Simultaneous quantification of ten Amadori compounds in tobacco using liquid chromatography with tandem mass spectrometry.

Amadori compounds are aroma precursors formed in the initial phase of the Maillard reaction. Based on their similar structures, simultaneous quantification of more than six Amadori compounds in tobacco has not been reported yet. In this study, a simple and rapid method was developed to simultaneously quantify ten Amadori compounds including the isomers of Fructose-isoleucine and Fructose-leucine in tobacco. The separation was performed on an Atlantis T3 column (2.1 × 250 mm, 5 µm) by gradient elution using acetonitrile and water as the mobile phases. The quantification method was systematically evaluated and proven to be sensitive and accurate. The linearity was good, with correlation coefficients of 0.9977-0.9999. The limits of detection and quantitation were 1.354-2.532 and 4.516-8.444 ng/mL, respectively. The recoveries were 84.0-119.6%, and the relative standard deviations were 1.33-5.40%. The method was used to analyze the changes in the amounts of ten Amadori compounds in tobacco before and after tobacco primary processing. The analysis shows that the Maillard reaction occurs during the short processing period.

Determination of nine volatile N-nitrosamines in tobacco and smokeless tobacco products by dispersive solid-phase extraction with gas chromatography and tandem mass spectrometry.

A method was developed for the determination of nine volatile N-nitrosamines in tobacco and smokeless tobacco products. The targets are N-nitrosodimethylamine, N-nitrosopyrrolidine, N-nitrosopiperidine, N-nitrosomorpholine, N-nitrosoethylmethylamine, N-nitrosodiethylamine, N-nitrosodipropylamine, N-nitrosobuylmethylmine, and N-nitrosodibutylamine. The samples were treated by dispersive solid-phase extraction using 1 g of primary secondary amine and 0.5 g of carbon and then analyzed by gas chromatography with tandem mass spectrometry with an electron impact ion source. The recoveries for the targets ranged from 84 to 118%, with <16% relative standard deviations at three spiking levels of 0.5, 1.25, and 2.5 ng/g. The limits of detection ranged from 0.03 to 0.15 ng/g. With the use of the proposed method, we detected the presence of six nitrosamines in the range of 0.4-30.7 ng/g. The study demonstrated that the method could be used as a rapid, convenient, and high-throughput method for N-nitrosamines analysis in tobacco matrix.

Distribution of toxic chemicals in particles of various sizes from mainstream cigarette smoke.

To accurately estimate the risk of inhaling cigarette smoke containing toxic chemicals, it is important that the distribution of these chemicals is accurately measured in cigarette smoke aerosol particles of various sizes. In this study, a single-channel smoking machine was directly coupled to an electrical low-pressure impactor. The particles of mainstream cigarette smoke were collected using 12 polyester films, and the particulate matter (PM) was characterized. Nicotine, tobacco-specific N-nitrosamines (TSNAs, including NNN, NAT, NAB, and NNK), polycyclic aromatic hydrocarbons (PAHs, including benzo(a)pyrene (BaP), benzo(a)anthracene, and chrysene), and heavy metals (including Cr, As, Cd, and Pb) present in the particles of different sizes were analyzed by GC, HPLC-MS/MS, GC/MS, or ICP-MS, respectively. The results demonstrated that the nicotine, TSNAs, PAHs, and heavy metals in mainstream cigarette smoke were dispersed over a particle size ranging from 0.1 µm to 2.0 µm, and the concentration of these toxic chemicals initially increased and then decreased the particle size grew. The distribution of nicotine was uniform for the PM in the size ranges of less than 0.1 µm, 0.1-1.0 µm, and 1.0-2.0 µm, TSNAs and heavy metals in particles of less 0.1 µm were more abundant, and PAHs in fine particles were also more abundant.

Development and Validation of a Modified QuEChERS Method for Simultaneous Analysis of 250 Flavor Constituents in Tobacco by Gas Chromatography Tandem Mass Spectrometry.

