Stratospheric chemical ionization mass spectrometry: nitric acid detection by different ion molecule reaction schemes

Detailed height profiles of stratospheric nitric acid mixing ratios have been derived with a baloon borne chemical ionization mass spectrometer by applying several ion molecule reaction schemes, each associated to a specific and selective ion source. These ions (CO₃⁻, Cl_n⁻, CF₃O⁻, and CF₃O⁻H₂O) give rise to specific product ions (mainly CO₃⁻HNO₃, NO₃⁻HCl, NO₃⁻HF, and CF₃O⁻HNO₃) upon reaction with ambient nitric acid molecules. This paper reports on the instrumental details as well as on the results obtained during two balloon flights with the instrument. Within the accuracy of the measurements, the nitric acid height profiles obtained with the three different ion sources are in good agreement with one another as well as with literature data.     

Selective determination of pyridine alkaloids in tobacco by PFTBA ions/analyte molecule reaction ionization ion trap mass spectrometry

The application of perfluorotributylamine (PFTBA) ions/analyte molecule reaction ionization for the selective determination of tobacco pyridine alkaloids by ion trap mass spectrometry (IT-MS) is reported. The main three PFTBA ions (CF(3)(+), C(3)F(5)(+), and C(5)F(10)N(+)) are generated in the external source and then introduced into ion trap for reaction with analytes. Because the existence of the tertiary nitrogen atom in the pyridine makes it possible for PFTBA ions to react smoothly with pyridine and forms adduct ions, pyridine alkaloids in tobacco were selectively ionized and formed quasi-molecular ion [M + H](+)and adduct ions, including [M + 69](+), [M + 131](+), and [M + 264](+), in IT-MS. These ions had distinct abundances and were regarded as the diagnostic ions of each tobacco pyridine alkaloid for quantitative analysis in selected-ion monitoring mode. Results show that the limit of detection is 0.2 microg/mL, and the relative standard deviations for the seven alkaloids are in the range of 0.71% to 6.8%, and good recovery of 95.6% and 97.2%. The proposed method provides substantially greater selectivity and sensitivity compared with the conventional approach and offers an alternative approach for analysis of tobacco alkaloids.     

Ion structure determinations and ion—molecule reactions by double quadrupole mass spectrometry

The QQ mass spectrometer is shown to be applicable to ion structure determination via collision-induced dissociations of mass-selected ions. The instrument can be scanned so as to record the products of dissociation as well as those of ion—molecule association reactions. The dissociations correspond to those observed at high kinetic energy in mass-analyzed ion kinetic energy spectrometers and the association reactions show parallels with reactions seen in ion cyclotron resonance spectroscopy and in high-pressure mass spectrometry     

Organic secondary ion mass spectrometry: Signal enhancement by water vapor injection

The enhancement of the static secondary ion mass spectrometry (SIMS) signals resulting from the injection, closely to the sample surface, of H₂O vapor at relatively high-pressure, was investigated for a set of organic materials. While the ion signals are generally improved with increasing H₂O pressure upon 12 keV Ga⁺ bombardment, a specific enhancement of the protonated ion intensity is clearly demonstrated in each case. For instance, the presence of H₂O vapor induces an enhancement by one order of magnitude of the [M+ H]⁺ static SIMS intensity for the antioxidant Irgafos 168 and a ∼1.5-fold increase for polymers such as poly(vinyl pyrrolidone).     

Structurally diagnostic ion/molecule reactions: class and functional-group identification by mass spectrometry

This article discusses the application of gas-phase ion/molecule reactions for fine structural elucidation in mass spectrometry. This approach is illustrated via a representative collection of class- and functional group-selective reactions, a few of historical relevance as well as by more recent and instructive examples, and their applications. The focus is on reactions performed under well-controlled conditions of sequential mass spectrometry, discussing key mechanistic details and potential applications. Recent and innovative strategies that allow these reactions to be performed under ambient conditions, making this fast, selective and sensitive approach for structural investigation much more generally applicable, are also discussed.     

Gas phase ion/molecule reactions in laser desorption mass spectrometry

The desorption of neutrals, alkali ions and quasimolecular ions of sucrose was studied as function of substrate temperature in laser desorption mass spectrometry. These phenomena were also investigated in thermal desorption experiments. It was concluded that in these experiments gas phase cationization is the major ionization process.     

Small molecule analysis by MALDI mass spectrometry

This review focuses on the application of matrix assisted laser desorption/ionization (MALDI) mass spectrometry to the characterization of molecules in the low mass range (<1500 Da). Despite its reputation to the contrary, MALDI is a powerful technique to provide both qualitative and quantitative determination of low molecular weight compounds. Several approaches to minimize interference via sample preparation and matrix selection are discussed, as well as coupling of MALDI to liquid and planar chromatographic techniques to extend its range of applicability.     

