Evaluation of micro-electrospray ionization with ion mobility spectrometry/mass spectrometry

In recent years, the resolving power of ion mobility instruments has been increased significantly, enabling ion mobility spectrometry (IMS) to be utilized as an analytical separation technique for complex mixtures. In theory, decreasing the drift tube temperature results in increased resolution due to decreased ion diffusion. However, the heat requirements for complete ion desolvation with electrospray ionization (ESI) have limited the reduction of temperatures in atmospheric pressure ion mobility instruments. Micro-electrospray conditions were investigated in this study to enable more efficient droplet formation and ionization with the objective of reducing drift tube temperatures and increasing IMS resolution. For small molecules (peptides), the drift tube temperature was reduced to ambient temperature with good resolution by employing reduced capillary diameters and flow rates. By employing micro-spray conditions, experimental resolution values approaching theoretically predicted resolution were achieved over a wide temperature range (30 to 250 °C). The historical heat requirements of atmospheric pressure IMS due to ESI desolvation were eliminated due to the use of micro-spray conditions and the high-resolution IMS spectra of GLY-HIS-LYS was obtained at ambient temperature. The desolvation of proteins (cytochrome c) was found to achieve optimal resolution at temperatures greater than 125 °C. This is significantly improved from earlier IMS studies that required drift tube temperatures of 250°C for protein desolvation.     

Separation of benzodiazepines by electrospray ionization ion mobility spectrometry-mass spectrometry

Benzodiazepines are a commonly abused class of drugs; requiring analytical techniques that can separate and detect the drugs in a rapid time period. In this paper, the two-dimensional separation of five benzodiazepines was shown by electrospray ionization (ESI) ion mobility spectrometry (IMS)-mass spectrometry (MS). In this study, both the two dimensions of separation (m/z and mobility) and the high resolution of our IMS instrument enabled confident identification of each of the five benzodiazepines studied. This was a significant improvement over previous IMS studies that could not separate many of the analytes due to low instrumental resolution. The benzodiazepines that contain a hydroxyl group in their molecular structure (lorazepam and oxazepam) were found to form both the protonated molecular ion and dehydration product as predominant ions. Experiments to isolate the parametric reasons for the dehydration ion formation showed that it was not the result of corona discharge processes or the potential applied to the needle. However, the potential difference between the needle and first drift ring did influence both the relative intensity ratios of the two ions and the ion sensitivity.     

Development of an ion mobility spectrometer for use in an atmospheric pressure ionization ion mobility spectrometer/mass spectrometer instrument for fast screening analysis

An ion mobility spectrometer that can easily be installed as an intermediate component between a commercial triple-quadrupole mass spectrometer and its original atmospheric pressure ionization (API) sources was developed. The curtain gas from the mass spectrometer is also used as the ion mobility spectrometer drift gas. The design of the ion mobility spectrometer allows reasonably fast installation (about 1 h), and thus the ion mobility spectrometer can be considered as an accessory of the mass spectrometer. The ion mobility spectrometer module can also be used as an independently operated device when equipped with a Faraday cup detector. The drift tube of the ion mobility spectrometer module consists of inlet, desolvation, drift, and extraction regions. The desolvation, drift and extraction regions are separated by ion gates. The inlet region has the shape of a stainless steel cup equipped with a small orifice. Ion mobility spectrometer drift gas is introduced through a curtain gas line from an original flange of the mass spectrometer. After passing through the drift tube, the drift gas serves as a curtain gas for the ion-sampling orifice of the ion mobility spectrometer before entering the ion source. Counterflow of the drift gas improves evaporation of the solvent from the electrosprayed sample. Drift gas is pumped away from the ion source through the original exhaust orifice of the ion source. Initial characterization of the ion mobility spectrometer device includes determination of resolving power values for a selected set of test compounds, separation of a simple mixture, and comparison of the sensitivity of the electrospray ionization ion mobility spectrometry/mass spectrometry (ESI-IMS/MS) mode with that of the ESI-MS mode. A resolving power of 80 was measured for 2,6-di-tert-butylpyridine in a 333 V/cm drift field at room temperature and with a 0.2 ms ion gate opening time. The resolving power was shown to be dependent on drift gas flow rate for all studied ion gate opening times. Resolving power improved as the drift gas flow increased, e.g. at a 0.5 ms gate opening time, a resolving power of 31 was obtained with a 0.65 L/min flow rate and 47 with a 1.3 L/min flow rate for tetrabutylammonium iodide. The measured limits of detection with ESI-MS and with ESI-IMS/MS modes were similar, demonstrating that signal losses in the IMS device are minimal when it is operated in a continuous flow mode. Based on these preliminary results, the IMS/MS instrument is anticipated to have potential for fast screening analysis that can be applied, for example, in environmental and drug analysis.     

