Quantification of oxygenated volatile organic compounds in seawater by membrane inlet-proton transfer reaction/mass spectrometry

The role of the ocean in the cycling of oxygenated volatile organic compounds (OVOCs) remains largely unanswered due to a paucity of datasets. We describe the method development of a membrane inlet-proton transfer reaction/mass spectrometer (MI-PTR/MS) as an efficient method of analysing methanol, acetaldehyde and acetone in seawater. Validation of the technique with water standards shows that the optimised responses are linear and reproducible. Limits of detection are 27 nM for methanol, 0.7 nM for acetaldehyde and 0.3 nM for acetone. Acetone and acetaldehyde concentrations generated by MI-PTR/MS are compared to a second, independent method based on purge and trap-gas chromatography/flame ionisation detection (P&T-GC/FID) and show excellent agreement. Chromatographic separation of isomeric species acetone and propanal permits correction to mass 59 signal generated by the PTR/MS and overcomes a known uncertainty in reporting acetone concentrations via mass spectrometry. A third bioassay technique using radiolabelled acetone further supported the result generated by this method. We present the development and optimisation of the MI-PTR/MS technique as a reliable and convenient tool for analysing seawater samples for these trace gases. We compare this method with other analytical techniques and discuss its potential use in improving the current understanding of the cycling of oceanic OVOCs.     

Rate constants for the OH reactions with oxygenated organic compounds in aqueous solution

The kinetics of the oxidation of functionalized organic compounds of atmospheric relevance by the hydroxyl radical (OH) was measured in the aqueous phase. Competition kinetics, using the thiocyanate anion (SCN^?) as competitor, was applied using both a laser flash photolysis long path absorption (LP‐LPA) setup and a Teflon AF waveguide photolysis (WP) system. Both experiments were intercompared and validated by measuring the rate coefficients for the reaction between OH and acetone where values of k₁ = (1.8 ± 0.4) × 10⁸ M^?1 s^?1 were obtained with the WP system, which agrees very well with the rate constant of k₁ = (2.1 ± 0.6) × 10⁸ M^?1 s^?1 determined before by LP‐LPLA [1]. The following temperature dependencies of the rate constants (M^?1 s^?1) for the reactions of OH with ketones, dicarboxylic acids, and unsaturated compounds were obtained in Arrhenius' form: Reaction of OH with: methylisobutyl ketone (MIBK): k₂ = (1.0 ± 0.1) × 10¹²

     

Development and validation of an automated monitoring system for oxygenated volatile organic compounds and nitrile compounds in ambient air

Few studies were conducted on oxygenated volatile organic compounds (OVOC) because of problems encountered during the sampling/analyzing steps induced by water in sampled air. Consequently, there is a lack of knowledge of their spatial and temporal trends and their origins in ambient air. In this study, an analyzer consisted of a thermal desorber (TD) interfaced with a gas chromatograph (GC) and a flame ionization detector (FID) was developed for online measurements of 18 OVOC in ambient air including 4 alcohols, 6 aldehydes, 3 ketones, 3 ethers, 2 esters and 4 nitriles. The main difficulty was to overcome the humidity effect without loss of compounds. Water amount in the sampled air was reduced by the trap composition (two hydrophobic graphitized carbons—Carbopack B:Carbopack X), the trap temperature (held at 12.5 °C), by diluting (50:50) the sample with dry air before the preconcentration step and a trap purge with helium. Humidity management allowed the use of a polar CP-Lowox column in order to separate the polar compounds from the hydrocarbon/aromatic matrix. The safe sampling volume for the dual-sorbent trap 75 mg Carbopack X:5 mg Carbopack B was found to 405 mL for ethanol by analyzing a standard mixture at a relative humidity of 80%. Detection limits ranging from 10 ppt for ETBE to 90 ppt for ethanol were obtained for 18 compounds for a sampling volume of 405 mL. Good repeatabilities were obtained at two levels of concentration (relative standard deviation <5%). The calibration (ranging from 0.5 to 10 ppb) was set up at three different levels of relative humidity to test the humidity effect on the response coefficients. Results showed that the response coefficients of all compounds were less affected by humidity except for those of ethanol and acetonitrile (decrease respectively of 30% and 20%). The target compounds analysis shows good reproducibility with response coefficient variability of less then 10% of the mean initial value of calibration for all the compounds. Hourly ambient air measurements were conducted in an urban site in order to test this method. On the basis of these measurements, ethanol, acetone and acetaldehyde have shown the highest concentration levels with an average of 2.10, 1.75 and 1.37 ppb respectively. The daily evolution of some OVOC, namely ethanol and acetaldehyde, was attributed to emissions from motor vehicles while acetone has a different temporal evolution that can be probably associated with remote sources.     

