Gas Phase Extraction Research Articles

Analysis of Temperature Effect on the Gasoline Evaporation in Fire Investigation by HS-GC-MS

ABSTRACT The aim of the research is to determine changes in the composition of selected gasoline compounds in cotton carpet samples due to different weathering times. EVO 95 gasoline was used as a fire accelerant and a cotton carpet was used as a matrix. The samples were exposed to various weathering durations (0–360 min) in laboratory conditions. We investigated samples that were unburnt (only weathered) and samples that were burned and subsequently subjected to further weathering. Residual gasoline compounds in carpet samples were determined by gas phase extraction (headspace – HS) coupled with gas chromatography (GC) and mass spectrometry (MS). We focused on the comparison of selected gasoline compounds; toluene, ethylbenzene, p-xylene, 1,2,3-trimethylbenzene (TMB), 1,3,5-trimethylbenzene and naphthalene. The biggest changes were determined in the reduction of the intensity of most volatile compounds (alkylalkanes), where toluene decreased by 11.92%. A similar but not so pronounced trend, occurred in the burned samples, where toluene decreased by 7.40%. Minor changes occurred in alkyl derivatives of benzene, where some of the total 15 gasoline markers also occur, e.g. (1,2,3-trimethylbenzene, 1,3,5-trimethylbenzene). On the contrary, naphthalene as a heavier compound showed an increase in intensity about 0.42%. For burnt samples, the increase was 1.31%. The results show that largest changes can be observed after four or five hours of weathering, which implies the need for rapid sampling and subsequent timely analysis.

Study on radius of influence of groundwater circulation well in the field experiment

In recent years, groundwater circulation wells (GCW) have gradually become a research hotspot as an In-situ remediation technology. This technology reduces the construction of gas phase extraction wells and saves underground space compared to the traditional Air sparging (AS) remediation technology, the remediation process involves both volatile removal and microbial degradation. This study fully combines the background conditions of an organic contamination site and designs a positive circulation airflow lift circulation well. By analyzing the diffusion law of chloride tracer with aeration time and the changes of water level and water pressure of the monitoring well, it is known that the influence radius of the circulation well can be stabilized at 5.00 m when the aeration volume is 10 L/min. It not only has an essential demonstration significance for the development of groundwater circulation well remediation technology, but also provides reference process parameters for subsequent applications in type site remediation engineering applications.

Rapid Fabrication of Superhydrophobic Virtual Walls for Microfluidic Gas Extraction and Sensing.

Based on the virtual walls concept, where fluids are guided by wettability, we demonstrate the application of a gas phase extraction microfluidic chip. Unlike in previous work, the chip is prepared using a simple, rapid, and low-cost fabrication method. Channels were cut into double-sided adhesive tape (280 µm thick) and bonded to hydrophilic glass slides. The tape was selectively made superhydrophobic by ‘dusting’ with hydrophobic silica gel to enhance the wettability contrast at the virtual walls. Finally, the two glass slides were bonded using tape, which acts as a spacer for gas transport from/to the guided liquids. In our example, the virtual walls create a stable liquid–vapor–liquid flow configuration for the extraction of a volatile analyte (ammonia), from one liquid stream to the other through the intermediate vapor phase. The collector stream contained a pH indicator to visualize the mass transport. Quantitative analysis of ammonium hydroxide in the sample stream (<1 mM) was possible using a characteristic onset time, where the first pH change in the collector stream was detected. The effect of gap length, flow rates, and pH of the collector stream on the onset time is demonstrated. Finally, we demonstrate the analysis of ammonium hydroxide in artificial human saliva to show that the virtual walls chip is suitable for extracting volatile analytes from biofluids.