High resolution electrospray ionization ion mobility spectrometry

Current commercially available ion mobility spectrometers are intended for the analysis of chemicals in the gas phase. Sample introduction methods, such as direct air sampling, a GC injector or a thermal desorber, are commonly an integral part of these instruments. This paper describes an electrospray ionization ion mobility spectrometer system that allows direct introduction samples in solution phase. This allows direct analysis of non-volatile organic and biological samples, and avoids decomposition of thermally liable samples, providing reliable chemical identification. In addition, the new ion mobility spectrometer allows mobility analysis with high resolving power. Commonly used commercial IMS systems provide resolving powers between 10 and 30; this new ion mobility spectrometer has resolving power greater than 60 for routine analysis. A high resolution instrument is necessary for many applications where a complex mixture needs to be separated and quantified. This paper demonstrates the advantages of using a high resolution ion mobility spectrometer and an electrospray ionization source for the analysis of non-volatile pharmaceuticals as well as dissolved explosive in solution phase.     

A novel ion detector aiming at the homogeneous of drift gas

In standalone ion mobility spectrometry (IMS) instruments, the effect of drift gas turbulence reduces the sensitivity and resolution of the instrument. A traditional ion detector constructed with a Faraday plate and used to detect ions in an IMS is positioned at the end of the drift region. Drift gas flowing through this detector may introduce turbulence near the detector, possibly affecting the sensitivity and resolution of the device. To address this problem, a novel Faraday detector with a double layer structure was constructed. A number of dense and staggered holes were created on each layer of the detector. This design enabled the drift gas to pass through the holes of the detector, and the staggered nature of holes in the detector ensured that the ions could be detected. Theoretical simulations were conducted using the finite element method to obtain velocity distributions for both a standard Faraday detector and the modified Faraday detector. The results indicated that the novel ion detector created a homogenous gas under at high inlet flow rate while turbulence was still evident for the traditional Faraday detector. When the inlet flow rate was 1000 mL/min, the range of the unstable region of the drift gas in the axis of the drift tube with the novel ion detector was reduced by 97% relative to that for the traditional detector. The data suggests that due to such gains, sensitivity and resolution may be improved for standalone IMS instruments.     

Coupling of capillary electrophoresis with electrospray ionization multiplexing ion mobility spectrometry

In this work, ion mobility spectrometry (IMS) function as a detector and another dimension of separation was coupled with CE to achieve two‐dimensional separation. To improve the performance of hyphenated CE‐IMS instrument, electrospray ionization correlation ion mobility spectrometry is evaluated and compared with traditional signal averaging data acquisition method using tetraalkylammonium bromide compounds. The effect of various parameters on the separation including sample introduction, sheath fluid of CE and drift gas, data acquisition method of IMS were investigated. The experimental result shows that the optimal conditions are as follows: hydrodynamic sample injection method, the electrophoresis voltage is 10 kilo volts, 5 mmol/L ammonium acetate buffer solution containing 80% acetonitrile as both the background electrolyte and the electrospray ionization sheath fluid, the ESI liquid flow rate is 4.5 μL/min, the drift voltage is 10.5 kilo volts, the drift gas temperature is 383 K and the drift gas flow rate is 300 mL/min. Under the above conditions, the mixture standards of seven tetraalkylammoniums can be completely separated within 10 min both by CE and IMS. The linear range was 5–250 μg/mL, with LOD of 0.152, 0.204, 0.277, 0.382, 0.466, 0.623 and 0.892 μg/mL, respectively. Compared with traditional capillary electrophoresis detection methods, the developed CE‐ESI‐IMS method not only provide two sets of qualitative parameters including electrophoresis migration time and ion drift time, ion mobility spectrometer can also provide an additional dimension of separation and could apply to the detection ultra‐violet transparent compounds or none fluorescent compounds.     

