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The properties of bioaerosols are complex and diverse, and have a direct impact on the environment, climate, and human health. The effective identification of bioaerosols in the atmosphere is very significant with regard to accurately obtaining the atmospheric chemical characteristics of bioaerosols. To improve the detection of large particle bioaerosol and non-bioaerosol interference in the process of bioaerosol recognition, this study detected a variety of bioaerosols and abiotic aerosols based on a single particle aerosol mass spectrometer (SPAMS). Furthermore, the bioaerosol particle identification and classification algorithm based on Zawadowicz the ratio of phosphate to organic nitrogen is optimized to distinguish bioaerosols from abiotic aerosols. The influence of ionized laser energy on classification methods is thoroughly explored here. The results show that 15 kinds of pure fungal aerosols were detected by SPAMS based on a wide size range sampling system, and that fungal aerosols with a particle size of up to 10 μm can be detected. Through the mass spectra peak ratio method of PO3−/PO2− and CNO−/CN−, when discriminating abiotic aerosols such as disruptive biomass combustion particles, automobile exhaust, and dust from pure bacterial aerosols, the discrimination degree is up to 97.7%. The optimized ratio detection method of phosphate to organic nitrogen has strong specificity, which can serve as the discriminant basis for identifying bioaerosols in SPAMS analytical processes.

Hazardous air pollutants can be unintentionally and intentionally released in many cases, such as industrial emissions, accidental events, and pesticide application. Under such events, the onsite operation is highly dependent on the molecular composition and spatial distribution of air pollutants in ambient air. However, it is usually difficult for people to reach hazardous and upper sites rapidly. In this work, we designed a new drone-based microextraction sampler array in which a solid-phase microextraction (SPME) fiber was mounted on drones for remote-control sampling at different spaces and was then coupled with a portable gas chromatography-mass spectrometry (PGC-MS) approach for quickly identifying hazardous air pollutants and their spatial distribution in ambient air within minutes. Acceptable analytical performances, including good sensitivity (detection limit at nanogram per liter level), reproducibility (relative standard deviation20%

This study describes a high-performance single-particle mass spectrometry (HP-SPAMS) design in detail. The comprehensive improvements of the injection system, optical sizing system, mass spectrometry, and data acquisition system have improved particle detection efficiency and chemical analysis. The combination of an aerodynamic particle concentrator (APC) system and a wide range of aerodynamic lenses (ADLs) enables the concentration of particles in the 100–5000 nm range by a factor of 3–5 times. The ion delayed exaction technology of bipolar time-of-flight mass spectrometry improves the mass resolution by 2~3 times, allowing the differentiation of multiple homogeneous masses of different substances. Moreover, the 4-channel data acquisition technology greatly enhances the dynamic range of mass spectrometry. The as-improved HP-SPAMS enhances the overall capability of the instrument in terms of particle detection number and detection efficiency. Moreover, it improves accuracy and sensitivity for component identification of individual particles. The experimental performance of HP-SPAMS shows that the sizing detection efficiency of polystyrene latex microspheres is almost 70 %–100 % in the range of 300–3000 nm. Compared to the previous SPAMS, HP-SPAMS has a larger inlet flow rate, detection efficiency, and higher laser frequency, which makes HP-SPAMS increase the effective number of particles detected in the air by 47.8 times and improve the temporal resolution of detection. For the analysis of individual particles, the HP-SPAMS's improved resolution helps distinguish between most organic fragment ions and metal ions and facilitates the analysis of complex aerosol particles. For the analysis of individual particles, the increased resolution of the HP-SPAMS contributes to the differentiation of most organic fragment ions and metal ions and facilitates the evaluation of complex aerosol particles. In the case of atmospheric lead-containing particles, for example, HP-SPAMS can completely differentiate the isotopes of lead elements and the number of lead-containing particles is 145 times higher than that detected by SPAMS. The outstanding detection efficiency and chemical analysis capability of HP-SPAMS will be of great importance for low concentration aerosol detection and complex aerosol component analysis.

The sources of bioaerosols are complex and diverse, which have a direct impact on the environment, climate, and human health. The effective identification of bioaerosols in the atmosphere is greatly significant for accurately obtaining the atmospheric chemical characteristics of bioaerosols and making biological early warnings and predictions. To improve the identification ability of bioaerosols, this study detected a variety of bioaerosols and abiotic aerosols based on a single particle aerosol mass spectrometry (SPAMS). Furthermore, the bioaerosol particle identification and classification algorithm based on the ratio of phosphate to organic nitrogen was optimized to distinguish bioaerosols from abiotic aerosols. The results show that 15 kinds of pure fungal aerosols were detected by SPAMS based on a wide range sampling system and that fungal aerosols with a particle size up to 10 μm could be detected. Through the mass spectra peak ratio method of PO3- / PO2- and CNO- / CN-, when discriminating abiotic aerosols, such as disruptive biomass combustion particles, automobile exhaust, and dust, from pure bacterial aerosols, the discrimination degree was up to 97.7 %. The optimized ratio detection method of phosphate to organic nitrogen has strong specificity, which can serve as the discriminant basis for identifying bioaerosols in SPAMS source analysis or other analytical processes.

