High-resolution multi-reflection time-of-flight mass spectrometer with atmospheric pressure interface.

RATIONALE: Atmospheric pressure interface multi-reflection time-of-flight mass spectrometry (API-MRTOF-MS) has the potential to be a rapid and high-resolution analytical tool for versatile applications in chemistry, biology, environmental science, and medicine. METHODS: The ions were reflected in a mass analyzer via electrostatic mirrors and folded flight path. Therefore, flight distances were significantly increased. The ion flight path of the API-MRTOF-MS was extended from meters to over 1 km, and the mass resolution was increased. Furthermore, the mass analysis could be completed at around 10 ms due to the rapid response of TOF-MS. RESULTS: A high-resolution API-MRTOF-MS approach is successfully developed in this study. The mass resolution could achieve 116 050 (full widths at half maximum [FWHM]) for Cs+ ions using an atmospheric pressure electrospray ionization within a total TOF of only 18 ms. An ion transmission efficiency of over 50% was achieved after 600 cycles. CONCLUSIONS: The analytical performance of the newly developed API-MRTOF-MS demonstrated that it is suitable for high resolution and rapid analysis in many fields.

Portable Mass Spectrometry Approach Combined with Machine Learning for Onsite Field Detection of Huanglongbing Disease.

Huanglongbing (HLB) is one of the most serious citrus diseases in the world. Rapid, onsite, and accurate field detection of HLB is a challenging task in analytical science for a long time. Herein, we have developed a novel HLB detection method that combines headspace solid phase microextraction with portable gas chromatography-mass spectrometry (PGC-MS) approach for onsite field detection of volatile metabolites of citrus leaves. Detectability and characteristics of HLB-affected metabolites from leaves were validated, and the important biomarkers were verified by authentic compounds. A machine learning approach based on random forest algorithm is established to model the volatile metabolites from healthy, symptomatic, and asymptomatic citrus leaves. In this work, a total of 147 citrus leaf samples were analyzed. Analytical performances of this newly developed method were investigated by in-field detection of various volatile metabolites. Results demonstrated limits of detection and quantification of 0.04-0.12 and 0.17-0.44 ng/mL for different metabolites, respectively. Linear calibration curves of various metabolites were established over a concentration dynamic range of at least three orders (R2 > 0.96). Good reproducibility was obtained for intraday (3.0-17.5%, n = 6) and interday precision (8.7-18.2%, n = 7). This new HLB field detection method provides a rapid detection with 6 min for each sample via a simple optimized procedure, including onsite sampling, PGC-MS analysis, and data process and provides a high accuracy (93.3%) for simultaneous identification of healthy, symptomatic, and asymptomatic trees. These data support the use of this new method for reliable field detection of HLB. Furthermore, metabolic pathways of HLB-affected metabolites were also proposed. Overall, our results not only provide a rapid and onsite field HLB detection method but also provide valuable information for understanding metabolic change of HLB infection.

Detection of abused drugs in human exhaled breath using mass spectrometry: A review.

RATIONALE: Human breath analysis has been attracting increasing interest in the detection of abused drugs in forensic and clinical applications because of its noninvasive sampling and distinctive molecular information. Mass spectrometry (MS)-based approaches have been proven to be powerful tools for accurately analyzing exhaled abused drugs. The major advantages of MS-based approaches include high sensitivity, high specificity, and versatile couplings with various breath sampling methods. METHODS: Recent advances in the methodological development of MS analysis of exhaled abused drugs are discussed. Breath collection and sample pretreatment methods for MS analysis are also introduced. RESULTS: Recent advances in technical aspects of breath sampling methods are summarized, highlighting active and passive sampling. MS methods for detecting different exhaled abused drugs are reviewed, emphasizing their features, advantages, and limitations. The future trends and challenges in MS-based breath analysis of exhaled abused drugs are also discussed. CONCLUSIONS: The coupling of breath sampling methods with MS approaches has been proven to be a powerful tool for the detection of exhaled abused drugs, offering highly attractive results in forensic investigations. MS-based detection of exhaled abused drugs in exhaled breath is a relatively new field and is still in the early stages of methodological development. New MS technologies promise a substantial benefit for future forensic analysis.

