Volatiles Emission by Crotalaria nitens after Insect Attack

Plants are known to increase the emission of volatile organic compounds upon the damage of phytophagous insects. However, very little is known about the composition and temporal dynamics of volatiles released by wild plants of the genus Crotalaria (Fabaceae) attacked with the specialist lepidopteran caterpillar Utetheisa ornatrix (Linnaeus) (Erebidae). In this work, the herbivore-induced plant volatiles (HIPV) emitted by Crotalaria nitens Kunth plants were isolated with solid phase micro-extraction and the conventional purge and trap technique, and their identification was carried out by GC/MS. The poly-dimethylsiloxane/divinylbenzene fiber showed higher affinity for the extraction of apolar compounds (e.g., trans-β-caryophyllene) compared to the Porapak™-Q adsorbent from the purge & trap method that extracted more polar compounds (e.g., trans-nerolidol and indole). The compounds emitted by C. nitens were mainly green leaf volatile substances, terpenoids, aromatics, and aldoximes (isobutyraldoxime and 2-methylbutyraldoxime), whose maximum emission was six hours after the attack. The attack by caterpillars significantly increased the volatile compounds emission in the C. nitens leaves compared to those subjected to mechanical damage. This result indicated that the U. ornatrix caterpillar is responsible for generating a specific response in C. nitens plants. It was demonstrated that HIPVs repelled conspecific moths from attacked plants and favored oviposition in those without damage. The results showed the importance of volatiles in plant–insect interactions, as well as the choice of appropriate extraction and analytical methods for their study.     

Automated dynamic sampling system for the on-line monitoring of biogenic emissions from living organisms

An automated system for continuous on-line monitoring of biogenic emissions is presented. The system is designed in such a way that volatiles, emitted as reaction to biotic or abiotic stress, can be unequivocally elucidated. Two identical sampling units, named target and reference bulb, are therefore incorporated into the system and consecutively analyzed in monitoring experiments. A number of precautions were considered during these experiments to avoid the application of unwanted stress onto both organisms. Firstly, the system is constructed in such a way that both bulbs are continuously flushed, i.e. before, during and after analysis, with high purity air to avoid any accumulation of emitted volatiles. Moreover, the air is pre-humidified by bubbling it through water to sustain the biological samples for longer periods in the in vitro environment. Sorptive enrichment on polydimethylsiloxane (PDMS) was used to trap the headspace volatiles. The hydrophobic nature of this material permitted easy removal of trapped moisture by direct flushing of the sampling cartridge with dry air before desorption. The system was used to monitor the emissions from in vitro mechanically wounded ivy (Hedera helix) and of in vitro grown tomato plants (Lycopersicon esculentum Mill.) upon cotton leafworm (Spodoptera littoralis) feeding. Differences in light and dark floral emissions of jasmine (Jasminum polyanthum) were also studied.     

A recirculating system for concentrating volatile samples

Summary A recirculating system powered by a diaphragm pump which may be readily dismantled for cleaning, is described. The results of operating this system for dynamic headspace sampling in the closed or open mode to load volatiles onto a Tenax trap over a range of temperatures and loading volumes are shown. The system was designed to facilitate the analysis of volatiles in natural products and tested using an equimolar solution of 7 esters of boiling points ranging from 120°C to 299°C. The results showed that compounds in the boiling point range 120–200°C could be loaded onto the trap at 30°C by passing 1–21 of carrier gas through. In order to trap compounds of boiling points approaching 300°C, a temperature of 50–70°C and a loading volume of 2.5–3 1 was necessary. Using the apparatus, human sweat was analysed to show the degree of concentration possible with a natural sample and the variation in the chromatogram profiles of successive trapping from the same sample. Twelve chromatograms from the sweat of two pairs of identical twins were pattern matched to show the high degree of reproducibility possible using this apparatus to trap biological volatiles.     

Analysis of volatile organic compounds in polymers by dynamic headspace and gas chromatography/mass spectrometry

An experimental method for the analysis of volatile organic compounds in polymers is described. The technique involves dynamic headspace sampling, collection, and concentration of the volatiles in a cold trap, followed by capillary column gas chromatography/mass spectometry. Flow switching is carried out by the Deans switching technique. Four technical polymers used as pharmaceutical packaging materials have been analyzed in order to demonstrate the method.     

Applications of heart cutting from packed to capillary columns

The power of capillary gas chromatography can be enhanced by selective fractionation of the sample. One way of doing this is heart cutting from a packed gas chromatographic column. This paper describes modification of a commercial instrument for such separations. Components of the system include an automated Deans switch and an electrically heated trap. The benefits of this arrangement are illustrated with chromatograms of naphtha, urinary aromatic acids, and wine volatiles.     

