Types and concentrations of tire wear particles (TWPs) in road dust generated in slow lanes.

Drivers commonly navigate their vehicles at moderate speeds in proximity to traffic lights. In this study, road dust samples were collected in the vicinity of traffic lights, as well as at a taxi stand (TS) situated between traffic lights, with considerations given to both forward direction (FD) and backward direction (BD). The characterization of tire wear particles (TWPs) in the road dust was meticulously conducted based on particle size. Notably, tire-road wear particles (TRWPs) were conspicuously absent in samples surpassing 500 µm. Furthermore, TRWPs comprised less than 1% of identified particles in the road dust samples of 212-500 µm, with their origin traceable to heavy vehicles rather than passenger cars. The abundance of TRWPs from heavy vehicles exhibited marked variations, with heightened prevalence in the TS and BD samples as opposed to the FD sample. For the samples smaller than 212 µm, the composition of natural rubber (NR) in TWPs demonstrated a diminishing trend with escalating particle size. Conversely, the composition of styrene-butadiene rubber (SBR) exhibited an upward trajectory independent of the sampling site. The NR composition ratio in TWPs followed the order: TS (17-55%) > FD (17-47%) > BD (13-36%), while the SBR composition ratio exhibited the sequence: BD (62-86%) > FD (48-79%) > TS (24-70%). The TWP concentrations in road dust obtained from the TS (0.35-0.82%) were discernibly lower than those in the FD (0.54-1.77%) and BD (0.61-1.29%) samples. Specifically, the average TWP concentrations in road dust samples, falling within the size range of 20-212 µm, were 0.45%, 1.06%, and 0.91% for the TS, FD, and BD samples, respectively. These concentrations were lower than the corresponding values observed in samples collected from a bus stop.

Concentrations of particulate matter (PM2.5) and contributions of tire wear particle to PM2.5 in an indoor parking garage: Comparison with the outside and the differences according to the sampling sites.

Particulate matter (PM) is increasingly affecting the social-economic development of countries. An increase in PM2.5 concentration increases susceptibility to cardiovascular and respiratory diseases and cancer. Tire wear particles (TWP) contribute to airborne PM. In the present work, we investigated the variation in the concentration of TWP of <2.5 µm in aerodynamic diameter (TWP2.5) in an indoor parking garage depending on the sampling sites. PM2.5 samples were collected at four sites in an indoor parking garage of a college campus: the entrance of the parking garage (Ent), the second floor toward the third floor (2F), the front of the parking zone on the second floor (2FP), and the third floor toward the fourth floor (3F). Each PM2.5 sampling was performed for 4 days during the fall season. The PM2.5 concentrations at the 2F and 2FP were similar to the outside PM2.5 concentrations, whereas those at the Ent and 3F were higher than the outside PM2.5 concentrations. The TWP2.5 concentrations in the indoor parking garage were 0.61-0.73 µg/m3. The differences in the TWP2.5 concentrations depending on the sampling sites were due to the differences in traffic volumes. The TWP2.5 concentration at the 2FP was higher than those at the other sampling sites owing to air stagnation and TWPs produced by the high friction when parking and exiting a car in the parking zone. The contributions of TWP2.5 to the PM2.5 concentrations were 3.9-11.7%, in the order of 2FP â‰« Ent > 3F > 2F. A good air ventilation system can be recommended to reduce TWP2.5 concentrations in indoor parking garages.

Characteristics of particulate matter from asphalt pavement and tire of a moving bus through driving tests in city road and proving ground.

Non-exhaust PM emissions from vehicles in real road have been conducted, but heavy vehicles have rarely been tested. In this study, PM2.5 and PM10 samples were directly collected from a tire of a moving bus and the composition was analyzed to investigate the sources of PM emissions. Driving tests were conducted at a proving ground (PG) and a city road (CR). PM2.5 emissions considerably increased when the lateral force of the tire increased and the vehicle accelerated. The PM emission rate was higher in the PG test than in the CR test because of the harsher driving conditions at PG. The emission rates of PM10 in the PG and CR tests were higher than those of PM2.5 by approximately 6 and 11 times, respectively. In the PG and CR tests, the proportions of tire wear particles (TWPs) were 4.9% and 2.1% in the PM2.5 samples, and 6.8% and 8.2% in the PM10 samples, respectively. Furthermore, TWPs with PM (TWPPM) were generated by other sources: secondary production of TWPPM by fragmentation of TWPs and resuspension of TWPPM on the road. The contributions of other sources to TWP2.5 generation were at least 6% and 57% in the PG and CR tests, respectively, whereas that to TWP10 generation was at least 3.5% in the CR test. Iron derived from brake abrasion and mineral particles was observed in the PM samples, and the Fe concentrations were higher in the PM10 samples than in the PM2.5 samples by over 9 and 18 times for the PG and CR tests, respectively. Sulfur sources, such as TWPs, exhaust gas, and bitumen, were observed in the PM samples. Based on our findings, we recommend that road wear particles should be removed from roads to reduce PM emissions upon driving.

