Leon D. Betowski

Measurement of high-molecular-weight polycyclic aromatic hydrocarbons in soils by particle beam high-performance liquid chromatography-mass spectrometry

Polycyclic aromatic hydrocarbons (PAHs) comprise a class of potentially hazardous com- pounds of concern to the U.S. EPA. The application of particle-beam (PB) liquid chromatography-mass spectrometry (LC-MS) to the measurement of high-molecular-weight PAHs was investigated. Instrument performance was evaluated for 16 PAHs in the molecular weight range 300–450 u. The PAHs were separated by reverse-phase high-performance liquid chromatography via a polymeric octadecylsilica (C-18) packing and gradient elution with methanol-tetrahydrofuran. On-column instrument detection limits, as measured by selected ion monitoring on the singly charged molecular ion of each PAH, were found to be 0.15–0.60 ng for PAHs with molecular weights up to 352 u and 2–4 ng for PAHs with molecular weights greater than 352 u. Instrument response was generally linear for PAHs with molecular weights 300–352 u and generally nonlinear for PAHs with molecular weights greater than 352 u. The PB electron impact mass spectra of the PAHs were found to vary with the ion distribution ratio of the singly charged molecular ion to the doubly charged molecular ion, dependent on molecular weight, ion source temperature, and concentration. Analysis by PB LC-MS was applied to extracts of PAH-spiked soil and a PAH-contaminated soil from the Pacific Northwest. Target analyte concentrations in the PAH-contaminated soil ranged from 0.85 to 84 µg/g. Quantitative estimates for nontarget PAHs also were determined. Analysis of a second soil extract from a hazardous waste site in the northeast part of the United States displayed isomeric patterns of high-molecular-weight PAHs similar to those of the Pacific Northwest extract.

Ab initio calculated gas-phase basicities of polynuclear aromatic hydrocarbons

Abstract The gas-phase basicities (GBs) of polynuclear aromatic hydrocarbons (PAHs) have been calculated using the semiempirical Austin model 1 method, ab initio quantum mechanical methods at the HF/3-21G, HF/6-31G(d), MP2/6-31G(d), MP2/6-31+G(d,p) levels, and the B3LYP/6-311G(d,p) density functional method. GBs calculated at these levels of theory are compared to experimentally known GBs measured by equilibrium mass spectrometric methods. Theoretically calculated entropies for PAHs and their protonated carbocations are used to reevaluate original experimental equilibrium data producing a revised set of experimental GBs and proton affinities for PAHs and related hydrocarbons. Experimental GBs for 40 hydrocarbons are found to correlate well with AM1, Hartree–Fock, DFT and MP2 calculated GBs, with regression analyses showing standard errors of 2.12, 1.53, 1.36, and 1.55 kcal mol −1 for each of the four methods, respectively. The results permit an evaluation of the reliability of experimental data and suggest a need for new experimental work for some molecules. Predictions are made for GBs for 12 new PAHs whose GBs have not yet been measured.

The phototoxicity of polycyclic aromatic hydrocarbons: a theoretical study of excited states and correlation to experiment.

Investigators using models to determine the phototoxic effects of sunlight on polycyclic aromatic hydrocarbons (PAHs) have invoked the excited states of the molecule as important in elucidating the mechanism of these reactions. Energies of actual excited states were calculated for ten PAHs by several ab initio methods. The main method used for these calculations was the Configuration Interaction approach, modeling excited states as combinations of single substitutions out of the Hartree-Fock ground state. These calculations correlate well with both experimentally measured singlet and triplet state energies and also previous HOMO-LUMO gap energies that approximate the singlet state energies. The excited state calculations then correlate well with general models of photo-induced toxicity based for the PAHs.

Determination of carbendazim in water by high-performance immunoaffinity chromatography on-line with high-performance liquid chromatography with diode-array or mass spectrometric detection

Abstract An automated method for the determination of carbendazim in water that combines high-performance immunoaffinity chromatography (HPIAC), high-performance liquid chromatography (HPLC) in the reversed-phase mode, and detection by either UV-Vis diode array detector (DAD0 spectroscopy or mass spectrometry (MS) is presented here. This method allows for the on-line extraction, preconcentration, and positive confirmation of carbendazim with a throughput of one sample analyzed every 10 min. The method requires minimal manual sample pretreatment, yet it is free from coextracted interferences that often occur in solid-phase extractions based on nonspecific sorbents. The linear range of the calibration curve for 200-μ1 injections of carbendazin is 0.025 to 100 μ/1 for HPIAC-HPLC-MS and 0.075 to 100 μg/1 for HPIAC-HPLC-DAD. Because the calibration curve is mass-dependent, lower detection limits could be achieved by applying larger sample volumes to the HPIAC column. The within-day precision is ±4.5% for HPIAC-HPLC-MS and ±16% for HPIAC-HPLC-DAD for samples containing 0.1 μg/l carbendazim. The results from this method correlate well with results from an ELISA.

Particle beam liquid chromatography—electron impact mass spectrometry of dyes☆

Abstract A liquid chromatograph was interfaced with a triple quadrupole mass spectrometer by means of a particle beam-type interface. The system was used for the analysis and characterization by electron impact mass spectra of a series of commercial dyes. The pure dyes were separated from their impurities with a reversed-phase C18 column using methanol—water as the mobile phase. Detection limits were determined using the system as a single quadrupole mass spectrometer. Sensitivity for dyes was found to be two to three orders of magnitude worse than with thermospray ionization using a wire repeller. Characterization of the azo dyes could be achieved by observing typical fragment ions formed by cleavage of the N—C and C—N bond on either side of the azo linkage and/or cleavage of the N  N double bond with transfer of two hydrogen atoms to form an amine.

Negative-ion fast atom bombardment mass spectrometry of sulfonylurea herbicides

Seven sulfonylurea herbicides were studied using negative-ion fast atom bombardment mass spectrometry (FAB-MS). The spectra were characteristic of the structure of the examined herbicides with fragmentation at the sulfonylurea bridge representing both aromatic moieties. The fragmentation pattern was established based on the FAB-B/E mass spectrome-try/mass spectrometry linked-scan spectra. Background-subtracted negative ion FAB-MS spectra of the herbicides exhibit [M–1]− peaks and their fragmentation products. Application of triethylenetetramine as a FAB matrix resulted in enhanced fragmentation. The 3-nitrobenzyl alcohol FAB spectra typically exhibited high-abundance [M–1]− peaks and fewer fragment peaks.

The nature of C10H2+ in mass spectra of polynuclear aromatic hydrocarbons☆

Abstract Ab initio and density functional theory (DFT) calculations have been performed to determine the heats of reaction for the process C 16 H 10 + → C 10 H 2 + that takes place in an ion trap mass spectrometer. Comparisons have been made with the experimental and derived data available for this process. The theoretical values at the DFT level verify the experimental heats of reaction within 0.4-0.8 eV. Furthermore, the structure of the product ion, C 10 H 2 + , has been investigated. Several structures have been proposed, and the ab initio and DFT geometry optimizations and frequency calculations have been performed to determine the most stable species. At the level of theory and the approximations that were used in this work, the linear form of C 10 H 2 + is the most stable species of three different geometries considered.