In vitro evaluation of the cytotoxicity, mutagenicity and DNA damage induced by particle matter and gaseous emissions from a medium-duty diesel vehicle under real driving conditions using palm oil biodiesel blends

The influence of palm oil biodiesel content on the cytotoxicity, mutagenicity and genotoxicity of particle- and gas-phase diesel vehicle emissions was investigated. The emissions were collected on-board of a EURO IV diesel truck, fuelled with mixtures of 10% (B10), 20% (B20) and 100% (B100) of palm oil biodiesel, under real driving conditions. Organic extracts of the particulate matter (PM) and gases were characterised for 17 PAH (including EPA priority) and used for the biological assay. Increasing biodiesel content in the fuel mixture results in a decrease in the PM and PAH emission factors, both in the particulate and gas-phase. The majority of the PAH are present in the gas-phase. The mutagenic potencies, in TA98 bacteria, are higher for B20 in both phases, whereas the mutagenicity emission factor, that takes into account the lower emission of PM and PAH, is not significantly different between the fuels. Higher direct mutagenicity (TA98 + S9) is observed in all the tested fuels, indicating the action of carcinogenic compounds other than non-substituted PAH. The gas-phase extracts present higher cytotoxicity and genotoxicity in lung epithelial cell A549, which may be related to the higher PAH content in the gas-phase. The increase in biodiesel content have a different impact on cytotoxicity, being larger in the gas-phase and lower in the particle-phase. This indicates that pulmonary toxicity may be higher for the gaseous emissions, due to the role of different toxic compounds compared to the PM. The adverse biological effects when biodiesel content increases are not consequent with the reduction of the PAH characterised, indicating that other toxic compounds are more relevant. Further investigations to identify these compounds are required in order to update and focus the efforts regarding emission targets and controls.

CFD modeling and simulation of gas-phase extraction processes in fluidized bed reactor

Recently, the gas-phase organic ligand extraction of metals from low-grade sources using the fluidized bed reactor (FBR) technique has garnered significant attention owing to its simplicity and advantages in reducing energy costs. In this study, a computational fluid dynamics (CFD) coupled model including a three-phase Eulerian model, kinetic theory of granular flow model, and reaction kinetics model was proposed to investigate gas-phase extraction processes encountered in an FBR. The developed three-phase CFD coupled model was first validated by comparing the obtained simulation results with the experimental data of cumulative iron extraction at different reaction temperatures and the classical calculated data of the pressure drop. Subsequently, the effects of the inlet gas velocity and particle phase holdup on the extraction were studied. Accordingly, both particle fluidization behaviors and extractive reaction kinetics characteristics were obtained. The simulation results indicated that the mentioned operating conditions significantly affected the distribution of particle phase holdup and subsequently influenced the cumulative iron yield through an extractive reaction. Furthermore, the developed CFD coupled model is beneficial for optimizing gas-phase extractive reaction process in FBRs.

A novel method based on functionalized bimodal mesoporous silica nanoparticles for efficient removal of lead aerosols pollution from air by solid-liquid gas-phase extraction.

In this study, the enrichment and novel sorbent based on functionalized bimodal mesoporous silica nanoparticles (HS-UVM7 and NH2-UVM7) was used for removal of lead aerosols pollution from air by solid liquid gas phase extraction method (SLGPE). In bench scale set up, the lead aerosols [(Pb (NO3)2, PbO] was generated by dispersive aerosols generator system (DAGS) and removed from air by reaction loop (RL) / impinger trap (IT) in a liquid phase which was mixed with nano adsorbent in optimized pH. The effect of parameters such as, flow rate, volume of liquid phase, time stirring, temperature, concentration, pH and amount of sorbent (mg) were studied and evaluated by flame atomic absorption spectrometry (FAAS). In optimized conditions, the adsorption capacity of HS-UVM7 and NH2-UVM7 for Pb(NO3)2 aerosols was obtained 255.6mgg-1 and 177.6mgg-1, respectively which was more than UVM7. The lead oxides aerosols (PbO) were extracted only by HS-UVM7 at acidic pH with the adsorption capacity of 271.2mgg-1. The characterization of SEM, XRD, TEM, and FTIR showed that the HS-UVM7 has beneficial surfaces for removal of (Pb (NO3)2 and PbO aerosols from the air by SLGPE method at pH = 5. The method validation was confirmed by standard addition and NIOSH method. Graphical abstract.

