Relaxed eddy accumulation, a new technique for measuring emission and deposition fluxes of volatile organic compounds by capillary gas chromatography and mass spectrometry.

The possibility afforded by a new relaxed eddy accumulation system in the determination of emission and deposition fluxes of volatile organic compounds (VOCs) by chromatographic techniques will be presented. The system, especially designed to limit sampling artifacts, uses adsorption traps filled with solid sorbents as reservoirs for VOC collection. Enriched compounds were analyzed by capillary GC and positive identification and quantification of eluted compounds was Achieved by mass-spectrometric detection. The method has been used to quantify the emission and deposition of both biogenic and anthropogenic VOCs over a Mediterranean forest ecosystem located in Central Italy. For the first time, both daily and seasonal trends of anthropogenic and biogenic VOCs will be reported. The consistency of monoterpene fluxes with predictions based on the knowledge of VOC emission from the dominant vegetation species will be tested. Data have been used to develop a novel algorithm to predict the seasonality of biogenic emission from the forest ecosystem.

Trace level determination of enantiomeric monoterpenes in terrestrial plant emission and in the atmosphere using a beta-cyclodextrin capillary column coupled with thermal desorption and mass spectrometry.

For the first time, enrichment on solid sorbents followed by thermal desorption has been used for the determination of the enantiomeric signature of monoterpenes in the gaseous emission of terrestrial plants. A beta-cyclodextrin capillary column has been used for the separation of critical pairs. The temperature program and column loading were optimized for making the accurate quantification of individual enantiomers possible by mass spectrometry. The resolution achieved was sufficient for separating enantiomeric monoterpenes from other biogenic and anthropogenic volatile organic compounds present in air and vegetation emission samples. The method has been applied to the determination of the enantiomeric ratios of monoterpenes in the gaseous emissions of some evergreen plants and in the open atmosphere.

Dynamic system for the calibration of semi-volatile carbonyl compounds in air.

A dynamic calibration system designed for generating accurate and precise concentrations of semi-volatile carbonyls in the ppb (v/v) (ppbv)-ppt (v/v) (pptv) range has been developed and tested. Alkanals from C6 to C9 were used as test compounds. Diffusion rates of their vapours from capillary tubes were determined theoretically and with two methods whose accuracy was independently evaluated with liquid standard solutions. Methods selected for testing the calibration system were those commonly used for the selective quantification of carbonyls in air. One is based on the well-known reaction with 2,4-dinitrophenylhydrazine (DNPH), followed by the analysis of formed hydrazones by HPLC-UV. The other is based on the retention of carbonyls on graphitic carbon adsorbents, followed by MS detection of the sample injected into a capillary column by thermal desorption. A good consistency was found between the values of the diffusion rates determined by the two methods. The scatter between the two methods was in the range of +/-10% when diffusion rates of ca. 1 ng/s were attained. Experimental values closely approached those calculated by applying the equation describing the diffusion of a vapour in equilibrium with the liquid through a capillary tube.

The volatile organic compounds from the mycelium of Tuber borchii Vitt.

The mycelium of T. borchii (characterized by DNA analysis) grown in sterile liquid medium produced some VOCs. The VOCs were retained on carbographs by passing a flow of helium, isolated and characterized in a GC-MS equipment after a thermal desorption. The compounds present in the VOCs from the mycelium cultures, but not in the VOCs from the control cultures, contained 29 compounds. The main compounds were 1,3-ditertbutylbenzene (16.1 ng/l), 3-methylheptane (9.2 ng/l), butan-2-one (8.8 ng/l), ethynylbenzene (5.6 ng/l), and octan-3-one (4.9 ng/l).

Simple laboratory-made system for the determination of C2-C7 hydrocarbons relevant to photochemical smog pollution.

