Corona Discharge Ionization Source Research Articles

Solid phase microextraction arrow-ion mobility spectrometry for determination of selected pesticides in water

Ion mobility spectrometry with corona discharge ion source was used for the measurements of selected pesticides cybutryne, terbutryn, dichlorvos, and quinoxyfen in water. The analyses were carried out by (i) direct injection of the aqueous solution of the pesticides and (ii) extraction using solid phase microextraction by commercial SPME arrows. The instrumental and the experimental extraction parameters including the drift tube temperature, injection port temperature, and the SPME fiber type were studied and optimized to achieve the maximum signal intensity. The limit of detections obtained by the direct injection were about 0.1–1.0 mg L−1. Using the SPME arrow-ion mobility spectrometry method, the detection limits were improved 7–50 times and obtained as 0.01, 0.015, 0.05, and 0.1 mg L−1 for terbutryn, dichlorvos, cybutryne, and quinoxyfen, respectively. The recovery rate for analysis in surface water (real samples) was approximately 90–110% for both the direct injection and solid phase microextraction method. The capability of ion mobility spectrometry for the simultaneous detection of a mixture of the studied pesticides was assessed, and it was found that terbutryn, dichlorvos, and quinoxyfen can be detected simultaneously without peak overlapping.

Synthesis and characterization of MoS2–COOH/gly/Mn nanocomposite as an efficient adsorbent for Ultra-trace determination of trifluralin herbicide

The world is confronting a severe water crisis. To clean up water from heavy metals, microorganisms, chemicals, and other types of pollutants, nanocomposites have been receiving great attention specifically due to the high surface area affording to work effectually even at low concentrations. In this research, we synthesized a new amino acid-modified MoS2 nanocomposite by chemically immobilizing Mn (II). The synthesized absorbent MoS2–COOH/gly/Mn was identified by thermogravimetric analysis (TGA), nitrogen adsorption measurement, X-ray diffraction (XRD), analysis of energy dispersive X-ray mapping (EDAX and MAP), field emission scanning electron microscopy (FE-SEM), and Fourier Transform Infrared spectrometry (FT-IR). The nanocomposite was employed as an adsorbent through the solid phase microextraction (SPME) method while trifluralin herbicide was chosen as a model compound. For the monitoring of trifluralin molecules, we employed an ion mobility spectrometry apparatus featuring a corona discharge ionization source. The SPME method's effectiveness was examined by investigating the stirring rate and extraction time as two crucial parameters, aiming to achieve trace analysis of trifluralin. Under the optimized condition of the trifluralin extraction, the coefficient (R2) and linear dynamic range (LDR) correlation were obtained at 0.9961 and 0.5–10 μg L−1, respectively. Relative recovery values the described approach were obtained in the span of 96–97% for agricultural wastewater samples. The quantification (LOQ) and limit of detection (LOD) were calculated at 0.5 and 0.15 μg L−1, respectively. The proposed nanocomposite absorbent has the capability to be applied as an efficient material for the extraction of trifluralin herbicide from different solutions.

Diverse thermal desorption combined with self-aspirating corona discharge ionization for direct mass spectrometry analysis of complex samples.

The thermal desorption (TD) technique is widely employed in modern mass spectrometry to facilitate the detection of non-volatile analytes. In this study, we developed a compact TD device based on a small resistance wire and coupled it with a self-aspirating corona discharge ionization (CDI) source to conduct direct MS analysis of various liquid and solid samples. Due to its small size and low heat capacity, the temperature of the TD module can be flexibly and rapidly modulated by controlling the power sequence. Multiple heating modes, including pulse heating (PH), isothermal heating, and step heating (SH), are realized and characterized, and then applied for the detection of different real samples. In particular, the PH mode is suitable for the simultaneous detection of multiple components in samples with relatively simple matrices, while the SH mode is capable of component separation. In addition, the sensitivity and quantitative capability of the TD-CDI system for DEP solutions were tested, showing acceptable stability with a relative standard deviation of about 6.7% and a detection limit of 0.088 ng. Overall, the developed TD-CDI system provides a simple, convenient, and versatile tool for direct mass spectrometry analysis of real samples.