Electron ionization time-of-flight mass spectrometry (EI-TOF-MS) has been widely used in the fields of chemical, environmental, food, medical and pharmaceutical, etc. Coupling gas chromatography (GC) with EI-TOF-MS yields promising qualitative and quantitative results, and the performance is closely related to with the ion guide devices. A good ion guide device for EI ion source can generate a narrow beam of low-energy ions, resulting in high ion transition efficiency. In this study, an ion transition system for EI ion source with radio frequency quadrupole (RFQ) as the collisional focusing ion guide was developed. The ions in the RFQ could be cooled by collisions with buffer gas molecules and focused to near the axis by a RF field. To determine the parameters of the RFQ, including rod length, rod radius, field radius, RFQ exit orifice diameter, RF frequency, RF amplitude, and other transmission electrode voltages, vacuum design theory, RF quadrupole field theory and SIMION software simulations were applied. The performance of a GC-EI-TOFMS instrument was significantly improved using RFQ as collisional focusing ion guide, and the evaluation results showed that the mass resolution was up to 6500 FWHM (m/z 502), the limit of detection (LOD) was 1 pg of OFN (S/N > 30:1), the mass range was 15–968 amu, the mass accuracy was below 0.01 amu, and the relative standard deviation (RSD) was below 1.5% within one week. This study provided an example to build an ion transition system for mass spectrometry, which had important theoretical and practical significance in design and development of new mass spectrometric instrument.

Inert metals are of much importance and play a key role in modern industrial manufacturing. The analytical techniques of inert metals remain challenging. In particular, the mass spectrometry of inert metal elements is yet to be further developed, which also limits the contemporary conceptual in situ analysis of inert metals. As the representative element, the mass spectral detection of palladium is critical and of far-reaching significance. Herein, we developed a mass spectrometry method, which can be used for the high-speed and in situ analysis of palladium, and even for other inert metals. Combining the line ion trap mass spectrometer with the versatile ambient ionization source, a novel kilowatt microwave plasma torch (MPT) can be used to obtain the fully characteristic MPT mass spectra of palladium. Detailed multistage tandem mass spectra show that the general form of target ions is [M(O2)x(NO)mNy(NO2)n]- for the negative ion mode and [M(H2O)x(NO2)y(N2)m]+ for the positive ion mode. Moreover, the formation and evolution of these palladium complex ions were reasonably derived based on the analysis of MPT background mass spectra. This mass spectrometric technique is also suitable for the determination of the palladium-containing solution in the sub-trace level. Semi-quantitative results showed that the detecting ability for palladium in the negative mode is better than that of the positive mode. Under the negative ion mode, the limit of detection (LOD) for m/z 259 were evaluated to be 0.5 μg L-1 under the optimized conditions of the negative mode, with the linear range of 1-100 μg·L-1 (R2 ≥ 0.9985) and the relative standard deviation (RSD, n = 11) being in the range of 1.20%-5.98% (refer to Table S3). Our experimental data showed that MPT-MS was a promising technique for providing another alternative in the on-site analysis of liquid samples and other intimate relevant fields, as the supplement of ICP-MS for the detection of inert metal elements. On the other hand, this work will also certainly promote the more broad applications of platinum-group elements (PGE) in modern science and industry.

A novel home-made H

In vivo sampling and sensitive detection of environmental pollutants and drugs in human body play a crucial role in understanding human health. In this study, in vivo solid-phase microextraction (SPME) swab was fabricated using a SPME fiber and a medical cotton swab for noninvasive sampling and extraction of environmental pollutants and drugs in human oral cavity, nasal cavity and on skin surface. After sampling, SPME was coupled with nano-electrospray ionization mass spectrometry (nanoESI-MS) for desorption, ionization, and detection of the extracted analytes. As a result, limit of detection (LOD) and limit of quantification (LOQ) of nicotine in oral fluid were found to be 1.0 pg/mL (S/N ≥ 3) and 4.0 pg/mL (S/N ≥ 10), respectively. Linear dynamic signal responses of nicotine exhibited excellent linearity (R2 = 0.9996) in human oral fluid ranging from 0.1 to 50 ng/mL. The coefficient of variation (CV) values of SPME swab for five measurements from sample vials and human body were 5.1–6.7% and 22.7–32.6%, respectively. Rapid analysis of a single sample could be completed within 10 min. Overall, our results demonstrated that SPME swab-MS is a promising noninvasive method for enhanced detection of analytes in human body.

A miniature reflectron time-of-flight mass spectrometer (TOF MS) with orthogonal extraction coupled with electron impact (EI) ionization source can be used to perform in situ gas composition analysis in a planetary environment. However, performances such as the mass resolution, sensitivity, limit of detection, mass range, and mass accuracy are often decreased because of miniaturization. Herein, a compact instrument for space applications has been developed, and its performance has been evaluated. The mass of the TOF MS is 13.4 kg, with dimensions of 300 mm × 200 mm × 200 mm, and the power consumption is 25 W. In this paper, the design of the ion source, mass analyzer, and detector is discussed in detail. The upper limit of the mass range is greater than 500 amu, and the best resolving power obtained so far on the miniature TOF MS is around 405 at full width half maximum (FWHM); other performance indexes of the instrument are also determined, where the worst case for mass stability is 0.49%, together with a mass accuracy of 0.12% and a sensitivity of 0.6 mV/ppm.