A new method for removal of hazardous toluene vapor from air based on ionic liquid-phase adsorbent

Toluene has toxic effects in environment and humans. In this study, five ionic liquids were pasted on microglassy balls and used for toluene removal from air by liquid–gas-phase extraction method. Based on the proposed procedure, toluene vapor was absorbed on ionic liquids (0.2 g, 25 °C) and desorbed from it at 110 °C before determined by gas chromatography. Also, the important parameters such as flow rate, toluene concentration, mass of sorbents and temperature were studied and evaluated. In optimized conditions, the removal efficiency of toluene with ionic liquid of 3-triphenylphosphonium-propane-1-sulfonic acid tosylate was obtained up to 99.5% which was more than other ionic liquids in this research. The results showed that the adsorption mechanism of toluene from air is mainly due to π–π interaction between toluene and the surface of the ionic liquids which depended on structure and aromatic cycles of ionic liquids.

Tetrachloroethene Release and Degradation During Combined ERH and Sodium Persulfate Oxidation

AbstractElectrical resistance heating (ERH) is a thermal treatment technology that involves passing electrical current through soil to increase subsurface temperatures. In addition to volatizing and recovering contaminant mass in the gas phase, heating the subsurface has the potential to decompose contaminants by increasing the rate of degradation reactions. Prior laboratory studies using convective heating demonstrated that the rate of tetrachloroethene (PCE) degradation was not sufficient to cause substantial in situ PCE mass destruction. However, similar experiments have not been performed using ERH, which has the potential to degrade PCE in reaction with the heating electrodes and electrochemically. Thus, the objective of this study was to determine the extent of PCE degradation during thermal treatment of PCE‐contaminated soil using a bench‐scale ERH system. The contaminated soil, a silty clay loam, was collected from a single borehole at a former dry cleaning facility prior to undergoing ERH treatment. After 30 days of ERH, 52% of the initial PCE mass was recovered, potentially indicating that 48% of the PCE was degraded during ERH. Although potential degradation products such as carbon dioxide were observed, their presence was attributed to the degradation of soil organic carbon and carbonates rather than PCE destruction. A second ERH experiment was conducted to assess the potential benefit of adding the heat‐activated oxidant, sodium‐persulfate, during treatment. After 19 days of ERH and three persulfate injections, 93% of the initial PCE was recovered, with 3% PCE destruction based on chloride evolution. However, the difference in mass recovery between the first and second experiments could have been due to differences in the initial mass of PCE, even though soil from the same core was used in both experiments. The results of this work suggest that the majority of mass recovered during ERH of the PCE‐contaminated soil at the former dry cleaning facility will be due to volatilization and gas phase extraction rather than abiotic degradation, even with the addition of sodium persulfate.

Validation of a new and cost-effective method for mercury vapor removal based on silver nanoparticles coating on micro glassy balls

Exposure to mercury vapor (Hg0) causes serious health problem in human body. In this study, a novel and applied method based on solid gas phase extraction (SGPE) with silver nanoparticles (AgNPs) coating on micro glassy balls (MGB) was used for Hg0 removal from artificial air. In bench scale set up, the mercury vapor in air composition was produced by mercury vapor generation system (HgGS) and restored in polyethylene air bag (5 Li). In optimized conditions, the mercury vapor in air bag, passed through AgNPs-MGB and absorbed on it. Then, the mercury was completely desorbed from AgNPs by increasing temperature up to 245 °C and online determined by cold vapor atomic absorption spectrometry (CV-AAS). By proposed procedure, the method recovery and capacity of AgNPs were obtained 98% and 91.8 mg g−1, respectively. A simple, fast and low cost synthesis of AgNPs causes, the SGPE introduce as a cost-effective method for mercury vapor removal from air. Validation of methodology was confirmed using ultra trace mercury analyzer (MC3000).

