•LPPI mass spectrometry were demonstrated to be ultrasensitive for realtime detection.•The obtained LODs are superior to those of other competitive techniques.•Limits of detection for benzene, toluene, and ethylbenzene are 0.5–0.8 pptv.•Detection sensitivities for benzene, toluene, and ethylbenzene are 4–7 counts/pptv.•Reliable accuracy and precision are demonstrated in two calibration methods.This paper reports on the advanced development of an ultrasensitive method for the detection of benzene, toluene, and ethylbenzene (or BTE) by low-pressure photoionization mass spectrometry (LPPI-MS). The LPPI source is composed of a laboratory-assembled krypton lamp and a stainless steel cylindrical ionizer. A compact V-shaped mass spectrometer is coupled to the LPPI source with a set of ion immigration optics under dc bias. The fixed standard concentration (FSC) and fixed standard volume (FSV) method are employed to calibrate the sensitivities of the instrument. The corresponding detection sensitivity toward BTE is 4–7 counts/pptv and the 2σ limit of detection (LOD) is 0.5–0.8 part per trillion by volume (pptv). In addition, the measurement accuracy is 95%–105%, and the corresponding precision ranges from 3% to 15% and from 9% to 31% for the FSC and FSV methods, respectively. The stability (standard deviation) of LPPI-MS for a 1 ppbv BTE mixture is less than 0.025 (>12 h). In the detection of BTE, water in ambient air is the most significant interfering factor, leading to the increased background, and inferior LODs of 1–2 pptv for BTE under an RH of ∼90% is observed. Experimental results indicated that LPPI-MS is reliable for the detection of sub-pptv levels of BTE under laboratory conditions.Download high-res image (210KB)Download full-size image

•Lung cancer related VOCs were sensitively detected by CH2Cl2-doped LPPI-MS.•n-Propanol, n-pentanal, acetone, and butyl acetate were tested as typical markers.•Eight-fold enhanced signals were observed in the normal and spiked breath samples.Real-time detection of lung cancer-related volatile organic compounds (VOCs) is a promising, non-intrusive technique for lung cancer (LC) prescreening. In this study, a novel method was designed to enhance the detection selectivity and sensitivity of LC-related polar VOCs by dichloromethane (CH2Cl2) doping-assisted low-pressure photoionization mass spectrometry (LPPI-MS). Compared with conventional LPPI-MS, CH2Cl2 doping-assisted LPPI-MS boosted the peak intensities of n-propanol, n-pentanal, acetone, and butyl acetate in nitrogen specifically by 53, 18, 16, and 43 times, respectively. The signal intensities of their daughter ions were inhibited or reduced. At relative humidity (RH) of 20%, the sensitivities of n-propanol, n-pentanal, acetone, and butyl acetate detection ranged from 116 to 452 counts/ppbv with a detection time of 10 s and R2 >0.99 for the linear calibration curves. The method was also applicable under higher RH levels of 50% and 90%. Breath samples obtained from 10 volunteers and spiked samples were investigated. Eight-fold enhancements in the signal intensities of polar VOCs were observed in the normal and spiked samples. These preliminary results demonstrate the efficacy of the dichloromethane doping-assisted LPPI technique for the detection of LC-related polar VOCs. Further studies are indispensible to illustrating the detailed mechanism and applying the technique to breath diagnosis.

•Low-pressure photoionization mass spectrometric technique was used.•The pptv-level threat agents were detected within 10 s.•The LODs were improved by 3–4 orders of magnitudes.On-spot monitoring of threat agents needs high sensitive instrument. In this study, a low-pressure photoionization mass spectrometer (LPPI-MS) was employed to detect trace amounts of vapor-phase explosives and chemical warfare agent mimetics under ambient conditions. Under 10-s detection time, the limits of detection of 2,4-dinitrotoluene, nitrotoluene, nitrobenzene, and dimethyl methyl phosphonate were 30, 0.5, 4, and 1 parts per trillion by volume, respectively. As compared to those obtained previously with PI mass spectrometric techniques, an improvement of 3–4 orders of magnitude was achieved. This study indicates that LPPI-MS will open new opportunities for the sensitive detection of explosives and chemical warfare agents.