Reducing ion diffusion at atmospheric pressure through intermingled positive and negative ions

Increasing ion molecule reaction times for ambient ionization techniques can increase sensitivity of detection. Longer reaction times result in an increase in analyte signal relative to the reactant ion signal, however with a subsequent decrease in the total ion intensity. This loss in the total number of ions reaching the detector limits the extent to which increased reaction time can improve detection in practical applications. In this study ion loss was measured using either electric fields or gas flow to control ion transit time. Ion transit times ranged from 40 ms to 8 s, which resulted in ion densities ranging from 5 × 106 to 2 × 104 ions/cm3, respectively. These results provide insights into practical reaction time limitations or experimental boundaries when exploring sensitivity enhancements in ambient ionization. When exploring longer reaction times with an atmospheric flow tube coupled to a mass spectrometer (AFT-MS), an additional corona discharge ionization source of the same polarity was added in an attempt to increase total ion signal, but no improvement in signal was observed. This observation suggested that there was a maximum ion density being reached by the corona discharge that could not be increased by adding more of the same polarity ions. A hypothesis was that intermingling both polarities of ions would reduce ion loss and increase the measured ion signal. When two corona discharge sources—one each of positive and negative polarity—were used simultaneously in an AFT-MS, the total ion signal of either polarity measured by the MS was approximately double the current from a single corona discharge source. An increase in the negative ion signal was also observed when ∼10 parts-per-trillion vapor levels of an explosive (RDX, also known as hexogen) were introduced. In this case both the nitrate reactant ions and the RDX signal more than doubled with the addition of a corona discharge source producing positive ions. When intermingling positive and negative ions, an increase in ion current was also observed when the AFT was coupled directly to a Faraday detector or to an ion mobility spectrometer (IMS). This was the first demonstration of interfacing the AFT to an IMS. The observations and developments from this work will help in creating more portable instruments with improved sensitivity for detection of chemicals.

Analysis of human skin sebum and animal meats by heat pulse desorption/mass spectrometry using proximity corona discharge ionization

Recently, we have developed heat pulse desorption/mass spectrometry (HPD/MS). In HPD/MS, a heated N2 gas pulse was directed to the sample surface and desorbed analytes were mass analyzed by corona discharge ionization/mass spectrometry using an Orbitrap mass spectrometer. In this work, HPD/MS was applied to the analysis of skin surface components sampled from the forehead, nose, and jaw of three volunteers. It was found that various kinds of biological compounds such as squalene, free fatty acids, wax esters, triacylglycerols, and amino acids were detected. The simultaneous detection of compounds with a wide range of proton affinities suggests that the occurrence of consecutive proton transfer reactions is less likely to occur in the present experimental system. This is mainly due to the short distance of 1.5 mm between the tip of the corona needle and the inlet of the mass spectrometer (i.e., proximity corona discharge ion source). Under this condition, the transition time of the primary reactant ions (e.g., H3O+) from the tip of the corona discharge needle to the ion sampling orifice is roughly estimated to be ∼20 μs. This value nearly corresponds to the reaction lifetime of exoergic proton transfer reactions with a rate constant: ∼10−9 cm3 s−1 for the analytes of 1 ppm. Accordingly, analytes with concentrations less than 1 ppm would be ionized semi-quantitatively by the present method, making this method highly suitable for the rapid analysis of samples composed of complex mixture of compounds, e.g., non-target lipidomics.

Effect of ion source polarity and dopants on the detection of auxin plant hormones by ion mobility-mass spectrometry.

Ion mobility spectrometry (IMS) equipped with a corona discharge (CD) ion source was used for measurement of three auxin plant hormones including indole-3-acetic acid (IAA), indole-3-propionic acid (IPA), and indole-3-butyric acid (IBA). The measurements were performed in both positive and negative polarities of the CD ion source. Dopant gases NH3, CCl4, and CHBr3 were used to modify the ionization mechanism. A time-of-flight mass spectrometer (TOFMS) orthogonal to the IMS cell was used for identification of the product ions. Density functional theory was used to rationalize formation of the ions, theoretically. The mixtures of the auxins were analyzed by CD-IMS. The separation performance depended on the ion polarity and the dopants. In the positive polarity without dopants, auxins were ionized via protonation and three distinguished peaks were observed. Application of NH3 dopant resulted in two ionization channels, protonation, and NH4+ attachment leading to peak overlapping. In the negative polarity, two ionization reactions were operative, via deprotonation and O2- attachment. The separation of the monomer peaks was not achieved while the peaks of anionic dimers [2M-H]- were separated well. The best LOD (4ng) was obtained in negative polarity with CCl4 dopant. Methylation (esterification) of IAA improved LODs by about one order.