Evaluation of capillary liquid chromatography-electrospray ionization ion mobility spectrometry with mass spectrometry detection

Due to the proteomics revolution, multi-dimensional separation and detection instruments are required to evaluate many peptides and proteins in single samples. In this study, electrospray ionization (ESI) ion mobility spectrometry (IMS) was evaluated as an additional separation after HPLC separations. Common HPLC mobile phase compositions (solvents, acid modifiers, and buffers) were assessed for the effect on ESI-IMS response. Up to 5 mM sodium phosphate, a non-volatile buffer, was able to be electrosprayed into the IMS without degradation of the instrumental performance. Due to the rapid separation times of IMS, multiple IMS spectra were obtained within a single HPLC peak. A five-peptide mixture was separated in a capillary HPLC column under isocratic conditions within 3 min. Coelution of two peaks due to non-optimal HPLC conditions occurred and these two peaks could not be distinguished by HPLC with UV detection. In contrast, the single ion mobility chromatograms provided separation of each peptide as well as providing a second degree of analyte identification (HPLC retention time and IMS mobility). Furthermore, IMS-MS analysis of the five peptides and comparison with HPLC retention times showed that each peptide had a unique retention time-ion mobility-mass to charge value. This work showed that IMS could be employed for direct separation and detection of HPLC eluents and also could be combined with HPLC-MS for three unique dimensions of separation.     

Ion mobility spectrometry—mass spectrometry performance using electrodynamic ion funnels and elevated drift gas pressures

The ability of ion mobility spectrometry coupled with mass spectrometry (IMS-MS) to characterize biological mixtures has been illustrated over the past eight years. However, the challenges posed by the extreme complexity of many biological samples have demonstrated the need for higher resolution IMS-MS measurements. We have developed a higher resolution ESI-IMS-TOF MS by utilizing high-pressure electrodynamic ion funnels at both ends of the IMS drift cell and operating the drift cell at an elevated pressure compared with that conventionally used. The ESI-IMS-TOF MS instrument consists of an ESI source, an hourglass ion funnel used for ion accumulation/injection into an 88 cm drift cell, followed by a 10 cm ion funnel and a commercial orthogonal time-of-flight mass spectrometer providing high mass measurement accuracy. It was found that the rear ion funnel could be effectively operated as an extension of the drift cell when the DC fields were matched, providing an effective drift region of 98 cm. The resolution of the instrument was evaluated at pressures ranging from 4 to 12 torr and ion mobility drift voltages of 16 V/cm (4 torr) to 43 V/cm (12 torr). An increase in resolution from 55 to 80 was observed from 4 to 12 torr nitrogen drift gas with no significant loss in sensitivity. The choice of drift gas was also shown to influence the degree of ion heating and relative trapping efficiency within the ion funnel.     

Ion mobility spectrometer—field asymmetric ion mobility spectrometer-mass spectrometry

Since the development of electrospray ionization (ESI) for ion mobility spectrometry mass spectrometry (IMMS), IMMS have been extensively applied for characterization of gas-phase bio-molecules. Conventional ion mobility spectrometry (IMS), defined as drift tube IMS (DT-IMS), is typically a stacked ring design that utilizes a low electric field gradient. Field asymmetric ion mobility spectrometry (FAIMS) is a newer version of IMS, however, the geometry of the system is significantly different than DT-IMS and data are collected using a much higher electric field. Here we report construction of a novel ambient pressure dual gate DT-IMS coupled with a FAIMS system and then coupled to a quadrupole ion trap mass spectrometer (QITMS) to form a hybrid three-dimensional separation instrument, DT-IMS-FAIMS-QITMS. The DT-IMS was operated at ~3 Townsend (electric field/number density (E/N) or (Td)) and was coupled in series with a FAIMS, operated at ~80 Td. Ions were mobility-selected by the dual gate DT-IMS into the FAIMS and from the FAIMS the ions were detected by the QITMS for as either MS or MSⁿ. The system was evaluated using cocaine as an analytical standard and tested for the application of separating three isomeric tri-peptides: tyrosine-glycine-tryptophan (YGW), tryptophan-glycine-tyrosine (WGY) and tyrosine-tryptophan-glycine (YWG). All three tri-peptides were separated in the DT-IMS dimension and each had one mobility peak. The samples were partially separated in the FAIMS dimension but two conformation peaks were detected for the YWG sample while YGW and WGY produced only one peak. Ion validation was achieved for all three samples using QITMS.     