BACKGROUND: Flavor constituents play an important role in the flavor characteristics of tobacco leaves and cigarettes. Sensitive, selective, and high-throughput multi-analyte analytical methods are needed to satisfy the demand for analyzing trace-level flavor constituents in tobacco. However, trace analysis of multi-targets in a complex tobacco matrix is significantly challenging. OBJECTIVE: This study was undertaken to develop and validate a fast, selective, sensitive, and accurate GC-tandem mass spectrometry (GC-MS/MS) method for the simultaneous analysis of 250 flavor constituents in tobacco using a modified QuEChERS (Quick, Easy, Cheap, Effective, Rugged, and Safe) extraction procedure and backflushing technique. METHODS: The samples were extracted with a mixture of acetonitrile and phosphate buffer. GC-MS/MS served as a reliable tool to quantify the flavor constituents due to its high sensitivity, selectivity, and good repeatability. RESULTS: Our evaluation showed that 243 flavor constituents presented good linearity. Average recoveries of 216 target compounds in tobacco ranged from 70 to 120% with RSDs less than 20% at three fortification levels. The limits of quantitation of 225 and 25 compounds were in the range of 2-50 and 51-112 µg/kg, respectively. This method was then successfully applied to the analysis of 15 commercial cigarette samples with different style characteristics. CONCLUSION: The modified QuEChERS method worked very well for a wide range of flavor constituents that have not been reported by QuEChERS pretreatment previously, and the use of concurrent backflushing offered significant increase in system robustness and sample throughput. The method greatly improved the detection performance and the range of the flavor constituents, and proved to be more accurate, sensitive, selective, convenient, and practical than the reported method, and thus, can be applied in routine analysis. HIGHLIGHTS: A validated QuEChERS-based GC-MS/MS method for multiple flavor constituents analysis in tobacco was reported for the first time. The use of concurrent backflushing markedly improved the instrument robustness and sample throughput.

Coupling of stir bar sorptive extraction with single photon ionization mass spectrometry for determination of volatile organic compounds in water.

A home-made stir bar sorptive extraction (SBSE) apparatus was combined to a single photon ionization time-of-flight mass spectrometer (SPI-TOFMS) for rapid and sensitive determination of trace volatile organic compounds (VOCs) in water. The home-made SBSE bar, low-cost and disposable, was used for VOCs extraction. A thermal desorption (TD) device was designed to desorb the analytes from the SBSE bar, and a high throughput interface was developed to transfer the analytes into the ionization chamber of the SPI-TOFMS. The combination of large extraction volume of SBSE bar, and the direct measurement power of SPI-TOFMS enable a short analysis time for VOCs in water with high sensitivity, for example the limits of detection (LODs) were in the range of 7.4-11.1 ng L(-1) for benzene, toluene, and p-xylene (BTX) within 15 min. BTX aqueous solutions were chosen to demonstrate the quantitative capability, the linear range was from 0.05 to 100 µg L(-1) and the correlation coefficients were better than 0.996. The proposed method was successfully applied for the analysis of VOCs in urban river water.

Electromembrane extraction of nicotine in inhaled aerosols from tobacco cigarettes, electronic cigarettes, and heated tobacco products.

Heated tobacco products and electronic cigarettes are considered as alternatives to traditional tobacco cigarettes. However, it is crucial to monitor and compare the nicotine concentration in inhaled aerosols from these tobacco products, owing to the addictive nature and adverse effects of nicotine on human health. This study aimed to provide an electromembrane extraction (EME) combined liquid chromatography method to extract and determine nicotine in different inhaled aerosols. EME showed high extraction efficiency, selectivity, and sample clean-up capability. Under the optimal parameters, the linear range for nicotine was 0.1-200 mg L-1 (r2 > 0.9998), and the limit of detection was 0.02 mg L-1. Good precision was obtained with the intra- and inter-day relative standard deviations of 2.2 % and 2.8 %, respectively. Repeatability was satisfactory (<7.7 %), and recoveries ranged from 81.0 % to 112.8 %. Finally, this method has been successfully used for the determination and comparison of nicotine in aerosols from these three tobacco products.