To identify the characteristics, sources, and formation mechanisms of aerosol particles during pollution episodes in the Pearl River Delta, 24 sets of size-segregated samples were collected in Heshan during July 2014 and January 2015 using a 10-stage Micro-Orifice Uniform Deposit Impactor (MOUDI), and nine ions, viz., Na+, NH4+, K+, Mg2+, Ca2+, Cl–, NO2–, NO3–, and SO42–, were investigated. The Na+, Mg2+, and Ca2+ were mainly distributed in the coarse particles, and were mainly from soil, dust, and sea salt. The fine-mode K+ during winter was mostly generated by biomass burning. The coarse-mode Cl– originated from sea salt, whereas the fine-mode Cl– resulted from the conversion of NH4Cl to the particle phase. Both the SO42– and the NO3– exhibited unimodal distributions during winter but bimodal ones during summer. The coarse-mode SO42– and NO3– arose from sea salt and heterogeneous reactions, respectively. An increase in the nitrogen oxidation ratio (NOR) and a decrease in the sulfur oxidation ratio (SOR) were observed on polluted days, with the highest values occurring in the 0.56–1 µm particle size fraction. The formation of NO3– was chiefly related toµ homogeneous gas-phase reactions during winter and nocturnal heterogeneous reactions involving N2O5 during summer, whereas the formation of SO42– was driven by gas-phase oxidation in the 0.056–0.32 µm size range and aqueous oxidation in the 0.56–3.2 µm range. Additionally, the SOR and the NO2 concentration displayed a positive correlation in the 0.056–1.8 µm particle size fraction, indicating that the potential formation of SO42– via aqueous reactions was accelerated by NO2.

To ensure honey foodstuff safety, a rapid and sensitive mass spectrometric analysis method with minimal or no prior sample pretreatment was developed for the direct detection of trace amounts of tetracycline (TC) in honey products by using a microwave plasma torch combined with mass spectrometry (MPT-MS). In the study, reagent ions observed in the MPT background spectrum were commonly formed from the MPT source-generated plasma reacting with discharge gas (Ar), H2O and O2 in air. Moreover, the ionization process of the MPT for target molecules (M) was summarized in the positive ion mode, including proton transfer, charge transfer, penning ionization, high energy electron–molecule reaction and so on. For semi-quantitative detection of tetracycline in honey by MPT-MS, considerations for each approach including adjustment of the microwave power and optimization of the discharge gas flow rate are discussed. The present research mainly focused on the most abundant precursor ion [M + H]+ (m/z 445) and its fragment ion (m/z 427) in collision-induced dissociated (CID) experiments. In addition, the semi-quantitative data by monitoring m/z 427 vs. the amounts of samples illustrated that the limit of detection (LOD) for tetracycline is 19.27 μg L−1, the linear dynamics range is from 0.05 mg L−1 to 10 mg L−1, and the correlation coefficient (R2) is 0.98812. Moreover, the direct detection of four kinds of honey samples was conducted, and the recoveries of samples were shown to be in the range of 84.35–112.86%, and relative standard deviations (RSD, n = 11) of the method were in the range of 0.35–3.59%. With advantages of rapidity and high sensitivity, this research showed that MPT-MS is promising to be applied in on-site analysis of samples which are a little glutinous involving several fields, such as drug quality control, food safety and criminal investigation.

Real-time monitoring of volatile organic compounds (VOCs) is critical for a better understanding of chemical processes in ambient air or making minute-by-minute decisions in emergency situations. Proton transfer reaction mass spectrometry (PTR-MS) is nowadays the most commonly used technique for real-time monitoring of VOCs while membrane single photon ionization mass spectrometry (MI-SPI-MS) is a promising MS technique for online detection of trace VOCs. Here, to evaluate the potential of MI-SPI-MS as a complementary tool to PTR-MS, a comprehensive comparison has been performed between MI-SPI-MS and PTR-MS. By using two sets of standard gas mixtures TO15 and PAMS, SPI-MS shows advantages in the detection of ≥C5 alkanes, aromatics and halogens; especially for aromatics, the LODs can reach the ppt level. PTR-MS has performed better in the detection of alkenes, ketones and aldehydes. For outdoor measurements, a number of VOCs have been detected while using MI-SPI-MS and PTR-MS in parallel. Consistent temporal variations have been observed for toluene, C8-aromatics and C9-aromatics by the two instruments, with a more sensitive response from the MI-SPI-MS. Thus by measuring both standard gas mixture and complex ambient air samples, we have successfully demonstrated that MI-SPI-MS will be a helpful tool to provide important complementary information on aromatics and alkanes in air, and proper application of MI-SPI-MS will benefit the real-time monitoring of trace VOCs in relative fields.

