Reduced Mobility Values Research Articles

Secondary electrospray ionization-ion mobility spectrometry for explosive vapor detection.

The unique capability of secondary electrospray ionization (SESI) as a nonradioactive ionization source to detect analytes in both liquid and gaseous samples was evaluated using aqueous solutions of three common military explosives: cyclo-1,3,5-trimethylene-2,4,6-trinitramine (RDX), nitroglycerin (NG) and pentaerythritol tetranitrate (PETN). The adducts formed between the compounds and their respective dissociation product, RDX.NO(2)(-), NG.NO(3)(-), and PETN.NO(3)(-), gave the most intense signal for the individual compound but were more sensitive to temperature than other species. These autoadducts were identified as RDX.NO(2)(-), NG.NO(3)(-), and PETN.NO(3)(-) and had maximum signal intensity at 137, 100, and 125 degrees C, respectively. The reduced mobility values of the three compounds were constant over the temperature range from 75 to 225 degrees C. The signal-to-noise ratios for RDX, NG, and PETN at 50 mg L(-1) in methanol-water were 340, 270, and 170, respectively, with a nominal noise of 8 +/- 2 pA. In addition to the investigation of autoadduct formation, the concept of doping the ionization source with nonvolatile adduct-forming agents was investigated and described for the first time. The SESI-IMS detection limit for RDX was 116 microg L(-1) in the presence of a traditional volatile chloride dopant and 5.30 microg L(-1) in the presence of a nonvolatile nitrate dopant. In addition to a lower detection limit, the nitrate dopant also produced a greater response sensitivity and a higher limit of linearity than did the traditional volatile chloride dopant.

NMR solution studies of hamster galectin-3 and electron microscopic visualization of surface-adsorbed complexes: evidence for interactions between the N- and C-terminal domains.

Galectin-3, a beta-galactoside binding protein, contains a C-terminal carbohydrate recognition domain (CRD) and an N-terminal domain that includes several repeats of a proline-tyrosine-glycine-rich motif. Earlier work based on a crystal structure of human galectin-3 CRD, and modeling and mutagenesis studies of the closely homologous hamster galectin-3, suggested that N-terminal tail residues immediately preceding the CRD might interfere with the canonical subunit interaction site of dimeric galectin-1 and -2, explaining the monomeric status of galectin-3 in solution. Here we describe high-resolution NMR studies of hamster galectin-3 (residues 1--245) and several of its fragments. The results indicate that the recombinant N-terminal fragment Delta 126--245 (residues 1--125) is an unfolded, extended structure. However, in the intact galectin-3 and fragment Delta 1--93 (residues 94--245), N-terminal domain residues lying between positions 94 and 113 have significantly reduced mobility values compared with those expected for bulk N-terminal tail residues, consistent with an interaction of this segment with the CRD domain. In contrast to the monomeric status of galectin-3 (and fragment Delta 1--93) in solution, electron microscopy of negatively stained and rotary shadowed samples of hamster galectin-3 as well as the CRD fragment Delta 1--103 (residues 104--245) show the presence of a significant proportion (up to 30%) of oligomers. Similar imaging of the N-terminal tail fragment Delta 126--245 reveals the presence of fibrils formed by intermolecular interactions between extended polypeptide subunits. Oligomerization of substratum-adsorbed galectin-3, through N- and C-terminal domain interactions, could be relevant to the positive cooperativity observed in binding of the lectin to immobilized multiglycosylated proteins such as laminin.

Detection of volatile vapors emitted from explosives with a handheld ion mobility spectrometer

AbstractVapor detection of plastic explosives is difficult because of the low vapor pressures of explosive components (i.e. RDX and PETN) present in the complex elastomeric matrix. To facilitate vapor detection of plastic explosives, detection agents (taggants) with higher vapor pressures can be added to bulk explosives during manufacture. This paper investigates the detection of two of these taggants, ethyleneglycol dinitrate (EGDN) and 2,3‐dimethyl‐2,3‐dinitrobutane (DMNB), using a handheld ion mobility spectrometer. These two taggants were detected both from neat vapor sources as well as from bulk explosives (nitroglycerin (NG)‐dynamite and C‐4 tagged with DMNB). EGDN was detected from NG‐dynamite as EGDN·NO3− at a reduced mobility value of 1.45 cm2 V−1 s−1 with detection limits estimated to be about 10 ppbv. DMNB was identified from tagged C‐4 as both negative and positive ions with reduced mobility values of 1.33 cm2 V−1 s−1 for DMNB·NO2− and 1.44 cm2 V−1s−1 for DMNB·NH4+. Positive ions for cyclohexanone were also apparent in the spectra from tagged C‐4 producing three additional peaks. © 2001 John Wiley & Sons, Inc. Field Analyt Chem Technol 5: 215–221, 2001

Evaluation of sulfonylurea herbicides using high resolution electrospray ionization ion mobility quadrupole mass spectrometry