Robust, comprehensive, sensitive analysis of flavour additives with carboxyl and hydroxyl groups in cigarette smoke combining silylation and gas chromatography-tandem mass spectrometry with an improved backflushing system.

Flavour additives with carboxyl and hydroxyl groups (FACHs), the key ingredients in characteristic flavours, are frequently detected in cigarette smoke. They are attracting increasing attention in regulating the flavour additives used in tobacco to curb youth tobacco use and prevent the use of additives that are harmful. In this study, a highly robust, sensitive, and precise method based on silylation and GC-MS/MS with an improved backflushing system was developed for the simultaneous analysis of 171 FACHs in cigarette smoke. Silylation has been shown to have advantages in terms of high selectivity and sensitivity to chemicals with carboxyl and hydroxyl groups, especially when combined with GC-MS/MS. The extraction and silylation conditions were optimised. Dichloromethane was used as the extraction agent. BSTFA in combination with 1% TMCS and 0.2% TMSI was selected as silylating agent for high silylation efficiency, particularly for hindered analytes. The method has been validated. The limit of detection (LOD) ranged from 0.6 to 332.3 ng/mL. 91.1% out of the analytes in QC samples had precisions lower than 10% during one month run. The improved backflushing system with a fused silica splitter was shown to be crucial in the excellent long-term robustness of the method. The developed method was used to determine flavour additives in 270 practical cigarette smoke samples with reliable results. A total of 154 FACHs were identified with wide-range levels among different cigarette brands.

Single photon ionization and chemical ionization combined ion source based on a vacuum ultraviolet lamp for orthogonal acceleration time-of-flight mass spectrometry.

A novel combined ion source based on a vacuum ultraviolet (VUV) lamp with both single photon ionization (SPI) and chemical ionization (CI) capabilities has been developed for an orthogonal acceleration time-of-flight mass spectrometer (oaTOFMS). The SPI was accomplished using a commercial 10.6 eV krypton discharge lamp with a photon flux of about 10(11) photons s(-1), while the CI was achieved through ion-molecule reactions with O(2)(+) reactant ions generated by photoelectron ionization at medium vacuum pressure (MVP). To achieve high ionization efficiency, the ion source pressure was elevated to 0.3 mbar and the photoionization length was extended to 36 mm. As a result, limits of detection (LODs) down to 3, 4, and 6 ppbv were obtained for benzene, toluene, and p-xylene in MVP-SPI mode, and values of 8 and 10 ppbv were obtained for toluene and chloroform, respectively, in SPI-CI mode. As it is feasible to switch between MVP-SPI mode and SPI-CI mode rapidly, this system is capable of monitoring complex organic mixtures with a wide range of ionization energies (IEs). The analytical capacity of this system was demonstrated by measuring dehydrogenation products of long-chain paraffins to olefins through direct capillary sampling and drinking water disinfection byproducts from chlorine through a membrane interface.

Vacuum ultraviolet lamp based magnetic field enhanced photoelectron ionization and single photon ionization source for online time-of-flight mass spectrometry.