β-Sitosterol is the most abundant phytosterol lipid in plants. This study demonstrates a method for analyzing β-sitosterol using a laboratory-built MALDI-TOF mass spectrometer. The matrix compound, solvent system, laser intensity, alkali ion, and analyte concentration for sample preparation were optimized to acquire reproducible and informative mass spectra of the analyte. The best MALDI spectrum of β-sitosterol was obtained by mixing the analyte solution with an equal volume of 2,4-DHB/iPrOH–H2O (9:1) solution (60 mM) at 13.5 mJ cm−2 laser intensity. Under the optimized experimental conditions, β-sitosterol generated intense peaks consisting of the initial lipids and their oxidation products. The former included mass peaks at m/z 396.6, 397.6, 436.9, and 452.6, which corresponded to the [M − H2O]+, [M + H − H2O]+, [M + Na]+, and [M + K]+ ions of β-sitosterol, respectively. The latter included mass peaks at m/z 412.7, 413.7, and 431.9, which corresponded to the [M′ − H2O]+, [M′ + H − H2O]+, and [M′ + H]+ ions of mono-oxidized β-sitosterol, respectively. A quantitative analysis of β-sitosterol was also conducted using a matrix peak. Calibration curves obtained for β-sitosterol show a good linear range of three orders of magnitude with a regression coefficient square of 0.992. The linear ranges were between 12.1 and 1207.5 μM. The detection limit was 10 nM. These results demonstrate the potential application of MALDI mass spectrometry for analyzing phytosterols.

As a renowned s-triazine herbicide, ametryn is worldwide emitted into the atmosphere in both gaseous and particulate phases via spray drifts from treatments and post application emissions, but its chemical degradation in the atmosphere has not been well characterized. In this study, the heterogeneous kinetics of particulate ametryn with NO3 radicals were investigated with a mixed-phase relative rate method. A vacuum ultraviolet photoionization aerosol time-of-flight mass spectrometer (VUV-ATOFMS) and an atmospheric gas analysis mass spectrometer were synchronously used to online monitor the decays of particulate ametryn and gas-phase isoprene. The reactive uptake coefficient of NO3 radicals on ametryn particles was calculated to be 2.9 × 10−2, according to the measured ametryn loss ratio and the average NO3 concentration. The effective rate constant for the heterogeneous reaction of particulate ametryn with NO3 radicals measured under experimental conditions was 8.4 × 10−13 cm3 molecule−1 s−1. In addition, atraton, ametryn sulfoxide and ametryn sulfone were identified as the reaction products by gas-chromatography-mass spectrometry (GC-MS) analysis. The experimental results might shed light on the chemical behavior of atmospheric ametryn at night-time.

In this study, MALDI-TOF lipid profiling was used as an experimental attempt to characterize pollen grains. Magnolia denudata, Lilium brownii var. viridulum, Pinus tabulaeformis, and Populus tomentosa pollen grains were collected as samples. The lipids in pollen grains were extracted by the methods of microwave-assisted formic acid digestion, microwave-assisted 2-aminoethanol solvolysis, and ultrasonic wave-assisted 2-aminoethanol solvolysis. The extracts were analyzed with an online MALDI-TOF mass spectrometer. Membrane-associated phospholipids (phosphatidylserine and phosphatidylcholine) and diacylglycerol in pollen coats were observed. The method of microwave-assisted formic acid digestion presented better lipid profiles. The characteristic mass peaks observed in the experiment may be used as potential signatures for characterizing pollen grains.Graphical abstractHighlights► Lipids in pollen grains of four species are extracted by digestion and solvolysis. ► The extracts are analyzed with an online MALDI-TOF mass spectrometer. ► Characteristic lipid profiles of pollen grains are obtained.

•Lipid profiles of six basidiospores were obtained with MALDI-TOF MS.•Sample preparation strategies of the MALDI analyses were optimized.•Phospholipids, diacylglycerols, and triacylglycerols were observed.Lipid profiles of microorganisms, such as bacteria and fungi, have been studied intensively and have shown great potential for species differentiation. However, lipid profiles of basidiospores are seldom reported in the literature. In this study, the MALDI-TOF mass spectra of lipids extracted from basidiospores of Auricularia auricula, Agaricus bisporus, Hypsizygus marmoreus, Lentinus edodes, Pleurotus ostreatus, and Volvariella volvacea were obtained using a laboratory-built MALDI-TOF mass spectrometer, equipped with an aerodynamic lens assembly as a direct deposition interface. The sample preparation strategies included matrices, solvents, and analyte/matrix ratios, which were optimized to acquire reproducible and informative mass spectra of lipid mixtures. Phospholipids, diacylglycerols, and triacylglycerols were observed by mixing the lipid extracts with equal volumes of 2,4-DHB/methanol solution (10 mg/mL). Species-specific lipid profiles of basidiospores were obtained. The experimental results demonstrate that the lipid profiles can be used to differentiate basidiospores.

