Investigations of chemical warfare agents and toxic industrial compounds with proton-transfer-reaction mass spectrometry for a real-time threat monitoring scenario.

RATIONALE: Security and protection against terrorist attacks are major issues in modern society. One especially challenging task is the monitoring and protection of air conditioning and heating systems of buildings against terrorist attacks with toxic chemicals. As existing technologies have low selectivity, long response times or insufficient sensitivity, there is a need for a novel approach such as we present here. METHODS: We have analyzed various chemical warfare agents (CWAs) and/or toxic industrial compounds (TICs) and related compounds, namely phosgene, diphosgene, chloroacetone, chloroacetophenone, diisopropylaminoethanol, and triethyl phosphate, utilizing a high-resolution proton-transfer-reaction time-of-flight mass spectrometry (PTR-TOFMS) instrument with the objective of finding key product ions and their intensities, which will allow a low-resolution quadrupole mass spectrometry based PTR-MS system to be used with high confidence in the assignment of threat agents in the atmosphere. RESULTS: We obtained high accuracy PTR-TOFMS mass spectra of the six compounds under study at two different values for the reduced electric field in the drift tube (E/N). From these data we have compiled a table containing product ions, and isotopic and E/N ratios for highly selective threat compound detection with a compact and cost-effective quadrupole-based PTR-MS instrument. Furthermore, using chloroacetophenone (tear gas), we demonstrated that this instrument's response is highly linear in the concentration range of typical Acute Exposure Guideline Levels (AEGLs). CONCLUSIONS: On the basis of the presented results it is possible to develop a compact and cost-effective PTR-QMS instrument that monitors air supply systems and triggers an alarm as soon as the presence of a threat agent is detected. We hope that this real-time surveillance device will help to seriously improve safety and security in environments vulnerable to terrorist attacks with toxic chemicals.

Bond dissociation of the dipeptide dialanine and its derivative alanine anhydride induced by low energy electrons.

Dissociative electron attachment to dialanine and alanine anhydride has been studied in the gas phase utilizing a double focusing two sector field mass spectrometer. We show that low-energy electrons (i.e., electrons with kinetic energies from near zero up to 13 eV) attach to these molecules and subsequently dissociate to form a number of anionic fragments. Anion efficiency curves are recorded for the most abundant anions by measuring the ion yield as a function of the incident electron energy. The present experiments show that as for single amino acids (M), e.g., glycine, alanine, valine, and proline, the dehydrogenated closed shell anion (M-H)(-) is the most dominant reaction product. The interpretation of the experiments is aided by quantum chemical calculations based on density functional theory, by which the electrostatic potential and molecular orbitals are calculated and the initial electron attachment process prior to dissociation is investigated.

Very low energy electrons transform the cyclobutane-pyrimidine dimer into a highly reactive intermediate.

Electrons with virtually no kinetic energy (close to 0 eV) trigger the decomposition of cytotoxic cyclobutane-pyrimidine dimer (CPD) into a surprisingly large variety of fragment ions plus their neutral counterparts. The response of CPD to low energy electrons is thus comparable to that of explosives like trinitrotoluene (TNT). The dominant unimolecular reaction is the splitting into two thymine like units, which can be considered as the essential molecular step in the photolyase of CPD. We find that CPD is significantly more sensitive towards low energy electrons than its thymine building blocks. It is proposed that electron attachment at very low energy proceeds via dipole bound states, supported by the large dipole moment of the molecule (6.2 D). These states act as effective doorways to dissociative electron attachment (DEA).

Identifying volatile organic compounds used for olfactory navigation by homing pigeons.

Many bird species have the ability to navigate home after being brought to a remote, even unfamiliar location. Environmental odours have been demonstrated to be critical to homeward navigation in over 40 years of experiments, yet the chemical identity of the odours has remained unknown. In this study, we investigate potential chemical navigational cues by measuring volatile organic compounds (VOCs): at the birds' home-loft; in selected regional forest environments; and from an aircraft at 180 m. The measurements showed clear regional, horizontal and vertical spatial gradients that can form the basis of an olfactory map for marine emissions (dimethyl sulphide, DMS), biogenic compounds (terpenoids) and anthropogenic mixed air (aromatic compounds), and temporal changes consistent with a sea-breeze system. Air masses trajectories are used to examine GPS tracks from released birds, suggesting that local DMS concentrations alter their flight directions in predictable ways. This dataset reveals multiple regional-scale real-world chemical gradients that can form the basis of an olfactory map suitable for homing pigeons.

Electron attachment to trinitrotoluene (TNT) embedded in He droplets: complete freezing of dissociation intermediates in an extended range of electron energies.

Electron attachment to the explosive trinitrotoluene (TNT) embedded in Helium droplets (TNT@He) generates the non-decomposed complexes (TNT)(n)(-), but no fragment ions in the entire energy range 0-12 eV. This strongly contrasts the behavior of single TNT molecules in the gas phase at ambient temperatures, where electron capture leads to a variety of different fragmentation products via different dissociative electron attachment (DEA) reactions. Single TNT molecules decompose by attachment of an electron at virtually no extra energy reflecting the explosive nature of the compound. The complete freezing of dissociation intermediates in TNT embedded in the droplet is explained by the particular mechanisms of DEA in nitrobenzenes, which is characterized by complex rearrangement processes in the transient negative ion (TNI) prior to decomposition. These mechanisms provide the condition for effective energy withdrawal from the TNI into the dissipative environment thereby completely suppressing its decomposition.

Formation of pyrimidine dimer radical anions in the gas phase.

Crossed-beam experiments revealed that attachment of a free electron to the cyclobutane pyrimidine dimers c,s-DMT<>DMT and c,a-DMT<>DMT leads to the formation of dimer radical anions with the lifetime of at least 80 micros, thus showing that the latter are much more stable than previously believed.