Rationale Herbal dietary supplements (HDSs) adulterated with undeclared synthetic drugs can lead to serious health problems METHODS: A fast-switching positive/negative high-voltage (+/- HV) was developed to apply on electrospray ionization mass spectrometry (ESI-MS) with porous tips for rapid screening of five antirheumatic drugs in antirheumatic HDSs. The fast-switching (switch-time: 100 ms) negative and positive ions were alternately generated to perform full-MS and tandem-MS analysis, providing an effective method for rapid detection of analytes in whichever mode of detection was most suitable (negative or positive ion mode). The use of different tips and solvents was also optimized in this work. Results The limits of detection of the five antirheumatic drugs were found to be less than 0.1 ng/g (S/N > 3). The reproducibility of the five drugs was measured to be 10.0-23.3% (n = 5). A single sample analysis could be completed within 1 min. Rapid screening of a total of 28 real HDS samples collected from the market was examined by the fast-switching HV substrate-tip ESI-MS method, and the screening result was further validated by conventional liquid chromatography/mass spectrometry. Conclusions Overall, our results demonstrated that fast-switching HV substrate-tip ESI-MS is a rapid, reliable, and effective method for simultaneous screening of various analytes in complex samples.

Electrospray ionization mass spectrometry (ESI-MS) is one of the most powerful ionization techniques for characterization of analytes in various areas. Polar solvents such as methanol, water and acetonitrile are commonly used for ESI-MS analysis, while nonpolar solvents such as hexane were usually considered as non-ESI-friendly solvents. Following our recent work on observation of ESI process from solid substrates using nonpolar solvents (Anal Chim Acta, 2018, 1004, 51–57), the analytical properties of ESI-MS with solid substrates and nonpolar solvents were further systematically investigated in this study. Compared to the uses of polar solvents, our results revealed that nonpolar solvents could serve as extractants for enhanced detection of low-polar analytes from complex samples, and could serve as refrigerants for rapid freezing of samples such as peptides, proteins and protein-ligand complexes. Furthermore, nonpolar solvents could be used for formation of ammonia-transition-metal acetylacetonates complexes under ambient conditions.

Delay Extraction (DE) in Single Particle Mass Spectrometry (SPMS) provides substantial resolution enhancement. However, DE has two main drawbacks which are discussed in our article. First, ion peak position in this case becomes very sensitive to initial ion coordinate. Therefore, substantial peak jitter is observed when switching between mass spectra of individual particles. This peak jitter obstructs correct mass spectra accumulation resulting in wide peaks with irregular shapes in the accumulated mass spectrum, which leads to the fact that isotopic pattern identification becomes difficult. In the present article two ways of the peak jitter compensation, Dynamic Calibration and Mass Spectra correction based on Spectra Correlation, are proposed. It was shown that both proposed techniques provide substantial resolution improvement in the summed mass spectrum especially for small peaks with complex isotopic patterns. Second, time delay distorts regular quadratic dependence between time-of-flight and m/z. In our paper we also propose calibration equation with variable exponent for SPMS modified with DE. It is shown that usage of an exponent as a fitting parameter allows to achieve mass accuracy comparable with 4th degree equation proposed earlier.

Ion funnel is a new-style ion guider which can reduce spatial divergence and energy dispersity of the transmission ions by using radio frequency (RF) electric field to confine the ions radially and the direct current (DC) axial electric field to move the ions toward the exit, and thus it can greatly increase the ion transmission efficiency and improve the sensitivity of the mass spectrometry. Since ion funnel was invented in 1997, it has attracted a close attention of mass spectrometry scientists all over the world. Ion funnel has been used in various kinds of mass spectrometry, and built a bridge with high efficiency ion transmission between low vacuum ionization source and high vacuum mass analyzer. In this paper, the principle, technology development, and application progress of ion funnel are reviewed, and the future prospects are prospected.

Solid phase microextraction (SPME) is one of the most powerful sample preparation techniques for analyte extraction and enrichment from complex matrices. SPME fibers are commonly used to extract analytes from collected samples. Following our recent work on development of in vivo SPME swab that integrates an SPME fiber and a medical swab (Anal Chim Acta, 2020, 1124, 71-77), the multiple SPME fibers inserted into a medical swab (multiple-SPME swab) is further developed to couple with different mass spectrometry (MS) approaches for multidimensional analysis of human saliva in this work. The new features of cotton ball and SPME fiber of multiple-SPME swab are investigated. Biomarker discovery and disease diagnosis using multiple-SPME swab are also demonstrated. The present study shows that direct coupling multiple-SPME swab with different MS-based approaches could be simple and versatile in vivo method to expand the classes of analytes extracted simultaneously from human saliva.

