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Methanol-to-olefins (MTO) is a very important industrial catalysis technique for the production of light olefins, which is of great economic value and strategic significance. However, it is a great challenge for the traditional analytical methods to obtain the real-time information of product variation during MTO reaction process, which is vital for the conversion process research and mechanism explanation. In this study, a single photon ionization time-of-flight mass spectrometry (SPI-TOFMS) based on a windowless RF-discharge (WLRF) lamp was developed for real-time measurement of catalytic product during the initial stage of MTO reaction. The vacuum ultraviolet (VUV) photon energy was easily adjusted by changing the discharge gas. Argon (Ar) gas was eventually adopted as the discharge gas, since it produces photons with appropriate energy of 11.6 eV and 11.8 eV for ionization of light olefin molecules. The detection sensitivities of ethylene and propylene were largely improved to a substantially similar level with limits of detection (LODs) down to 16.98 and 9.64 ppbv, respectively. The initial stage of MTO reaction was real-time monitored with a high temporal resolution of 0.5 s, revealing that ethylene was the first olefin product followed by propylene. The successful application of WLRF-SPI-TOFMS in the monitoring of MTO catalytic process indicated broad application prospects of this instrument in the industrial reaction process monitoring. [ABSTRACT FROM AUTHOR]

An in-source, stretched, hollow fiber membrane (HFM) inlet has been developed to improve the sensitivity of on-line time-of-flight mass spectrometry (TOFMS) with a vacuum ultraviolet (VUV) lamp based single photon ionization (SPI) source for the direct analysis of liquid samples. A 2-cm HFM was stretched to 8 cm in length, and placed in the ion source and directly under the VUV lamp window with a distance of 15 mm. Compared with the conventional flow-through configuration under the same experimental conditions, the signal intensities of selected volatile organic compounds (VOCs) of methyl tert-butyl ether (MTBE), ethyl tert-butyl ether (ETBE), benzene, toluene and p-xylene were increased over 5-fold in magnitude, and the response time was shortened to one-third. The limits of detection (LOD) of MTBE, ETBE, benzene, toluene and p-xylene ranged from 0.25 to 1.3 μg L−1 with a measurement time of 60 s, and three orders of linear range were obtained with correlation coefficients of 0.9972–0.9992. The present results suggest that the in-source stretched HFM is a simple and effective way to increase the sensitivity and shorten response time of the membrane inlet, and we believe that it will also be beneficial to other types of on-line mass spectrometer for the on-line analysis of VOCs in water with a VUV lamp based SPI ion source. [ABSTRACT FROM AUTHOR]

Abstract: As efforts continue to elucidate laser–cluster interactions, we investigated the influence of laser wavelength on ion products. In this study, a pulsed methyl iodide cluster was irradiated with a Nd–YAG nanosecond laser, and the ion products were analyzed using time-of-flight mass spectrometry. Multiple-charge atomic ions of C q+ and I q+(q ⩾2) were observed using 532 and 1064nm laser wavelengths; however, only single-charge atomic and molecular ions appeared at 266 and 355nm. We show that the charge-state distribution for multiple-charge ions is almost independent of laser intensity. A three-stage model was developed to further understand these experimental results: the inverse electron bremsstrahlung heating rate is proportional to the square of laser wavelength, which seems to explain the dependence of multiple-charge ions on the wavelength. [Copyright &y& Elsevier]

Highly sensitive and rapid detection of ethylene, the smallest alkene of great significance in human physiological metabolism remains a great challenge. In this study, we developed a new photoionization-induced substitution reaction chemical ionization time-of-flight mass spectrometry (PSCI-TOFMS) for trace exhaled ethylene detection. An intriguing ionization phenomenon involving a substitution reaction between the CH 2 Br 2 + reactant ion and ethylene molecule was discovered and studied for the first time. The formation of readily identifiable [CH 2 Br·C 2 H 4 ]+ product ion greatly enhanced the ionization efficiency of ethylene, which led to approximately 800-fold improvement of signal intensity over that in single photon ionization mode. The CH 2 Br 2 + reactant ion intensity and ion-molecule reaction time were optimized, and a Nafion tube was employed to eliminate the influence of humidity on the ionization of ethylene. Consequently, a limit of detection (LOD) as low as 0.1 ppbv for ethylene was attained within 30 s at 100 % relative humidity. The application of PSCI-TOFMS on the rapid detection of trace amounts of exhaled ethylene from healthy smoker and non-smoker volunteers demonstrated the satisfactory performance and potential of this system for trace ethylene measurement in clinical diagnosis, atmospheric measurement, and process monitoring. [Display omitted] • A new PSCI-TOFMS was developed for highly sensitive detection of trace exhaled ethylene. • Ethylene could be measured by [CH 2 Br·C 2 H 4 ]+ substituent ions with a distinct 1:1 abundance ratio. • 800-fold increase in signal intensity was obtained compared to SPI mode. • The LOD of ethylene was as low as 0.1 ppbv within 30 s at 100 % humidity. • The variations of 8 common VOCs, including ethylene, in the exhaled breath of healthy smokers were tracked. [ABSTRACT FROM AUTHOR]