Determination of volatiles in beer using solid-phase microextraction in combination with gas chromatography/mass spektrometry

Headspace solid phase microextraction and purge and trap analysis were used for the determination of volatiles in beer. These methods were compared with the analysis of unconcentrated gas phase and liquid extraction. Solid phase microextraction proved to be the most useful and was investigated more closely. Volatiles were isolated by the means of different combinations of sorbents, sorption was performed at various temperatures and times. The addition of salt to the sample and stirring of the sample were examined to enhance the analyte concentration in the gas phase. Ultrasonic bath and filtration were tested to remove carbon dioxide. Not all methods improved the sorption of volatiles. Stirring was characterised by low repeatability and ultrasonic bath causes to the loss of volatile analytes. Distribution constants of volatiles depend on their boiling points and thus different sorption temperatures are suitable for different substances.

Alternative techniques for extracting alumina from coal fly ash

The extraction of aluminium from coal fly ash (CFA) has been carried out using two extraction techniques, acid leaching with an inorganic acid and gas phase extraction with acetylacetone, a beta-diketone. The acid leaching experiments were carried out at varying factor values of temperature, time, solid to liquid ratio, and acid concentration. Factors investigated for gas phase extraction included acetylacetone flow rate, extraction temperature and time, and aluminium (III) oxide source.Direct leaching of fly ash in 6M sulphuric acid at a solid to liquid ratio of 1:4 gave an extraction of 23.5% at 75°C after 8h 45min of leaching time. With gas phase extraction, 17.9% aluminium extraction was achieved at 250°C, 6mL/min acetylacetone flow rate, after 6h. This represents 85% and 64% extraction from the CFA amorphous phase respectively. It was also found that when a synthetic aluminium (III) oxide mixture with a similar content to CFA (31wt%) was subjected to gas phase extraction, 46.7% extraction could be achieved after 6h at 250°C. The difference in extraction levels could be explained by the fact that the alumina in CFA occurs in both mullite and amorphous phase compared with only the amorphous phase in synthetic fly ash, an indication that mineralogy has a significant effect on the extraction. Therefore the lower extraction from CFA by acetylacetone is possibly due to the non-amenability of the mullite phase to the acetylacetone beta-diketone. The results presented in this paper show that extractions using acetylacetone in the gas phase are comparatively lower than acid leaching but have advantages of reduced extraction times and the possibility of recycling the unreacted acetylacetone.

Gas phase extraction of iron from its oxide in a fluidized bed reactor

Interest in extraction processes that utilise organic ligands in the gas phase has been growing since such processes appear to eliminate many of the problems of high energy costs and complexity encountered in conventional hydrometallurgical and pyrometallurgical processes. The effect of temperature, ligand concentration and metal oxide concentration on such an iron extraction process was investigated. The ligand was introduced to the fluidized bed reactor containing the different concentrations of metal oxides at different flow rates through an evaporator. Gas phase extraction was shown to result in reasonable extractions in short periods of time, with iron extraction above 80% after 4 h for the low metal oxide concentration charge. The process was shown to depend on all the mentioned variables, and there is need to find a relationship which will be able to predict how extraction proceeds with time.

Volatile and non-volatile monoterpenes produced by elicitor-stimulated Cupressus lusitanica cultured cells

Elicitor treatment initiates defense responses in cultured Cupressus lusitanica cells. In order to investigate the defense mechanism with a yeast extract elicitor, we carried out solid-phase microextraction coupled with gas chromatography for monoterpene analysis. Ten hydrocarbon monoterpenes, including high amounts of sabinene and limonene, were detected in the gas phase of the elicitor-treated cell cultures. Six oxidized monoterpenes including beta-thujaplicin were also detected in the ether extract of the cells and the medium. Time-course profiles of volatile monoterpenes showed that one group of hydrocarbon monoterpenes was maximized on the second day after elicitation, while the other group was maximized on the third day. There were no oxidized monoterpenes that are structurally related to sabinene and limonene in the gas phase or cell extracts, suggesting that these compounds are produced exclusively for emission. Other monoterpenes, which are produced during later stages of elicitation, are metabolized into more complex compounds such as oxidized monoterpenes, including beta-thujaplicin. Although terpinolene synthase was the principal monoterpene synthase in these cell cultures, terpinolene was detected only as a minor compound in the gas phase. The time course for terpinolene synthase activity coincided with beta-thujaplicin biosynthesis. Thus, most of the terpinolene is metabolized rapidly to oxidized terpenes such as beta-thujaplicin rather than emitted.