Breath volatile biomarkers are capable of distinguishing patients with various cancers. However, high throughput analytical technology is a prerequisite to a large-cohort study intended to discover reliable breath biomarkers for cancer diagnosis. Single-photon ionization (SPI) is a universal ionization technology, and SPI-mass spectrometry (SPI-MS) shows a remarkable advantage in the comprehensive detection of volatile organic compounds (VOCs), in particular, nonpolar compounds. In this study, we have introduced SPI-MS coupled with on-line thermal desorption (TD-SPI-MS) to demonstrate nontarget analysis of breath VOCs for gastric cancer patients. The breath fingerprints of the gastric cancer patients were significantly distinct from that of the control group. Acetone, isoprene, 1,3-dioxolan-2-one, phenol, meta-xylene, 1,2,3-trimethylbenzene, and phenyl acetate showed higher relative peak intensities in the breath profiles of gastric cancer patients. A diagnostic prediction model was further developed by using a training set (121 samples) and validated with a test set (53 samples). The predication accuracy of the developed model was 96.2%, and the area under the curve (AUC) of the receiver operator characteristic curve (ROC) was 0.997, indicating a satisfactory prediction ability of the developed model. Thus, by taking gastric cancer as an example, we have shown that TD-SPI-MS will be a promising tool for high throughput analysis of breath samples to discover characteristic VOCs in patients with various cancers.

Chemical mass shifts between isomeric ions of o-, m-, and p-xylene were measured using a digital linear ion trap, and the directions and values of the shifts were found to be correlated to the collision cross sections of the isomers. Both forward and reverse scans were used and the chemical shifts for each pair of isomers in scans of opposite directions were in opposite signs. Using different voltage settings (namely the voltage dividing ratio-VDR) of the ion trap allows adding high order field components in the quadrupole field and results in larger chemical mass shifts. The differential chemical mass shift which combined the shifts from forward and reverse scans doubled the amount of chemical shift, e.g., 0.077 Th between o- and p-xylene, enough for identification of the type of isomer without using an additional ion mobility spectrometer. The feature of equal and opposite chemical mass shifts also allowed to null out the chemical mass shift by calculating the mean m/z value between the two opposite scans and remove or reduce the mass error caused by chemical mass shift. Graphical Abstract ᅟ.

Matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) is an important analytical technique for biological macromolecules, such as proteins, peptides and nucleic acid, especially in the field of microbial identification. On the basis of previous study, a linear MALDI-TOF MS was been designed and assembled for biological applications. The instrument comprised a vacuum system, a vacuum fast sample introduction system, an optical system, a time-of-flight mass analyzer, an ion source, a data acquisition system and an electronic control system. The ion source adopted two-stage source acceleration, delayed extraction and dynamic pulse focusing technique. The time-of-flight distance of field-free drift region was about 1 m. The optical system adopted a solid-state laser with adjustable frequency of 1–2000 Hz and spots of 20–100 μm. The angle of incidence laser was controlled at 5°. A series of experiments were carried out to further evaluate the instrument performances. It could not only analyze the samples more than 199 kDa, but also achieve isotope resolution at 1000–3000 Da and up to 900 (FWHM) at 5000–17000 Da. The minimum detectable concentration of gramicidin was 10 amol μL−1, absolute sensitivity reached up to 2.56 amol. Independent detection of saliva samples from different targets showed that the instrument had higher producibility. We identified Escherichia coli and Shigella spp., which are two common bacteria but difficult to be differentiated by mass spectrometry, showing its potential identification for clinical microorganism. In summary, this instrument can play a role on clinical examination in the near future.

Paper spray mass spectrometry (PSMS) is a powerful analytical technique for direct analysis of human body fluids. Schirmer paper is commonly used to collect human tears in clinical examination. In this work, Schirmer paper was used for noninvasive sampling and storing of healthy and disease-infected human tears, and was then performed PSMS for direct tear analysis under both positive and negative detection modes. 24 healthy tear samples, 34 tear samples of meibomain gland dysfunction, 44 tear samples of senile cataract, and 32 tear samples of allergic conjunctivitis were investigated in this work. Screening potential biomarkers of different eye diseases were carried out by combining multivariate analysis methods. 41 positive ions and 53 negative ions were proposed to be potential biomarkers in this work. The capacity of Schirmer paper for storing tear sample at different temperatures was investigated. The present study shows that direct coupling Schirmer PSMS with multivariate analysis could be a simple, rapid, and in vivo method for screening the biomarkers from human tears that involved different eye diseases.

Rationale Linear matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) is widely used in analytical and biomedical applications. The use of delayed extraction increases the resolution, but the roughness of the matrix crystals and the misalignment of the target plate in the order of a few micrometers cause a substantial spread in the ion TOF values and a decrease in mass accuracy. Methods The method of mass spectra correction based on the correlation of matrix fragment peaks in MALDI mass spectra was used. Experiments were performed using the MALDI-TOF instrument CMI-1600. SIMION 8.1 and MATLAB were used for ion motion simulations. Data analysis was done using the home-built custom-developed software and MATLAB. Results It was shown that the peak position drift in the MALDI-TOF mass spectra depends linearly on the TOF in a wide mass range. While using the linear correction of the TOF scale, an increase in m/z accuracy of more than 10 times was achieved. The mass accuracy was limited by the resolution of the fast Analog-to-Digital Converter (ADC) used. Conclusions It is expected that the proposed method will significantly increase the dynamic range, since it becomes possible to sum up corrected individual mass spectra without a significant loss of resolution. Timescale adjusting can be used for both linear TOF instruments and reflector systems of various configurations.

