A Renewable Liquid Droplet Method for On-Line Pollution Analysis by Multi-Photon Ionization

Multiphoton electron extraction spectroscopy and its comparison with other spectroscopies for direct detection of solids under ambient conditions

Multiphoton electron extraction spectroscopy (MEES) is an analytical method for direct analysis of solids under ambient conditions in which the samples are irradiated by short UV laser pulses and the photocharges emitted are recorded as a function of the laser wavelength. The method is very sensitive, and many peaks are observed at wavelengths that are in resonance with the surface molecules. The analytical capabilities of MEES have recently been demonstrated, and here we perform a systematic comparison with some traditional spectroscopies that are commonly applied to material analysis. These include absorption, reflection, excitation and emission fluorescence, Raman, Fourier transform IR, and Fourier transform near-IR spectroscopies. The comparison is conducted for powders and for thin films of compounds that are active in all spectroscopies tested. Besides the obvious spectral parameters (signal-to-noise ratio, peak density, and resulting limits of detection), we introduce two additional variables-the spectral quality and the spectral quality density-that represent our intuitive perception of the analytical value of a spectrum. It is shown that by most parameters MEES is a superior analytical tool to the other methods tested for both sample morphologies.

Removal of naphthalene from aqueous systems by poly(divinylbenzene) and poly(methyl methacrylate-divinylbenzene) resins

Treatment of the oily wastewater from crude oil extraction is a growing challenge due to rising concern for the environment. Polyaromatic hydrocarbons (PAHs) deserve special attention because of their high toxicity. There is a need to develop processes able to minimize the discharge of these compounds and analytic techniques to monitor the levels of PAHs in aqueous media. In this study poly(methyl methacrylate-divinylbenzene) (MMA-DVB) and poly(divinylbenzene) (DVB) were assessed with respect to their capacity to retain naphthalene (NAF) in continuous flow and batch processes (adsorption equilibrium and kinetics). The analytic techniques applied were gas chromatography and spectrofluorimetry, which was adapted for quantification of NAF. The batch adsorption studies showed that DVB is more efficient in adsorption than MMA-DVB, and the Freundlich model and pseudo-second-order model better fitted the equilibrium data and adsorption kinetics, respectively. The elution results showed that both resins are highly efficient in removing NAF, with DVB outperforming MMA-DVB. However, MMA is cheaper raw material, making MMA-DVB more competitive for treatment of oily wastewater. The resins were regenerated by eluting about 7.2 and 2.5 L of methanol:water (70:30 v/v), respectively for DVB and MMA-DVB. Regarding to the useful life after regeneration, the resins presented a reduction about 30%, relating to zero concentration of NAF.

Multiphoton ionization spectroscopy as a diagnostic technique of surfaces under ambient conditions

Direct detection of solid substances is an important yet challenging issue in analytical chemistry. Laser multiphoton ionization spectroscopy has been applied for the first time for direct analysis of solids under ambient conditions. In this method, a solid powder/film is placed on a conductive surface and is irradiated by a pulsed tunable laser while an electrical field of approximately 2 kV cm(-1) is applied across this conductive surface and another electrode. The resulting photoelectrons and negative ions are measured by recording the current as a function of wavelength to produce a multiphoton ionization spectrum that is characteristic of the surface. Results indicate rich spectral features that can be used for compound identification. The present sensitivity is in the low picomole range. This method has been successfully tested for direct detection of various organic molecules, including explosives, narcotic drugs, and polycyclic aromatic compounds.

Laser-induced fluorescence studies of polycyclic aromatic hydrocarbons (PAH) vapors at high temperatures

In this work, we present the fluorescence spectra of anthracene and pyrene vapors at different elevated temperatures (from 150 to 650 degrees C) excited with the 337 nm line of a nitrogen laser. We describe the high temperature effects on the resulting spectral properties including spectral intensity, spectral bandwidth and spectral shift. We found that the PAH fluorescence spectral bandwidths become very broad as the temperature increases. The broadening is mainly due to thermal vibrational sequence congestion. We also have found that the fluorescence intensity of pyrene vapor increases with increasing temperature, which results from the increase of the pyrene vapor absorption cross section at 337 nm.