Laboratory investigations of negative ion molecule reactions of formic and acetic acids: implications for atmospheric measurements by ion-molecule reaction mass spectrometry

Laboratory measurements of gas-phase ion-molecule reactions of several negative ion species with formic and acetic acid have been carried out. A flow reactor operating at a temperature of 293 ± 3 K and total gas pressures of either 3 or 9 hPa was used. The negative reagent ion species investigated included OH⁻, O₂⁻, O₃⁻, CO₄⁻, CO₃⁻, CO₃⁻H₂O, HCO₃⁻H₂O, NO₃⁻, NO₃⁻H₂O, NO₂⁻, and NO₂⁻H₂O. The reactions were found to proceed either via proton transfer or clustering. Our measurements of ion-molecule reactions of negative ions with gaseous formic and acetic acids provide a firm base for quantitative detection of these acidic trace gases in the atmosphere by negative ion ion-molecule reaction mass spectrometry.     

Speciation of metal-EDTA complexes by flow injection analysis with electrospray ionization mass spectrometry and ion chromatography with inductively coupled plasma mass spectrometry

Flow injection analysis (FIA) with ESI-MS and ion chromatography (IC) with inductively coupled plasma-MS (ICP-MS) as the complementary technique have been explored for the determination of metal ions as their metal-EDTA complexes. ESI-MS enabled the identification of metal-EDTA complexes such as [Mn(EDTA)](2-), [Co(EDTA)](2-), [Ni(EDTA)](2-), [Cu(EDTA)](2-), [Zn(EDTA)](2-), [Pb(EDTA)](2-), and [Fe(EDTA)](1-) and their MS spectral showed that these metal-EDTA complexes were present in solution. Based on the ESI-MS, ion chromatographic separation and ICP-MS detection of these complexes are possible because IC-ICP-MS requires stable metal-EDTA complex during the chromatographic separation. The separation of these metal-EDTA complexes was achieved on an anion-exchange column with a mobile phase containing 30 mM NH(4)(HPO(4))(2) at pH 7.5 within 7 min with ICP-MS providing element specific detection. The ICP-MS LODs for the metal-EDTA were in the range of 0.1-0.5 microg/L with the exception of Fe (15 microg/L). The proposed method was a simple procedure for sample processing, using direct injection of sample without removal of sample matrix and was successfully applied to the determination of metal-EDTA complexes in real samples.     

Ion/molecule reactions investigated by using tandem mass spectrometry in an ion trap: halomethylation

The ion-trap mass spectrometer has several features which make it a useful device for the study of ion/molecule reactions, viz., the ability to store ions for long periods, mass-selective storage, access to time and pressure-resolved data, and MS/MS capabilities in which the fragmentation behavior of selected ions may give insight into ion structure. These capabilities are used to study the gas-phase halomethylation of a variety of organic compounds with CH₂Cl⁺ as the reagent ion. The ion/molecule reaction of greatest interest involves addition of CH₂Cl⁺, followed by the elimination of HCl, resulting in a net addition of methyne. This methyne-addition reaction is observed in many aromatic compounds as well as such compounds as cycloheptatriene and cyclo-octene. The structures of the product ions were probed using collision-activated dissociation.     

Probing trapped ion energies via ion-molecule reaction kinetics: Quadrupole ion trap mass spectrometry

We present a detailed study of the energies of the ions stored in a quadrupole ion trap mass spectrometer (QITMS). Previous studies have shown that the rate constant, k, for the charge exchange reaction Ar⁺ N⁺ ₂ →, N⁺ ₂+Ar increases with increasing ion-molecule center-of-mass kinetic energy (K.E._cm). Thus, we have determined k for this chemical “thermometer” reaction at a variety of Ar and N₂ pressures and have assigned K.E._cm values as a function of the q₂ of the Ar⁺ ion both with and without He buffer gas present in the trap. The K.E._cm energies are found to lie within the range 0.11–0.34 eV over the variety of experimental conditions investigated. Quantitative “cooling” effects due to the presence of He buffer gas are reported, as are increases in K.E._cm due to an increase in the q₂ of the Ar⁺ ion. “Effective” temperatures of the Ar⁺ ions in He buffer are determined based on a Maxwell-Boltzmann distribution of ion energies. The resulting temperatures are found to lie within the range ≈ 1700–3300 K. We have also examined the K.E._cm, values arising from the chemical thermometer reaction of O⁺ ₂ with CH₄, as previous assignments of effective ion temperatures based on this reaction have been called into question.     

Polyelectrolytes as new matrices for secondary ion mass spectrometry

Significant enhancements in ion yields in time-of-flight secondary ion mass spectrometry (TOF-SIMS) are observed when water-soluble analytes are mixed with a polyelectrolyte, e.g., poly(diallyldimethylammonium chloride) or poly(sodium 4-styrenesulfonate), and then deposited in the layer-by-layer method on a surface. This previously unobserved effect is demonstrated for 5-chloro-8-methoxyquinoline appended diaza-18-crown-6, 5-(2-aminoethoxy)methyl-5-chloro-8-methoxyquinoline appended diaza-18-crown-6, acridine, 9-anthracenecarboxylic acid, and ferrocenecarboxylic acid. By optical ellipsometry film thicknesses range from ca. 5-20 angstroms. X-ray photoelectron spectroscopy shows significantly less analyte in the polyelectrolyte-analyte films than in the neat analytes. However, TOF-SIMS generally shows significant enhancements in ion yields from the polyelectrolyte films compared with either the neat compounds or the compounds solubilized with acid or base and then dried on a surface. These significant enhancements in ion yields also appear to extend to analyte fragments and cationized molecular species. Some enhancement is also observed for dried droplets of analytes mixed with a polyelectrolyte on surfaces.     