Trimethylamine (TMA) is ubiquitous in the marine systems and may affect atmospheric chemistry as a precursor and strong stabilizer of atmospheric secondary aerosol, influencing cloud formation. Rapid and accurate measurement of the concentration of TMA in seawater is challenging due to their polarity, aqueous solubility, volatility and existence at low concentrations in marine environments. In this study, a dopant-assisted atmospheric pressure photoionization time-of-flight mass spectrometry (DA-APPI-TOFMS) coupled with a dynamic purge-release method was developed for rapid and sensitive analysis of TMA in seawater. A novel three-zones ionization source has been developed for improving the ionization efficiency of analyte molecules and minimizing the influence of high-humidity of the sample gas, which allowed direct analysis of high-humidity (RH> 90%) gas samples from microbubble purging process by the mass spectrometer. At atmospheric pressure, the three-zones ionization source allows the use of high-speed purge gas to quickly purge all organic amines dissolved in the water into the gas phase, ensuring quantitative accuracy. The limit of quantification (LOQ) for TMA down to 0.1 μg L−1 was obtained in less than 2 min by consuming only 2 mL seawater sample. This method was applied for the determination of the concentrations of TMA in the coastal seawater to validate its practicability and reliability for analysis of trace amines in marine environments. Image 1 • Dynamic purge-release combined with dopant-assisted APPI-TOFMS. • A novel three-zones ionization source has been developed for improving the ionization efficiency and minimizing the influence of high-humidity. • The limit of quantification for TMA down to 0.1 μg L-1 was obtained in less than 2 min by consuming only 2 mL seawater sample. [ABSTRACT FROM AUTHOR]

Exhaled hydrogen cyanide (HCN) has been extensively investigated as a promising biomarker of the presence of Pseudomonas aeruginosa in the airways of patients with cystic fibrosis (CF) disease. Its concentration profile for exhalation can provide useful information for medical disease diagnosis and therapeutic procedures. However, the complexity of breath gas, like high humidity, carbon dioxide (CO 2) and trace organic compounds, usually leads to quantitative error, poor selectivity and sensitivity for HCN with some of existing analytical techniques. In this work, acetone-assisted negative photoionization (AANP) based on a vacuum ultraviolet (VUV) lamp with a time-of- flight mass spectrometer (AANP-TOFMS) was firstly proposed for online measurement of trace HCN in human breath. In-source collision-induced dissociation (CID) was adopted for sensitivity improvement and the signal response of the characteristic ion CN− (m/z 26) was improved by about 24-fold. For accurate and reliable analysis of the exhaled HCN, matrix influences in the human breath including humidity and CO 2 were investigated, respectively. A Nafion tube was used for online dehumidification of breath samples. Matrix-adapted calibration in the concentration range of 0.5–50 ppbv with satisfactory dynamic linearity and repeatability was obtained. The limit of quantitation (LOQ) for HCN at 0.5 ppbv was achieved in the presence of 100% relative humidity and 4% CO 2. Finally, the method was successfully applied for online determination of human mouth- and nose-exhaled HCN, and the nose-exhaled HCN were proved to be reliable for assessing systemic HCN levels for individuals. The results are encouraging and highlight the potential of AANP-TOFMS with in-source CID as a selective, accurate, sensitive and noninvasive technique for determination of the exhaled HCN for CF clinical diagnosis and HCN poisoning assessment. Image 1 • Acetone-assisted negative photoionization-TOFMS was firstly proposed for online measurement of trace HCN in human breath. • In-source collision-induced dissociation (CID) was adopted for sensitivity improvement. • Matrix influences in the human breath including humidity and CO 2 were investigated for accurate and reliable analysis. • Satisfactory selectivity, sensitivity and repeatability was obtained with this method. [ABSTRACT FROM AUTHOR]