Test method for vapor collection and ion mobility detection of explosives with low vapor pressure.

RATIONALE: Ion mobility spectrometry (IMS) has been widely used for on-site detection of explosives. Air sampling method is applicable only when the concentration of explosive vapor is considerably high in the air, but vapor pressures of common explosives such as 2,4,6-trinitrotoluene (TNT), 1,3,5-trinitro-1,3,5-triazacyclohexane (RDX), and pentaerythritol tetranitrate (PETN) are very low. A test method for analyzing the vapor detection efficiency of explosives with low vapor pressure via IMS was developed using artificial vapor and collection matrices. METHODS: Artificial explosive vapor was produced by spraying an explosive solution in acetone. Fifteen collection matrices of various materials with woven or nonwoven structures were tested. Two arrangements of horizontal and vertical positions of the collection matrices were employed. Explosive vapor collected in the matrix was analyzed using IMS. RESULTS: Only three collection matrices of stainless steel mesh (SSM), polytetrafluoroethylene sheet (PFS), and lens cleansing paper (LCP) showed the TNT and/or RDX ion peaks at an explosive vapor concentration of 49 ng/L. There was no collection matrix to detect PETN vapor at or lower than 49 ng/L. For the PFS, TNT and RDX were detected at a vapor concentration of 49 ng/L. For the LCP, TNT and RDX were detected at vapor concentrations of 14 and 49 ng/L, irrespectively. CONCLUSIONS: The difference in the explosive vapor detection efficiencies could be explained by the adsorption and desorption capabilities of the collection matrices. The proposed method can be used for evaluating the vapor detection efficiency of hazardous materials with low vapor pressure.

Ionization behaviors of nitrotoluenes and dinitrotoluenes by reactions with acetone-related reactant ion.

Dinitrotoluenes (DNTs) and nitrotoluenes (NTs) are found in the environment as metabolites of trinitrotoluene (TNT). When acetone is used as the solvent/eluent in atmospheric pressure chemical ionization-mass spectrometry (APCI-MS), the reactant ion is [2Acetone + O2 ]•- for the negative ion mode. The reactant ion reacts with an analyte to produce M•- and/or [M - H]- under atmospheric pressure. In this study, ionization behaviors of NT (2-, 3-, and 4-NTs) and DNT isomers (2,3-, 2,4-, and 2,6-DNTs) by reactions with [2Acetone + O2 ]•- were investigated. The energy-minimized structures of the product ions and their energies were calculated to explain the differences in the ionization behaviors. Typical NT- and DNT-related ions were produced by reactions with [2Acetone + O2 ]•- ; NT•- , [NT - H]- , DNT•- , [DNT - H]- , and [DNT - NO]- ions. The ionization efficiencies of NT- and DNT-related ions increased by increasing the source fragmentor voltage, and those of DNT-related ions were higher than those of the NT-related ions owing to the presence of an additional nitro group. The ionization efficiency of 3-NT•- was higher than that of [NT - H]- , while that of [DNT - H]- was higher than those of DNT•- and [DNT - NO]- . The ionization efficiency order of NT•- was 3-NT > 4-NT > 2-NT, while that of [DNT - H]- was 2,4-DNT > 2,6-DNT > 2,3-DNT. The [NT - H]- and [DNT - H]- ions were stabilized by resonance structures containing nitro groups. The [DNT - NO]- ions were formed through the transition state.

Quantification of tire tread wear particle in road dust through pyrolytic technique.