AbstractThe purpose of the current study was to explore and assess the potential of high resolution electrospray ionization atmospheric pressure ion mobility spectrometry (ESI–AP‐IMS) as a field analytical method for the detection and identification of mixtures of sulfonylurea (SU) herbicides in aqueous samples. Because of increased usage, persistent behavior, and potential for crop damage, an environmental method of analysis capable of evaluating SU herbicides in a swift and effective manner is necessary. Eight SU herbicides were evaluated using ESI–AP‐IMS quadrupole mass spectrometry. The selected herbicides were chosen based upon availability and scope of use. The SU herbicide species were qualitatively identified using quadrupole mass spectrometry, followed by the determination of reduced mobility values for characteristic ions. Various mixtures of rimsulfuron, metsulfuron‐methyl, prosulfuron, sulfometuron‐methyl, tribenuron‐methyl, and primisulfuron‐methyl could be revealed using AP‐IMS. The ease of use, ability to operate under ambient conditions, and relatively rapid data acquisition times make ESI–AP‐IMS an attractive candidate for the analysis of aqueous environmental field samples. © 2002 Wiley Periodicals, Inc. Field Analyt Chem Technol 5: 302–312, 2001; DOI 10.1002/fact.10010

Enhanced selectivity in ion mobility spectrometry analysis of complex mixtures by alternate reagent gas chemistry

Ion mobility spectrometry (IMS) analysis of a complex mixture of volatile organic compounds (VOCs) and organophosphorus compounds (OPCs) at vapor levels of 10–40 mg/m 3 produced mobility spectra with broad profiles illustrating limitations of ion mobility spectrometry (IMS) for screening such mixtures. Preseparation of this mixture with a gas Chromatograph inlet to an ion mobility spectrometer enhanced analytical selectivity although OPC detection was complicated by co-elution with other VOCs. Water reagent gas in the ion source of the ion mobility spectrometer yielded 46 gas Chromatographic peaks in a mixture of 45 VOCs and 19 OPCs. Co-elution of two materials was observed in eight of the Chromatographic peaks and co-elution of three materials occurred in four instances. Further selectivity was gained using reagent gases of elevated proton affinity in the ion source. Reagent gas chemistry for acetone and dimethylsulfoxide reduced the number of GC peaks to 26 and 20, respectively. Moreover, spectral integrity and quantitative response for OPCs were retained at 50 to 1000 pg levels with these reagent gases. For OPCs, analyte ions were shown to be of the type M 2H + under these conditions of analysis and the mobilities of the product ions were independent of reagent gas. Reduced mobility values were assigned to OPC spectra using a well-characterized OPC ion as the reference. Spectral profiles and reduced mobilities suggested that the OPC product ions were not clustered with reagent gas molecules at 100 °C.

Table of reduced mobility values from ambient pressure ion mobility spectrometry

This review presents a list of reduced ion mobilities that have been measured under ambient pressure conditions and reported in the open literature during the 16-year period of 1970-1985. Ions reported are listed in order of increasing reduced

Mass identified mobility spectra of p-nitrophenol and reactant ions in plasma chromatography

An interfaced plasma chromatograph/mass spectrometer (ALPHA-II) permits Identification of the positlve and negative ionic specles associated with ionlc peaks In the plasma chromatographic mobility spectra of pnitrophenol. The posltive ions observed and their reduced mobility values (KO) are MNO+ (1.67), MH+ (1.80) and the negative ion is [M - HI- at (1.87). These are essentially the ions that are predicted from chemical ionization mass spectrometry princlples and mobility data alone. An ion observed at mass 108 (KO 1.91) results from a thermal decomposition product of pnitrophenol. The major reactant ions were found at m/e 18, 30, 37, and 65, with probable structures of NH4+, NO', (H20)*H+and ( H20)2N2H+. The 37 and 65 ions occur at the same mobility. Comparison of reduced mobllity values, KO, between two independent laboratories gives an agreement within experimental reproducibility of f0.02 for these spectra. The technique of plasma chromatography (PC) allows observation of the characteristic positive and negative ionic mobility spectra of nanogram and picogram quantities of organic compounds at atmospheric pressure. The mobility spectra give qualitative and quantitative information for organic compounds much like that from infrared spectra. The method involves reaction of organic molecules with ions and electrons generated by a 63Ni source in a nitrogen carrier gas, followed by mobility separation of the products in an ion-drift spectrometer. A recent review and its references describe the technique and summarize its capabilities (I).

Plasma chromatography of heroin and cocaine with mass-identified mobility spectra

Plasma chromatography detects and identifies compounds in trace quantities at atmospheric pressure through characteristic positive and negative mobility spectra. To facilitate use of the technique to detect gas chromatographic effluents, a number of reference mobility spectra for different classes of compounds have been reported. Reference spectra for two more compounds, heroin and cocaine, are presented in this study. The primary ions found in these mobility spectra were determined to be M +, (M  H 2) +, and (M  CH 3CO 2) + for heroin and M +, (M  C 6H 5CO 2) + and (M  C 6H 5CO 2  CO 2CH 3) + for cocaine using a directly interfaced plasma chromatograph-mass spectrometer. The identified ions agree closely with those predicted in the ion mobility spectra using mass-mobility correlation data coupled with chemical ionization mass spectrometry data. Also, an independent check demonstrating the reliability of reduced mobility values reported in earlier reference spectra was made.