Analysis of headspace samples using off-line sorbent trapping coupled with automated thermal desorption and splitless injection onto a cryogenically cooled wide bore capillary column

Gas chromatographic equipment and procedures are described for automated splitless injection of pseudo-static headspace samples collected externally onto a sorbent trap. The GC microprocessor controls, in sequence, carrier gas backflushing of the sorbent trap for water removal, splitless thermal desorption into a cryogenically cooled wide bore (0.53 mm i. d.) capillary column and oven temperature programming. The method has been routinely applied for profiling the mid-to-high boiling compounds (bp 80–225°C) in the headspace of a variety of foods and beverages. Method criteria, advantages and limitations are discussed. FID and NPD chromatograms for brewed coffee and peanut butter volatiles are presented as typical examples.     

Dynamic headspace enrichment system for CGC analysis of volatiles released by plants

The aim of the present study is to develop a method for following the changes in the chemical composition of volatile substances released by plants. Dynamic headspace enrichment, followed by on-line thermal desorption and cryotrapping was coupled with capillary gas chromatography. The technique was optimized by adjusting the sampling and desorption parameters and by designing a special condensing device to avoid the transfer of excessive amounts of water into the analytical column. Details are given for the characterization of volatiles compounds released by mosses.     

Dynamic headspace enrichment/reinjection for open tubular GC/FTIR analysis of volatiles in polymers

An analytical system for the analysis of volatiles entrained in polymers is described. This system is based on a thermal desorption oven connected to a cold trap. After enrichment of headspace vapor, trapped material is reinjected and analyzed by open tubular gas chromatography/Fourier transform infrared spectroscopy, OTGC/FTIR. The thermal desorption oven is designed to provide different modes of sample introduction: use of a pyroprobe; insertion of a piece of quartz tubing with applied sample; or syringe injection. Headspace enrichment is carried out in a piece of fused silica capillary tubing filled with glass beads. The trap may be cooled either electrically using Peltier elements or with liquid nitrogen. A six-port rotary valve is used for flow switching between enrichment and reinjection modes. All system parameters, temperatures, and timed events, are controlled from the gas chromatograph. Dynamic headspace analysis is demonstrated as a method for polymer characterization.     

An Improved Method for Testing Weak VOCs in Dry Plants with a Purge and Trap Concentrator Coupled to GC-MS

The purge and trap (P&T) technique was improved for measuring the release of organic compounds with weak volatility (weak VOCs) from dry plant materials. Using distilled water as a dispersant, the plant tissues were mulled and placed in the purge tube of a P&T concentrator. Then the sample-containing purge tube was heated to 80 °C with helium as the carrier gas, and the purged volatiles were preconcentrated in the trap prior to analysis with GC-MS. The VOCs in Chinese herbal medicinal plants Swertia tetraptera, Saussurea involucrate and S. lacostei, which had been stored dry for 1–2.5 years were assayed with this improved method and conventional P&T techniques. Our results show this new P&T method had great promise for determining the VOCs in dry plant materials. Using this new technique, we identified 38 weak VOCs with a large peak area from the dry samples. In contrast, less than five VOCs were detected by the conventional P&T method. So the improved heat-purge and trap system showed to be more efficient for measuring the release of the weak VOCs from dry plant materials.     

Leaf volatiles and secretory cells of Alpinia zerumbet (Pers.) Burtt et Smith (Zingiberaceae)

Plant leaves are commonly used in folk medicine and food industry. Their volatile composition is an important determinant in such applications. However, to properly assess the quality of volatiles, proper analytic tools must be utilised. Accordingly, the static headspace technique was used to evaluate the main volatiles emitted from in vitro-grown Alpinia zerumbet plants cultured with indole-3-acetic acid, thidiazuron, benzyladenine or kinetin, under standard physical conditions, as compared to those of field-grown donor plants. Although the leaf aroma of the donor plants was found to be a complex mixture, mainly consisting of sabinene, α and γ-terpinene, 1,8-cineole and caryophyllene, volatile analyses from most of the in vitro samples only revealed the presence of sabinene and caryophyllene. Many alkanes were found in the aromas after treating plantlets with cytokinins. Histochemical analysis of leaf sections was also carried out. Secretory cells found in the epidermis and mesophyll showed a strong positive reaction to lipophilic compounds using Oil red and Nile blue reagents. These findings demonstrated how in vitro conditions may alter the quality of volatiles in micropropagation systems, while leaf anatomy analysis revealed a large quantity of oil cells in the mesophyll as a constant feature responsible for the production of volatile compounds in both donor and in vitro-grown plants.     

