The purpose of this study was to evaluate the antibacterial efficacy of an intracanal medication composed of calcium hydroxide with 2% chlorhexidine. Dentin from 24 bovine incisors was used. The incisors were made into standardized cylindrical segments of dentin and infected with Enterococcus faecalis. They were then treated with an intracanal paste composed of calcium hydroxide and sterile water or an intracanal paste composed of calcium hydroxide and 2% chlorhexidine for 1 week. Dentin shavings were collected, suspended in solution, and spread on brain-heart infusion agar. After incubation, colony-forming units were enumerated. The amount of bacteria per mg of dentin was determined. The calcium hydroxide paste with 2% chlorhexidine was significantly more effective at killing E. faecalis in the dentinal tubules than calcium hydroxide with water.One of the goals of endodontic therapy is the reduction or elimination of bacteria and their by-products from the root canal system. Proper cleaning, shaping, and irrigation have been shown to significantly reduce and sometimes eliminate bacteria from canals (1). The use of intracanal medications to disinfect the root canal system has been advocated (2). Reasons for the use of intracanal medications are: (a) to eliminate bacteria in the root canal; (b) to prevent bacterial proliferation between appointments; and (c) to act as a physiochemical barrier, preventing root canal reinfection and nutrient supply to the remaining bacteria (3). Calcium hydroxide has been the intracanal medication of choice (4). Calcium hydroxide has been demonstrated to improve dissolution of the pulp tissue by sodium hypochlorite (NaOCl) and provide antimicrobial activity (2, 5). However, the antimicrobial activity of calcium hydroxide seems dependent upon direct contact with bacteria (4). Haapasalo and Ørstavik (6) have demonstrated that it is not effective in eliminating bacteria from dentinal tubules.Recently, chlorhexidine has been shown to be an effective antimicrobial endodontic irrigant (7,8). However, chlorhexidine does not have the ability to dissolve tissue, and gels containing chlorhexidine can be difficult to remove from the canal space.White et al. (9) and Leonardo et al. (10) demonstrated the property of substantivity for chlorhexidine. They demonstrated that chlorhexidine irrigation continued to prevent reinfection of dentin for up to 72 h. Several investigators have demonstrated the antimicrobial effectiveness of chlorhexidine gel or sustained release vinyl ribbons containing chlorhexidine as intracanal medications (11,12). The purpose of this investigation was to evaluate a paste made of calcium hydroxide mixed with 2% chlorhexidine for antimicrobial efficacy against Enterococcus faecalis in the dentinal tubules of bovine incisors. MATERIALS AND METHODSTwenty-four bovine incisors were extracted and prepared according to the methods of Haapasalo and Ørstavik (6) as modified by Lenet et al. (12). The incisors were placed in 5.25% NaOCl after extraction to remove any soft tissue. T...

At the Advanced Light Source an undulator beamline, with an energy range from 6 to 30 eV, has been constructed for chemical dynamics experiments. The higher harmonics of the undulator are suppressed by a novel, windowless gas filter. In one branchline high-flux, 2% bandwidth radiation is directed toward an end station for photodissociation and crossed molecular-beam experiments. A photon flux of 10 16 photon/s has been measured at this end station. In a second branchline a 6.65 m off-plane Eagle monochromator delivers narrow bandwidth radiation to an end station for photoionoization studies. At this second end station a peak flux of 3 ϫ 10 11 was observed for 25 000 resolving power. This monochromator has achieved a resolving power of 70 000 using a 4800 grooves/mm grating, one of the highest resolving powers obtained by a vacuum ultraviolet monochromator.

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...

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Articles you may be interested inPhotofragmentations, state interactions, and energetics of Rydberg and ion-pair states: Two-dimensional resonance enhanced multiphoton ionization of HBr via singlet-, triplet-, Ω = 0 and 2 states Photo-versus pulsed field-ionization of individual high n (n 57) Rydberg states: Resolved d,g series of benzene Rotationally resolved pulsed field ionization photoelectron study of CO + (X 2 Σ + ,v + =0-42) in the energy range of 13.98-21.92 eV J. Chem. Phys. 111, 8879 (1999); 10.1063/1.480259Mass-resolved two-photon and photoelectron spectra of Xe 2 in the Xe (4f) region above the first molecular ionization limit