A magnetic field enhanced photoelectron ionization (MEPEI) source combined with single photon ionization (SPI) was developed for an orthogonal acceleration time-of-flight mass spectrometer (oaTOFMS). A commercial radio frequency (rf) powered vacuum ultraviolet (VUV) lamp was used as SPI light source, and the photoelectrons generated by photoelectric effect were accelerated to induce electron ionization (EI). The MEPEI was obtained by applying a magnetic field of about 800 G with a permanent annular magnet. Compared to a nonmagnetic field photoelectron ionization source, the signal intensities for SO(2), SF(6), O(2), and N(2) in MEPEI were improved more than 2 orders with the photoelectron energy around 20 eV, while most of the characteristics of soft ionization still remained. Simulation with SIMION showed that the sensitivity enhancement in MEPEI was ascribed to the increase of the electron moving path and the improvement of the electrons transmission. The limits of detection for SO(2) and benzene were 750 and 80 ppbv within a detection time of 4 s, respectively. The advantages of the source, including broad range of ionizable compounds, reduced fragments, and good sensitivity with low energy MEPEI, were demonstrated by monitoring pyrolysis products of polyvinyl chloride (PVC) and the intermediate products in discharging of the SF(6) gas inpurity.

[Realtime analysis of volatile organic compounds in source water by membrane inlet/time-of-flight mass spectrometry].

To establish an early-warning system for source water pollution accident, a membrane inlet/time-of-flight mass spectrometry technology was applied to a series of pollution scenarios as an online monitoring method for typical volatile organic compounds such as BTEX (benzene, toluene, ethylbenzene and xylene), substituted benzenes, and halogenated aliphatic hydrocarbons. It was shown that this technology can adequately meet the requirements of realtime analysis with short response time to the target organic pollutants (30-70 s for BTEX and 30 s for halogenated aliphatic hydrocarbons) in a linear detecting range of 3-4 magnitudes; the detection limits of BTEX and chlorobenzene were less than 10 microg x L(-1). The results of 52 simulated water pollution accidents in a 30-days' continuous monitoring indicated that the monitoring system was stable with the relative standard deviation less than 5%; the accuracy was acceptable and could be reduced to within 10% by periodical calibrations. Membrane inlet/time-of-flight mass spectrometry technology was proven to be available for the remote monitoring and early-warning of source water pollution accident.

A simple multi-scale Gaussian smoothing-based strategy for automatic chromatographic peak extraction.

Peak detection is a critical step in chromatographic data analysis. In the present work, we developed a multi-scale Gaussian smoothing-based strategy for accurate peak extraction. The strategy consisted of three stages: background drift correction, peak detection, and peak filtration. Background drift correction was implemented using a moving window strategy. The new peak detection method is a variant of the system used by the well-known MassSpecWavelet, i.e., chromatographic peaks are found at local maximum values under various smoothing window scales. Therefore, peaks can be detected through the ridge lines of maximum values under these window scales, and signals that are monotonously increased/decreased around the peak position could be treated as part of the peak. Instrumental noise was estimated after peak elimination, and a peak filtration strategy was performed to remove peaks with signal-to-noise ratios smaller than 3. The performance of our method was evaluated using two complex datasets. These datasets include essential oil samples for quality control obtained from gas chromatography and tobacco plant samples for metabolic profiling analysis obtained from gas chromatography coupled with mass spectrometry. Results confirmed the reasonability of the developed method.

Simple automatic strategy for background drift correction in chromatographic data analysis.

Chromatographic background drift correction, which influences peak detection and time shift alignment results, is a critical stage in chromatographic data analysis. In this study, an automatic background drift correction methodology was developed. Local minimum values in a chromatogram were initially detected and organized as a new baseline vector. Iterative optimization was then employed to recognize outliers, which belong to the chromatographic peaks, in this vector, and update the outliers in the baseline until convergence. The optimized baseline vector was finally expanded into the original chromatogram, and linear interpolation was employed to estimate background drift in the chromatogram. The principle underlying the proposed method was confirmed using a complex gas chromatographic dataset. Finally, the proposed approach was applied to eliminate background drift in liquid chromatography quadrupole time-of-flight samples used in the metabolic study of Escherichia coli samples. The proposed method was comparable with three classical techniques: morphological weighted penalized least squares, moving window minimum value strategy and background drift correction by orthogonal subspace projection. The proposed method allows almost automatic implementation of background drift correction, which is convenient for practical use.

[Real-time analysis of polyvinyl chloride thermal decomposition/combustion products with single photon ionization/photoelectron ionization online mass spectrometer].