Decomposition of overlapping plasmagram peaks by spectral subtraction

Low field atmospheric pressure Ion Mobility Spectroscopy (IMS) involves the careful analysis of plasmagrams with multiple peaks which can mask one another when they are closely spaced in drift time or corresponding reduced mobility. A typical signal processing approach to decomposing overlapped peaks would be to use an orthogonal decomposition technique, but unfortunately Gaussian-like functions are not orthogonal, so no unique decomposition can be guaranteed. However, each ion species in the drift tube will arrive at the Faraday plate with a known statistical distribution determined by the IMS instrument’s drift tube design, electric field strength, reagent gas flow and other instrument-specific factors such as the ion gate function. This paper presents a straightforward algorithm for decomposing plasmagrams into distinct peaks using a subtractive technique that independently estimates the statistical parameters of each peak, rejecting spurious peaks and electrical noise. The results show that for relatively short gate times, the plasmagram peaks are nearly Gaussian-shaped, but slightly fatter and asymmetric. We show that including of the gate rise and fall times is also significant in matching the plasmagram peak shape. We also show that the diffusion effects on resolution can be attributed to combinations of non-uniform ion distributions in the reaction chamber as well as detritus effects in the drift tube. Given the known peaks statistical parameters, one can then separate overlapping peaks using a straightforward spectral subtractive technique.     

一种基于离子迁移谱的气相色谱检测器及其应用

离子迁移谱作为气相色谱的检测器,兼有色谱的高分离能力和离子迁移谱的高灵敏度,有利于实现复杂混合物的实时在线监测。基于在色谱、离子迁移谱方面的研究基础,本实验室搭建了一套以离子迁移谱为检测器的气相色谱仪,分别对检测器的温度、总电压、尾吹气流速等参数进行了系统优化,并用于碘甲烷、1,2-二氯乙烷、四氯化碳和二溴甲烷4种卤代烃化合物的检测。实验结果表明,参数优化后的离子迁移谱检测器对碘甲烷、1,2-二氯乙烷、四氯化碳和二溴甲烷的检出限可分别达到2、0.02、1和0.1 ng,线性范围有两个数量级。离子迁移谱与气相色谱联用,其二维的分离能力可以为复杂混合物的准确定性提供更多的信息,还可以实现不同化合物的选择性检测。     

The novel use of gas chromatography-ion mobility-time of flight mass spectrometry with secondary electrospray ionization for complex mixture analysis

Increasing the dimensionality of an analysis enables more detailed and comprehensive investigations of complex mixtures. One dimensional separation techniques like gas chromatography (GC) and ion mobility spectrometry (IMS) provide limited chemical information about complex mixtures. The combination of GC, ion mobility spectrometry, and time-of-flight mass spectrometry (GC-IM-TOFMS) provides three-dimensional separation of complex mixtures. In this work, a hybrid GC-IM-TOFMS with a secondary electrospray ionization (SESI) source provided four types of analytical information: GC retention time, ion mobility drift time, mass-to-charge ratios, and ion intensity. The use of secondary electrospray ionization enables efficient and soft ionization of gaseous sample vapors at atmospheric pressure. Several complex mixtures, including lavender and peppermint essential oils, were analyzed by GC-SESI-IM-TOFMS. The resulting 3D data from these mixtures, each containing greater than 50 components, were plotted as 3D projections. In particular, post-processed data plotted in three dimensions showed that many mass selected GC peaks were resolved into different ion mobility peaks. This technique shows clear promise for further in-depth analyses of complex chemical and biological mixtures.     

Stable gradient nanoflow LC-MS

This paper demonstrates improved nanoflow LC-MS performance on a QqTOF instrument with the incorporation of a heated nanoflow interface (particle discriminator) and a nebulizer assisted sprayer. It is shown that the nebulizer broadens the usable range of electrospray potentials, simplifying the tuning procedure, particularly for negative mode nanoflow gradients. The improved desolvation capability with the particle discriminator results in signal/noise improvements of approximately 3.5x for negative ion mode samples prepared in predominantly acidified water as well as increased ion current stability. For nanoLC applications, the combined desolvation capabilities of a counter-current gas and heated laminar flow chamber provide reduced background, increased signal stability, reduced background drift, and improved protein sequence coverage when compared with data generated with only a counter-current gas for desolvation. This system is capable of subfemtomole nanoflow LC-MS sensitivity in both positive and negative ion mode across the solvent gradient.     