Road dust cotains tire wear particles (TWPs) and a large amount of mineral particles (MPs). Given that tire tread in vehicles is mainly comprised of natural rubber (NR), isoprene and dipentene could be the main pyrogenic products stemmed from the thermolysis of NR. This offers a great chance to quantify the exact mass of TWP in road dust. As such, this study focused on the influence of MPs on the trends in thermolytic behaviors of NR using the resistive furnace (furnance) and Curie point pyrolyzers. This study confirmed that a reliable correlation in line with the formation of isoprene and dipentene could not be realized using the furnace type of a pyrolyzer. This means that employing the furnace type of a pyrolyzer in quantitification of TWPs could not be a viable and approproiate option due to the diverted thermolytic trends of NR due to differences in the heat transfer and adsoprtion of the pyrogenic products triggered by MPs. In the Curie point type of a pyrolyzer, the production rates of isoprene and dipentene were linearly responded to the mass of NR. The ferromagnetic substance in MPs could lead to the thermolytic trend change of NR. Thus, adopting the Curie point type of a pyrolyzer could be a viable option for quantification of TWPs in road dust when the effects of ferromagnetic substance are well neutralized.

Comparison of polymeric components and tire wear particle contents in particulate matter collected at bus stop and college campus.

Particulate matter (PM2.5) samples were collected at two different places of a college campus (CC) and a bus stop (BS) nearby the college campus. The traffic volume of college campus was very low due to untact classes. Polymeric components and tire wear particle (TWP) contents in the PM2.5 samples were analyzed using pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS). Various polymeric components such as natural rubber (NR), bitumen, saturated hydrocarbons, poly(ethylene terephthalate) (PET), and plant-related particles (PRPs) were observed. NR and bitumen are key components of TWP of bus tire tread and asphalt pavement wear particle (APWP), respectively. The TWP contents in the PM2.5 samples collected at the bus stop were larger than those collected at the college campus. For the same sampling site, the TWP content in the PM2.5 sample collected for higher fine dust concentration in the air was greater than that for lower one. The TWP2.5 concentration in the air for the BS sampling was higher than those for the CC sampling, even when the PM2.5 concentration in the air for the former was lower than those for the latter. It can be concluded that the TWPs and APWPs in the PM2.5 samples collected at the college campus should be transferred mostly from the outside road.

Variation in Abundance Ratio of Isoprene and Dipentene Produced from Wear Particles Composed of Natural Rubber by Pyrolysis Depending on the Particle Size and Thermal Aging.

Tire wear particles (TWPs) are generated by friction between the road and the tire. TWPs are one of the major microplastics found in environmental samples, such as road dust, particulate matter (PM), and sediment. TWP contents in environmental samples are generally analyzed using the pyrolysis technique. Tire tread compounds of heavy vehicles are usually composed of natural rubber (NR). Isoprene and dipentene are the principal pyrolysis products of NR, and dipentene is employed as the key marker for the determination of the TWP contents. In this study, an NR abrasion specimen was thermally aged, and an abrasion test was performed to obtain the wear particles. The influence of the wear particle size and thermal aging on the pyrolysis behavior of NR was investigated. The isoprene/dipentene ratio exponentially increased as the wear particle size decreased, and it was also increased by the thermal aging of the abrasion specimen. The increased isoprene/dipentene ratio by thermal aging was explained by increasing the crosslink density. Using the relationship between the wear particle size and the isoprene/dipentene ratio, it is possible to estimate the isoprene/dipentene ratio for very small TWP such as PM. The experimental results concluded that the wear particle size and thermal aging affect the formation of the key pyrogenic products, and the influencing factors should be considered for the quantification of TWP contents in the environmental samples.

Deprotonation of trinitrotoluene by dichloromethane in atmospheric pressure chemical ionization mass spectrometry.