With the features of a broad range of ionizable compounds, reduced fragments and simple mass spectrum, a homemade magnetic field enhanced photoelectron ionization (MEPEI) source combined with single photon ionization (SPI) for time-of-flight mass spectrometer was built and applied to analyze thermal decomposition/combustion products of polyvinyl chloride (PVC). The combined ion source can be switched very fast between SPI mode and SPI-MEPEI mode for detecting different targeted compounds, and only adjusting the voltage of the electrode in the ionization region to trigger the switch. Among the PVC thermal decomposition/combustion products, HCl and CO2, which ionization energies (12.74 eV, 13.77 eV respectively) were higher than the energy of photon (10.60 eV), were ionized by MEPEI, while alkenes, dichloroethylene, benzene and its homologs, monochlorobenzene, styrene, indane, naphthalene and its homologs were ionized by SPI and MEPEI simultaneously. Spectra of interested products as a function of temperatures indicated that products are formed via two main mechanisms: (1) dechlorination and intramolecular cyclization can lead to the formation of HCl, benzene and naphthalene at 250-370 degrees C; (2) intermolecular crosslinking leads to the formation of alkyl aromatics such as toluene and xylene/ethylbenzene at 380-510 degrees C. The experimental results show that the combined ion source of SPI/ SPI-MEPEI for TOF-MS has broad application prospects in the online analysis field.

[Monitoring of methyl methacrylate monomer released from autopolymerized denture base polymers during processing using time-of-flight mass spectrometer].

OBJECTIVE: To analyze the amount and tendency of methyl methacrylate (MMA) released from autopolymerized denture base polymer (self-curing resin) during processing using time-of-flight mass spectrometer (TOF-MS). METHODS: Self-curing resin was mixed in the container using a ratio of 2 g of powder to 1 g of liquid in accordance with the manufacturer's instructions for 40 s as a specimen. The amount of MMA released from the specimen was continuously monitored and simultaneously recorded every minute by TOF-MS since immediately after mixing. A total of five specimens were monitored. RESULTS: The amount of MMA increased dramatically at 11 min [(45.2 ± 3.5) mg/L] after mixing, and reached the highest level at 13 min [(228.9 ± 22.6) mg/L], then become stable at 23 min [(8.8 ± 2.3) mg/L] after mixing. CONCLUSIONS: The releasing tendency of MMA could be analyzed accurately with continuously monitoring during processing. The amount of MMA released from self-curing resin changed rapidly and the processing was complicated and changeful.

[Development of a membrane inlet-single photon ionization/chemical ionization-mass spectrometer for online analysis of VOCs in water].

A home-made membrane inlet- single photon ionization/chemical ionization- time-of-flight mass spectrometer has been described. A vacuum ultraviolet (VUV) lamp with photon energy of 10.6 eV was used as the light source for single photon ionization (SPI). Chemical ionization (CI) was achieved through ion-molecule reactions with O2- reactant ions generated by photoelectron ionization. The two ionization modes could be rapidly switched by adjusting electric field in the ionization region within 2 s. Membrane inlet system used for rapid enrichment of volatile organic compounds (VOCs) in water was constructed by using a polydimethylsiloxane (PDMS) membrane with a thickness of 50 microm. A purge gas was added to accelerate desorption of analytes from the membrane surface. The purge gas could also help to prevent the pump oil back-streaming into the ionization region from the analyzer chamber and improve the signal to noise ratio (S/N). Achieved detection limits were 2 microg x L(-1) for methyl tert-butyl ether (MTBE) in SPI mode and 1 microg x L(-1) for chloroform in SPI-CI mode within 10 s analysis time, respectively. The instrument has been successfully applied to the rapid analysis of MTBE in simulated underground water nearby petrol station and VOCs in disinfected drinking water. The results indicate that the instrument has a great application prospect for online analysis of VOCs in water.