Analysis of explosives using electrospray ionization/ion mobility spectrometry (ESI/IMS)

The analysis of explosives with ion mobility spectrometry (IMS) directly from aqueous solutions was shown for the first time using an electrospray ionization technique. The IMS was operated in the negative mode at 250°C and coupled with a quadrupole mass spectrometer to identify the observed IMS peaks. The IMS response characteristics of trinitrotoluene (TNT), 2,4-dinitrotoluene (2,4-DNT), 2-amino-4,6-dinitrotoluene (2-ADNT), 4-nitrotoluene (4-NT), trinitrobenzene (TNB), cyclo-1,3,5-trimethylene-2,4,6-trinitramine (RDX), cyclo-tetramethylene-tetranitramine (HMX), dinitro-ethyleneglycol (EGDN) and nitroglycerine (NG) were investigated. Several breakdown products, predominantly NO₂⁻ and NO₃⁻, were observed in the low-mass region. Nevertheless, all compounds with the exception of NG produced at least one ion related to the intact molecule and could therefore be selectively detected. For RDX and HMX the [M+Cl⁻]⁻ cluster ion was the main peak and the signal intensities could be greatly enhanced by the addition of small amounts of sodium chloride to the sprayed solutions. The reduced mobility constants (K₀) were in good agreement with literature data obtained from experiments where the explosives were introduced into the IMS from the vapor phase. The detection limits were in the range of 15–190 μg l⁻¹ and all calibration curves showed good linearity. A mixture of TNT, RDX and HMX was used to demonstrate the high separation potential of the IMS system. Baseline separation of the three compounds was attained within a total analysis time of 6.4 s.     

Development and evaluation of a nano-electrospray ionisation source for atmospheric pressure ion mobility spectrometry

A nano-electrospray ionisation source has been designed and constructed for a high temperature ion mobility spectrometer. The drift cell was modified by replacement of the 63Ni atmospheric pressure chemical ionisation source with a tube lens/desolvation region and operated using commercial nano-electrospray capillaries. Ions were introduced into the drift region via a Bradbury-Nielson gate (pulse width 50 micros, repetition period 20 ms). A unidirectional flow of nitrogen was used as the drift gas at temperatures in the range 100-150 degrees C to aid desolvation. The performance of the nano-electrospray ion source has been demonstrated for analytes including crown ethers, amino acids and peptides. Reduced mobilities determined by nano-ESI were consistent with those reported using a 63Ni ion source.     

纳升电喷雾-离子迁移谱及其与高效液相色谱的联用

搭建了一套纳升级电喷雾-离子源离子迁移谱仪。首先,分别对尾吹气流速、溶剂流速等影响仪器去溶剂化效果的参数进行了研究和优化。在此基础上,用一系列胺类化合物对该仪器的去溶剂化效果、分辨能力以及灵敏度进行了表征。实验结果表明,该仪器能够对电喷雾离子液滴实现完全去溶剂化;三辛胺的检出限可以达到10 μg/L。最后,将该仪器用作高效液相色谱的检测器,在无需衍生化的条件下对胺类混合物样品进行检测。由三乙胺、二乙胺以及丁胺组成的混合样品被成功分离并测定。该系统对三乙胺、二乙胺以及丁胺的线性响应范围均达到近两个数量级。     

Experimental determination of acetamiprid pesticide residue in three different types of pistachio by ion mobility spectrometry and using QuEChERS method in the different temperatures and in the presence of ammonia as dopant gas

In this project, Ion Mobility Spectrometer (IMS) instrument in the positive mode and with corona ionization source was utilized to determine the residue of acetamiprid pesticide in three different types of pistachio (Akbari, Fandoghi and Kalachuchi). The QuEChERS method, notable because of easy and quick preparation of sample and using lower amounts of organic solvents with harmful environmental effects and high costs, was used in this study. Many experiments were performed in the different temperatures in order to obtain optimum temperature for cell and injection. Ammonia and acetone were considered as dopant substances and it turned out that the ammonia gas, contrary to acetone, increased significantly the signal intensity and sensitivity and avoided the overlap of desired peaks. The LOD of device for acetamiprid pesticide was estimated to be 0.5 μg g^?1 and the LOQ of instrument was obtained as 1.66 μg g^?1. The calibration curve was in the dynamic range between 0.5–11.5 μg g^?1 and the Correlation Coefficient was 0.998. Also, the ion mobility and the reduced ion mobility were calculated for acetamiprid ion. After analysis of five samples with IMS instrument, the acetamiprid residue was determined and it turned out that it was under allowed limit in all three types of pistachio. In addition, the amount of acetamiprid residue was higher for Akbari type relative to Fandoghi and Kalachuchi ones. The reason for this observation is the higher vulnerability of Akbari trees to insects and pests and this in turn causes more pesticide to be consumed.     