Ultra-Fast Polarity Switching, Non-Radioactive Drift Tube for the Miniaturization of Drift-Time Ion Mobility Spectrometer.

Drift-time ion mobility spectrometer (DT-IMS) is a promising technology for gas detection and analysis in the form of miniaturized instrument. Analytes may exist in the form of positively or negatively charged ions according to their chemical composition and ionization condition, and therefore require both polarity of electric field for the detection. In this work the polarity switching of a drift-time ion mobility spectrometer based on a direct current (DC) corona discharge ionization source was investigated, with novel solutions for both the control of ion shutter and the stabilization of aperture grid. The drift field is established by employing a switchable high voltage power supply and a serial of voltage regulator diode, with optocouplers to drive the ion shutter when the polarity is switched. The potential of aperture grid is stabilized during the polarity switching by the use of four diodes to avoid unnecessary charging cycle of the aperture grid capacitor. Based on the proposed techniques, the developed DT-IMS with 50 mm drift path is able to switch its polarity in 10 ms and acquire mobility spectrum after 10 ms of stabilization. Coupled with a thermal desorption sampler, limit of detection (LoD) of 0.1 ng was achieved for ketamine and TNT. Extra benefits include single calibration substance for both polarities and largely simplified pneumatic design, together with the reduction of second drift tube and its accessories. This work paved the way towards further miniaturization of DT-IMS without compromise of performance.

Portable Digital Linear Ion Trap Mass Spectrometer Based on Separate-Region Corona Discharge Ionization Source for On-Site Rapid Detection of Illegal Drugs.

As narcotic control has become worse in the past decade and the death toll of drug abuse hits a record high, there is an increasing demand for on-site rapid detection of illegal drugs. This work developed a portable digital linear ion trap mass spectrometer based on separate-region corona discharge ionization source to meet this need. A separate design of discharge and reaction regions was adopted with filter air as both carrier gas for the analyte and protection of the corona discharge needle. The linear ion trap was driven by a digital waveform with a low voltage (±100 V) to cover a mass range of 50–500 Da with a unit resolution at a scan rate of 10,000 Da/s. Eighteen representative drugs were analyzed, demonstrating excellent qualitative analysis capability. Tandem mass spectrometry (MS/MS) was also performed by ion isolation and collision-induced dissociation (CID) with air as a buffer gas. With cocaine as an example, over two orders of magnitude dynamic range and 10 pg of detection limit were achieved. A single analysis time of less than 10 s was obtained by comparing the information of characteristic ions and product ions with the built-in database. Analysis of a real-world sample further validated the feasibility of the instrument, with the results benchmarked by GC-MS. The developed system has powerful analytical capability without using consumables including solvent and inert gas, meeting the requirements of on-site rapid detection applications.

Significance of Competitive Reactions in an Atmospheric Pressure Chemical Ionization Ion Source: Effect of Solvent.

Ionization of organic compounds with different structural and energetic properties including benzene derivatives, polycyclic aromatic hydrocarbons (PAHs), ketones, and polyenes was studied using a commercial atmospheric pressure corona discharge (APCI) ion source on a drift tube ion mobility-quadrupole-time-of-flight mass spectrometer (IM-QTOFMS). It was found that the studied cohort of compounds can be experimentally ionized via protonation, charge transfer, and hydride abstraction leading to formation of [M + H]+, [M]+•, and [M – H]+ species, respectively. By experimentally monitoring the product ions and comparing the thermodynamic data for different ionization paths, it was proposed that NO+ is one of the main reactant ions (RIs) in the ion source used. Of particular focus in this work were theoretical and experimental studies of the effect of solvents frequently used for analytical applications with this ion source (acetonitrile, methanol, and chloroform) on the ionization mechanisms. In methanol, the studied compounds were observed to be ionized mainly via proton transfer while acetonitrile suppressed the protonation of compounds and enhanced their ionization via charge transfer and hydride abstraction. Use of chloroform as a solvent led to formation of CHCl2+ as an alternative reactant ion (RI) to ionize the analytes via electrophilic substitution. Density functional theory (DFT) was used to study the different paths of ionization. The theoretical and experimental results showed that by using only the absolute thermodynamic data, the real ionization path cannot be determined and the energies of all competing processes such as charge transfer, protonation, and hydride abstraction need to be compared.

