Multifunctional organic nitrates as constituents in European and US urban photo-smog

Air samples of the atmospheric ground layer in the cities of Ulm in Germany, Las Vegas, Nevada, and Salt Lake City, Utah, in the US were analyzed for organic nitrates. The air samples were taken around noon in summer at sunny weather conditions. 43 (C6-C13) alkyl mononitrates, 24 (C3-C6) alkyl dinitrates, and 19 (C2-C6) hydroxy alkyl nitrates have been identified. The analytical protocol included high-volume-sampling, NP-HPLC group separation, high resolution capillary gas chromatography, and detection by the highly selective mass spectrometer detector (SIM mode, m/z = 46). The levels of the sum of 15 (C6-C10) alkyl mononitrates ranged from 2.9 to 11.0 parts per trillion (ppt(v)). The levels of the sum of 21 (C3-C6) alkyl dinitrates ranged from 2.3 to 10.5 ppt(v), and the levels of the sum of 7 (C2-C4) hydroxy alkyl nitrates ranged from 7.3 to 28 ppt(v), respectively, in the urban air samples. These results emphazise the contribution of the alkyl dinitrates and hydroxy alkyl nitrates besides the alkyl mononitrates to the budget of NO(Y) compounds. No major differences in levels and pattern of the organic nitrates are present in air of the German and the US cities.     

Bifunctional alkyl nitrates – trace constituents of the atmosphere

Mono- and multifunctional esters of nitric acid (alkyl nitrates or organonitrates) form very complex mixtures of organic trace constituents in air. An analytical method was developed which combines selectivity in separation and detection in order to simplify this complexity in analytical terms. Mononitrates, dinitrates, keto nitrates, hydroxy nitrates of alkanes and alkenes, respecitvely, and bifunctional terpene nitrates were synthesized as reference substances. A specially developed new HPLC stationary phase (organonitrate phase) allows a group separation of mono-, di-, and hydroxy nitrates. After the HPLC preseparation the single components were finally separated by capillary HRGC-ECD and HRGC-MSD on polar and non-polar stationary phases. Mass spectrometric detection in the selected-ion-mode using the highly selective NO₂ ⁺ fragment (m/z = 46 amu) led to very good selectivities for the nitric acid ester moiety. The analysis of a 100 m³ ambient air sample using this new analytical protocol allowed the identification of seven hydroxy nitrates and 24 dinitrates ranging from C2 to C7, 22 of them for the first time ever.     

New stationary phase based on beta-cyclodextrin for normal-phase HPLC group-separation of organic nitrates

The synthesis of a beta-cyclodextrin-silica normal-phase (NP)-liquid chromatography (LC) stationary phase is reported. Silica gel was modified with (3-bromopropyl)trimethoxysilane to a 3-bromopropyl-silica that was reacted with beta-cyclodextrin, resulting in a beta-cyclodextrin-silica. To prove its usefulness in group-separation of organic nitrates among others, a mixture of three groups of organic nitrates was separated. The results are compared with those obtained on a nitrated polyol-silica that has recently been reported. The alkyl dinitrates exhibt higher retention relatively to alkyl mononitrates on the new phase. This allows to cut the LC fractions in a way that the alkyl mononitrates and phenylalkyl nitrates appear in one fraction and the dinitrates in a second one without any overlap of the two fractions.     

New stationary phase based on β-cyclodextrin for normal-phase HPLC group-separation of organic nitrates

The synthesis of a β-cyclodextrin-silica normal-phase (NP)-liquid chromatography (LC) stationary phase is reported. Silica gel was modified with (3-bromopropyl)trimethoxysilane to a 3-bromopropyl-silica that was reacted with β-cyclodextrin, resulting in a β-cyclodextrin-silica. To prove its usefulness in group-separation of organic nitrates among others, a mixture of three groups of organic nitrates was separated. The results are compared with those obtained on a nitrated polyol-silica that has recently been reported. The alkyl dinitrates exhibt higher retention relatively to alkyl mononitrates on the new phase. This allows to cut the LC fractions in a way that the alkyl mononitrates and phenylalkyl nitrates appear in one fraction and the dinitrates in a second one without any overlap of the two fractions. Received: 3 August 1999 / Revised: 27 September 1999 / Accepted: 30 September 1999     