Single particle mass spectrometer is the instrument providing a plenty of valuable information on chemical and physical parameters of individual particles in real time. One of the main performance criteria of the instrument is the efficiency of particles detection (hit rate). Most of SPMS instruments use DC extraction, when the stationary high voltage is applied to the extraction electrodes. As the aerosol particles initially carry a certain charge, they can be deflected by this electric field thus decreasing the hit rate. It was realized in this work, that the delay extraction technique can eliminate the stochastic dispersion of the particles beam caused by their deflection in the stationary electric field. As the result, the hit rate of the instrument can be significantly improved. Also, as the effect of deflection in the electric field is mass dependent, it can cause the distortion of the measured size distribution of the particles. Hence, the delay extraction can bring the measured distribution closer to the real one. Thus, the delay extraction technique provides not only mass resolution improvement, but also increases the hit rate. The gain in the hit rate depends on the type of the particles. It can be two orders of magnitude for model particles, and up to 2–4 times for real particles. In the present work we report experiments and results showing the effect of the delay extraction on the particles beam divergence caused by particles charge, the hit rate improvement and the effect of the delay extraction on the measured particles size distribution.

Many field studies have investigated the formation mechanisms of organic aerosol (OA) based on bulk analysis, yet the source and formation process of individual organic particles may be quite different due to the diversity of chemical composition and mixing state in single particles. Here we present the observation results of chemical composition and mixing state of carbonaceous single particles at an urban site in Guangzhou. The carbonaceous particles accounted for 74.6% of the total detected single particles, and were grouped into four types including elemental carbon-aged (EC-aged), elemental and organic carbon (ECOC), organic carbon-rich (OC-rich) and secondary ions-rich (SEC) particles. The formation of EC-aged particles was closely associated with the absorption of organics onto fresh EC particles from primary sources, and the further enrichment of organics in EC-aged particles resulted in the production of ECOC particles. In the daytime OC-rich and SEC particles were mainly produced from the photochemical reactions, while in the nighttime their sharp increases were found along with the enrichment of nitrate and organic nitrogen fragments, suggesting the heterogeneous formation of nitrate and organic nitrogen in OC-rich and SEC particles. The production rates of carbonaceous particles were also investigated in an episodic event, and the EC-aged particles showed the highest production rate compared to the other carbonaceous particles both in the daytime and nighttime, suggesting a significant role of EC in the formation and aging process of carbonaceous particles. The results from this work have revealed different formation processes and production rates of carbonaceous particles due to their diversity in mixing state, providing further insights into the formation mechanisms of OA in field studies.

Non-thermal plasma (NTP) has developed into an emerging end-of-pipe technology for treating volatile organic compounds (VOCs) present in unhygienic point source of air streams. In this work, NTP oxidation of low-concentration ethyl acetate was performed in a coaxial double dielectric barrier discharge reactor. The effects of initial ethyl acetate concentration, gas flow rate, and external electrode length on ethyl acetate degradation were systematically investigated as a function of discharge power. In addition, detailed real-time and online proton transfer reaction mass spectrometry analysis was used to identify the transient species formation and transition in the various NTP oxidation periods of ethyl acetate. Based on the analysis of organic by-products, the degradation mechanism was speculated and the major reaction channels were presented. This study would deepen the understanding of plasma degradation of VOCs and reveal the plasma-chemical mechanism.

The eutrophication of surface water sources and climate changes have resulted in an annual explosion of cyanobacterial blooms in many irrigating and drinking water resources. To decrease health risks to the public, a rapid real time method for the synchronous determination of two usually harmful microcystins (MC-RR and MC-LR) in environmental water samples was built by employing a paper spray ionization method coupled with a time-of-flight mass spectrometer system. With this approach, direct analysis of microcystin mixtures without sample preparation has been achieved. Rapid detection was performed, simulating the release process of microcystins in reservoir water samples, and the routine detection frequency was every three minutes. The identification time of microcystins was reduced from several hours to a few minutes. The limit of detection is 1 μg/L, and the limit of quantitation is 3 μg/L. This method displays the ability for carrying out rapid, direct, and high-throughput experiments for determination of microcystins, and it would be of significant interest for environmental and food safety applications.

A special linear time-of-flight mass spectrometer, with relatively high mass resolution of 120 full width at half maximum (FWHM), for vacuum arc discharge ion source was developed. The instrument comprises a two-electrode ion extraction system, an ion gate, a drift tube, an einzel lens system and a micro channel plate (MCP) detector. Wire type ion gate is used for precise extraction of high energy (up to 40 keV) ion beam, and the drift tube length is 1.5 m. The extracted ion bunch is focused by the einzel lens system before it arrives the MCP detector, in order to improve the detection efficiency. The low mass ions in plasma extracted during the first few microseconds of discharge process are mainly O+ (m/z 16), C+ (m/z 12), O2+ (m/z 8) and C2+ (m/z 6). The instrument we have described can be a valuable diagnostic tool for high energy ion beam composition. It can be used both in fundamental research and in technological applications such as ion implantation.