Analysis of volatiles and semivolatiles in drinking water by microextraction and thermal desorption

A new technique to analyze aqueous samples for nanograms per liter levels of volatile and semivolatile compounds using microextraction and thermal desorption into a gas chromatograph/ion trap mass spectrometer (GC/MS) is described. This method is inherently sensitive (50 mL of aqueous sample is extracted prior to each desorption), uses no solvents, and detects volatiles and semivolatiles in the same analysis. Aqueous standards and environmental samples are pumped through a length of porous-layer open-tubular capillary column, which is then thermally desorbed onto a 30 m × 0.25 mm i.d. analytical column interfaced to an ion trap mass spectrometer for subsequent separation and detection. Sharp chromatographic peaks and reproducible retention times (RT) were observed. Replicate injections of surrogates (n = 6) averaged 32.6% R.S.D. Analysis of domestic tap water detected 55 analytes, some at the low-nanograms per liter level, and detected 3 halogenated ethenes, not previously reported in drinking water. Analysis of an aqueous sample from a municipal ground water source detected the presence of numerous semivolatile compounds at trace-levels.     

A novel system for purge-and-trap with thermal desorption: Optimization using tomato juice volatile compounds

A system for purge-and -trap with thermal desorption was developed and optimized to moniotor aroma compounds at ambient temperatures. Canned tomato juice volatiles were used as a model system to develop and evaluate the method. Volatile components were first adsorbed on insert-traps packed with Tenax-TA polymer, then thermally desorbed directly inside a gas chromatograph injector. Volatile matgerials occuring in Very low amounts could be entrained and subsequently chrfomatographed, with sensitivity limited by the purity of the sweep gas. Quantitative measurement of tomato juice volatiles was linear with sample size upn to 100 gram samples. The amount of trapped volatiles was proportional to trapping time; howver, low-and intermediate-boilers broke through the trap after one hour while high-boilers continued to be retained. Apurge gas flow rate of 20ml/min gave optimum results mediate-biolers. Optimum recovery of volatile compounds was obtained with a desorption temperature of 200°c for 5 min. Coefficients of variation from triplicate runs were relatively small. The method showed promise for a simple, sensitive, and reproducibel flavor volatiles collection system for the accurate analysis of tomato compounds.     

Gas chromatographic-mass spectrometric analysis of some potential toxicants amongst volatile compounds emitted during large-scale thermal degradation of poly(acrylonitrile-butadiene-styrene) plastic

A number of compounds emitted during the thermal degradation of plastics are potentially toxic. This study was aimed at identifying the volatile compounds emitted during large-scale thermal degradation of poly(acrylonitrile-butadiene-styrene). About 5 g of the sample were degraded at between 25 and 470 degrees C in air and nitrogen in a device that can simulate temperature-programmed thermogravimetry. The volatiles were collected in dichloromethane using the solvent trap technique. Some of the 92 compounds identified by gas chromatography-mass spectrometry were found to have no hitherto documented toxicological profiles, even though they are potentially dangerous.     

Simultaneous determination of sulphide and sulphite by gas-phase molecular absorption spectrometry. Comparative study of different calculation methods

A method for the simultaneous determination of sulphide and sulphite is described, which involves continuous H(2)S and SO(2) generation, preconcentration in a liquid nitrogen trap and measurement of the molecular absorption spectra of volatiles in the gas phase in 190-220 nm range. Under the recommended conditions (sample flow: 50 ml/min and concentrated sulphuric acid flow: 12 ml/min; generation time: 4 min) linear response ranges from 0.05 mug/ml for S(2-) and 0.20 mug/ml SO(2-)(3) are obtained with detection limits of 0.05 and 0.20 mug/ml respectively. Synthetic mixtures of the two components have been solved and a comparative study of different calculation methods has been made. In conclusion, multiwavelength methods offer better precision and accuracy.     

Duftstoffe: Die Sprache der Pflanzen. Signalrezeption,Biosynthese und Ökologie

Plants respond with coordinated actions to threats from their environment. After being attacked by a herbivorous insect, plants are able to emit a complex blend of volatiles, which attract carnivorous arthropods that reduce the number of herbivores and thus benefit the plant. By modulating the emitted volatile spectrum, plants are able to transmit information on type and intensity of their infestation to their defenders. Using either various elicitors from the saliva secretion of the herbivore or differences in the spatio‐temporal pattern of wounding, the plant is able to discriminate between different herbivore species. Subsequently, a complex signalling network ensures the specific reaction to various stresses. Moreover, also plant roots are able to emit volatiles upon attack to attract the predators of root‐feeding insects. New studies suggest that plants may also be able to communicate with each other: By “eavesdropping” on their damaged neighbour, plants of the same or another species can use the information on a currently increased risk of being attacked by herbivores and, as a precaution, activate its own defences. However, most of these interactions between plants and other organisms have been studied mainly under laboratory conditions and we are only starting to understand the ecology of these mechanisms in nature.     