A Measurement Technique for Organic Nitrates and Halocarbons in Ambient Air

A cryogenic preconcentration/high-resolution gas chromatographic technique has been developed for the rapid, simultaneous quantitation of C₁–C₄ organic nitrates and halocarbons in ambient air. Whole-air samples are collected in Tedlar^TM bags by an evacuated-chamber method. Samples were stable in 0.010-cm-thick bags for 24 h if they were immediately stored in a freezer at −25°C. Analytes in a 50-cm³ air sample were efficiently preconcentrated on fused-silica beads at −180°C and thermally desorbed at 30°C. High-resolution gas chromatography with a cross-linked polydimethylsiloxane fused-silica capillary column and an electron-capture detector were used for separation and quantitation of the analytes. An analysis time of about 12 min was facilitated by sample cryofocusing at −180°C and oven temperature programming. Recoveries of the analytes by the evacuated-chamber method were better than 95%. The sensitivity of the technique for sample volumes of 50 cm³ is in the sub-parts-per-trillion by volume (ppt[v]) range for many of the analytes, with an average precision of about ±5% for analytes at levels of about 10 ppt(v).     

Separation, detection and occurrence of (C2–C8)-alkyl- and phenyl-alkyl nitrates as trace compounds in clean and polluted air

Nitric acid, HNO₃, and nitrous acid, HNO₂, are forming stable esters with alcohols, the alkyl nitrates and alkyl nitrites. Both groups of compounds are used as fuel additives, explosives and pharmaceuticals. Alkyl nitrates are also formed as complex mixtures during incomplete combustion and the abiotic transformation of alkanes, alkenes and aldehydes in air. Organic nitrates can be assigned to anthropogenic and natural sources alike. Here the synthesis of reference mixtures of alkyl nitrates is described starting with alcohols, alkyl bromides, alkyl iodides or alkanes, respectively, sampling techniques in air analysis, and the separation of alkyl nitrates and alkyl dinitrates by high resolution capillary gas chromatography using various stationary phases and electron capture (HRGC/ECD) as well as mass spectrometric detection (HRGC/MSD). A highly selective detection mode for alkyl nitrates and alkyl di- and trinitrates — in general in the presence of other organic trace compounds — is the single ion monitoring of 46 amu in GC/MS. The separation and occurrence of alkyl- and phenyl-alkyl nitrates in polluted air is reported using capillary gas chromatography with electron capture and ion trap MS detection. The reaction of alkanes with nitric acid at room temperature simulates in a good approximation the pattern of alkyl nitrates formed in air chemistry.     

Analysis of light hydrocarbons (C2?C6) at PPT levels by high resolution gas chromatography

An analytical technique is described which allows the determination of C₂? C₆ hydrocarbons in the ppt-range from up to 21 air samples after removal of air humidity. Preconcentration is carried out on a two stage cryotrap system. The compounds are separ ated on a temperature-programmed capillary coated with Al₂ O₃. Detection limits (S/N 2:1) of 1.5 to 5 ppt were obtained for air samples from the Arctic. The reproducibility of the method was about 3% at the 50–100 ppt level. Practical problems are discussed in detail.     

Identification of alkyl dinitrates in ambient air of Central Europe

Bifunctional organic nitrates – organic esters of nitric acid – are part of the pool of components of odd nitrogen (NO_Y) in the atmosphere. In this paper, we report the identification of dinitrates in ambient air of Central Europe (Ulm, Germany). The organic nitrates were sampled by adsorptive high volume sampling of 100 m³ of air with 100 g precleaned silica. Sample preparation and group separation was performed by NP-HPLC. Separation and detection was done by HRGC/EI-MSD. We have extended the identification of dinitrates in ambient air to a number of 30, of which only five have been reported by other authors before. To our knowledge, this is the first time that 13 non-vicinal dinitrates and two branched dinitrates have been identified in ambient air. Four organic nitrates have never been reported before: the non-vicinal 1,3-dinitrooxy-pentane (1,3C5), the two branched 2-methyl-1,2-dinitrooxy-propane (2M1,2C3) and 2-methyl-2,3-dinitrooxy-butane (2M2,3C4), and one diastereomer of 3,4-dinitrooxy-hexane (RR/SS-3,4C6). We are also assigning the configuration of the two diastereomers of 2,4-dinitrooxy-pentane (2,4C5) found in air before using reference standards obtained by enantioselective synthesis. Received: 8 June 1998 / Revised: 7 September 1998 / Accepted: 14 September 1998     

C4-C14-alkyl nitrates as organic trace compounds in air

The long chain alkyl nitrates (C _n >5) form a complex spectrum of natural and anthropogenic organic trace compounds in air. HRGC/ECD and HRGC/MSD using 56 amu as the signal reveal a standard pattern of isomeric n-alkyl nitrates in semi-rural air. This is regulated by the input of the corresponding alkanes, their rate constants for the reaction with OH, the rate constant of the alkylperoxy radicals for the reaction to alkyl nitrates, the atmospheric concentrations of NO/NO₂ and by the rate constants of the alkyl nitrates for the reaction with OH radicals as the major removal reaction. The complex pattern of signals given by the ECD in the retention index range between 700 and 2000 has been observed before but this is the first time that it has been assigned to a defined group of chemical compounds.The environmental impact of the occurrence of the different groups of alkyl nitrates has yet to be evaluated. Their general property as organic stabilizers for NO/NO₂ and therefore as precursors of NO ₃ ^- ions in rain and their biological potentials are also known. The long chain alkyl nitrates act as lipophilic carriers for nitric acid.     