Polycyclic aromatic hydrocarbons (PAHs) and their derivates are mutagenic and carcinogenic substances widely distributed in the atmospheric environment. In this study, effective rate constants for heterogeneous reactions of NO3 radicals with five 4-ring PAHs [benzo[a]anthracene (BaA), chrysene (Ch), pyrene (Py), 1-nitropyrene (1-NP), and 1-hydroxypyrene (1-OHP)] adsorbed on suspended azelaic acid particles are investigated by a mixed-phase relative rate method with gas-phase isoprene as the reference substance. The concentrations of suspended PAH particles and gas-phase isoprene are monitored concurrently by a real-time vacuum ultraviolet photoionization aerosol time-of-flight mass spectrometer (VUV-ATOFMS) and an online atmospheric gas analysis mass spectrometer, respectively. The obtained effective rate constants for the reactions of BaA, Ch, Py, 1-NP, and 1-OHP particles with NO3 radicals are 4.3 × 10–12, 4.0 × 10–12, 6.4 × 10–12, 1.3 × 10–12, and 1.0 × 10–11 cm3·molecule–1·s–1, respectively, and their corresponding atmospheric lifetimes range from several minutes to half an hour at the NO3 radical concentration of 5 × 108 molecules·cm–3. In addition, the NO3 uptake coefficients on particulate PAHs are estimated according to the consumption of PAHs under the exposure of NO3 radicals. The experimental results of these heterogeneous reactions in the aerosol state provide supplementary knowledge for kinetic behaviors of airborne PAHs particles.

Methoxyphenols, tracers for wood smoke, are emitted into the atmosphere in large quantities, but their chemical degradation in the atmosphere has not been well characterized. In this study, heterogeneous kinetics of particulate syringaldehyde (SA), vanillic acid (VA), and coniferyl aldehyde (CA) with NO3 radicals is investigated with a mixed-phase relative rate method. A vacuum ultraviolet photoionization aerosol time-of-flight mass spectrometer and an atmospheric gas analysis mass spectrometer are used to monitor online the decays of particulate methoxyphenols and gas-phase isoprene synchronously. The reactive uptake coefficients of NO3 radicals on SA, VA, and CA particles are calculated to be 0.33, 0.31, and 0.28, respectively, according to the measured methoxyphenol loss ratios and the average NO3 concentrations. The effective rate constants for heterogeneous reactions of particulate SA, VA, and CA with NO3 radicals measured under experimental conditions are 5.7 × 10–12, 5.2 × 10–12, and 3.5 × 10–12 cm3 molecule–1 s–1, respectively. In addition, oxalic acid, 2,6-dimethoxybenzoquinone, 5-nitro-VA, 4,6-dinitrogaiacol, protocatechuic acid, vanillin, 5-nitrovanillin, VA, and 5-nitro-CA are identified as the reaction products by gas chromatography–mass spectrometry analysis. On the basis of the identified products, the reaction mechanisms of methoxyphenols with NO3 radicals are proposed. The main transformation pathway of methoxyphenols is the NO3 electrophilic addition, followed by H-abstraction and nitro-substituted processes. The experimental results might shed light on the chemical behaviors of methoxyphenols at night.

Rapid identification of Bacillus spores has attracted great interest in the medical and forensic communities due to the highly pathogenic nature of certain Bacillus species and its potential application in bioweapons. In this study, we evaluated the feasibility of rapid and reliable identification of several Bacillus spp. (B. subtilis, B. cereus, B. megaterium, B. pumilus, and B. sphaericus) using online MALDI-TOF mass spectrometry combined with lipid profiling. The bacterial cultures in liquid medium were extracted with methanol and chloroform, and the extracts were aerosolized into droplets and immediately analyzed with an online MALDI-TOF mass spectrometer. Results showed that phosphatidylethanolamine (PE), phosphatidylglycerol (PG), and diglycosyldiacylglycerol (DGDG) were present in the mass spectra, as alkali metal adducts. The unique lipid profiles obtained from these Bacillus spp. allowed us to differentiate between them. The reliability and reproducibility of the rapid identification method for Bacillus were tested under different experimental conditions. An alternative online chemotaxonomic method for bacterial identification is demonstrated.