On-line analysis of volatile chlorinated hydrocarbons in air by gas chromatography–mass spectrometry: Improvements in preconcentration and injection steps

An analytical system composed of a cryofocusing trap injector device coupled to a gas chromatograph with mass spectrometric detection (CTI-GC–MS) specific for the on-line analysis in air of volatile chlorinated hydrocarbons (VCHCs) (dichloromethane; chloroform; 1,1,1-trichloroethane; tetrachloromethane; 1,1,2-trichloroethylene; tetrachloroethylene) was developed. The cryofocusing trap injector was the result of appropriate low cost modifications to an original purge-and-trap device to make it suitable for direct air analysis even in the case of only slightly contaminated air samples, such as those from remote zones. The CTI device can rapidly and easily be rearranged into the purge-and-trap allowing water and air analysis with the same apparatus. Air samples, collected in stainless steel canisters, were introduced directly into the CTI-GC–MS system to realize cryo-concentration (at −120 °C), thermal desorption (at 200 °C) and for the subsequent analysis of volatiles. The operating phases and conditions were customised and optimized. Recovery efficiency was optimized in terms of moisture removal, cold trap temperature and sampling mass flow. The injection of entrapped volatiles was realized through a direct transfer with high chromatographic reliability (capillary column–capillary column). These improvements allowed obtaining limits of detection (LODs) at least one order of magnitude lower than current LODs for the investigated substances. The method was successfully employed on real samples: air from urban and rural areas and air from remote zones such as Antarctica.     

Multi-channel open tubular traps for headspace sampling, gas chromatographic fraction collection and olfactory assessment of milk volatiles

A headspace sampling method is described for concentrating milk volatiles onto a multi-channel open tubular silicone rubber trap (MCT) for thermal desorption into a GC-FID. Sections of the chromatographic profile, single peaks or combinations of compounds are recaptured with secondary MCTs during a subsequent run. The recaptured aroma is released in a controlled manner by heating the MCT in a portable heating device. An aroma release window of several minutes allows up to six people the opportunity to sniff each aroma fraction more than once. Olfactory results suggest that a synergistic combination of 2-heptanone and 2-nonanone could be responsible for a pungent cheese, sour milk-like aroma. MCTs containing single components or fractions can be desorbed into a GC-MS for compound identification.     

Comparison of two methods based on dynamic head-space for GC-MS analysis of volatile components of cheeses

Summary Two methods based in dynamic headspace sampling have been compared for GC/MS analysis of volatile components in hard cheeses (Manchego and other ewe’s milk varieties). In the first approach a purge & trap concentrator allowed volatile on-line determination with reduced sample handling. The second method consisted of a manual device for trapping dinamically purged volatiles, which were then anaysed by using an automatic thermal desorption system, coupled on-line with a GC-MS. The influence of the most significant operating parameters (desorption times, flows and temperatures) on recovery and repeatability was studied for both methods. Automatic purge & trap gave the best sensitivity and repeatability for high valatility components, probably because its on-line operation mode, while the second procedure allowed the determination of a greater number of volatile components and gave better yields for fatty acids and other medium volatility components.     

Electroanalytical studies on green leaf volatiles for potential sensor development

An electrochemical study for detecting green leaf plant volatiles from healthy and infected plants has been devised and tested. The electrocatalytic response of plant volatiles at a gold electrode was measured using cyclic voltammetry, amperometric current-time (i-t) analysis, differential pulse voltammetry (DPV) and hydrodynamic experiments. The sensitivity of the gold electrode in i-t analysis was 0.13 mA mM(-1) cm(-2) for cis-3-hexenol, 0.11 mA mM(-1) cm(-2) for cis-hexenyl acetate and 0.02 mA mM(-1) cm(-2) for hexyl acetate. The limits of detection of cis-3-hexenol, cis-hexenyl acetate and hexyl acetate by i-t analysis were 0.5, 0.3 and 0.6 μM, respectively, at a signal to noise ratio of 3. The hydrodynamic studies yielded the electro-kinetic parameters such as diffusivities of plant volatiles in solution and the rate constants for their electrochemical reactions. The DPV and interference studies reveal that the gold electrode possessed high sensitivity for plant volatiles determination in synthetic samples, which imitates both healthy and infected plants.     

Trapping system for trace organic volatiles.

A technique is described for the collection and concentration of volatile compounds produced by plants, insects, animals and other materials. The method is a modification of the continuous-flow system based on absorption of volatiles in a low amount of solvent at low temperature. The advantages and disadvantages of the technique used are described in detail.