Ion transmission and ion/molecule separation using an electrostatic ion guide in chemistry ionization mass spectrometry

The performance of an electrostatic ion guide for use in chemical ionization mass spectrometry is evaluated. The study focuses on the use of the ion guide to extract charged particles in a rapidly expanding beam consisting of ions and neutral molecules. A theoretical analysis of this system is presented, using three-dimensional calculations of the trajectories of ions. Laboratory measurements verifying the theoretical calculations are also reported. The results illustrate the two principal advantages for this system: efficient ion transmission and ion–neutral molecule separation. A comparison between the ion guide and the commonly used electrostatic ion lenses shows that the ion guide is significantly more efficient in capturing and transporting charged particles from a diverging ion source.     

Depth profile measurement by secondary ion mass spectrometry

The possibilities of measuring depth profiles by secondary ion mass spectrometry are evaluated. The influence of different instrumental and experimental parameters on depth resolution in the profiles are studied: the effects of primary ion beam characteristics, reactive gas adsorption and mechanical aperturing in secondary ion extraction are discussed. Beam effects are studied from the point of view of surface damage. The effects of secondary processes, such as crater edge effects, element mixing, preferential sputtering, background signals, (residual) gas contamination and ion-induced topographical and compositional changes are studied for thin metal and binary materials.     

Differentiation and quantification of xylene isomers by combining headspace solid-phase microextraction/gas chromatography and self-ion molecule reaction in an ion trap tandem mass spectrometry

A headspace solid-phase microextraction (HS-SPME) method using polydimethylsiloxane (PDMS)-coated fiber coupling with GC/self-ion molecule reaction (SIMR)/MS/MS (GC/SIMR/MS/MS) has been developed for the differentiation of o-, m-, and p-xylene isomers. The optimization parameters of this method are: extraction time 20 min, stirring rate 1200 rpm, sampling temperature 28 degrees C, and salt concentration 5%. The LODs were found to be in the range of 3-9 ng/mL under the SIM mode of GC/MS. The RSDs were below 1% (n=5). The linear dynamic range of the calibration curve was from 0.05 to 10.0 microg/mL with correlation coefficient (r2)>0.9089. The advantages of this technique are sensitive, selective, ease of operation, simple device, solvent free, and extremely little sample consumption. This technique is the first example using SIMR combined MS/MS applied in the GC/MS and it can be applied to other volatile compounds for future application.     

Shapes of supramolecular cages by ion mobility mass spectrometry

Mass spectrometry and drift tube ion mobility mass spectrometry have been used to analyse several isobaric, multicomponent cages yielding information on three dimensional structure, interactions and dynamics of assembly in the gas phase.     

Diffusion of beryllium in copper as determined by ion and spark probe mass spectrometry

Diffusion profiles of Be in Cu, which extend over some millimeters, are studied laterally by both SSMS and SIMS. The diffusion of Be in Cu is investigated in the temperature range from 650 to 900 (± 5)°C for annealing times from 313 to 502 h. The Arrhenius equation is obeyed in the chosen temperature range. The diffusion coefficients obtained from both experimental approaches are in reasonable agreement.     

Ion characterisation by comparison of ion mobility spectrometry and mass spectrometry data

The major uncertainty related to ion mobility spectrometry is the lack of knowledge about the characteristics of the ions detected. When using a radioactive atmospheric pressure ionisation source (e.g. ⁶³Ni), from theory proton bound water clusters are expected as reactant ions. When analyte ions occur, proton transfer should lead to proton-bound monomer and dimer ions. To increase the knowledge about those ionisation processes in an ion mobility spectrometer (IMS), a ß-radiation ionisation source was coupled to a mass spectrometer (MS) and an identical one to an IMS. Exemplarily, acetone, limonene and 2- and 5-nonanone were introduced into both instruments in varying concentrations. By correlating the MS and IMS spectra, conclusions about the identities of the ions detected by IMS could be drawn. Proton-bound monomer, dimer and even trimer ions (MH⁺, 2MH⁺, 3MH⁺) could be observed in the MS spectra for acetone and 5-nonanone and could be assigned to the related signals detected by IMS. The oligomers could be expected from theory for increasing concentration. Limonene and 2-nonanone yielded in a variety of different ions and fragments indicating complex gas phase ion chemistry. Those findings on the obviously different behaviour of different analytes require further research focussed on the ion chemistry in IMS including the comparison of different ionisation sources.