Richard E. Rebbert

Photodecomposition of CFCl3 and CF2Cl2

Abstract The photochemical decomposition of CFCl 3 and CF 2 Cl 2 has been investigated, using added CH 4 and C 2 H 6 as chlorine atom interceptors. From the quantum yields of the stable products formed at 213.9, 184.9, 163.3 and 147 nm, quantum yields of the primary photofragments CFCl 2 , CF 2 Cl, CFCl, CF 2 , CF and Cl, were derived. At wavelengths close to the absorption threshold, detachment of one chlorine atom from CFCl 3 and CF 2 Cl 2 occurs with a quantum yield of 0.95 ± 0.05. As the photon energy is increased, there is a rapidly increasing probability that absorption of a photon will lead to the release of two chlorine atoms: The CFCl or CF 2 formed in these processes (which are most likely in the ground singlet state) are unreactive towards the parent halocarbons, or alkanes. They combine with other free radicals to form stable products. No evidence was found for the cleavage of CF bonds, or the elimination of stable chlorine molecules. In the vicinity of the absorption threshold, the absorption cross-sections of CF 2 Cl 2 and CFCl 3 diminish sharply with a decrease in temperature.

Standard reference materials for the determination of polycyclic aromatic hydrocarbons

SummarySince 1980 a number of Standard Reference Materials (SRMs) have been issued by the National Bureau of Standards (NBS) to assist in validating measurements for the determination of polycyclic aromatic hydrocarbons (PAH) and other polycyclic aromatic compounds (PAC). These SRMs are certified for selected PAC and range in analytical difficulty from calibration solutions to complex natural matrix materials, such as air and diesel particulate matter, shale oil, and crude oil. In the past year three new SRMs have been introduced: (1) SRM 1647a “Priority Pollutant PAH in Acetonitrile”, (2) SRM 1491 “Aromatic Hydrocarbons in Hexane/Toluene”, and SRM 1597 “Complex Mixture of PAH from Coal Tar”. The SRMs available from NBS for use in the determination of PAC are described and the concentrations of PAC determined in the natural matrix SRMs are summarized and compared. The primary analytical techniques used for the measurement of PAC in these SRMs were gas chromatography, liquid chromatography, and gas chromatography/mass spectrometry.

Preparation and analysis of a marine sediment reference material for the determination of trace organic constituents

SummaryA river sediment Standard Reference Material (SRM) has been prepared and analyzed for determination of the concentrations of trace organic constituents. SRM 1939, “Polychlorinated Biphenyls (PCBs) in River Sediment A”, has been certified for the concentrations of three PCB congeners using the results obtained from capillary column gas chromatography with electron capture detection (GC-ECD) and from multidimensional (dual column) capillary gas chromatography with mass spectrometric detection (MCGC-MSD). For SRM certification, two independent analytical procedures are usually required. If only one analytical technique is used or if the procedures are not independent, then the concentrations are reported as “noncertified or informational” values rather than “certified” values. Noncertified values for 14 additional PCB congeners and five chlorinated pesticides, determined by GC-ECD, are also reported as well as noncertified concentrations for five polycyclic aromatic hydrocarbons (PAHs), determined using gas chromatography with mass spectrometric detection (GC-MSD). SRM 1939 complements SRM 1941, “Organics in Marine Sediment”, since both materials have 12 PCB congeners, five PAHs and five chlorinated pesticides in common. However, the concentrations differ by an order of magnitude for PAHs, and from one to over two orders of magnitude for the PCB congeners and chlorinated pesticides.

Photolysis of methane: Quantum yield of C(1D) and CH

Abstract It is demonstrated that C(1D) and CH(2π) species are formed in the photodissociation of CH4 at λ = 123.6 nm [Φ(C) = 0.4 ± 0.1 × 10−3, Φ(CH) = 5.9 ± 0.5 × 10−2] and at λ = 104.8–106.7 nm [Φ(C) = 6.5 ± 0.5 × 10−3, Φ(CH) = 0.23 ± 0.03]. There is no evidence for C or CH production at wavelengths where the photoionization quantum yield is equal to unity.

Quantification of polycyclic aromatic hydrocarbons and nitro-substituted polycyclic aromatic hydrocarbons and mutagenicity testing for the characterization of ambient air particulate matter☆

Abstract As part of a study to identify mutagenic and potentially carcinogenic compounds in urban air particulate extracts, the polycyclic aromatic hydrocarbon (PAH) mixture isolated from a large sample collected in Philadelphia, PA, was characterized by liquid chromatography (LC), gas chromatography (GC), and gas chromatography-mass spectrometry (GC-MS). After isolation of the aromatic fraction from the extract using classical liquid-liquid partitioning and silica gel column chromatography, the PAH fraction was isolated by normal-phase LC. A number of the major PAH constituents were quantified by GC and LC. Quantification of the minor constituents was accomplished by further subfractionation of the PAH mixture into eight fractions based on the number of aromatic carbons in the PAH. These fractions were then characterized by GC and GC-MS. More than 100 PAH components were quantified in this sample. Approximately 40 unsubstituted PAH and 10 methyl-substituted PAH were identified based on GC retention, LC retention, fluorescence, and/or mass spectral data. Several nitro-substituted PAH were also found in the PAH fraction and the more polar fractions isolated from the original aromatic fraction.