Rapid simultaneous determination of ketamine and midazolam in biological samples using ion mobility spectrometry combined by headspace solid-phase microextraction

Ketamine (Ket) and midazolam (Mdz) are among well-known anesthetic agents which frequently coadministered in surgical procedures and emergency department. Only a few reports have been published for the simultaneous analysis of these compounds. In the present study, we reported a simple, sensitive, and rapid method for simultaneous determination of Ket and Mdz based on headspace solid-phase microextraction coupled with ion mobility spectrometry (HS-SPME-IMS). Ion mobility spectrometer operated under positive mode of a corona discharge ionization source using ammonia as a dopant. The effective parameters on the extraction process consisting of pH of the sample, extraction temperature, extraction time, salt concentration were optimized. The calibration plots exhibited good linearity over the concentration ranges of 10-800 and 100-1500 µg L−1 and detection limit of 8.9 and 52 µg L−1 for Ket and Mdz respectively with correlation coefficients greater than 0.99. The relative standard deviation (RSD) for five replicate measurements was determined to be less than 8%. Finally, the applicability of the proposed method was tested in human plasma and serum samples. These tests showed that the matrix in serum samples interfere with midazolam determination but quantitative recoveries from 85 to 95 % were obtained for both drugs in the human plasma samples. The method herein provides simple and suitable approach while minimizing sample preparation and the overall complexity of the analysis in comparison to existing methodologies.

Comparison of the positive and negative modes of corona discharge ion source for direct determination of aspirin in urine by ion mobility spectrometry

Ionization of aspirin (A) in positive and negative modes of a corona discharge (CD) ion source was studied by ion mobility spectrometry (IMS). The IMS spectra showed that aspirin can be both protonated, AH+, and deprotonated, (A-H)-, in positive and negative modes of CD, respectively. Using DFT calculations, it was found that the carbonyl oxygen of COOH group is the most preferred site of protonation with proton affinity of 867.8 kJ mol-1. Also, the calculated ΔG values for deprotonation of aspirin by O2- and O3- were -71.2 and -28.5 kJ mol-1, respectively, indicating its deprotonation is thermodynamically possible. Hydration of AH+ and (A-H)- was studied theoretically and it was found that AH+ and AH+(H2O) are the most abundant species in the ionization region in the presence of 40 ppm of water vapor at 100–200 °C, while (A-H)- is not hydrated in the same condition. The results of measurements in urine showed that urea content of urine interferes with detection of aspirin in positive CD, while urea was not ionized in the negative CD so that aspirin was determined in urine with recovery of 94% in negative CD.

Formation of anionic clusters of triols in the atmospheric pressure chemical ionization source: An ion mobility spectrometry and theoretical study

Ionization of glycerol (Gly), triethanolamine (TEA), and tris(hydroxymethyl)aminomethane (Tris) was investigated in the negative mode of an atmospheric pressure corona discharge ion source by ion mobility spectrometry. It was found that ionization of the triols proceeds via both deprotonation and anion attachment. Thermodynamics of these reactions were studied in gas phase employing density functional theory using B3LYP and ωB97xD functionals. Chloroform and bromoform were used as dopants to produce alternative reactant ions Cl− and Br− in the ionization region. Because of the lower basicity of Cl− and Br−, the ionization mechanism of the triols was only halide attachment.

Using gas-phase chloride attachment for selective detection of morphine in a morphine/codeine mixture by ion mobility spectrometry.