An ion mobility spectrometer sensor system for subsurface use

An ion mobility spectrometer (IMS) probe system for real-time, subsurface soil-gas sampling applications is presented. The system includes an IMS and supporting electronics encased in a 51 mm diameter stainless steel probe housing. The IMS was challenged in the laboratory with 2,6-di-tert-butylpyridine (DtBP) and tetrachloroethylene (PCE) in zero air yielding reduced ion mobility constants (K_o) values of 1.42 cm²/Vs (n = 3) and 1.79 ± 0.01 cm²/Vs (n = 3), respectively. A resolving power of 38 and 31 was obtained for DtBP and PCE, respectively. The system was deployed at a PCE-contaminated site to demonstrate its performance under field conditions. PCE was detected in the vapor samples as evidenced by peaks with a K_o value of 1.80 ± 0.01 cm²/Vs for two measurements that were taken 6 min apart. The presence of PCE at the contaminated site was confirmed by GC-MS analysis of a gas sample at an EPA-certified laboratory, suggesting that this IMS system can be used to detect PCE under field conditions.     

Electrospray ionization-ion mobility spectrometry: a rapid analytical method for aqueous nitrate and nitrite analysis

This paper reports the first example of electrospray ionization (ESI) for the separation and detection of anions in aqueous solutions by ion mobility spectrometry (IMS). Standard solutions of arsenate, phosphate, sulfate, nitrate, nitrite, chloride, formate, and acetate were analyzed using ESI-IMS and distinct peak patterns and reduced mobility constants (K(0)) were observed for respective anions. Real world water samples were analyzed for nitrate and nitrite to determine the feasibility of using ESI-IMS as a rapid analytical method for monitoring nitrate and nitrite in water systems. The data showed satisfactory correlation between the measured value ([similar]0.16 ppm) and the reported maximum nitrate-nitrogen concentration (0.2 ppm) found in a local drinking water system. For on-site measurement applications, direct sample introduction and air as an alternate drift gas to nitrogen were evaluated. The identities of the nitrite and nitrate mobility peaks were verified by comparison of reduced mobility constants with mass identified nitrate and nitrite ions reported in literature. In the mixing ratio, a linear dynamic range of 3 orders of magnitude and instrument detection limits of 10 ppb for nitrate and 40 ppb for nitrite were obtained. The calibration curves showed r(2) value of 0.98 and slope of 0.06 for nitrate and r(2) value of 0.99 and slope of 0.11 for nitrite.     

A simulation model study of the coupled field in the IMS drift tube

The performance of the IMS was influenced by many parameters, like temperature, gas flow rate, etc. in the drift tube. An exact and comprehensive simulation model was very useful for the IMS design and optimization. A combined simulation model was build up for the parameters simulation in the drift tube. Based on this simulation model, the heat transfer, velocity distribution, humidity and ion transportation inside the drift tube in bidirectional flow stream was simulated, and the impact on the IMS was studied. And the simulation was also validated using an IMS constructed in our laboratory. The experiment showed that the RIP intensity weakened as the humidity increasing, but the signal intensity of NO was enhanced first, and then decreased with the humidity increasing sequentially. This can be explained from the simulation results. The simulation results showed that the distribution of the velocity and temperature was not uniformed in the drift tube. And this phenomenon was more clearly when the gas flow velocity increased. It can be seen from the simulation that the humidity in the drift tube region was smaller than the sample moisture, and the resolution of the ion mobility spectrometry will be reduced by the humidity. But in the region rich in water molecules, ultraviolet photons re-acting with acetone would be obviously decreased and fewer re-agent ions were produced owing to the strong absorption of photons by water neutrals. The results showed that the coupled field simulation model can be used to study parameters effects on the IMS.