RATIONALE: Trinitrotoluene (TNT) and its derivatives are found in the environment. Depending on the analysis conditions, TNT may be detected as a deprotonated molecule or a molecular ion through atmospheric pressure chemical ionization (APCI). Dichloromethane (CH2 Cl2 ) is used as an extraction solvent for TNT from environmental samples and as an ionizing agent to generate chlorinated species. APCI mass spectra of TNT dissolved in CH2 Cl2 revealed the presence of only the [TNT - H]- ion. This phenomenon was investigated by reactions with the CH2 Cl2 -related reactant ions. METHODS: TNT in CH2 Cl2 was ionized through APCI, and CH2 Cl2 and acetone were used as the eluent. The vaporizing temperature was varied from 200 to 350°C. TNT-related ions and reactant ions were analyzed. Detection limits for TNT were determined under different conditions. Energy-minimized structures of the product ions were used to interpret the analysis results. RESULTS: Significant [TNT - H]- ion was observed, but the [TNT + Cl]- and TNT•- ions were not detected. The [HCl + Cl]- and [3acetone + Cl]- ions were detected as reactant ions when using CH2 Cl2 and acetone as eluent, respectively. Other potential reactant ions such as CH2 Cl2 •- and [CH2 Cl2  + Cl]- were not observed. The detection limit improved as the vaporizing temperature increased. The favorability of [TNT - H]- formation was explained on the basis of the heats of reactions. CONCLUSIONS: The [TNT - H]- ion was primarily produced by the deprotonation reaction between CH2 Cl2 •- and neutral TNT. This reaction was determined to be significantly exothermic. CH2 Cl2 can be helpful for the analysis of TNT in environmental samples through APCI mass spectrometry.

Analysis of Polymeric Components in Particulate Matter Using Pyrolysis-Gas Chromatography/Mass Spectrometry.

Particulate matters (PMs) such as PM10 and PM2.5 were collected at a bus stop and were analyzed using pyrolysis-gas chromatography/mass spectrometry to identify organic polymeric materials in them. The major pyrolysis products of the PM samples were isoprene, toluene, styrene, dipentene, and 1-alkenes. The pyrolysis products generated from the PM samples were identified using reference polymeric samples such as common rubbers (natural rubber, butadiene rubber, and styrene-butadiene rubber), common plastics (polyethylene, polypropylene, polystyrene, and poly(ethylene terephthalate)), plant-related components (bark, wood, and leaf), and bitumen. The major sources of the principal polymeric materials in the PM samples were found to be the abrasion of the tire tread and asphalt pavement, plant-related components, and lint from polyester fabric. The particles produced by the abrasion of the tire tread and asphalt pavement on the road were non-exhaustive sources, while the plant-related components and lint from polyester fabric were inflowed from the outside.

Characteristics of ionization behaviors of aminonitrotoluene isomers produced by atmospheric pressure chemical ionization.

RATIONALE: Six of the isomers of aminonitrotoluene (ANT) are 2-amino-3-nitrotoluene (2A3NT), 2A4NT, 2A5NT, 2A6NT, 4A2NT, and 4A3NT. Some of them can be identified by chromatography and spectroscopy. Biochemical transformation of 2,4,6-trinitrotoluene (TNT) and dinitrotoluenes (DNTs) is very complex and ANTs are decomposition products of TNT and DNTs. METHODS: Each isomer in acetone was ionized using atmospheric pressure chemical ionization in positive and negative ion modes, and kinds and abundances of the product ions were analyzed. Energy-minimized structures of the product ions and their energies were calculated to explain the analysis results. RESULTS: The [M + H]+ , [M + H + Acetone - H2 O]+ , and [M + H + Acetone]+ ions as positive product ions were detected, while [M - H]- , M•- , and [M + O2 ]•- ions as negative ones were observed. The order of the ionization efficiencies for the positive product ions was 4A3NT > 4A2NT > 2A4NT > 2A6NT > 2A5NT > 2A3NT, while that of the negative ones was 2A5NT > 2A3NT > 4A3NT > 2A4NT > 2A6NT > 4A2NT. Ion abundance ratios for 2A3NT and 2A5NT showed very similar trends, while those of 2A6NT and 4A2NT also showed similar trends. Differences in the ionization behaviors were explained using the heats of reaction. CONCLUSIONS: The product ions were produced by ion-molecule reactions with the reactant ions of [2Acetone + H]+ and [Acetone + O2 ]•- . The [M + H + Acetone]+ ion was fragmented to produce [M + H]+ and [M + H + Acetone - H2 O]+ , while the [M + O2 ]•- ion was fragmented to generate the [M - H]- and M•- ions. Differences in the ionization behaviors of the ANTs can be used for their differentiation.

Preparation and Characterization of Model Tire-Road Wear Particles.