Use of Trifluoromethyl Groups for Catalytic Benzylation and Alkylation with Subsequent Hydrodefluorination

The electrophilic organofluorophosphonium catalyst [(C₆F₅)₃PF][B(C₆F₅)₄] is shown to effect benzylation or alkylation by aryl and alkyl CF₃ groups with subsequent hydrodefluorination, thus resulting in a net transformation of CF₃ into CH₂–aryl fragments. In the case of alkyl CF₃ groups, Friedel–Crafts alkylation by the difluorocarbocation proceeded without cation rearrangement, in contrast to the corresponding reactions of alkyl monofluorides.     

Influence of fullerene on the kinetics of thermal and thermo-oxidative degradation of high-density polyethylene by capturing free radicals

The influence of fullerene (C₆₀) on the thermal and thermal-oxidative degradation of high-density polyethylene (HDPE) was studied using non-isothermal thermogravimetric analysis under nitrogen (N₂) and air atmosphere. Kinetic parameters of the degradation were evaluated using the Flynn–Wall–Ozawa method, which does not require the knowledge of the reaction mechanism. The results showed that the addition of C₆₀ enhanced the thermal stability of HDPE and increased the activation energy both in N₂ and air atmosphere and especially affected the initial stage of degradation. In N₂, C₆₀-trapped carbon-centered radical originated from the degradation of HDPE to improve the thermal stability and increase the activation energy. While in air, C₆₀ trapped the alkyl radicals and alkyl peroxide radicals to inhibit the hydrogen abstraction (especially the initial stage of thermo-oxidative degradation) and form more stable species, which improved the thermal stability and increased the activation energy during the thermal degradation of HDPE. Comparing with that of pure HDPE, the changes of activation energy for HDPE/C₆₀ nanocomposites were higher in air than in N₂, especially in the initial stage.     

EI- and NCI-mass spectrometry of arylalkyl nitrates and their occurrence in urban air

The overall probability of the formation of arylalkyl nitrates is low in comparison to alkyl nitrates. However, measurable amounts of arylalkyl nitrates are found in traffic influenced air. It is reported here an analytical protocol based on high-volume sampling, adsorption liquid chromatography as a step in sample preparation, and high-resolution gas chromatography with electron ionization mass selective detection (HRGC/EI-MSD) as well as high-resolution gas chromatography with negative chemical ionization mass selective detection (HRGC/NCI (methane)-MSD) for the determination of arylalkyl nitrates as atmospheric constituents in urban air. The synthesis of arylalkyl nitrates as reference compounds is described. The arylalkyl nitrates can be selectively detected by the fragments M-46 (M-NO₂) and M-48 (M-NO₂-2H) in HRGC/NCI(methane)-MSD. In EI(70 EV)-MSD the dominating ions are at 46, 77, 91 and 105 u, which correspond to the NO₂ ⁺ and the phenyl, benzyl, and ethylbenzene fragments, respectively. The molecular ions are missing in (NCI-methane)-MSD and are of medium intensity in EI-MSD. Phenylethyl and phenylpropyl nitrates elute in GC in the range of n-octyl to n-dodecyl nitrate. The following arylalkyl nitrates have been identified in urban air: Benzyl nitrate (PhC1) and the three xylyl nitrates (M-PhC1), phenylethyl-1-nitrate (1Ph1C2), phenylethyl-2-nitrate (1Ph2C2), phenyl-n-propyl-1-nitrate (1Ph1C3), and phenyl-n-propyl-2-nitrate (1Ph2C3). Benzyl nitrate is the dominating compound in this group and is found at levels of 10–300 ng/m³ in urban air.     

Qualitative and quantitative analysis of the n-alkanes C9-C17 and pristane in clean air masses

Summary An analytical method was developed for measuring n-alkanes (C₉ to C₁₇) and other hydrocarbons in tropospheric air with mixing ratios of a few ppt (10^–12) and higher. The hydrocarbons are collected in situ in absorption tubes, carefully protected against contamination and analysed later in the laboratory by gas chromatography. First data are reported for Atlantic air masses at the west coast of Ireland.