High-pressure photoionization time-of-flight mass spectrometry (HPPI-TOFMS) is a versatile and highly sensitive analytical technique for online and real-time analysis of trace volatile organic compounds in complex mixtures. However, discrimination of isomers is usually a great challenge for the soft ionization method, and matrix effect is also inevitable under high pressure in the HPPI source. In this work, we describe a first attempt to develop a two-dimensional (2D) hyphenated instrument by coupling of a multi-capillary column (MCC) with a HPPI-TOFMS to overcome these problems. The capability of the MCC-HPPI-TOFMS for discrimination of isomeric compounds and elimination of the matrix effect was demonstrated by analyzing flavor mixtures. With the merits of fast separation, soft ionization and high detection sensitivity, satisfactory effects in the 2D analysis were achieved, despite the relatively low chromatographic resolution of MCC. As a result, three isomers, eucalyptol, l -menthone and linalool, in a flavor mixture were successfully categorized within 90 s, and the matrix effect caused by solvent ethanol was significantly eliminated as well. The limits of detection (LODs) down to sub-ppbv level were achieved for the investigated five flavor compounds without any enrichment process, and an excellent repeatability was obtained with the relative standard deviations (RSDs) of signal intensities ≤5%. The MCC-HPPI-TOFMS system was preliminarily applied for rapid and online analysis of flavor compounds in the exhaled gas of a volunteer after mouth rinsing with a gargle product. The rapid changes of the three flavor compounds, as well as the steady endogenous metabolite acetone, in the exhaled gas were successfully determined with a time-resolution of only 1.5 min. Image 1 • Multi-capillary column high-pressure photoionization time-of-flight mass spectrometry. • Isomeric compounds was easily separated and elimination of the matrix effect in a complex flavor mixture was demonstrated. • The analysis time was less than 90s. • The limits of detection down to sub-ppbv level were achieved for the five flavor compounds without any enrichment process. • An excellent repeatability was obtained with the relative standard deviations (RSDs) of signal intensities ≤5%. [ABSTRACT FROM AUTHOR]

[Display omitted] • HPPI-TOFMS was introduced for rapid evaluation of oxidative deterioration in edible oils via effective detection of their VOCs fingerprints change under thermal-oxidation or photo-oxidation. • For the first time, non-targeted discrimination of oxidized oils into various oxidation degrees was realized by coupling HPPI-TOFMS with OPLS-DA. • Nonanal in extra virgin olive oils, 2-pentylfuran in peanut oils, trans -2-heptenal in sunflower oils and trans– trans -2, 4-heptadienal in corn oils were selected as potential oxidation indicators. Since lipid oxidation often causes serious food safety issues worldwide, determination of oil's oxidative deterioration becomes quite significant, which still calls for efficient analytical methods. In this work, high-pressure photoionization time-of-flight mass spectrometry (HPPI-TOFMS) was firstly introduced for rapid detection of oxidative deterioration in edible oils. Through non-targeted qualitative analysis, oxidized oils with various oxidation levels were successfully discriminated for the first time by coupling HPPI-TOFMS with the orthogonal partial least squares discriminant analysis (OPLS-DA). Furthermore, by targeted interpretation of the HPPI-TOFMS mass spectra and the subsequent regression analysis (signal intensities vs TOTOX values), good linear correlations were observed for several predominant VOCs. Those specific VOCs were promising oxidation indicators, which would play important roles as TOTOX to judge the oxidation states of tested samples. The proposed HPPI-TOFMS methodology can be used as an innovative tool for accurate and effective assessment of lipid oxidation in edible oils. [ABSTRACT FROM AUTHOR]