Analysis and Monitoring of Volatile Analytes from Aqueous Solutions by Extractions into the Gas Phase Using Microdialysis Membranes and Coupling to Fast GC

Microdialysis membranes (3 mm lengthx200 microm i.d.) have been used to extract volatile analytes from aqueous samples into the gas phase and interfaced with fast gas chromatography. Gas-phase extracts generated from aqueous samples reach steady-state concentrations and are transported to the detector in 5 s. The recovery of the system ranges from 1.28% for toluene to less than 0.1% for ethanol. The lowest detectable concentration without preconcentration was 5 mM for most compounds using a flame ionization detector, and as low as 0.01 mM for more volatile hydrophobic analytes. When interfaced with a fast GC system, changes in aqueous phase concentrations were monitored with a temporal resolution of 10 s.

An investigation into the feasibility of recovering valuable metals from solid oxide compounds by gas phase extraction in a fluidised bed

Recent years have seen the application of the concept of fluidisation extended to different kinds of industrial processes. This technology now plays a central role in the chemical and petrochemical industries, in power generation and in mineral processing and metallurgy. The current research is directed towards gas-phase extraction of metals because of the high yield of recovery that can potentially be achieved. This process achieves the extraction of metals by using a volatile organic reagent, which passes through the feed material and reacts selectively with the metal to be extracted. The product is a volatile metal complex, which is removed from the residual gangue by a carrier gas. The results showed that the procedure could be successfully applied to recover aluminium, chromium, vanadium and iron with acetylacetone from their respective solid oxides in a fluidised bed. The percentage recovery ranged from 75.2% for iron to 48.2% for chromium. Kinetic investigations were performed to estimate the activation energy required for each reaction. The recovery of the metals depended on the temperature and reaction time.

Online headspace chromatographic method for measuring VFA in biogas reactor

A headspace chromatographic method has been applied to measure volatile fatty acids in anaerobic digesters using gas phase extraction at pH less than 2 and temperature higher than 65 degrees C. The concentration of volatile fatty acids in liquid and gas phase can be correlated in the form of Henry's coefficient. Analysis of different factors in the batch indicated that pH, temperature, and salt addition had a strong impact on apparent solubility, while liquid/gas volume ratio and organic acid concentration had little impact. Larger liquid volume had a positive impact on extraction efficiency, while increased gas headspace had a negative impact, indicating that the system was total mass-limited. The best conditions were at pH < 2.0, and temperatures above 75 degrees C. The advantage of an automated gas-extraction system for organic acid analysis, compared to an automated liquid system is that it contains no filter element, which is 4 susceptible to fouling in manure samples or samples with high solid content. An automated system which included a valerate pulse to the parent reactor was implemented, and operated for a short period.

Headspace sorptive extraction (HSSE), stir bar sorptive extraction (SBSE), and solid phase microextraction (SPME) applied to the analysis of roasted Arabica coffee and coffee brew.

