Supercritical fluid extraction of vapor-deposited pyrene from carbonaceous coal stack ash.

The efficiencies of extraction of vapor-deposited pyrene from a high-carbon coal stack ash by Soxhlet extraction with methanol, ultrasonic extraction with toluene, acid pretreatment and subsequent ultrasonic extraction with toluene, batch extraction with toluene, and supercritical fluid extraction (SFE) are compared. SFE using CO(2) or isobutane yielded extraction recoveries virtually identical with those obtained using ultrasonic or Soxhlet extraction processes. Collection of the SFE extract was performed by expansion into a solvent or onto the head of a gas chromatography (GC) column. No loss of extracted pyrene was observed upon collection of methanol-modified CO(2) SFE by expansion into methanol. Also, no loss of pure CO(2) SFE extract was observed upon collection on the head of a GC column. However, use of a methanol or toluene modifier for CO(2) SFE directly coupled to GC effected complete loss of extracted pyrene.

Laser-induced site-selection matrix-isolation fluorescence spectrometry of dibenzacridine isomers.

Laser-induced matrix-isolation site-selection fluorescence spectrometry is used to obtain narrowed-line spectra, linear dynamic ranges and limits of detection for four isomeric dibenzacridines in argon at 15 K. Site-selection fluorescence is used to determine dibenzacridines in two synthetic mixtures, a four-component mixture of the isomeric dibenzacridines and a thirteen-component polycyclic aromatic hydrocarbon mixture. The capabilities of site-selection and Shpol'skii fluorescence spectrometry for the identification and determination of aza-arenes in complex mixtures are compared.

Determination of molecular nitrogen by electron-impact induced fluorescence.

When a sample of nitrogen gas is bombarded by 100-eV electrons, fluorescent emission from the nitrogen molecular ion, N(+)(2), is observed. The intensity of this fluorescence can be related to the pressure (or molar concentration) of the parent molecule, N(2). The limit of detection for N(2) by means of electron-impact induced fluorescence is 5.0 x 10(-8)mmHg (1.6 x 10(9) molecules/cm(3) or 2.7 x 10(-12) mole/l.). The fluorescence signal is linearly related to N(2) pressure over a range of four orders of magnitude, and relative standard deviations of less than 2% are observed for replicate measurements.

Fragmentation-fluorescence spectrometric determination of nonfluorescent compounds.

The use of molecular fragmentation for fluorometric detection and quantification of nonfluorescent organic and organometallic compounds is described. The measurements are based on the emissive characteristics of many small molecular fragments (OH, CN, CH, etc.). Fragmentation is induced by 100-eV electrons or 193-nm photons. Limits of detection, linearity, reproducibility, and range of applicability of the measurements are discussed. The merits of laser photolysis and electron impact as techniques for generating fluorescent fragments from nonfluorescent analyte molecules are compared.

Oxidative transformations of polycyclic aromatic hydrocarbons adsorbed on coal fly ash.

Polycyclic aromatic hydrocarbons adsorbed onto coal fly ash were found to be stabilized against photochemical decomposition. However, a number of adsorbed polycyclic aromatic hydrocarbons will spontaneously oxidize in the absence of light, with those compounds containing a benzylic carbon being particularly susceptible. The decomposition rate appears to be fly ash-dependent.