Julius Pavlov

Degradation of high energetic and insensitive munitions compounds by Fe/Cu bimetal reduction

A reductive technology based on a completely mixed two-phase reactor (bimetallic particles and aqueous stream) was developed for the treatment of aqueous effluents contaminated with nitramines and nitro-substituted energetic materials. Experimental degradation studies were performed using solutions of three high energetics (RDX, HMX, TNT) and three insensitive-munitions components (NTO, NQ, DNAN). The study shows that, on laboratory scale, these energetic compounds are easily degraded in solution by suspensions of bimetallic particles (Fe/Ni and Fe/Cu) prepared by electro-less deposition. The type of bimetal pair (Fe/Cu or Fe/Ni) does not appear to affect the degradation kinetics of RDX, HMX, and TNT. The degradation of all components followed apparent first-order kinetics. The half-lives of all compounds except NTO were under 10 min. Additional parameters affecting the degradation processes were solids loading and initial pH.

Quantification and remote detection of nitro explosives by helium plasma ionization mass spectrometry (HePI‐MS) on a modified atmospheric pressure source designed for electrospray ionization

Helium Plasma Ionization (HePI) generates gaseous negative ions upon exposure of vapors emanating from organic nitro compounds. A simple adaptation converts any electrospray ionization source to a HePI source by passing helium through the sample delivery metal capillary held at a negative potential. Compared with the demands of other He-requiring ambient pressure ionization sources, the consumption of helium by the HePI source is minimal (20-30 ml/min). Quantification experiments conducted by exposing solid deposits to a HePI source revealed that 1 ng of 2,4,6-trinitrotoluene (TNT) on a filter paper (about 0.01 ng/mm(2)) could be detected by this method. When vapor emanating from a 1,3,5-trinitroperhydro-1,3,5-triazine (RDX) sample was subjected to helium plasma ionization mass spectrometry (HePI-MS), a peak was observed at m/z 268 for (RDX●NO(2))(-). This facile formation of NO(2)(-) adducts was noted without the need of any extra additives as dopants. Quantitative evaluations showed RDX detection by HePI-MS to be linear over at least three orders of magnitude. TNT samples placed even 5 m away from the source were detected when the sample headspace vapor was swept by a stream of argon or nitrogen and delivered to the helium plasma ion source via a metal tube. Among the tubing materials investigated, stainless steel showed the best performance for sample delivery. A system with a copper tube, and air as the carrier gas, for example, failed to deliver any detectable amount of TNT to the source. In fact, passing over hot copper appears to be a practical way of removing TNT or other nitroaromatics from ambient air.

Real-Time Monitoring of In Situ Gas-Phase H/D Exchange Reactions of Cations by Atmospheric Pressure Helium Plasma Ionization Mass Spectrometry (HePI-MS)

An enclosed atmospheric-pressure helium-plasma ionization (HePI-MS) source avoids, or minimizes, undesired back-exchange reactions usually encountered during deuterium incorporation experiments under ambient-pressure open-source conditions. A simple adaptation of an ESI source provides an economical way of conducting gas phase hydrogen/deuterium (H/D) exchange reactions (HDX) in real time without the need for complicated hardware modifications. For example, the spectrum of [(2)H8]toluene recorded under exposed ambient conditions showed the base peak at m/z 96 due to fast leaching of ring hydrogens because of interactions with H2O vapor present in the open source. Such D/H exchanges are rapidly reversed if the deuterium-depleted [(2)H8]toluene is exposed to D2O vapor. In addition to the enumeration of labile protons, our procedure enables the identification of protonation sites in molecules unambiguously, by the number of H/D exchanges observed in real time. For example, molecules such as tetrahydrofuran and pyridine protonate at the heteroatom and consequently undergo only one H/D exchange, whereas ethylbenzene, which protonates at a ring position of the aromatic ring, undergoes six H/D exchanges. In addition, carbocations generated in situ by in-source fragmentation of precursor protonated species, such as benzyl alcohol, do not undergo any rapid H/D exchanges. Because radical cations, second-generation cations (ions formed by losing a small molecule from a precursor ion), or those formed by hydride abstraction do not undergo rapid H/D exchanges, our technique provides a way to distinguish these ions from protonated molecules.