Microwave and mass spectrometric studies of afterglow processes in plasmas produced in rare gases

An experimental system comprising a conventional X-band cavity arrangement in conjunction with a quadrupole mass spectrometer has been developed to allow simultaneous measurement of the time-dependent number densities of electrons and positive ions in decaying rare gas plasmas. In argon, ions at m/e=20, 40 and 80 amu, identified as Ar2+, Ar+ and Ar2+ respectively were detected and measurement of the decay time constants yielded reduced mobilities of Ar+ and Ar2+. The lifetime of the ion identified as Ar2+ was too short to allow accurate time resolved measurements to be carried out. In krypton, ions identified as Kr2+, Kr+ and Kr2+ were detected and reduced mobility values for the two singly charged ions deduced. Experiments in xenon were limited by the mass range capabilities of the mass spectrometer, but gave reduced mobilities for the singly charged atomic and molecular ions.

Mobilities of Uranium and Mercury Ions in Helium

The mobilities of mass-identified U+ and Hg+ ions in helium have been determined in a drift tube-mass spectrometer apparatus. For uranium ions a reduced mobility value μ0=(16.0± 0.5) cm2/V·sec is obtained at 305°K and a standard gas density of 2.69× 1019cm−3. The mobility of mercury ions is μ0=(19.4± 0.5) cm2/V·sec at 292°K, in agreement with two previous determinations. The effect of fast ion injection in drift mobility measurements is discussed, and a new technique to circumvent these problems is described. The results are compared with existing theories of ion mobilities.

Mobilities, Diffusion Coefficients, and Reaction Rates of Mass-Indentified Nitrogen Ions in Nitrogen

Measurements at room temperature of the drift velocity, the longitudinal diffusion coefficient, and the transverse diffusion coefficient have been made for low-energy mass-identified nitrogen ions in nitrogen gas in a drift-tube mass spectrometer. These parameters were evaluated using an analysis described in the article immediately preceding this one. The mobilities of ${\mathrm{N}}^{+}$ and $\mathrm{N}_{2}^{}{}_{}{}^{+}$ were obtained over the $\frac{E}{N}$ range from 7 to 700 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}17}$ V ${\mathrm{cm}}^{2}$, yielding zero-field reduced mobility values of 2.97 and 1.87 ${\mathrm{cm}}^{2}$/V sec, respectively. The mobilities of $\mathrm{N}_{3}^{}{}_{}{}^{+}$ and $\mathrm{N}_{4}^{}{}_{}{}^{+}$ were obtained over the $\frac{E}{N}$ range from 2 to 40 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}17}$ V ${\mathrm{cm}}^{2}$, yielding zero-field reduced mobility values of 2.26 and 2.33 ${\mathrm{cm}}^{2}$/V sec, respectively. For ${\mathrm{N}}^{+}$ and $\mathrm{N}_{2}^{}{}_{}{}^{+}$, the longitudinal diffusion coefficients were determined from the widths of the experimental arrival time spectra, and the transverse diffusion coefficients were determined from the attenuation of the ion count rate as the drift distance was increased. For both ions the two diffusion coefficients were observed to be equal and in agreement with the Einstein relation at low $\frac{E}{N}$, but to behave quite differently as $\frac{E}{N}$ was increased. It has previously been reported that the longitudinal diffusion coefficients of both ions increase rapidly by more than an order of magnitude; the transverse diffusion coefficient of ${\mathrm{N}}^{+}$ has been found to increase in a similar fashion, although much less rapidly, while that of $\mathrm{N}_{2}^{}{}_{}{}^{+}$ remains nearly constant. Measurements were made up to an $\frac{E}{N}$ of 700 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}17}$ V ${\mathrm{cm}}^{2}$. The rates of the two ion-molecule reactions, ${\mathrm{N}}^{+}$ + 2${\mathrm{N}}_{2}$ \ensuremath{\rightarrow} $\mathrm{N}_{3}^{}{}_{}{}^{+}$ + ${\mathrm{N}}_{2}$ and $\mathrm{N}_{2}^{}{}_{}{}^{+}$ + 2${\mathrm{N}}_{2}$ \ensuremath{\rightarrow} $\mathrm{N}_{4}^{}{}_{}{}^{+}$ + ${\mathrm{N}}_{2}$, were also measured by an attenuation technique over the $\frac{E}{N}$ range from thermal to 100 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}17}$ V ${\mathrm{cm}}^{2}$. The reaction rates at thermal energy were determined to be 1.8 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}29}$ ${\mathrm{cm}}^{6}$/sec and 5.0 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}29}$ ${\mathrm{cm}}^{6}$/sec, respectively, and both rates were observed to decrease as $\frac{E}{N}$ was increased.