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Qualitative und quantitative Analyse der n-Alkane C₉-C₁₇ und von Pristan in reiner Luft

Zusammenfassung Es wurde eine analytische Methode entwickelt zur Messung der n-Alkane (C₉ bis C₁₇) und anderer Kohlenwasserstoffe in reiner troposphärischer Luft mit Mischungsverhältnissen von einigen ppt (10^–12) und aufwärts. Die Kohlenwasserstoffe wurden am Beobachtungsort angereichert, sorgfältig gegen Verunreinigung geschützt und später im Laboratorium gas-chromatographisch analysiert. Erste Daten für atlantische Luftmassen an der Westküste Irlands werden mitgeteilt.

     

Rapid screening of alkylphenol exposure in fish bile using an enzymatic peroxidase biosensor

This article deals with the development and novel application of an amperometric peroxidase biosensor for monitoring fish exposure to petroleum-related discharges, in particular, to alkyl phenols (AP) using fish bile as the main sample material. The biosensor consisted of a screen-printed electrode coupled with peroxidase immobilized by glutaraldehyde cross-linking. The sensor was optimized with regards to factors such as immobilization procedures, substrate selectivity, and matrix effects. The biosensor was used for the analysis of fish bile samples from Atlantic cod (Gadus morhua L.) exposed in the laboratory during a 2 week period to different petroleum related compounds. The biosensor could distinguish between bile samples of fish exposed to water containing high concentrations (a mixture of C₄–C₇) to moderate levels (mainly C₀–C₅) of alkylphenols and that of the control group.     

Synthesis and physico-chemical properties of ionic liquids based on 1-butyl-3-alkylimidazolium with inorganic anions

Ionic liquids with 1-butyl-3-alkylimidazolium (alkyl = C₄H₉, C₈H₁₇, or C₁₀H₂₁) cation and Br^–, BF ₄ ^– , or PF ₆ ^– anions have been obtained. Composition and structure of the compounds have been confirmed by elemental analysis and IR spectroscopy data. Electrical conductivity of solutions of the synthesized compounds in acetonitrile has been studied, and association constant as well as equivalent electrical conductivity at infinite dilution have been calculated. Thermal stability of the prepared ionic liquids in air at 25–500°С has been studied.     

Displacement of weakly coordinating anions from zirconocene alkyl cations by trialkyl phosphines: A model for olefin coordination in homogeneous Ziegler–Natta catalysis

Displacement of the anion H₃C–B(C₆F₅)₃⁻ from the zirconocene contact-ion pair [(C₅H₅)₂Zr(CH₃)⁺⋯(μ-H₃C)–B(C₆F₅)₃⁻] by a series of phosphines and formation of a bisphosphine complex by uptake of a second phosphine ligand have been studied by NMR methods in C₆D₆ solutions. Evidence is presented that associated, outer-sphere ion pairs [(C₅H₅)₂Zr(CH₃)(PR₃)]⁺ H₃C–B(C₆F₅)₃⁻ predominate at zirconocene concentrations up to ca. 2 mM; higher aggregates become apparent at higher zirconocene concentrations. Equilibrium constants for the formation of mono- and bis-PMe₃ complexes have been determined; the latter are found to be highly sensitive to steric perturbations. These data, together with density-functional estimates for reaction enthalpies, lead to the following qualitative conclusions with regard to olefin coordination in zirconocene-based polymerization catalysts: (i) The olefin substrate displaces the borate anion only from a small equilibrium fraction of the zirconocene alkyl cations present; (ii) the predominant fraction of the resulting zirconocene alkyl olefin cation remains in an outer-sphere association with the counteranion; (iii) mutual displacement of olefin and counteranion from the Zr center is slow compared to typical olefin insertions; (iv) uptake of a second olefin under formation of a cationic zirconocene alkyl diolefin complex is rather unlikely even at elevated olefin concentrations.     

Luminescent Amphiphilic 2,6‐Bis(1‐alkylpyrazol‐3‐yl)pyridyl Platinum(II) Complexes: Synthesis,Characterization, Electrochemical,Photophysical, and Langmuir–Blodgett Film Formation Studies