High-resolution state-selected ion-molecule reaction studies using pulsed field ionization photoelectronsecondary ion coincidence method Rev. Sci. Instrum. 74, 4096 (2003); 10.1063/1.1599071High-resolution pulsed field ionization photoelectron-photoion coincidence spectroscopy using synchrotron radiation Rev.A study of the SO molecule with photoelectron spectroscopy using synchrotron radiationWe have demonstrated a resolution of 0.8 meV ͓full width at half-maximum ͑FWHM͔͒ for threshold photoelectron measurements using a steradiancy-type zero kinetic energy photoelectron ͑ZEKE-PE͒ analyzer and the high resolution monochromatized vacuum ultraviolet ͑VUV͒ undulator synchrotron radiation of the chemical dynamics beamline at the advanced light source ͑ALS͒. Using this high resolution ZEKE-PE energy analyzer to filter prompt electrons and by employing a proper voltage pulsing scheme adapted to the timing structure of the ALS, we have achieved a resolution of 0.5 meV ͑FWHM͒ for pulsed field ionization photoelectron ͑PFI-PE͒ measurements with little contamination from prompt photoelectrons produced from direct photoionization and autoionizing processes. The experiment scheme presented here is generally applicable to PFI-PE studies using multi-bunch VUV synchrotron radiation at other synchrotron radiation facilities.

We have obtained rotationally resolved pulsed filed ionization photoelectron (PFI-PE) spectra of NO in the energy range of 9.2–16.8 eV, covering ionization transitions of NO+(X 1Σ+,v+=0–32,J+)←NO(X 2Π3/2,1/2,v″=0,J″). The PFI-PE bands for NO+(X 1Σ+,v+=6–32) obtained here represent the first rotationally resolved spectroscopic data for these states. The simulation using the Buckingham–Orr–Sichel model provides accurate molecular constants for NO+(X 1Σ+,v+=0–32), including ionization energies, vibrational constants (ωe+=2 382.997±0.122 cm−1, ωe+χe+=17.437 84±0.000 90 cm−1, ωe+ye+=0.063 209 5±3.2×10−6 cm−1, and ωe+ze+=−0.001 400 0±7.2×10−8 cm−1), and rotational constants (Be+=1.996 608±0.006 259 cm−1, αe+=0.020 103±6.3×10−5 cm−1, and γe+=−(7.22±2.26)×10−6 cm−1). For v+=0–15, the rotational branches are ΔJ=J+−J″=±1/2, ±3/2, ±5/2, ±7/2, and ±9/2, which correspond to the formation of photoelectron angular momentum states l=0, 1, 2, and 3. The ΔJ=±1/2, ±3/2, ±5/2, ±7/2, ±9/2, and ±11/2 rotational branches are observed in the spectra for v+=16–32, revealing the production of continuum photoelectron states l=0, 1, 2, 3, and 4. The maximum ΔJ value and intensities for high ΔJ rotational branches are found to generally increase as v+ is increased in the range of 0–32. This observation is attributed to an increase in inelastic cross sections for collisions between the outgoing photoelectron and the nonspherical molecular ion core as the bond distance for NO+ is increased. Thus, this observation can be taken as strong support for the electron-molecular-ion-core scattering model for angular momentum and energy exchanges in the threshold photoionization of NO.

The vacuum ultraviolet pulsed field ionization photoelectron (PFI-PE) band for OCS+(X 2Π) in the energy region of 11.09–11.87 eV has been measured using high resolution monochromatized synchrotron radiation. The ionization energies (IEs) for the formation of the (0,0,0) X 2Π3/2 and (0,0,0) 2Π1/2 states of OCS+ are determined to be 11.1831±0.0005 and 11.2286±0.0005 eV, respectively, yielding a value of 367±1.2 cm−1 for the spin–orbit splitting. Using the internally contracted multireference configuration interaction approach, three-dimensional potential energy functions (PEFs) for the OCS+(X 2Π) state have been generated and used in the variational Renner–Teller calculations of the vibronic states. The energies of all vibronic states (J=P) for J=1/2, 3/2, 5/2, and 7/2 have been computed in the energy range of ≈4000 cm−1 above the IE[OCS+(X 2Π3/2)] for the assignment of the experimental spectrum. By a minor modification of the ab initio PEFs, good correlations are found between the experimental and theoretical Renner–Teller structures. Similar to the PFI-PE bands for CO2+(X 2Πg) and CS2+(X 2Πg), weak transitions have been detected in the PFI-PE band for OCS+(X 2Π), which are forbidden in the Franck–Condon approximation. The nonvanishing single-photon ionization cross sections involving the excitation of the bending vibrational modes of OCS+, CO2+, and CS2+, in their ground electronic states are attributed to the symmetries of the geometry-dependent electronic transition dipole operator components.