A simple gas chromatographic system suitable for determining volatile organic compounds from C2 to C7 in air is described. It consists of a capillary cold trap filled with graphitic carbon, a thermodesorbing device, a capillary gas chromatograph equipped with an alumina column and a flame ionization detector. Dry, as well as humid, air samples can be analysed with our system. Up to 2-1 samples of air can be enriched on our trapping device by using Nafion membranes for removing water. Direct analysis of air samples is possible by enriching 250 ml on the carbon trap. The recovery, sensitivity and linearity of our system have been checked with standard mixtures and real samples. The performances have been compared with those afforded by a commercially available instrument exploiting a different enrichment procedure. The results obtained show that our analyser can be successfully applied to determinations of C2 to C7 hydrocarbons present in air samples at levels of 0.01 ppb (v/v).

Different sources of reduced carbon contribute to form three classes of terpenoid emitted by Quercus ilex L. leaves.

Quercus ilex L. leaves emit terpenes but do not have specialized structures for terpene storage. We exploited this unique feature to investigate terpene biosynthesis in intact leaves of Q. ilex. Light induction allowed us to distinguish three classes of terpenes: (i) a rapidly induced class including alpha-pinene; (ii) a more slowly induced class, including cis-beta-ocimene; and (iii) the most slowly induced class, including 3-methyl-3-buten-1-ol. Using 13C, we found that alpha-pinene and cis-beta-ocimene were labeled quickly and almost completely while there was a delay before label appeared in linalool and 3-methyl-3-buten-1-ol. The acetyl group of 3-methyl-3-buten-1-yl acetate was labeled quickly but label was limited to 20% of the moiety. It is suggested that the ocimene class of monoterpenes is made from one or more terpenes of the alpha-pinene class and that both classes are made entirely from reduced carbon pools inside the chloroplasts. Linalool and 3-methyl-3-buten-1-ol are made from a different pool of reduced carbon, possibly in nonphotosynthetic plastids. The acetyl group of the 3-methyl-3-buten-1-yl acetate is derived mostly from carbon that does not participate in photosynthetic reactions. Low humidity and prolonged exposure to light favored ocimenes emission and induced linalool emission. This may indicate conversion between terpene classes.

Evidence of the Photosynthetic Origin of Monoterpenes Emitted by Quercus ilex L. Leaves by 13C Labeling.

The carbon of the four main monoterpenes emitted by Quercus ilex L. leaves was completely labeled with 13C after a 20-min feeding with 99% 13CO2. This labeling time course is comparable with the labeling time course of isoprene, the terpenoid emitted by other Quercus species and synthesized in leaf chloroplasts. It is also comparable with that of phosphoglyceric acid. Our experiment therefore provides evidence that monoterpenes emitted by Q. ilex are formed from photosynthesis intermediates and may share the same synthetic pathway with isoprene. By analyzing the rate and the distribution of labeling in the different fragments, we looked for evidence of differential carbon labeling in the [alpha]-pinene emitted. However, the labeling pattern was quite uniform in the different fragments, suggesting that the carbon skeleton of the emitted monoterpenes comes from a unique carbon source.

Influence of Environmental Factors and Air Composition on the Emission of [alpha]-Pinene from Quercus ilex Leaves.

We studied the emission of [alpha]-pinene from Quercus ilex leaves. Only the abaxial side of the hypostomatous Q. ilex leaf emits [alpha]-pinene. Light induced photosynthesis and [alpha]-pinene emission. However, the response of photosynthesis to dark-to-light transitions was faster than that of [alpha]-pinene, suggesting that ATP controls the emission. The emission was higher at 30 than at 20[deg]C, whereas photosynthesis did not change. Therefore, the relationship between photosynthesis and [alpha]-pinene emission does not always hold. When CO2 was removed from the air, transpiration was stimulated but photosynthesis and [alpha]-pinene emission were inhibited. [alpha]-Pinene inhibition was more rapid under low O2. When CO2 in the air was increased, photosynthesis was stimulated and transpiration was reduced, but [alpha]-pinene emission was unaffected. Therefore, the emission depends on the availability of photosynthetic carbon, is not saturated at ambient CO2, and is not dependent on stomatal opening. The pattern of [alpha]-pinene emission from Q. ilex is different from that of plants having specialized structures for storage and emission of terpenes. We suggest that [alpha]-pinene emitted by Q. ilex leaves is synthesized in the chloroplasts and shares the same biochemical pathway with isoprene emitted by isoprene-emitting oak species.