Onsite Identification and Spatial Distribution of Air Pollutants Using a Drone-Based Solid-Phase Microextraction Array Coupled with Portable Gas Chromatography-Mass Spectrometry via Continuous-Airflow Sampling.

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 deviation < 20%, n = 6), analytical speed (single sample within minutes), and excellent linear dynamic response (3 orders of magnitude) were obtained for direct measurement of air samples. The drone-SPME sampling mechanism of air pollutants involving an airflow adsorptive microextraction process was proposed. Overall, this drone-SPME sampling array can access hard-to-reach and dangerous environmental sites and provide air pollution distribution in different spaces, showing versatile potential applications in environmental analysis.

A home-made sampling system coupled to hectowatt-MPT mass spectrometry in positive ion mode to confirm target ions of copper and zinc from Poyang Lake, China.

A novel home-made H2SO4-Nafion (HN) tube sampling system coupled to a line ion trap mass spectrometer (LTQ-MS) with a versatile ambient ionization source, hectowatt microwave plasma torch (HMPT), has manifested unique advantages for picking directly metal elements in aqueous samples and acquiring the fully characteristic MPT mass spectra of copper and zinc composite ions. Here, we report the development of a novel HN-HMPT-LTQ-MS for metal elements assay based on environmental water to analyze samples of Poyang Lake, China. Detailed multi-stage tandem mass spectra show that the general structural form of target ions is [M(NO3)x(H2O)y(OH)z]+ for the positive ion mode. Under the optimized conditions, the proposed method provided low limits of detection (LODs) of 0.23 µg.L-1 for 63Cu+ and 1.1 µg.L-1 for 66Zn+, with relative standard deviations (RSDs) of less than 12.7% by MPT-LTQ-MS. This new result has met the requirements of national standards (GB 5750.6-2006) and is only about one magnitude order larger than the LOD of ICP-MS method. A wide linear response range of about 4 orders of magnitude for the method with linear coefficients (R2) of 0.99709 - 0.99962 for copper and zinc tested was in accordance with that of ICP-MS. Except for the recovery of 79% for the third sample and 123.8% for the seventh sample, the present method also provided good recoveries (84 - 119.3%) in spiked 10 batches of drinking water samples. Furthermore, it is envisioned that the developed approach might build a powerful hectowatt-MPT-MS platform for food security detection, drug analysis, and origin traceability.

Comparative study on a kilowatt-MPT-MS-based method with two ion polarity modes for the inert palladium metal.

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.

Improvement of m/z accuracy for linear matrix-assisted laser desorption/ionization time-of-flight mass spectrometer.

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.

Fast-switching high-voltage porous-tip electrospray ionization mass spectrometry for rapid detection of antirheumatic drugs in adulterated herbal dietary supplements.

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.

A hand-portable digital linear ion trap mass spectrometer.

A hand-portable digital linear ion trap mass spectrometer (DLIT-MS) has been developed for VOC analysis. It has a weight of 18 kg with dimensions of 49 cm × 39 cm × 16 cm, and consumes an average power of ca. 60 W. As a result of the introduction of a digital waveform, the DLIT-MS can be driven at a lower voltage (±100 V) to cover a mass range of 30-300 Th with a unit resolution. Compact electronics has been designed to control the DLIT-MS and record mass spectra. The mass drift was reduced after the improvement in electronics to stabilize the digital waveform voltage during the mass scan. Tandem mass spectrometry (MS) has been achieved by using digital asymmetric waveform isolation (DAWI), forward and reverse scan, and collision induced dissociation (CID). The isolation and CID efficiency for methyl salicylate were 83.9% and 81.3%, respectively. A novel buffer gas inlet system was designed to enhance the sensitivity and allow easy and safe use of the instrument. Limits of detection below 1 ppbv were obtained for several mixed gaseous samples.

Development of an air-flow-assisted extractive electrospray ionization source for rapid analysis of phthalic acid esters in spirits.

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.

A high-efficiency real-time digital signal averager for time-of-flight mass spectrometry.