Direct Detection of Inorganic Nitrate Salts by Ambient Pressure Helium-Plasma Ionization Mass Spectrometry

Inorganic nitrates in solid deposits were detected directly by ambient-pressure helium-plasma ionization-mass spectrometry (HePI-MS), without the need for extensive sample preparation. Nitrates were detected even from complex matrices such as meats and fruit juices. Any electrospray-ionization mass spectrometer can be modified to perform ambient-pressure HePI-MS by simply passing helium through the metal capillary intended for liquid-sample delivery. Nitrates on paper strips, glass slides, or cotton swabs (sometimes wetted with a mineral acid) were inserted directly into the ambient-pressure HePI source. The spectra acquired under negative-ion generating conditions showed a peak at m/z 62 for the nitrate ion, along with a lower-intensity peak at m/z 125 for the nitrate adduct of nitric acid. Apparently, it is nitric acid that is initially transferred to the gas phase, forming an ion-molecule complex with hydroxyl anions present in the plasma. The ion-neutral complex then dissociates by eliminating water to produce gaseous NO(3)(-) ions. This hypothesis was supported by the observation that certain solid nitrate salts, which were not readily amenable to HePI (notably the alkali nitrates), were immediately detected as m/z 62 and 125 ions upon acidification by a strong acid. Quantitative evaluations showed that the nitrate-signal response versus the deposited mass is linear for over 3 orders of magnitude. With the use of (15)N-labeled nitrate (m/z 63), the limit of detection was determined to be as low as 200 fg.

Generation and Detection of Gaseous W12O41-˙ and Other Tungstate Anions by Laser Desorption Ionization Mass Spectrometry

The presence of a peak centered near m/z 2862, observed for the first time for the caged dodecatungstate radical-anion, [W12O41]−·, enables distinguishing WO2 from WO3 by Laser Desorption Ionization mass spectrometry (LDI-MS). In addition to WO2, laser irradiation of dry deposits made from aqueous ammonium paratungstate, and calcium and lead orthotungstate also produce the [W12O41]−·. In contrast, spectra recorded from deposits made from aqueous Na2WO4, sodium metatungstate, and WO3, or non-aqueous calcium and lead orthotungstate, and ammonium paratungstate, failed to show the m/z 2862 peak cluster. These observations support the hypothesis that polycondensation reactions to form [W12O41]−· occur solely in the presence of water. Although dry spots are irradiated for ionization, the solvent used for sample preparation plays an important role on the chemical composition endowed to ions detected. For example, the m/z 2862 peak seen from deposits made from aqueous ammonium paratungstate, and calcium and lead orthotungstate, is absent in the spectra recorded either from pristine deposits or those derived from solutions made with organic solvents such as acetonitrile or ethanol.

Enhancement of laser desorption ionization mass spectrometric signals of cesium iodide by elemental sulfur

RATIONALE The utility of elemental sulfur as a matrix for inorganic salts such as CsI, AgI, and KI was investigated because the conventional matrices deployed to generate gaseous ions from organic compounds, upon irradiation with a laser beam, are not suitable for inorganic salts. METHODS Sulfur and inorganic salts were admixed and irradiated with a 337-nm UV laser. Laser desorption ionization (LDI) mass spectra were recorded in both positive and negative ion mode on a time-of-flight mass spectrometer. RESULTS The positive ion laser desorption ionization mass spectrum of CsI showed peaks at m/z 133, 393, etc. for [(CsI)(n)Cs](+) ions. Similarly, negative ion spectra showed peaks at m/z 387, 647, etc. for [(CsI)(n)I](-) ions. However, for n >2 ion clusters, the intensities of peaks were negligibly small in both ionization modes. In contrast, spectra recorded from CsI admixed with elemental sulfur showed peaks up to n = 13 for (CsI)(n)Cs(+), and n = 9 for (CsI)(n)I(-). A similar enhancement of ion abundances by sulfur was observed for the cluster ions generated from KI and AgI. CONCLUSIONS The dramatic increase in intensities of the higher-mass CsI cluster peaks suggests that sulfur acts as a laser-absorbing matrix for inorganic salts far superior to conventional matrices such as 2,5-dihydroxybenzoic acid and α-cyano-4-hydroxycinnamic acid.

Hydrolysis of Hexanitrohexaazaisowurtzitane (CL-20)

The hydrolysis of the α, β, and ϵ polymorphs of 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane(CL-20) was investigated in dilute buffered aqueous solutions over a pH range of 4–10 and at 35, 43, 50, 58 and 65°C, with starting concentrations of CL-20 at one half the solubility limit for the respective temperature. In all cases, an overall first-order kinetic behavior was observed. The rate constants, half-lives, activation energies, and Arrhenius pre-exponential factors were determined. The latter was found to vary linearly with pH. Based on these findings, general formulas for the hydrolysis kinetics of the three polymorphs were developed.