Tire tread wear particles (TWPs) are one of major sources of microplastics in the environment. Tire-road wear particles (TRWPs) are mainly composed of TWPs and mineral particles (MPs), and many have long shapes. In the present work, a preparation method of model TRWPs similar to those found in the environment was developed. The model TRWPs were made of TWPs of 212-500 µm and MPs of 20-38 µm. Model TWPs were prepared using a model tire tread compound and indoor abrasion tester while model MPs were prepared by crushing granite rock. The TWPs and MPs were mixed and compressed using a stainless steel roller. The TWPs were treated with chloroform to make them stickier. Many MPs in the model TRWP were deeply stuck into the TWPs. The proper weight ratio of MP and TWP was MP:TWP = 10:1, and the double step pressing procedure was good for the preparation of model TRWPs. The model TRWPs were characterized using scanning electron microscopy (SEM) and thermogravimetric analysis (TGA). The model TRWPs had long shapes and the MP content was about 10%. The model TRWPs made of TWPs and asphalt pavement wear particles showed plate-type particles deeply stuck into the TWP. Characteristics of model TRWPs can be controlled by employing various kinds and sizes of TWPs and MPs. The well-defined model TRWPs can be used as the reference TRWPs for tracing the pollutants.

Classification and Characterization of Tire-Road Wear Particles in Road Dust by Density.

Tire treads are abraded by friction with the road surface, producing tire tread wear particles (TWPs). TWPs combined with other particles on the road such as road wear particles (RWPs) and mineral particles (MPs), forming tire-road wear particles (TRWPs). Dust on an asphalt pavement road is composed of various components such as TRWPs, asphalt pavement wear particles (APWPs), MPs, plant-related particles (PRPs), and so on. TRWPs have been considered as one of major contaminants produced by driving and their properties are important for study on real abrasion behaviors of tire treads during driving as well as environmental contamination. Densities of the TRWPs are totally dependent on the amount of the other components deposited in the TWPs. In this study, a classification method of TRWPs in the road dust was developed using density separation and the classified TRWPs were characterized using image analysis and pyrolytic technique. Chloroform was used to remove APWPs from mixture of TRWPs and APWPs. TRWPs were found in the density range of 1.20-1.70 g/cm3. By decreasing the particle size of the road dust, the TRWP content in the road dust increased and its density slightly tended to increase. Aspect ratios of the TRWPs varied and there were many TRWPs with low aspect ratio below 2.0. The aspect ratio range was 1.2-5.2. Rubber compositions of the TRWPs were found to be mainly NR/SBR biblend or NR/BR/SBR triblend.

Complex formation of lactic acid by atmospheric pressure chemical ionization.

Oligomers and polymers of lactic acid are generally synthesized through condensation reactions by dehydration at high emperature under catalysis. In the present work, ionization behaviors of lactic acid produced by atmospheric pressure chemical ionization were investigated. Influence of the sample concentration, the heating zone temperature, and the source fragmentor voltage on kinds and abundances of the product ions was examined. Complex formation of the product ions with neutral species was also investigated. Not only lactate, [M-H]- and its complexes but also ions of condended species, [nM-(n-1)H2 O-H]- with n = 2-5, and their complexes were observed. The condensation reactions occurred in an aerosol state generated in the heating zone for evaporation. By increasing the concentration of lactic acid, abundances of the product ions were increased and the increase of larger ones was noticeable. By increasing the heating zone temperature, abundances of the product ions were decreased and the decrease of larger ones was remarkable. By increasing the source fragmentor voltage, abundances of small product ions were increased and those of the complexes, [nM-(n-2)H2 O-H]- with n = 2-5, were significantly decreased. Complex formation of lactate with the neutral condensed species was more favorable than that of the condensed oligomer ions with a neutral lactic acid. The experimental results were explained by energies and structures of the product ions and neutral species obtained by theoretical calculations.

Direct detection of diphenylamino radical formed by oxidation of diphenylamine using atmospheric pressure chemical ionization mass spectrometry.