Cyanide is inevitably present in fermented liquors made from cyanogenic plants, which should be strictly controlled for safe drinking. Rapid access to cyanide content during liquor production is crucial for product safety and quality control. In this study, a rapid and high-throughput method for the measurement of cyanide in liquor was developed by coupling negative photoionization time-of-flight mass spectrometry (NPI-TOF) and a simple alkalization-dilution-acidification pretreatment procedure. The method detection limit (MDL) and practical quantitation limit (PQL) of 0.05 and 2.50 μg L−1 for cyanide in liquor were obtained within 1 min. The cyanide concentrations in 200 samples of Chinese liquor from the 2nd to 7th distillation rounds were rapidly determined by the developed method, and the samples from the 4th and 5th distillation rounds had the lowest cyanide content with average concentrations of 309 and 306 μg L−1, respectively, which were consistent with the final quality assessment results. [Display omitted] • Rapid derivatization of cyanide in liquor into gas phase HCN. • Unique ion CN- for cyanide analysis without spectral interference within 1 min • Method detection limit and practical quantitation limit of 0.05 and 2.50 μg/L. • Good agreement of the results between NPI-TOF and ion chromatography methods. [ABSTRACT FROM AUTHOR]

Increasing in cases involving drugs of abuse leads to heavy burden for law enforcement agencies, exacerbating demand for rapid screening technique. In this study, atmospheric pressure ionization technologies including direct analysis in real time (DART) ion source coupled to a time-of-flight mass spectrometer (DART-TOF-MS)as well asdopant-assisted positive photoionization ion mobility spectrometry (DAPP-IMS) without radioactivity were utilized together as the powerful analytical tool for the rapid screening and identification of 53 abused drugs.The limits of detection (LOD) were 0.05-2μg/mL when using DART-TOF-MS and 0.02-2μg when using DAPP-IMS which could satisfy the actual requirement in forensic science laboratory. The advantages of this method included fast response, high-throughput potential, high specificity, and minimal sample preparation. A screening library of reduced mobility (K0), accurate mass of informative precursor ion ([M+H]+) and fragment ions was established respectively by employing a bench-top DAPP-IMS and TOF-MS in-source collision induced dissociation (CID) mode. Then the standardized screening procedure was developed with criteria for the confirmation of positive result. A total of 50 seized drug samples provided by local forensic laboratory we reanalyzed to testify the utility of the method. This study suggests that a method combing DART-TOF-MS and DAPP-IMS is promising for the rapid screening and identification of abused drugs with minimal sample preparation and absence of chromatography. [ABSTRACT FROM AUTHOR]

Chlorinated benzenes are typical precursors and indicators for polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) emissions from waste incinerators. Online and real-time monitoring of chlorobenzenes is a challenge due to their low concentration and complex nature of the flue gas. In this work, a continuous online monitoring system was built for detection of trace chlorinated benzenes based on a time-of-flight mass spectrometer (TOFMS). A single photon ionization (SPI) source based on a radiofrequency-excited windowless vacuum ultraviolet (VUV) lamp was developed for the first time to eliminate the signal attenuation resulting from the contamination of magnesium fluoride windows and to avoid the fragment ions. An automatic enrichment system including three parallel Tenax TA adsorption tubes was designed and coupled to the TOFMS to achieve the required ultrahigh sensitivity. The limits of quantitation at 7.65, 5.37 and 6.77 pptv were obtained for monochlorobenzene (MCBz), dichlorobenzene (DCBz) and trichlorobenzene (TrCBz), respectively, within a 29-min analytical period. Moreover, this apparatus was applied to continuously online monitor the actual flue gas from a waste incinerator for three months. During this period, the concentrations of MCBz, DCBz and TrCBz detected in the flue gas were in the range of 100–1200, 50–800 and 50–300 pptv, respectively. The relative standard deviation (RSD) of the sensitivity for the windowless VUV lamp ion source was 9.71% evaluated by the internal standard benzene over the 3-months flue gas monitoring. These results demonstrated the capability of this method in long-term analysis of the trace chlorinated benzenes in the flue gas. [ABSTRACT FROM AUTHOR]