Influence of Ionization Source Conditions on the Gas-Phase Protomer Distribution of Anilinium and Related Cations

AbstractThe gas-phase-ion generation technique and specific ion-source settings of a mass spectrometer influence heavily the protonation processes of molecules and the abundance ratio of the generated protomers. Hitherto that has been attributed primarily to the nature of the solvent and the pH. By utilizing electrospray ionization and ion-mobility mass spectrometry (IM-MS), we demonstrate, even in the seemingly trivial case of protonated aniline, that the protomer ratio strongly depends on the source conditions. Under low in-source ion activation, nearly 100% of the N-protomer of aniline is produced, and it can be subsequently converted to the C-protomer by collisional activation effected by increasing the electrical potential difference between the entrance and exit orifices of the first vacuum region. This activation and transformation process takes place even before the ion is mass-selected and subjected to IM separation. Despite the apparent simplicity of the problem, the preferred protonation site of aniline in the gas phase—the amino group or the aromatic ring—has been a topic of controversy. Our results not only provide unambiguous evidence that ring- and nitrogen-protonated aniline can coexist and be interconverted in the gas phase, but also that the ratio of the protomers depends on the internal energy of the original ion. There are many dynamic ion-transformation and fragmentation processes that take place in the different physical compartments of a Synapt G2 HDMS instrument. Such processes can dramatically change the very identity even of small ions, and therefore should be taken into account when interpreting product-ion mass spectra. Graphical Abstractᅟ

Collision-induced dissociation processes of protonated benzoic acid and related compounds: competitive generation of protonated carbon dioxide or protonated benzene: CID spectra of protonated benzoic acids

Upon activation in the gas phase, protonated benzoic acid (m/z 123) undergoes fragmentation by several mechanisms. In addition to the predictable water loss followed by a CO loss, the m/z 123 ion more intriguingly eliminates a molecule of benzene to generate protonated carbon dioxide (H - O+  ═ C ≡ O, m/z 45), or a molecule of carbon dioxide to yield protonated benzene (m/z 79). Experimental evidence shows that the incipient proton ambulates during the fragmentation processes. For the CO2 or benzene loss, protonated benzoic acid transfers the charge-imparting proton initially to the ortho position and then to the ipso position to generate a transient species which dissociates to form an ion-neutral complex between benzene and protonated CO2 . The formation of the m/z 45 ion is not a phenomenon unique to benzoic acid: spectra from protonated isophthalic acid, terephthalic acid, trans-cinnamic acid and some aliphatic acids also displayed a peak for m/z 45. However, the m/z 45 peak is structurally diagnostic only for certain benzene polycarboxylic acids because the spectra of compounds with two carboxyl groups on adjacent ring carbons do not produce a peak at m/z 45. For the m/z 79 ion to be formed, an intramolecular reaction should take place in which protonated CO2 within the ion-neutral complex acts as the attacking electrophile to transfer a proton to benzene. Copyright

Competitive homolytic and heterolytic decomposition pathways of gas-phase negative ions generated from aminobenzoate esters

An alkyl-radical loss and an alkene loss are two competitive fragmentation pathways that deprotonated aminobenzoate esters undergo upon activation under mass spectrometric conditions. For the meta and para isomers, the alkyl-radical loss by a homolytic cleavage of the alkyl-oxygen bond of the ester moiety is the predominant fragmentation pathway, while the contribution from the alkene elimination by a heterolytic pathway is less significant. In contrast, owing to a pronounced charge-mediated ortho effect, the alkene loss becomes the predominant pathway for the ortho isomers of ethyl and higher esters. Results from isotope-labeled compounds confirmed that the alkene loss proceeds by a specific γ-hydrogen transfer mechanism that resembles the McLafferty rearrangement for radical cations. Even for the para compounds, if the alkoxide moiety bears structural motifs required for the elimination of a more stable alkene molecule, the heterolytic pathway becomes the predominant pathway. For example, in the spectrum of deprotonated 2-phenylethyl 4-aminobenzoate, m/z 136 peak is the base peak because the alkene eliminated is styrene. Owing to the fact that all deprotonated aminobenzoate esters, irrespective of the size of the alkoxy group, upon activation fragment to form an m/z 135 ion, aminobenzoate esters in mixtures can be quantified by precursor ion discovery mass spectrometric experiments.