A special cubic spline for histograms was examined as a possible tool for the processing of mass spectrometry data. Algorithms of interpolating and smoothing cubic splines are described shortly. It was shown that peak apex localizations using splines yield similar results as peak apex determinations using parabolas and centroids for high intensity peaks, while for low intensity peaks, the peak apex localizations using splines are superior. It also was shown that peak localization accuracies for real experimental time-of-flight mass spectral data are higher in case of peak localizations that use apex determinations as compared to peaks determined by centroid or Gaussian approximation of peaks. Some examples of peak detection algorithms using splines are given. A new method of peak intensity calculations is proposed taking into account the baseline. All approaches are directly applicable for the processing of TOF MS data, though specific changes may be desirable for other MS data.

A single particle aerosol mass spectrometer (SPAMS) was employed to characterize the particles in urban Beijing in the spring of 2011. The whole sampling time was divided into clear, hazy, and dusty day periods. Based on SPAMS results, the chemical composition of size-resolved particles in five major classes, including K-rich, carbonaceous, industry metal, dust, and Na-rich particles, and their corresponding sources were compared during clear, hazy, and dusty days. Air mass back trajectories are used to identify likely source regions for each period. Under stagnant meteorological conditions, local and regional emissions are a key factor in haze formation. K-rich and carbonaceous particles dominated under all conditions (25–54%), with higher contributions (23% and 29%) from industrial metal particles during hazy days, which could be attributed to the emission of biomass burning, coal combustion, and vehicle exhaust during all periods, whereas industrial metal processes are also a likely source for K-rich particles during hazy days. The aging of particles was observed over the whole sampling period, as evidenced by the presence of secondary species in all particle classes. Industrial metal particles possibly originate from industrial metal processes, vehicle exhaust, and coal combustion etc, while road and soil dust is also a possible source during dusty days. Dust particles increased greatly (17%) in a dust storm event with a coarse mode distribution, which are mainly associated with the mineral dust from deserted regions, whereas they could originate from local dust and coal combustion during non-dusty days. Last, Na-rich particles are mainly associated with industrial metal particles, coal, and fuel combustion during hazy days, and mineral dust during dusty days, respectively. Sea salt is a possible source of Na-rich particles under all conditions. Our analysis could shed a light on the understanding of the different source apportionment of aerosol particles under different meteorology/pollution conditions.

A specific delayed ion extraction (DIE) technique, which combines a standard rectangular extraction pulse with an exponential pulse, was introduced for a single particle mass spectrometry (SPMS) instrument, and it can focus ions in a wide mass range and results in a mass resolution improvement for the mass range of the studied ions. The experimental results indicate that the average mass resolution for positive ions is about 1000 when the mass-to-charge ratio (m/z) is greater than 70, and for negative ions, when the m/z is greater than 70, the average resolution can reach 2000. The highest mass resolutions achieved so far are 1260 for positive ions and 2400 for negative ions for SPMS, which are very beneficial for mass peak interpretation and chemical compound identification. The primary applications for atmospheric particle measurements show that the high mass resolution of SPMS with the DIE technique is very beneficial for the analysis of carbon and metallic element containing particles, and 39K+ with C3H3+ and 41K+ and C3H5+ in organic particles were successfully differentiated using SPMS. The results indicate that SPMS with DIE technique can significantly ease mass peak interpretation and improve the mass assignment ability during analysis. Furthermore, existing SPMS instruments can be improved by a facile retrofitting process to implement the DIE technique. Graphical Abstract The delayed ion extraction method shows a great mass resolution improvement for single particle mass spectrometry.

The extremely high concentrations of PM 2.5 (particulate matter with an aerodynamic meter ≤ 2.5 μm) during severe and persistent haze events in China have been closely related to the formation of secondary aerosols (SA). New particle formation (NPF) is the critical initial step of SA formation. New particles are commonly formed from gas-phase precursors (e.g., SO 2 , volatile organic compounds) via nucleation and initial growth, in which molecular clusters with a mobility diameter smaller than 3 nm (hereafter referred to nanoscale molecular clusters) will be involved throughout the whole process. Recently, significant breakthroughs have been obtained on NPF studies, which are mostly attributed to the technical development in the real-time analysis of size-resolved number concentration and chemical composition of nanoscale molecular clusters. Regarding the detection of size-resolved number concentrations of nanoscale molecular clusters, both methods and instruments have been well built up; practical application in laboratory-scale experiments and field measurements have also been successfully demonstrated. In contrast, real-time analysis of chemical composition of nanoscale molecular clusters has still encountered the great challenges caused by the complex organic compositions of the clusters, and improvement of present analytical strategies is urgently required. The better understanding in NPF will not only benefit the atmospheric modeling and climate predictions but also the source control of SA.