RATIONALE: Diphenylamine (DPAH) and its derivatives have been widely used as antioxidants. Its antioxidation behaviors are started with the formation of diphenylamino radical (DPA• ) by loss of hydrogen atom through reaction with oxygen or ozone. DPAH was oxidized by ozonation to produce DPA• and DPA• was directly detected using atmospheric pressure chemical ionization mass spectrometry (APCI-MS). The influence of oxidation time on generation of DPA• and consumption of DPAH was also investigated. METHODS: Experiments were performed using a home-made ozone bubbling apparatus for oxidation of DPAH. DPAH solution (1000 ppm) in acetone was stirred during the ozonation. The oxidized sample was diluted 100-fold and analyzed using APCI-MS. Structures and energies of DPAH, DPA• and detected ions were obtained using electronic structure calculations with Spartan 10 and Gaussian 09. RESULTS: DPA• was detected in positive APCI-MS in the form of DPAH•+ by proton transfer reaction with protonated acetone. Formation of DPAH•+ from DPA• was more favorable than that of [DPAH + H]+ from DPAH and it was also much more favorable than that of DPA+ from DPA• . By increasing the oxidation time, the relative abundance of DPAH•+ was increased whereas that of [DPAH + H]+ was notably decreased. CONCLUSIONS: Existence of DPA• was directly analyzed using APCI-MS. DPAH and DPA• were differently detected as [DPAH + H]+ and DPAH•+ , respectively. Direct APCI-MS analysis is a suitable technique for identification and quantitation of DPA• .

Quantification of tire tread wear particles in microparticles produced on the road using oleamide as a novel marker.

In general, tire tread rubber compounds contain oleamide for improvement of manufacturing processibility, mold release characterization, and abrasion resistance. Tire tread wear particles (TWPs) are one of major contributors to microplastic emissions. In this study, a novel analytical method for quantification of TWP in microparticles produced on the road (road dust, MPRs) was developed by employing oleamide as a new marker. MPRs were collected at bus stops in autumn, winter, and summer seasons. MPRs of 38-63, 63-106, 106-212, and 212-500 µm obtained by size separation were employed for the analysis. Rubber components for bus and passenger car tire tread compounds were identified using pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS). Oleamide was extracted from the MPRs with acetone and was identified using GC/MS. The oleamide concentration was analyzed using GC equipped with flame ionization detector (FID). The TWP contents of the MPRs were determined using the oleamide concentrations and the reference compound formulations. In order to reduce the sampling errors, each experiment was carried out five times and the results were averaged. The TWP contents of the MPRs were 1.4-4.7 wt% and were different according to the sampling seasons and places. The TWP contents were increased by increasing the traffic volume and the temperature.

Characterization of the fragmentation behaviors of protonated α-cyclodextrin generated by electrospray ionization.

RATIONALE: Electrospray ionization (ESI) of an aqueous solution of α-cyclodextrin (α-CD) gave a protonated molecule, [α-CD + H]+ . The fragmentation behavior of the protonated molecule, including direct decomposition and ring cleavage, was investigated by varying the source fragmentor voltage. The possible chemical structures of the product ions were also examined using electronic structure calculations. METHODS: An aqueous α-CD solution was ionized by ESI and the source fragmentor voltage was varied to examine changes of the product ions depending on collision energy. The structures and energies of the precursor and product ions were obtained by electronic structure calculations using Spartan'10 and Gaussian09. RESULTS: The major product ions were [M + H - 162m]+ (where m = 1-5), with the most abundant being [M + H - 162 × 4]+ . The product ions had two chemical structures of the cationic site in the ether linkage ([DPDn - OH]+ ) and in the terminal oxonium ion ([DPn - OH]+ ) formed by direct decomposition of [α-CD + H]+ and fragmentation of the open structure ([DP6 - OH]+ ), respectively. The [DP6 - OH]+ ion is more stable than the [α-CD + H]+ ion. CONCLUSIONS: The fragmentation behavior of protonated α-CD was characterized by two pathways: direct decomposition of [α-CD + H]+ and decomposition of the [DP6 - OH]+ open structure. Differences in the relative abundances of product ions were explained by the different fragmentation pathways of [α-CD + H]+ and [DP6 - OH]+ .

The influence of different types of reactant ions on the ionization behavior of polycyclic aromatic hydrocarbons in corona discharge ion mobility spectrometry.