The rapid identification of bacteria is of increasing interest in food, biosafety, and clinical analysis. In this paper, we report a technique for rapid lipid profiling of bacteria by online droplet-deposited MALDI mass spectrometry. In the experiment, lipids in bacterial cells (Escherichia coli, Salmonella, and Bacillus subtilis) are extracted with the mixture of chloroform/methanol via ultrasonication. The extracts are nebulized into suspended droplets and then instantly analyzed with an online droplet-deposited MALDI-TOF mass spectrometer. The lipid profiles of the three bacteria cultured in nutrient broth and LB (Lysogeny Broth) medium are obtained. The lipids phosphatidylethanolamine (PE), diglycosyl diacylglycerol (DGDG), and phosphatidylglycerol (PG) are observed in the MALDI-TOF mass spectra. The MALDI-TOF mass spectrum of each bacterial extract shows a characteristic profile. The experimental results demonstrate that the present technique is capable of conducting rapid lipid analysis and has the potential for rapid bioaerosol detection.Graphical abstractHighlights► Online droplet-deposited MALDI mass spectrometer is applied to detect bacteria. ► Characteristic lipid profiling of three bacteria are obtained. ► The present technique is capable of conducting rapid lipid analysis and has the potential for rapid bioaerosol detection.

This technical note reports a design utilizing an aerodynamic lens assembly to transport suspended sample particles directly onto the target plate and conduct in situ MALDI analysis. The design provides a new alternative method for online MALDI analysis. The matrix/analyte/salt-contained particles sampled by a nozzle are focused into a particle beam with an aerodynamic lens assembly and then deposited on the target plate directly. The deposited particles are in situ desorbed/ionized by a 266 nm laser beam with an incidence angle of 50 degrees. The generated ions are detected with a reflectron mass spectrometer capable of delayed ion extraction and ion gating. The MALDI-TOF mass spectra of poly(ethylene glycol) (PEG) 1000, 2000, and 4000 particles are obtained in the experiment. The initial experimental results demonstrate that the design can be used for online MALDI analysis.

Pirimiphos-methyl (PMM) is a widely used pesticide that can be released into the atmosphere in the gas phase and the condensed phase. The reaction of suspended PMM particles with ozone is investigated using an online vacuum ultraviolet photoionization aerosol time-of-flight mass spectrometer (VUV-ATOFMS) and a scanning mobility particle sizer (SMPS). The reactions are conducted in an 180 L reaction chamber. The identification of particulate products detected with VUV-ATOFMS is proposed on the basis of GC-MS analysis of PMM ozonation products in methylene dichloride solution. The heterogeneous reactive rate constant of PMM with azelaic acid as matrix under room temperature (293 ± 2 K) is (1.97 ± 0.25) × 10−17 cm3 molecules−1 s−1. The corresponding lifetime at 100 ppbv of ozone is 5.2 ± 0.66 h, and the reactive uptake coefficient (γ) for ozone on PMM particles is (8.5 ± 1.1) × 10−4. Additionally, ozonation of PMM vapor is conducted, and the rapid formation of secondary organic aerosol (SOA) is observed in the homogeneous ozonation of gas-phase PMM. The experimental results indicate that ozone is an important atmospheric oxidant for the transformation of PMM in the atmosphere.

Vinclozolin is a widely used fungicide that can be released into the atmosphere via application and volatilization. This paper reports an experimental investigation on the heterogeneous ozonation of vinclozolin particles. The ozonation of vinclozolin adsorbed on azelaic acid particles under pseudo-first-order conditions is investigated online with a vacuum ultraviolet photoionization aerosol time-of-flight mass spectrometer (VUV-ATOFMS). The ozonation products are analyzed with a combination of VUV-ATOFMS and GC/MS. Two main ozonation products are observed. The formation of the ozonation products results from addition of O3 on the C−C double bond of the vinyl group. The heterogeneous reactive rate constant of vinclozolin particles under room temperature is (2.4 ± 0.4) × 10−17 cm3 molecules−1 s−1, with a corresponding lifetime at 100 ppbv O3 of 4.3 ± 0.7 h, which is almost comparable with the estimated lifetime due to the reaction with atmospheric OH radicals (∼1.7 h). The reactive uptake coefficient for O3 on vinclozolin particles is (6.1 ± 1.0) × 10−4.

