In this work, we describe the performance of an atmospheric pressure photoionization (APPI) source for sampling liquid flows. The results presented here primarily focus on the mechanism of direct photoionization (PI), as compared to the dopant mechanism of PI. Measured detection limits for direct APPI were comparable to atmospheric pressure chemical ionization (APCI; e.g., 1 pg for reserpine). The ion signal is linear up to 10 ng injected quantity, with a useful dynamic range exceeding 100 ng. Evidence is presented indicating that APPI achieves significantly better sensitivity than APCI at flow rates below 200 microL/min, making it a useful source for capillary liquid chromatography and capillary electrophoresis. Results are presented indicating that APPI is less susceptible to ion suppression and salt buffer effects than APCI and electrospray ionization (ESI). The principal benefit of APPI, as compared to other ionization sources, is in efficiently ionizing broad classes of nonpolar compounds. Thus, APPI is an important complement to ESI and APCI by expanding the range and classes of compounds that can be analyzed. In this paper, we also discuss the role of direct APPI vs PI-induced APCI using dopants.

In this paper we examine the mechanism of [M ϩ H] ϩ (henceforth MH ϩ ) formation by direct photoionization. Based on comparisons of the relative abundance of M ϩ and MH ϩ ions for photoionization of a variety of compounds M as vapor in air versus in different solvents, we conclude that the mechanism is M ϩ h 3 M ϩ ϩ e Ϫ followed by the reaction M ϩ ϩ S 3 MH ϩ ϩ S(ϪH). The principal evidence for molecular radical ion formation M ϩ followed by hydrogen atom abstraction from protic solvent S are: (1) Nearly exclusive formation of M ϩ for headspace ionization of M in air, (2) significant relative abundance of MH ϩ in the presence of protic solvents (e.g., CH 3 OH, H 2 O, c-hexane), but not in aprotic solvents (e.g., CCl 4-), (3) observation of induced equilibrium oscillations in the abundance of MH ϩ and M ϩ , and (4) correlation of the ratio of MH ϩ /M ϩ to reaction length in the photoionization source. Thermodynamic models are advanced that explain the qualitative dependence of the MH ϩ /M ϩ equilibrium ratio on the properties of solvent S and analyte M. Though the hydrogen abstraction reaction is endothermic in most cases, it is shown that the equilibrium constant is still expected to be much greater than unity in most of the cases studied due to the very slow reverse reaction involving the very low abundant MH ϩ and S(ϪH) species. (J Am Soc Mass Spectrom 2004, 15, 1521-1533

In this work, we demonstrate the utility of ultra performance liquid chromatography-atmospheric pressure photoionization-tandem mass spectrometry (UPLC-APPI-MS/MS) for high-sensitivity and high-throughput analysis of United States Environmental Protection Agency (U.S. EPA) 16 priority pollutants polycyclic aromatic hydrocarbons (PAHs). Analyses were performed on a Waters Acquity-TQD equipped with Syagen's PhotoMate APPI source. All 16 PAHs were analyzed on column in approximately 3.5 min with excellent chromatographic separation for all PAH isomers and with low picogram detection limits on column for all analytes using chlorobenzene as a dopant. Dynamic linear ranges were evaluated and found to cover at least 3-4 orders of magnitude. In comparison with the existing U.S. EPA methods, this approach improves instrument sample throughput by at least 10-fold.

This work is focused on developing a fast gas chromatograph, time-of-flight mass spectrometer (GC/TOFMS) for man-portable field use. The goal is to achieve a total system solution for meeting performance, size, weight, power, cost, and ruggedness requirements for a laboratory in the field. The core technology will also be adaptable to specific applications including real-time point detection for hazardous chemical releases (e.g., chemical weapons), for biological agent signature identification, and for mobile monitoring platforms (e.g., air, ship, truck). Previously we presented results of a feasibility demonstration for a 30-lb field-portable TOFMS system. In this work we present recent progress in integrating a low-power, high-speed GC and show the capability for accurately recording fast GC transients for targeted compound detection using a quadrupole ion trap, time-of-flight instrument (QitTof). n this paper we review our progress toward developing a field-portable, high performance mass spectrometer (MS) system with applications to a variety of fast screening requirements. Previously we reported on a 30-lb class photoionization, quadrupole ion trap, time-of-flight system (PI/QitTof) [1]. More recently we have been developing a low-power, high-speed gas chromatography (GC) sampling system for the QitTof mass analyzer. The intent is to develop a compact system that can perform direct, real-time air and liquid sampling of targeted compounds in complex mixtures in a GC-bypass mode. If a targeted compound is detected during fast screening, the sample can then be subjected to GC/MS analysis for confirmation. This mode of operation achieves high-throughput molecular detection, while affording the option of confirming the results by GC/MS. We present here an overview of our field-portable MS program and then discuss future plans and directions.The focus of this instrumentation development is to develop a "laboratory-in-the-field" capability to conduct general environmental assessments [2] and a "rapid-response monitor" to quickly and accurately detect toxic compounds, such as chemical agents, resulting from leaks or releases. Other military applications include military force protection and chemical demilitarization. Civilian applications include high-profile event security, emergency first responder protection, and hazardous materials investigations. These applications require systems that can detect in real-time (1-10 s) a host of target compounds at ultralow concentrations (e.g., 1-100 ppb air sampling, 10 -100 pg residue) in the presence of a complex matrix that would otherwise obscure signals of interest due to overlapping signal.Several manufacturers have developed products for field applications with GC capabilities (e.g., Bruker's MEM line [3], Varian's Saturn Air); however, these are not man-portable. Viking Instruments, recently acquired by Bruker, offers a portable GC/MS (SpectraTrak) billed as a "real-time" monitor for toxic air, water, and soil pollutants; however, its portability is limited by weight...

In this contribution, studies of the dynamics of proton-transfer reactions in solvent cages are presented, building on earlier work [Breen, J. J.; et al. J. Chem. Phys. 1990, 92, 805. Kim, S . K.; et al. Chem. Phys. Lett. 1994, 228, 3691. The acid-base system studied in a molecular beam is 1-naphthol as a solute and ammonia, piperidine, or water as the solvent, with the number of solvent molecules (n) varying. The rates and threshold for proton transfer have been found to be critically dependent on the number and type of solvent molecules: n = 2 for piperidine and n = 3 for ammonia; no proton transfer was observed for water up to n = 21. With subpicosecond time resolution, we observe a biexponential transient for the n = 3 cluster with ammonia.From these observations and the high accuracy of the fits, we provide the rate of the proton transfer at short times and the solvent reorganization at longer times. From studies of the effect of the total energy, the isotope substitution, and the number and type of solvent molecules, we discuss the nature of the transfer and the interplay between the local structure of the base solvent and the dynamics. The effective shape of the potential energy surface is discussed by considering the anharmonicity of the reactant states and the Coulombic interaction of ion-pair product states. Tunneling is related to the nature of the potential and to measurements specific to the isotope effect and energy dependence. Finally, we discuss a simple model for the reaction in finite-sized clusters, which takes into account the proton affinity and the dielectric shielding of the solvent introduced by the local structure.