Determination of oxygenated compounds in secondary organic aerosol from isoprene and toluene smog chamber experiments

The determination of multifunctional oxygenated compounds in secondary organic aerosols (SOA) usually requires a derivatisation protocol prior to gas chromatography-mass spectrometry analysis (GC-MS). Our proposed protocol, a combination of O-(2,3,4,5,6-pentafluorobenzyl) hydroxylamine (PFBHA) plus diluted N-methyl-N-trimethyl-silyltrifluoroacetamide (MSTFA) without catalyst, has improved the determination of carbonyls, polyhydroxyl-compounds, hydroxyl-carbonyls, hydroxyl-carboxylic acids and di-carboxylic acids. The optimised derivatisation protocol has been successfully used for blanks, standard mixtures and photo-oxidation products from isoprene and toluene generated in a high-volume simulation chamber (European Photoreactor, EUPHORE).

Some previously identified degradation products for isoprene including tetrols such as threitol, erythritol; 2-methyltetrols and 2-methylglyceric acid; and for toluene including nitrophenols, methyl-nitrophenols, benzaldehyde, p-cresol, benzoic acid, glyoxylic acid and methyl-glyoxylic acid, have been identified in our aerosol samples, thus confirming the successful applicability of the proposed derivatisation protocol. Moreover, the reduction of artefacts and enhanced signal-to-noise ratio, have allowed us to extend the number of multifunctional compounds determined. These findings have demonstrated the validity of this analytical strategy, which will contribute to a better understanding of the atmospheric degradation chemistry of biogenic and anthropogenic pollutants.     

Measurement of triplet extinction coefficients of organic compounds by McClure's method

We tested McClure's method for measuring the triplet extinction coefficients ε_T of organic compounds on anthracene and pyrene, using the u.v. lines from a krypton ion cw laser as a steady-state excitation source. Our values for anthracene ε_T = 82 × 10³1/mole cm at 426 nm and pyrene ε_T = 37 × 10³l/mole cm at 413 nm agree well with values obtained by other methods. McClure derived his linear relationship from kinetic considerations. One simply measures triplet optical densities (OD_T) at a fixed wavelength (e.g. at a triplet absorption maximum) as functions of different cw laser excitation intensities (powers) I_ex. A plot of 1/OD_T against 1/I_ex yields a straight line. Extrapolating to the intersection of the ordinate (1/I_ex = 0, or I_ex = ∞) yields 1/OD^∞_T. Since, at infinite excitation intensity I_ex, the concentration of the triplet state molecules N_T is equal to the original concentration N_S of the ground state concentration, ε_T can be easily calculated from ε_T = OD^∞_T/N_Sd where OD^∞_T is the triplet optical density at infinite excitation intensity, N _S is the original concentration of molecules (at ground state), and d is the thickness of the sample. The success of this method requires the production of high concentrations of triplet state molecules N_T, as well as steady-state excitation. CW lasers fulfill all these requirements. We discuss the spectroscopic equipment employed for measuring triplet optical densities in some detail. Methods for reducing heat gradients (noise) in liquid nitrogen, laser excitation spot sizes, reduction of spherical aberrations, etc., are reviewed. We varied the cw laser illumination density (laser power/area) by setting the focusing lens at different distances from the sample, and measured 1/OD_T as a function of 1/I_ex. As long as the size of the excitation area was not below a critical size, all the straight lines obtained at different lens settings converged well into only one value of 1/OD^∞_T. Measurements were also performed at different concentrations of the solutes.     

Prediction of FCC gasoline octane numbers using FT-MIR and PLS

A method for predicting "octane numbers" (RON and MON) in fluid catalytic cracking (FCC) gasolines is proposed. Using FT-MIR and PLS, improvements have been obtained in sample throughput, reduced delay times, accuracy (repeatability and reproducibility), amounts of samples and reagents and environmental working conditions when compared with current standard methods. A total number of 140 daily production samples were taken; and from there, a learning group was prepared (44 samples); a validation set (96 samples) was prepared, as well. Sample spectra were recorded from 4000 to 600 cm(-1) at 4 cm(-1) intervals (traditional sealed NaCl cells). The PLS technique was used in its two variants (1 and 2-block). Both provided similar results. Their predictive characteristics are very good: SEP(RON)=0.38; SEP(MON)=0.40; repeatability <0.1 O.N.; reproducibility <0.3 O.N. (SEP=Standard Error of Prediction).     

Prediction of FCC gasoline octane numbers using FT-MIR and PLS

A method for predicting octane numbers (RON and MON) in fluid catalytic cracking (FCC) gasolines is proposed. Using FT-MIR and PLS, improvements have been obtained in sample throughput, reduced delay times, accuracy (repeatability and reproducibility), amounts of samples and reagents and environmental working conditions when compared with current standard methods. A total number of 140 daily production samples were taken; and from there, a learning group was prepared (44 samples); a validation set (96 samples) was prepared, as well. Sample spectra were recorded from 4000 to 600 cm^-1 at 4 cm^-1 intervals (traditional sealed NaCl cells). The PLS technique was used in its two variants (1 and 2-block). Both provided similar results. Their predictive characteristics are very good: SEP_RON=0.38; SEP_MON=0.40; repeatability <0.1 O.N.; reproducibility <0.3 O.N. (SEP=Standard Error of Prediction).     