The heterogeneous ozonation of suspended malathion and chlorpyrifos particles are studied in real-time with a vacuum ultraviolet photoionization aerosol time-of-flight mass spectrometer (VUV-ATOFMS). The pesticide particles with the diameter of hundreds of nanometers are generated by the homogeneous nucleation method using azelaic acid as nucleus. The reactions are carried out in an aerosol reaction chamber under ambient pressure (1 atm) and room temperature (298 K), respectively. The time-of-flight mass spectra of the solid-state ozonation products of malathion and chlorpyrifos are obtained. The assignments of the mass spectra reveal that the major ozonation products of malathion particles are s-(1,2-diethoxycarbonyl)ethyl-O,O-dimethylphosphorothioate (malaoxon), 2-mercapto-succinic acid diethylester, 1,2-dicarbethoxyethyl-dimethoxyphosphinyldisulfide and bis(1,2-bis-ethoxycarbonyl-ethyl)disulfide. The experimental results reveal that water vapor can enhance the formation of malaoxon, 2-mercapto-succinic acid diethylester and bis(1,2-bis-ethoxycarbonyl-ethyl)disulfide. In the case of chlorpyrifos, the sole ozonation product observed is 3,5,6-trichloro-2-pyridyl-diethylphosphate (chlorpyrifos oxon). The pathways of heterogeneous ozonation of malathion and chlorpyrifos particles are proposed. The atmospheric lifetimes of malathion and chlorpyrifos particles towards ozone reaction are estimated based on the time-dependent mass spectrometric signals obtained.

As a renowned s-triazine herbicide, ametryn is worldwide emitted into the atmosphere in both gaseous and particulate phases via spray drifts from treatments and post application emissions, but its chemical degradation in the atmosphere has not been well characterized. In this study, the heterogeneous kinetics of particulate ametryn with NO3 radicals were investigated with a mixed-phase relative rate method. A vacuum ultraviolet photoionization aerosol time-of-flight mass spectrometer (VUV-ATOFMS) and an atmospheric gas analysis mass spectrometer were synchronously used to online monitor the decays of particulate ametryn and gas-phase isoprene. The reactive uptake coefficient of NO3 radicals on ametryn particles was calculated to be 2.9 × 10−2, according to the measured ametryn loss ratio and the average NO3 concentration. The effective rate constant for the heterogeneous reaction of particulate ametryn with NO3 radicals measured under experimental conditions was 8.4 × 10−13 cm3 molecule−1 s−1. In addition, atraton, ametryn sulfoxide and ametryn sulfone were identified as the reaction products by gas-chromatography-mass spectrometry (GC-MS) analysis. The experimental results might shed light on the chemical behavior of atmospheric ametryn at night-time.

β-Sitosterol is the most abundant phytosterol lipid in plants. This study demonstrates a method for analyzing β-sitosterol using a laboratory-built MALDI-TOF mass spectrometer. The matrix compound, solvent system, laser intensity, alkali ion, and analyte concentration for sample preparation were optimized to acquire reproducible and informative mass spectra of the analyte. The best MALDI spectrum of β-sitosterol was obtained by mixing the analyte solution with an equal volume of 2,4-DHB/iPrOH–H2O (9:1) solution (60 mM) at 13.5 mJ cm−2 laser intensity. Under the optimized experimental conditions, β-sitosterol generated intense peaks consisting of the initial lipids and their oxidation products. The former included mass peaks at m/z 396.6, 397.6, 436.9, and 452.6, which corresponded to the [M − H2O]+, [M + H − H2O]+, [M + Na]+, and [M + K]+ ions of β-sitosterol, respectively. The latter included mass peaks at m/z 412.7, 413.7, and 431.9, which corresponded to the [M′ − H2O]+, [M′ + H − H2O]+, and [M′ + H]+ ions of mono-oxidized β-sitosterol, respectively. A quantitative analysis of β-sitosterol was also conducted using a matrix peak. Calibration curves obtained for β-sitosterol show a good linear range of three orders of magnitude with a regression coefficient square of 0.992. The linear ranges were between 12.1 and 1207.5 μM. The detection limit was 10 nM. These results demonstrate the potential application of MALDI mass spectrometry for analyzing phytosterols.