Rationale Although traditional analytical techniques like gas chromatography (GC) and GC/mass spectrometry (MS) offer satisfactory sensitivity and good reproducibility for the detection of phthalic acid esters (PAEs) in a variety of matrices, they involve laborious sample pretreatment, are time-consuming, and some are expensive and environmentally unfriendly. Furthermore, there are thousands of spirits on the market; therefore, rapid and high-throughout methods suitable for the consistent detection and quantification of PAEs in spirits are urgently required. Methods A new atmospheric pressure ionization method, named air-flow-assisted extractive electrospray ionization (EESI), has been developed. It is a variant on EESI and possesses the advantages of both EESI and air-flow-assisted ionization for direct analysis of samples without pretreatment. Combined with a quadrupole time-of-flight (QTOF) mass spectrometer, the method was used to directly analyze four PAEs, i.e., dipentyl phthalate, diethyl phthalate, benzyl butyl phthalate and didecyl phthalate, in spirits. Results The method exhibits excellent sensitivity, stability and convenience. Four different brands of spirits have been successfully analyzed. The total analysis time for one sample was within 1 min, and the limits of detection and limits of quantification of the samples are located in the range 0.011–0.035 and 0.038–0.087 µg g–1, respectively. Very good linearities, with correlation coefficients of 0.9758–0.9990, are observed for the samples in the range of 0.035 to 10 µg g–1. Conclusions The results indicate that the air-flow-assisted EESI combined with tandem mass spectrometry is an effective method for rapid and direct determination of PAEs in spirits without sample pretreatment. Copyright © 2015 John Wiley & Sons, Ltd.

To diagnose the vacuum arc discharge process, a miniature time-of-flight mass spectrometer (TOF MS) with compact structure was developed for cathodic vacuum arc discharge ion source. An orthogonal acceleration region and an angle reflector were employed for the miniature TOF MS instrument. Especially, a small extraction hole in the acceleration region was set for getting relative high mass resolution, an ion detector with a large rectangular effective area were designed for getting wide ion kinetic energy distribution measurement capability. The compact size of the TOF MS is 413 mm × 250 mm × 414 mm, the mass resolution is 600 (FWHM) and the detection range of ion kinetic energy is two orders of magnitude. A copper cathodic vacuum arc discharge ion source was tested and the charge states of Cu ions from 1+ to 3+ were detected. The miniature TOF MS was successfully developed with relative high mass resolution and wide ion kinetic energy distribution measurement capability which could be used to diagnose the cathodic vacuum arc discharge plasma.

To investigate the composition and possible sources of aerosol particles in Beijing urban area, a single particle aerosol mass spectrometer (SPAMS) was deployed from April 22 to May 4, 2011. 510,341 particles out of 2,953,200 sized particles were characterized by SPAMS in combination with the ART-2a neural network algorithm. The particles were classified as rich-K (39.79%), carbonaceous species (32.7%), industry metal (19.2%), dust (5.7%), and rich-Na (1.76%). Industrial emissions related particles, rich-Fe, rich-Pb, and K-nitrate, were the major components of aerosol particles during haze periods, which were mainly from the steel plants and metal smelting processes around Beijing. Under stagnant meterological conditions, these regional emissions have a vital effect on haze formation. Organic carbon (OC) particles were attributed to biomass burning. NaK-EC was likely to come from local traffic emissions. Internally mixed organic and elemental carbon (OCEC) was found to be from possible sources of local traffic emission and biomass burning. It was found that coarse dust particles were mainly composed of four different types of dust particles, dust-Si, dust-Ca, dust-Al, and dust-Ti. It is the first time that SPAMS was used to study a dust storm in Beijing. Our results showed that SPAMS could be a powerful tool in the identification and apportionment of aerosol sources in Beijing, providing useful reference information for environmental control and management.

The formation of oxalic acid and its mixing state in atmospheric particulate matter (PM) were studied using a single particle aerosol mass spectrometer (SPAMS) in the summer and winter of 2014 in Heshan, a supersite in the rural area of the Pearl River Delta (PRD) region in China. Oxalic acid-containing particles accounted for 2.5 % and 2.7 % in total detected ambient particles in summer and winter, respectively. Oxalic acid was measured in particles classified as elemental carbon (EC), organic carbon (OC), elemental and organic carbon (ECOC), biomass burning (BB), heavy metal (HM), secondary (Sec), sodium-potassium (NaK) and dust. Oxalic acid was found predominantly mixing with sulfate and nitrate during the whole sampling period, likely due to aqueous phase reactions. In summer, oxalic acid-containing particle number and ozone concentration followed a very similar trend, which may reflect the significant contribution of photochemical reactions to oxalic acid formation. Furthermore, favorable in-situ pH (2–4) conditions were observed, which promote Fenton like reactions for efficient production of •OH in HM type particles. A mechanism in which products of photochemical oxidation of VOCs partitioned into the aqueous phase of HM particles, followed by multistep oxidation of •OH through Fenton like reactions to form oxalic acid is proposed. In wintertime, carbonaceous type particles contained a substantial amount of oxalic acid as well as abundant carbon clusters and biomass burning markers. The general existence of nitric acid in oxalic acid-containing particles indicates an acidic environment during the formation process of oxalic acid. Organosulfate-containing particles well correlated with oxalic acid-containing particles during the episode, which suggests the formation of oxalic acid is closely associated with acid-catalyzed reactions of organic precursors.