Two series of novel platinum(II) 2,6‐bis(1‐alkylpyrazol‐3‐yl)pyridyl (N5Cn) complexes, [Pt(N5Cn)Cl][X] ( 1 – 9 ) and [Pt(N5Cn)(C?CR)][X] ( 10 – 13 ) (X=trifluoromethanesulfonate (OTf) or PF₆; R=C₆H₅, C₆H₄‐p‐CF₃ and C₆H₄‐p‐N(C₆H₅)₂), with various chain lengths of the alkyl groups on the nitrogen atom of the pyrazolyl units have been successfully synthesized and characterized. Their electrochemical and photophysical properties have been studied. Some of their molecular structures have also been determined by X‐ray crystallography. Two amphiphilic platinum(II) 2,6‐bis(1‐tetradecylpyrazol‐3‐yl)pyridyl (N5C14) complexes, [Pt(N5C14)Cl]PF₆ ( 7 ) and [Pt(N5C14)(C?CC₆H₅)]PF₆ ( 13 ), were found to form stable and reproducible Langmuir–Blodgett (LB) films at the air–water interface. The characterization of such LB films has been investigated by the study of their surface pressure–area (π–A) isotherms, UV/Vis spectroscopy, XRD, X‐ray photoelectron spectroscopy (XPS), FTIR, and polarized IR spectroscopy. The luminescence property of 13 in LB films has also been studied.     

Influence of alkyl chain length of alpha olefin sulfonates on surface and interfacial properties

Alpha olefin sulfonates (AOS) with various alkyl chain lengths have been used to investigate the influence of alkyl chain length on the interfacial properties at air–water, liquid paraffin–water, and parafilm–water interfaces. It was found that the critical micelle concentration decreased with increasing alkyl chain length, while the efficiency of reducing surface tension was inverse relationship with alkyl chain length. The diffusion coefficient obviously reduced with an increase of surfactant concentration and alkyl chain length. The C_14-16AOS shows better wettability and emulsification than C_16-18AOS and C_20-24AOS. For foaming properties, the foamability and foam stability dramatically decreased with increasing alkyl chain length.     

Determination of trace volatile fatty acids in ambient air by capillary gas chromatography–mass spectrometry in SIM mode

A simple, rapid and sensitive method was developed and validated for the analysis of C₂–C₅ volatile fatty acids (VFAs) in ambient air. This method involves preconcentration of VFAs with a sodium carbonate-impregnated silica gel tube, ultrasonic extraction with pure water, partition of VFAs to diethyl ether and determination using gas chromatography with a mass selective detector in the selected ion monitoring mode. A water-resistant free fatty acid phase capillary column was used to directly separate C₂–C₅ VFAs without the time-consuming derivatisation process. The limits of detection ranged from 0.001 to 0.003 µg m^?3 and the limits of quantification ranged from 0.003 to 0.010 µg m^?3. The validated method was successfully applied to the analysis trace-level VFAs in ambient air and in air samples from a landfill with perceived odour pollution.     

Formation of alkyl nitrates from the reaction of branched and cyclic alkyl peroxy radicals with NO

The yields of C₅ and C₆ alkyl nitrates from neopentane, 2-methylbutane, 2-methylpentane, 3-methylpentane, and cyclohexane have been measured in irradiated CH₃ONONO-alkane-air mixtures at 298 ± 2 K and 735-torr total pressure. Additionally, OH radical rate constants for neopentyl nitrate, 3-nitro-2-methylbutane, 2-nitro-2-methylpentane, 2-nitro-3-methylpentane, and cyclohexyl nitrate, relative to that for n-butane, have been determined at 298 ± 2 K. Using a rate constant for the reaction of OH radicals with n-butane of 2.58 × 10^?12 cm³ molecule^?1 s^?1, these OH radical rate constants are (in units of 10^?12 cm³ molecule^?1 s^?1): neopentyl nitrate, 0.87 ± 0.21; cyclohexyl nitrate, 3.35 ± 0.36; 3-nitro-2-methylbutane, 1.75 ± 0.06; 2-nitro-2-methylpentane, 1.75 ± 0.22; and 2-nitro-3-methylpentane, 3.07 ± 0.08. After accounting for consumption of the alkyl nitrates by OH radical reaction and for the yields of the individual alkyl peroxy radicals formed in the reaction of OH radicals with the alkanes studied, the alkyl nitrate yields (which reflect the fraction of the individual RO₂ radicals reacting with NO to form RONO₂) determined were: neopentyl nitrate, 0.0513 ± 0.0053; cyclohexyl nitrate, 0.160 ± 0.015; 3-nitro-2-methylbutane, 0.109 ± 0.003; 2-nitro-2methylbutane, 0.0533 ± 0.0022; 2-nitro-2-methylpentane, 0.0350 ± 0.0096; 3- + 4-nitro-2-methylpentane, 0.165 ± 0.016; and 2-nitro-3-methylpentane, 0.140 ± 0.014. These results are discussed and compared with previous literature values for the alkyl nitrates formed from primary and secondary alkyl peroxy radicals generated from a series of n-alkanes.