Direct and rapid analysis of glyoxal by soft ionization mass spectrometry remains a great challenge due to its low ionization efficiency in existing soft ionization techniques, such as proton transfer reaction (PTR) and photoionization (PI). In this work, we developed a new VUV lamp-based cluster-mediated CH 2 Br 2 + chemical ionization (CMCI) source for time-of-flight mass spectrometry (TOFMS), which was accomplished by employing photoionization-generated CH 2 Br 2 + as the reactant ion and co-sampling of glyoxal with high-concentration ethanol (EtOH). The signal intensity of glyoxal could be enhanced by more than 2 orders of magnitude by generating protonated cluster ion [Glx·EtOH·H]+. Density function theory (DFT) calculations was performed to obtain the most stable structure of neutral glyoxal-ethanol cluster and confirm that the ionization energy (IE) of glyoxal-ethanol cluster was significantly lower than that of glyoxal and CH 2 Br 2 molecules, which makes it possible for effective ionization of glyoxal. The ionization efficiency of glyoxal could be dramatically enhanced via ion-molecule reaction between CH 2 Br 2 + and glyoxal-ethanol cluster, as larger ionization cross section of glyoxal-ethanol cluster than glyoxal molecule might be achieved. The cluster-mediated signal enhanced effect was also verified by using other alcohols, such as methanol and isopropanol. Consequently, the limit of quantitation (LOQ, S/N = 10) down to 0.17 ppbv for gas-phase glyoxal was achieved. The analytical capacity of this system was demonstrated by trace analysis of glyoxal in food contact papers, exhibiting new insights and wide potentials of chemical ionization and photoionization mass spectrometry for VOCs measurement with higher sensitivity and wider detectable sample range. [Display omitted] • Cluster-mediated signal enhanced effect for high-efficiency ionization of glyoxal. • Co-sampling of glyoxal with high-concentration ethanol to generate neutral glyoxal-ethanol cluster. • Density function theory calculations confirmed lower ionization energy of glyoxal-ethanol cluster. • More than 2 orders of magnitude improvement in signal intensity of glyoxal. • An outstanding performance for trace analysis of glyoxal in food contact papers. [ABSTRACT FROM AUTHOR]

Abstract: A novel ion source has been introduced in the present study, which combines the characteristics of single photon ionization (SPI) and photoelectron ionization (PEI). The VUV photons for SPI were generated by a commercial krypton discharge lamp (10.6eV), and the photoelectrons for electron ionization (EI) were produced through photoemission from a stainless-steel skimmer. The energy of photoelectrons can be well controlled by adjusting the voltages applied on the skimmer. The ionization methods, SPI (SPI mode) and SPI combined photoelectron ionization (SPI–PEI mode), can be rapidly switched. Benefited from the higher working pressure in the ion source, the achieved detection limit of benzene and SO2 were 0.1ppmV and 20ppmV, respectively. The experimental results show the combined ion source has the potential in chemical process and environmental monitoring. [ABSTRACT FROM AUTHOR]

In-vehicle air pollution has become a major concern to public health in recent years. The traditional analytical methods for detection of volatile organic compounds (VOCs) pollutants in air are based on gas chromatography - mass spectrometry (GC-MS) or high-performance liquid chromatography (HPLC), including complicated pretreatment and separation procedures, which are not only time-consuming and labor-intensive, but also incapable of simultaneously measuring both aldehydes and benzenes. In this work, a new photoionization-induced NO+ chemical ionization time-of-flight mass spectrometry (PNCI-TOFMS) was developed for real-time and continuous measurement of aldehydes and benzenes in vehicles. High-intensity NO+ reactant ions could be generated by photoionization of NO reagent gas, and efficient chemical ionization between NO+ reactant ions and analyte molecules occurred to produce adduct ions M·NO+ at an elevated ion source pressure of 800 Pa. Consequently, the achieved LODs for aldehydes and benzenes were down to sub-ppbv within 60 s. The analytical capacity of this system was demonstrated by continuous and online monitoring of in-vehicle VOCs in a used car, exhibiting broad potential applications of the PNCI-TOFMS in air pollutants monitoring and in-vehicle air quality analysis. [Display omitted] • A new photoionization-induced NO+ chemical ionization TOFMS was developed for rapid measurement of aldehydes and benzenes. • Efficient CI between NO+ ions and analyte molecules occurred to produce adduct ions M·NO+ at 800 Pa. • LODs of formaldehyde, acetaldehyde, acrolein, benzene, toluene, p-xylene, and styrene were 0.010-0.064 ppbv within 60 s. • Continuous and online monitoring of in-vehicle aldehydes and benzenes has been realized. [ABSTRACT FROM AUTHOR]