Far ultra-violet photolysis of ammonia quantum yield determination for the primary process: NH3 (ND3) + hv → NH (ND) + H2 (D2)

Abstract The gas phase photolysis of NH3-C2D4 and ND3-C2H4 mixtures has been investigated at 147 nm (8.4 eV), 123.6 nm (10 eV) and 104.8-106.7 nm (11.6-11.8 eV). The quantum yield of D2 in the irradiation of ND3-C2H4 mixtures is independent of the concentration of C2H4 and of the pressure of ND3 (10 to 180 Torr). It is concluded that in these mixtures D2 is entirely formed by molecular elemination from excited ND3. The quantum yields of such a process are as follows at these energies: 147 nm, 0.032 ± 0.005; 123.6 nm, 0.244 ± 0.01; and 104.8-106.7 nm, 0.306 ± 0.007 (M/Nex = 0.52 ± 0.02). Although the NH3-C2D4 photolysis data exhibit less reliability, it can be concluded that the quantum yield of molecular H2 at 147 nm is twice that of melecular D2. Isotope effects are much less pronounced at higher photon energies. At 147 and 123.6 nm, D2 is eliminated via primary process: and/or: On the basis of the spectroscopic observation of Okabe and Lenzi it can be concluded that at 104.8-106.7 nm the primary process: must also contribute significantly to the formation of molecular hydrogen. It is suggested that the ND3+ ions which are formed at these energies do not contribute to the formation of molecular D2, but that the occurence of an overall process: cannot be ruled out. The extinction coefficients of NH3 and ND3, at the rare gas lines have been redetermined and were found to differ significantly from those derived from published absorption curves.

The photochemistry of methyl chloride

Abstract Methyl chloride and CH3ClCD3Cl, CH3ClBr2 and CD3ClHI mixtures have been photolyzed at 163.3, 147.0 and 123.6 nm in the gas phase and methyl chloride has also been photolyzed at 147.0 nm in the liquid phase. Over this range of wavelengths, there are four principal primary processes: At 163.3 nm, process (1) is almost exclusively responsible for the photodecomposition. However, at shorter wavelengths processes (2), (3) and (4) increase while process (1) decreases in importance. At all wavelengths these four processes account for a total quantum yield of 0.75 – 1.0.

Liquid chromatography—gas chromatography procedure to determine the concentration of dibenzothiophene in a crude oil matrix

Abstract The concentration of dibenzothiopene in SRM 1582, Wilmington crude oil, was determined using a technique which combines liquid chromatography and gas chromatography. In particular, liquid chromatography was utilized for initial sample clean-up and separation of the thiophenes. A dual-flame photometric detector specific for sulfur-containing compounds was used as the detector for gas chromatography. In order to further minimize possible sources of error due to the natural hydrocarbon matrix of the oil, a standard addition method was also utilized.

Standard Reference Materials for the Determination of Polycyclic Aromatic Hydrocarbons in Environmental Samples -- Current Activities

SummaryRecent activities at the National Institute of Standards and Technology (NIST) related to the development of standard reference materials (SRMs) for the determination of polycyclic aromatic hydrocarbons (PAHs) are described. These activities include: (1) the development of four new calibration solution SRMs, a marine sediment SRM, and a frozen mussel tissue SRM; (2) noncertified measurements of PAHs for two additional sediment SRMs; and (3) the establishment of reference Ames bioassay mutagenicity values on three existing SRMs. Activities in progress include the recertification of the existing air particulate and diesel particulate SRMs and the preparation of a new diesel particulate extract SRM.

Gas phase photolysis of CF2Cl2, CFCl3 and CCl4 in the presence of bromine at 213.9, 163.3, 147.0 and 123.6 nm

Abstract CF 2 Cl 2 Br 2 , CFCl 3 Br 2 and CCl 4 Br 2 mixtures were photolyzed at 213.9, 163.3 and 147.0 nm. The first two mixtures were also photolyzed at 123.6 nm. In the CF 2 Cl 2 Br 2 system the quantum yields for the formation of CF 2 Cl radicals (as determined by the formation of CF 2 ClBr) were 1.0 ± 0.1, 0.67 ± 0.07, 0.05 ± 0.02 and not more than 0.02 respectively. For the CFCl 3 Br 2 system the quantum yields of formation of CFCl 2 radicals (as CFCl 2 Br) were 1.0 ± 0.1, 0.53 ± 0.05, 0.02 ± 0.01 and 0.03 ± 0.02 respectively. In the CCl 4 Br 2 experiments the quantum yields of formation of CCl 3 radicals (as CCl 3 Br) were 1.0 ± 0.1, 0.41 ± 0.04 and 0.02 ± 0.01 at the wavelengths 213.9, 163.3 and 147.0 nm respectively. These results are in excellent agreement with some earlier determinations which utilized a different technique. In all such cases the quantum yields, determined by the bromine addition technique for such fragments as CF 2 , CFCl, CCl 2 , CF and CCl, can only be used to set lower limits for the quantum yields of formation of these radicals. There are complications in this method for these fragments which cannot at present be taken entirely into account.