Kinetics of the reactions of OH radicals with some oxygenated volatile organic compounds under simulated atmospheric conditions

Some relative rate experiments have been carried out at room temperature and at atmospheric pressure. This concerns the OH-oxidation of some oxygenated volatile organic compounds including methanol (k₁), ethanol (k₂), MTBE (k₃), ethyl acetate (k₄), n-propyl acetate (k₅), isopropyl acetate (k₆), n-butyl acetate (k₇), isobutyl acetate (k₈), and t-butyl acetate (k₉). The experiments were performed in a Teflon-film bag smog chamber. The rate constants obtained are (in cm³ molecule⁻¹ s⁻¹): k₁=(0.90±0.08)×10⁻¹²; k₂=(3.88±0.11)×10⁻¹²; k₃=(2.98±0.06)×10⁻¹²; k₄=(1.73±0.20)×10⁻¹²; k₅=(3.56±0.15)×10⁻¹²; k₆=(3.97±0.18)×10⁻¹²; k₇=(5.78±0.15)×10⁻¹²; k₈=(6.77±0.30)×10⁻¹²; and k₉=(0.56±0.11)×10⁻¹². The agreement between the obtained rate constants and some previously published data has allowed for most of the studied compounds to point out a coherent group of values and to suggest recommended values. Atmospheric implications are also discussed. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 839–847, 1998     

Chromatoconductometric method of determining sulfur in organic compounds

Conclusions Achromatoconductometric method was developed for the determination of sulfur in organic compounds. The length of the determination is 10 min and the accuracy is ± 0.3 abs.%.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 964–965, April, 1969.     

Determination of oxygenated volatile organic compounds in ambient air using canister collection-gas chromatography/mass spectrometry.

This research attempts to establish a method to measure 11 kinds of oxygenated volatile organic compound (OVOC) in ambient air by using the canister collection-gas chromatography/mass spectrometry (GC/MS) method. Since several compounds such as acetone exhibited high blank concentrations due to their laboratory use, stringent quality control was conducted for the VOC-free added water and the VOC-free nitrogen gas. In order to prevent the decline of recovery rates due to lack of sufficient relative humidity, it is necessary to add VOC-free water when pressurizing and diluting the air samples. Thus, all the target compounds in ambient air were obtained from the canisters at high recovery rates without significant contamination. Furthermore, the canister collection-GC/MS method makes it possible to apply simultaneous air monitoring of OVOCs as well as volatile hazardous air pollutants without additional sampling.     

应用图论方法探索烷烃异构系列辛烷值的变化规律

考察了10种常用拓扑指数与烷烃辛烷值的相关关系, 探索了结构排序法预测烷烃辛烷值的变化趋势及其分布规律。     

Aerobic oxidation of organic compounds catalyzed by vanadium compounds

Aerobic oxidation of α-hydroxy ketones catalyzed by dichloroethoxyoxovanadium in ethanol causes a carbon–carbon bond cleavage that produces diesters or diketones. This reaction is highly chemoselective, and disecondary glycols do not react at all. However, ditertiary glycols effectively react with dichloroethoxyoxovanadium or trichlorooxovanadium to provide the corresponding ketones. Aerobic oxidation of α-hydroxy ketones catalyzed by dichloroethoxyoxovanadium or trichlorooxovanadium in aprotic solvents almost quantitatively affords the corresponding α-diketones. The reaction of tertiary cyclopropanol compounds with vanadyl acetylacetonate under an oxygen atmosphere causes fragmentation of the cyclopropane moiety to produce β-hydroxy ketones and β-diketones. For the 6-substituted bicyclo[4.1.0]heptanol derivatives, the endoperoxides are also obtained together with β-hydroxy ketones. Conversely, 2-ethoxycarbonylcyclopropyl silyl ethers produce γ-oxocarboxylate derivatives given the same reaction conditions. Monothioacetals are easily deprotected into carbonyls using a catalytic amount of trichlorooxovanadium in 2,2,2-trifluoroethanol under an oxygen atmosphere. Thiols are converted into the corresponding disulfides by the aerobic oxidation catalyzed by trichlorooxovanadium in the presence of molecular sieves 3A. Polymer-supported vanadium compounds are synthesized by the reaction of vanadium oxytrichloride with polymers bearing hydroxyl moieties. The catalyst prepared from TentaGel S OH was highly active and reusable for the aerobic oxidations.     

Determination of iodine in organic iodine compounds by the non-equilibrium isotopic exchange method

A new type of the isotope exchange method of analysis is proposed. The method can be applied to the exchange system in which the rate of the exchange reaction is rather slow but measurable, before the exchange equilibrium is attained. The validity of the principle of the method is verified experimentally with several exchange systems of RyI+KI^*⇌RyI^*+KI (RyI stands for alkyl, alkylene or benzyl iodide) type. The iodine content of the organic iodine compounds can be determined with an error of ±4%.