Morphine and codeine are two important compounds of the opiate family that have vast applications in medicine. Several techniques have been reported for the determination of these opiates. Although ion mobility spectrometry (IMS) in positive ion mode can be applied for detection of both morphine and codeine, this technique on its own cannot detect a mixture of these two compounds because of the overlapping of their peaks. An IMS instrument equipped with a corona discharge ion source operating in negative ion mode was used for the detection of anionic clusters of morphine and codeine. In normal negative ion mode, NOx - , CO3 - , and On - act as the main reactant ions (RIs) which can deprotonate the analytes. We also used chloroform as a dopant to produce Cl- as an alternative RI. Morphine has a phenolic and an alcoholic OH group, while codeine bears only an alcoholic OH group. Because the phenolic OH group is more acidic, only morphine is deprotonated in negative ion mode in a morphine/codeine mixture. Furthermore, since morphine has two OH groups that can act as hydrogen-bond donors, it acts as an anion receptor. Hence, in the presence of chloroform where Cl- acts as the RI, morphine traps the Cl- anion to form a morphine-Cl- (Mor.Cl- ) adduct ion, while because of its structure codeine does not have this capability. Using the difference in the structures of morphine and codeine, two ionization methods were proposed for selective detection of morphine. Morphine is more acidic than codeine and has greater anion-receiving capability than codeine. Hence, it can both be deprotonated and form a adduct anion with Cl- . The Cl- attachment method is recommended for measurements at ambient temperature.

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

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. 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. 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. 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.

Mechanism of atmospheric pressure chemical ionization of morphine, codeine, and thebaine in corona discharge-ion mobility spectrometry: Protonation, ammonium attachment, and carbocation formation.

Atmospheric pressure chemical ionizations (APCIs) of morphine, codeine, and thebaine were studied in a corona discharge ion source using ion mobility spectrometry (IMS) at temperature range of 100°C-200°C. Density functional theory (DFT) at the B3LYP/6-311++G(d,p) and M062X/6-311++G(d,p) levels of theory were used to interpret the experimental data. It was found that in the presence of H3 O+ as reactant ion (RI), ionization of morphine and codeine proceeds via both the protonation and carbocation formation, whereas thebaine participates only in protonation. Carbocation formation (fragmentation) was diminished with decrease in the temperature. At lower temperatures, proton-bound dimers of the compounds were also formed. Ammonia was used as a dopant to produce NH4 + as an alternative RI. In the presence of NH4 + , proton transfer from ammonium ion to morphine, codeine, and thebaine was the dominant mechanism of ionization. However, small amount of ammonium attachment was also observed. The theoretical calculations showed that nitrogen atom of the molecules is the most favorable proton acceptor site while the oxygen atoms participate in ammonium attachment. Furthermore, formation of the carbocations is because of the water elimination from the protonated forms of morphine and codeine.

Small Host–Guest Systems in the Gas Phase: Tartaric Acid as a Host for both Anionic and Cationic Guests in the Atmospheric Pressure Chemical Ionization Source of Ion Mobility Spectrometry

The ionization of tartaric acid (TA) in an atmospheric pressure chemical ionization corona discharge ion source was studied by ion mobility spectrometry (IMS) with zero air as the drift gas. Density functional theory was used for structural and thermodynamic analyses of the produced ionic clusters. Ion mobility spectra of TA were recorded in both positive and negative modes of CD with and without ammonia and chloroform as dopants in order to produce NH4+ and Cl-, respectively, as the reactant ions (RIs). In the absence of these dopants, the RIs were mainly H3O+ and O2- in the positive and negative CD, respectively. TA solutions in water and methanol were injected into the ionization region of the IMS instrument, and the product cations TA·H+(H2O)n, TA·H+(CH3OH), TA·NH4+, and TA·NH4+(CH3OH) were observed in the positive CD. Anionic clusters (TA-H)-, (TA-H)-·CH3OH, (TA-H)-·TA, TA·Cl-, and (TA)2Cl- were produced in the negative CD. The anions TA·Cl- and (TA)2Cl- were not produced in an air atmosphere, and we observed their peaks when pure oxygen was used as the drift gas. Optimized structures of the clusters showed that TA·NH4+, TA·Cl-, and (TA)2Cl- are small host-guest systems in the gas phase, with TA as a host. (TA)2Cl- is a weakly bonded complex (an anion-bound dimer) that was observed at atmospheric pressure. The proton-bound dimer TA·H+·TA was not produced in the positive CD, while the anionic dimer (TA-H)-·TA was observed in the negative CD. This phenomenon was interpreted on the basis of the hydration of TA·H+ and (TA-H)-.

