longer wavelengths and slower response time of an Nd-YAG laser. Single particle instruments can make special demands on the speed and dynamic range of the mass spectrometers. This review explains some of the choices made for instruments that were developed for different types of measurements in the atmosphere. Some practical design notes are also given from the author's experience with each section of the instrument.

Chemical and microphysical characterization of ambient aerosols with the aerodyne aerosol mass spectrometer

The application of mass spectrometric techniques to the real-time measurement and characterization of aerosols represents a significant advance in the field of atmospheric science. This review focuses on the aerosol mass spectrometer (AMS), an instrument designed and developed at Aerodyne Research, Inc. (ARI) that is the most widely used thermal vaporization AMS. The AMS uses aerodynamic lens inlet technology together with thermal vaporization and electron-impact mass spectrometry to measure the real-time non-refractory (NR) chemical speciation and mass loading as a function of particle size of fine aerosol particles with aerodynamic diameters between approximately 50 and 1,000 nm. The original AMS utilizes a quadrupole mass spectrometer (Q) with electron impact (EI) ionization and produces ensemble average data of particle properties. Later versions employ time-of-flight (ToF) mass spectrometers and can produce full mass spectral data for single particles. This manuscript presents a detailed discussion of the strengths and limitations of the AMS measurement approach and reviews how the measurements are used to characterize particle properties. Results from selected laboratory experiments and field measurement campaigns are also presented to highlight the different applications of this instrument. Recent instrumental developments, such as the incorporation of softer ionization techniques (vacuum ultraviolet (VUV) photo-ionization, Li+ ion, and electron attachment) and high-resolution ToF mass spectrometers, that yield more detailed information about the organic aerosol component are also described.

Identification of High Explosives Using Single-Particle Aerosol Mass Spectrometry

The application of single-particle aerosol mass spectrometry (SPAMS) to the real-time detection of micrometer-sized single particles of high explosives is described. Dual-polarity time-of-flight mass spectra from 1000 single particles each of 2,4,6-trinitrotoluene (TNT), 1,3,5-trinitro-1,3,5-triazinane (RDX), and pentaerythritol tetranitrate (PETN), as well as those of complex explosives, Composition B, Semtex 1A, and Semtex 1H, were obtained over a range of desorption/ionization laser fluences between 0.50 and 8.01 nJ/microm2. Mass spectral variability with laser fluence for each explosive is discussed. The ability of the SPAMS system to identify explosive components in a single complex explosive particle ( approximately 1 pg) without the need for consumables is demonstrated.

Online aerosol mass spectrometry of single micrometer-sized particles containing poly(ethylene glycol)

The analysis of poly(ethylene glycol) (PEG)-containing particles by online single particle aerosol mass spectrometers equipped with laser desorption/ionization (LDI) is reported. We demonstrate that PEG-containing particles are useful in the development of aerosol mass spectrometers because of their ease of preparation, low cost, and inherently recognizable mass spectra. Solutions containing millimolar quantities of PEGs were nebulized and, after drying, the resultant micrometer-sized PEG-containing particles were sampled. LDI (266 nm) of particles containing NaCl and PEG molecules of average molecular weight<500 Da generated mass spectra reminiscent of mass spectra of PEG collected by other mass spectrometer platforms including the characteristic distribution of positive ions (Na+ adducts) separated by the 44 m/z units of the ethylene oxide units separating each degree of polymerization. PEGs of average molecular weight>500 Da were detected from particles that also contained the tripeptide tyrosine-tyrosine-tyrosine or 2,5-dihydroxybenzoic acid, which were added to nebulized solutions to act as matrices to assist LDI using pulsed 266 nm and 355 nm lasers, respectively. Experiments were performed on two aerosol mass spectrometers, one reflectron and one linear, that each utilize two time-of-flight mass analyzers to detect positive and negative ions created from a single particle. PEG-containing particles are currently being employed in the optimization of our bioaerosol mass spectrometers for the application of measurements of complex biological samples, including human effluents, and we recommend that the same strategies will be of great utility to the development of any online aerosol LDI mass spectrometer platform.

An ion optics for effective ion detection in single particle mass spectrometry

Recently, we reported that significant ion loss occurs prior to detection in conventional single particle mass spectrometry. A more serious type of loss is ion-kinetic-energy-dependent loss. This leads to significant errors in the measured chemical composition of nanoparticles, especially when they have a core-shell structure. In this paper, a novel ion optics for effective detection of ions generated from a single nanoparticle is designed. Using the commercial software SIMION, the trajectories of ions launched at different speeds inside a single particle mass spectrometer are simulated. The effects of changes are investigated with different repelling plates, Einzel lens additions, and substitutions of the tube electrode between extraction and acceleration grids on the ion flight. The best design was found when assembling the trials in the present condition. It was demonstrated experimentally that the new ion optics works well not only in theory, but also in practice.