RATIONALE: Some polycyclic aromatic hydrocarbons (PAHs) are considered to be cancer-causing chemicals, and ion mobility spectrometry (IMS) is used for on-site detection of such hazardous chemicals. In IMS, the ionization behavior of analytes is affected by the types of reactant ions (RIs). In the present work, the influence of different types of RIs on the ionization behaviors of PAHs in an ion mobility spectrometer equipped with a corona discharge ionization source was investigated using various RIs. METHODS: Selected PAHs were dissolved in anisole, fluorobenzene, chlorobenzene, or bromobenzene. The IMS analysis procedure was performed as follows: (a) the PAH solution was dropped onto the smear matrix; (b) the smear matrix was immediately inserted into the sample inlet to minimize evaporation of the solvent; and (c) the IMS analysis was performed. The lowest amount studied was 10 ng. Variations in the IMS spectra with time were investigated. RESULTS: PAHs were not ionized by RIs of protonated molecules ([M + H]+ ) such as air/moisture and acetone, but they were ionized by charge transfer reactions with RIs of molecular ions (M•+ ) of solvents such as anisole, fluorobenzene, chlorobenzene, and bromobenzene. The PAH ions were detected following a time delay of ~1-5 s after the sample introduction, and the times at which the maximum intensities for the PAHs were observed were different. The detection limits of PAHs in chlorobenzene were on the whole better than those in other solvents, whereas those in fluorobenzene were worse. The detection limits of pyrene and benzo[a]anthracene were better than those of the other PAHs irrespective of the solvent used. CONCLUSIONS: PAH molecules were ionized by charge transfer reactions with RIs of the solvents, and their ions were detected ~1-5 s after sample introduction. The order of the ionization efficiency was chlorobenzene > anisole > bromobenzene > fluorobenzene.

Influence of smear matrix types on detection behaviors and efficiencies of polycyclic aromatic hydrocarbons using ion mobility spectrometry.

Influence of smear matrix types on detection behaviors and efficiencies of polycyclic aromatic hydrocarbons (PAHs) with different molecular weights in ion mobility spectrometry (IMS) were investigated. Various smear matrices of stainless steel mesh (SM), cellulose paper (CP), and cotton fabric (CF) were employed. Anisole was used as the solvent and IMS analysis was performed without evaporation step of the solvent to apply charge transfer reactions between PAH molecules and the molecular ions of solvent. Shapes of reactant ion peaks (RIPs) were varied according to the smear matrix types. At the beginning of the sample inlet, intensity of RIPs of air and moisture notably decreased due to the lots of solvent vapor. The SM with good gas permeability showed relatively strong RIPs of air and moisture, whereas the CP with no gas permeability showed weak ones. Detection times and efficiencies of PAH ions were varied according to the smear matrix types as well as the kinds of PAHs. PAHs were on the whole detected well in 1-3 s after the sample inlet. Detection limits of PAHs measured using the SM were slightly better than those measured using the CP, while those measured using the CP were much better than those measured using the CF. The experimental results could be explained by structures of the smear matrices and evaporation behaviors of the PAH solutions.

Formation of deaminated dimer species of amino acids by atmospheric pressure chemical ionization.

RATIONALE: Interactions of biological molecules to form cluster species play a key role in biological processes and investigation of non-covalent complexes is one of the research fields using mass spectrometry. Atmospheric pressure chemical ionization mass spectrometry (APCI-MS) is a useful method for the investigation of cluster formation of amino acids (AAs) by ion-molecule reactions. METHODS: A mixture of 20 protein AAs was ionized by APCI and the product ions were analyzed. The ionization was performed in the positive and negative ion modes. Formation of the homo- and heterocluster ions of AAs was investigated. Mechanism for the formation of AA homo- and heterocluster ions was examined using hydrogen/deuterium (H/D)-exchange experiments. RESULTS: In the positive ion mode, of the dimer species only the [2Pro+H](+) ion was detected. In the negative ion mode, the [2M - H](-) ions of His, Val, Ser, and Gln were observed. The deaminated dimers such as the [2Gln - H - NH3](-) and [His + Gln - H - NH3](-) ions were also observed. In the negative ion mass spectra of the His/Arg, His/Asn, and His/Lys binary mixture solutions, the [His + AA - H - NH3](-) ions of Asn, Arg, and Lys were also detected. CONCLUSIONS: The number and abundances of the negative product ions were much greater than those of the positive ones. Mechanism for the formation of [2Gln - H - NH3](-) and [His+AA - H - NH3](-) was examined by deuterium replacement of the amine and hydroxide groups to distinguish the deamination and dehydration reactions with a single quadrupole mass spectrometer. The [His + AA - H - NH3](-) ion is formed by ion-molecule reaction between the [His-H](-) ion and a neutral AA.