Solid-phase microextraction based on nickel-foam@polydopamine followed by ion mobility spectrometry for on-site detection of Sudan dyes in tomato sauce and hot-pot sample

Sudan dyes are one kind of synthetic azo dyes that are forbidden to use in foodstuffs according to the European Union Rule. In this work, considering the structure of Sudan dyes, nickel-foam@polydopamine (NF@PDA) was prepared through the self-polymerization of dopamine on the nickel-foam surface under weak alkaline conditions and used as SPME material to selectively extract the Sudan dyes. With the feature of three dimension (3D) cross-linked grid structure, large porosity and specific surface area, Ni-foam was selected as carrier material which can increase mass adsorption capacity. The primary parameters affecting extraction efficiency such as extraction time, extraction temperature, stirring speed, pH value, ionic strength and desorption time were investigated and optimized. After the Sudan dyes were eluted from the NF@PDA, the eluate was detected by IMS with a corona discharge (CD) ionization source. Thus, an innovative and rapid screening method coupling the NF@PDA to ion mobility spectrometry (IMS) was developed. Under the optimal extraction conditions, the detection limits for Sudan dyes were in the range from 0.005 μg g−1 to 0.25 μg g−1. The spiked recoveries were in the range from 81% to 91.3% by testing tomato sauce and hot-pot sample and validated by the UPLC-MS. Based on the results, the PDA coating has great ability for the extraction of Sudan dyes, mainly due to the catechol structure, electron-deficient quinones and amine groups on its surface. Thus, the developed method has great potential for on-site rapid screening of the Sudan dyes in food quarantine field.

Thermionic sodium ion source versus corona discharge in detection of alkaloids using ion mobility spectrometry

IMS spectra obtained by using a thermal ionization sodium ion (SI) source and a corona discharge (CD) source were compared in terms of resolution, selectivity and sensitivity. The reactant ion peak (RIP) for the SI source is a single narrow peak which appears in a shorter drift time compared to the main RIP of the CD ion source, (H2O)nH3O+. Comparison of the IMS spectra of selected alkaloids obtained with both the CD and the SI sources shows that the latter exhibits simpler pattern, including a narrow single peak for each compound, well separated from other samples peak. Furthermore, the product ion peaks (PIP) in the SI source appeared at higher drift times leading to higher peak-to-peak resolution. However, the sodium ion source is less sensitive to the selected alkaloids compared to the CD ion source.

Direct detection of glyphosate in drinking water using corona-discharge ion mobility spectrometry: A theoretical and experimental study

Glyphosate is utilized extensively as a herbicide in the world. According to EPA regulation in 2009, it is recommended to monitor of glyphosate in drinking water. In this work the capability of ion mobility spectrometry (IMS) as an analytical technique for determination of glyphosate in drinking water is presented. The measurements were carried out in positive mode of a corona discharge ionization source with NH3 as a dopant. Glyphosate was directly detected in concentration higher than 10 μg/L in drinking water without sample preparation. Also, mechanism of ionization of glyphosate in corona discharge with and without NH3 dopant is discussed, theoretically.

Effect of Basicity and Structure on the Hydration of Protonated Molecules, Proton-Bound Dimer and Cluster Formation: An Ion Mobility-Time of Flight Mass Spectrometry and Theoretical Study.

Protonation, hydration, and cluster formation of ammonia, formaldehyde, formic acid, acetone, butanone, 2-ocatanone, 2-nonanone, acetophenone, ethanol, pyridine, and its derivatives were studied by IMS-TOFMS technique equipped with a corona discharge ion source. It was found that tendency of the protonated molecules, MH+, to participate in hydration or cluster formation depends on the basicity of M. The molecules with higher basicity were hydrated less than those with lower basicity. The mass spectra of the low basic molecules such as formaldehyde exhibited larger clusters of MnH+(H2O)n, while for compounds with high basicity such as pyridine, only MH+ and MH+M peaks were observed. The results of DFT calculations show that enthalpies of hydrations and cluster formation decrease as basicities of the molecules increases. Using comparison of mass spectra of formic acid, formaldehyde, and ethanol, effect of structure on the cluster formation was also investigated. Formation of symmetric (MH+M) and asymmetric proton-bound dimers (MH+N) was studied by ion mobility and mass spectrometry techniques. Both theoretical and experimental results show that asymmetric dimers are formed more easily between molecules (M and N) with comparable basicity. As the basicity difference between M and N increases, the enthalpy of MH+N formation decreases.