Headspace sorptive extraction (HSSE) and stir bar sorptive extraction (SBSE), two recently introduced solventless enrichment techniques, have been applied to the analysis of the headspace of Arabica roasted coffee and of the headspace of the brew and of the brew itself. In both HSSE and SBSE enrichment is performed on a thick film of poly(dimethylsiloxane) (PDMS) coated onto a magnet incorporated in a glass jacket. Sampling is done by placing the PDMS stir bar in the headspace (gas phase extraction or HSSE) or by immersing it in the liquid (liquid phase extraction or SBSE). The stir bar is then thermally desorbed on-line with capillary GC-MS. The performance of HSSE and SBSE have been compared through the determination of the recoveries and relative abundances of 16 components of the coffee volatile fraction to classical static headspace (S-HS) and to headspace and in-sample solid phase microextraction (HS-SPME and IS-SPME, respectively) applying the fibers PDMS 100 microm, Carbowax/divinylbenzene 65 microm (CW/DVB), Carboxen/PDMS 75 microm(CAR/PDMS), polyacrylate 85 microm(PA), PDMS/divinylbenzene 65 microm(PDMS/DVB), and Carboxen/divinylbenzene/PDMS 50-30 microm(CAR/PDMS/DVB). In all cases, HSSE and SBSE gave higher recoveries, and this is entirely due to the high amount of PDMS applied.

Mercury speciation using the capillary cold trap coupled with microwave-induced plasma atomic emission spectroscopy

In this paper the capillary cold trap (CCT) is presented as a novel sample introduction and separation system for microwave-induced plasma detection. The method is based on cryogenic trapping and gas chromatographic separation carried out within the same capillary. The device, which comprises a derivatization step, on-line gas phase extraction, preconcentration and analyte separation, is semi-automated and all operational parameters are adjustable via an in-house developed control unit, regulating the selected parameters throughout the analysis process. Detection was carried out using a 2.45 GHz microwave-induced argon discharge sustained in a TM010 Beenakker cavity and emission lines were recorded by means of a ST6-UV CCD camera provided by the Santa Barbara Instrument Group. The detection limits achieved were 6.0, 0.95 and 1.25 ng L−1 for dimethylmercury, methylmercury and inorganic mercury, respectively. A complete chromatogram could be obtained within 3 min, resulting in the duration of one whole analysis cycle of about 15 min. The proposed method was validated by the analysis of a reference material (BCR 710) and applied to mercury speciation in different sample matrices such as oyster, tuna fish and sediments after microwave-assisted extraction. The total mercury concentration in real samples was in the range of 0.2–11 mg kg−1, of which up to 75% corresponded to organic mercury species.

Volatile Compounds in the Production of Liquid Beet Sugar

Samples from different parts of a beet sugar factory and refinery were analyzed with respect to volatile compounds by means of liquid-liquid extraction followed by gas chromatography-mass spectrometry (GC-MS). A limited number of the samples were analyzed by means of gas phase extraction (headspace) followed by GC-MS. Selected compounds were followed through the sugar manufacturing process. The behavior of different compounds varied greatly throughout the process, with some compounds such as geosmin (trans-1, 10-dimethyl-trans-9-decalol), dimethyl disulfide, and propionic and hexanoic acid present at the beginning of the process but disappearing rapidly after further processing. Other compounds, such as indole, dihydrobenzofuran, and 2-phenylethanol, were not detected at the start of the process but were formed later on and removed in the final product. In the final product, three pyrazines remained at fairly low concentrations, together with 3-methylcyclopentadione, ethylhexanol, and methyl pyrrole ketone.

The capillary cold trap as a suitable instrument for mercury speciation by volatilization, cryogenic trapping, and gas chromatography coupled with atomic absorption spectrometry.

An innovative accessory for speciation analysis has been developed. The system is based on the combination of cryogenic trapping and gas chromatographic separation, carried out within the same capillary. The instrument, hyphenating derivatization, gas-phase extraction, preconcentration, and analyte separation, is semiautomated, and all operational parameters are adjustable via an in-house-developed control unit, which regulates the selected parameters throughout the analysis process. Species detection was carried out by atomic absorption spectrometry. The detection limits achieved were 33, 39, and 71 ng L(-1) for dimethylmercury, methylmercury, and inorganic mercury, respectively. A complete chromatogram could be obtained within three minutes, resulting in the duration of one whole analysis cycle of about 15 min. The proposed method was applied to mercury speciation in freeze-dried tuna fish powder after microwave-assisted extraction, finding that mercury is present at 80% as methylmercury and about 20% as inorganic mercury, in this kind of biological material.