RATIONALE: Analog-to-digital converter (ADC)-based acquisition systems are widely applied in time-of-flight mass spectrometers (TOFMS) due to their ability to record the signal intensity of all ions within the same pulse. However, the acquisition system raises the requirement for data throughput, along with increasing the conversion rate and resolution of the ADC. It is therefore of considerable interest to develop a high-performance real-time acquisition system, which can relieve the limitation of data throughput. METHODS: We present in this work a high-efficiency real-time digital signal averager, consisting of a signal conditioner, a data conversion module and a signal processing module. Two optimization strategies are implemented using field programmable gate arrays (FPGAs) to enhance the efficiency of the real-time processing. A pipeline procedure is used to reduce the time consumption of the accumulation strategy. To realize continuous data transfer, a high-efficiency transmission strategy is developed, based on a ping-pong procedure. RESULTS: The digital signal averager features good responsiveness, analog bandwidth and dynamic performance. The optimal effective number of bits reaches 6.7 bits. For a 32 µs record length, the averager can realize 100% efficiency with an extraction frequency below 31.23 kHz by modifying the number of accumulation steps. In unit time, the averager yields superior signal-to-noise ratio (SNR) compared with data accumulation in a computer. CONCLUSIONS: The digital signal averager is combined with a vacuum ultraviolet single-photon ionization time-of-flight mass spectrometer (VUV-SPI-TOFMS). The efficiency of the real-time processing is tested by analyzing the volatile organic compounds (VOCs) from ordinary printed materials. In these experiments, 22 kinds of compounds are detected, and the dynamic range exceeds 3 orders of magnitude.

A miniaturised electron ionisation time-of-flight mass spectrometer that uses a unique helium ion removal pulsing technique specifically for gas analysis.

A miniaturised reflectron time-of-flight mass spectrometer combined with an electron ionisation ion source has been developed for the analysis of gases. An entirely new helium ion removal pulsing technique in this mass spectrometer is used to achieve an improved performance for the first time. The helium carrier gas, which enters into the source along with the gaseous sample, is simultaneously ionised and then orthogonally introduced into the time-of-fight mass analyser. Once the relatively light helium ions in the ion packet become extremely close to the reflectron plate (B-plate for short in this article), a modulated pulse is instantaneously applied on the B-plate and a negative reflectron voltage is set to the B-plate and lasts for a very short period, during which all the helium ions are directly bumped into the B-plate and subsequently removed. The helium ion removal pulsing technique can efficiently avoid saturation of the micro-channel plate caused by too many helium ions. A compact and durable instrument is designed, which has a mass resolving resolution greater than 400 FWHM for online gas analysis. The technology may also be further developed to remove other ions for TOF mass spectrometry.

Aroma correlation assisted volatilome coupled network analysis strategy to unveil main aroma-active volatiles of Rosa roxburghii.

To investigate the main aroma-active volatiles out from comprehensive chemical profile, we proposed an aroma correlation assisted volatilome coupled network analysis strategy and applied it to the study of Rosa roxburghii. Based on 475 detected volatiles with GC × GC-TOF/MS analysis, the volatilome was screened with both positive aroma activities and high contents to discover some aliphatic acids, alcohols, aldehydes and esters, terpenoids as well as some alkenes and ketones. Especially, a series of homologous C6- and C8- acids, alcohols, aldehydes, esters as well as some terpenoids like limonene take the predominant contributions to the aromas. Moreover, two aroma-active and aroma-contributing volatile groups including acid-aldehyde-alcohol-ester and terpenoid groups were clustered to integrally be responsible for the major aromas of R. roxburghii with network analysis. Additionally, the accumulation of C6- and C8-family homologous aliphatic volatiles was also elucidated with linoleic and linolenic acid derived pathways. This strategy is practical to investigate the main aroma-active volatiles based on volatilome.

In vivo solid-phase microextraction swab-mass spectrometry for multidimensional analysis of human saliva.

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.

Real-time analysis of intermediate products from non-thermal plasma degradation of ethyl acetate in air using PTR-MS: Performance evaluation and mechanism study.

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.

Single particle diversity and mixing state of carbonaceous aerosols in Guangzhou, China.

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.

Exhaled breath analysis using on-line preconcentration mass spectrometry for gastric cancer diagnosis.

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.

In vivo solid-phase microextraction swab sampling of environmental pollutants and drugs in human body for nano-electrospray ionization mass spectrometry analysis.

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.

Real time analysis of trace volatile organic compounds in ambient air: a comparison between membrane inlet single photon ionization mass spectrometry and proton transfer reaction mass spectrometry.

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.