Polar volatile organic compounds (VOC) of natural origin as precursors of ozone.

HRGC-MS determinations carried out on samples collected in urban, suburban, rural, forest and remote areas suggest that several other classes of non-methane VOC than isoprene and monoterpene hydrocarbons can be emitted by plants. Because of their high photochemical reactivity, they can contribute to tropospheric ozone production which, in turn, can cause climate changes through radiative forcing.

Characterization of oxidative and reductive metabolism in vitro of nitrofluoranthenes by rat liver enzymes.

Nitrofluoranthenes (NFs) are mutagenic and carcinogenic environmental pollutants found in incomplete combustion products and urban air particulate. We have studied both oxidative and reductive metabolism in vitro of different NF isomers mediated by subcellular rat liver fractions. Under aerobic conditions only ring hydroxylation of NFs by rat liver microsomes occurred and the isomeric position of the nitro group affected both the amount and the type of phenolic metabolites formed. Liver microsomes from 3-methylcholanthrene-induced rats were most effective in giving ring hydroxylated 7- and 8-nitrofluoranthene, whereas liver microsomes from phenobarbital-pretreated rats were the most active in metabolizing 1- and 3-nitrofluoranthene. Under anaerobic conditions, only reduction of NFs mediated by both cytosolic and microsomal rat liver enzymes occurred. Cofactor requirements and inhibition experiments indicated that the reductase activity in rat liver cytosolic fractions could be ascribed to DT-diaphorase, aldehyde oxidase and/or other unknown enzymes. The microsomal reductase activity was inhibited by oxygen, carbon monoxide, 2-diethylaminoethyl-2,2-diphenylvalerate hydrochloride and n-octylamine, and slightly by cytochrome c; flavin mononucleotide greatly enhanced this activity. 3-Nitrofluoranthene microsomal nitroreductase activity was increased by phenobarbital rat pretreatment and this increment correlated well with the content of cytochrome P450. These results indicate a participation of cytochrome P450 in the reductive metabolism of NFs by rat liver microsomes.

Experimental parameters affecting hypercoulometric response in gas-phase coulometry.

The response of an electron-capture detector designed for coulometric response was examined as a function of solute, pulse interval, carrier-gas type, solute amount, carrier-gas flow rate, and chromatographic-peak profile. For CCl3F, it was shown that the average numbers of electrons absorbed per molecule ranged from 1.0 to 4.1, varying primarily with pulse interval but also displaying a complex dependence on sample amount. Comparison of these results with theoretical expectations leads to the conclusion that a 1:1 "coulometric response" may not be observed under certain operating conditions. Because the specific conditions required depend on many variables, including, to some extent, sample amount, true coulometric operation of an electron-capture detector is difficult to establish and maintain. Effects which may contribute to the production of hypercoulometric response are critically discussed.

[Evaluation of atmospheric pollution in industrial environment using gas-chromatographic technics]. / Sulla valutazione dell'inquinamento atmosferico in ambienti industriali mediante tecniche gas cromatografiche.

Several analytical techniques for the evaluation of different classes of air pollutants that can be found in working places are described. Particularly an automatic apparatus for monitoring total organic substances less methane, and one, employing specific detection and selective columns for the automatic and continuous determination of light sulfur compounds, are described. An analytical procedure for trapping and selective analysis of organic substances is presented. This includes the description of trapping and enriching devices and of a semi-automatic apparatus for the gaschromatographic analysis of the samples trapped. Some applications of these analytical techniques are described.

Evaluation of organic pollutants in the open air and atmospheres in industrial sites using graphitized carbon black traps and gas chromatographic-mass spectrometric analysis with specific detectors.

A method for evaluating the organic content of the atmosphere, involving the use of personal samplers, is described. A comparison of the performances of Tenax GC and Carbopack B is given in terms of sample recovery. Apparatus including selective columns, specific detectors and combined gas chromatography-mass spectrometry is also described. Practical examples of the analysis of organic air pollutants trapped in the open air and the atmosphere in a chemical plant are discussed. A comparison of the results of complete gas chromatography and of the total hydrocarbon content is also made.