Adsorbent Trap Research Articles

Improved On-Column Injection System and Large Volume Needle Trap Device Used in Water Headspace Analysis

An improvement of the on-column injection system for the use of large diameter inside needle capillary adsorption trap devices is presented. A modified glass liner in combination with a gas tight glass fitting, used in the conventional split/splitless gas chromatographic inlet, enables to keep impurities desorbing from the outside of the needle trap and septum from being injected into the analytical GC column. The performance of the system was verified by headspace analysis of model and real water samples for benzene, toluene, ethylbenzene and xylenes. The analytical method shows good linearity, repeatability, sensitivity and advantages such as simplicity, low cost and feasibility.

Comparison of gas–solid chromatography and MM2 force field molecular binding energies for greenhouse gases on a carbonaceous surface

Gas–solid chromatography was used to determine B 2s (gas–solid virial coefficient) values for eight molecular adsorbates interacting with a carbon powder (Carbopack B, Supelco). B 2s values were determined by multiple size variant injections within the temperature range of 313–553 K. The molecular adsorbates included: carbon dioxide (CO 2); tetrafluoromethane (CF 4); hexafluoroethane (C 2F 6); 1,1-difluoroethane (C 2H 4F 2); 1-chloro-1,1-difluoroethane (C 2H 3ClF 2); dichlorodifluoromethane (CCl 2F 2); trichlorofluoromethane (CCl 3F); and 1,1,1-trichloroethane (C 2H 3Cl 3). Two of these molecules are of special interest because they are “super greenhouse gases”. The global warming potential, GWP, for CF 4 is 6500 and for C 2F 6 is 9200 relative to the reference value of 1 for CO 2. The GWP index considers both radiative blocking and molecular lifetime. For these and other industrial greenhouse gases, adsorptive trapping on a carbonaceous solid, which depends on molecule–surface binding energy, could avoid atmospheric release. The temperature variations of the gas–solid virial coefficients in conjunction with van’t Hoff plots were used to find the experimental adsorption energy or binding energy values ( E *) for each adsorbate. A molecular mechanics based, rough-surface model was used to calculate the molecule–surface binding energy (Ecal *) using augmented MM2 parameters. The surface model consisted of parallel graphene layers with two separated nanostructures each containing 17 benzene rings arranged in linear strips. The separation of the parallel nanostructures had been optimized in a prior study to appropriately represent molecule–surface interactions for Carbopack B. Linear regressions of E * versus Ecal * for the current data set of eight molecules and the same surface model gave E * = 0.926Ecal * and r 2=0.956. A combined set of the current and prior Carbopack B adsorbates studied (linear alkanes, branched alkanes, cyclic alkanes, ethers, and halogenated hydrocarbons) gave a data set with 33 molecules and a regression of E * = 0.991Ecal * and r 2=0.968. These results indicated a good correlation between the experimental and the MM2 computed molecule–surface binding energies.

On-column injection system for use of large diameter inside needle capillary adsorption trap devices

Direct coupling of the needle trap to the capillary column in the split/splitless gas chromatographic (GC) inlet with simple modification facilitates full exploitation of the column efficiency, even when using the large volume trap filled with 35 mg of Tenax TA. A schematic diagram of the inlet and of the new modification of the INCAT device and an example of BTEX (benzene, toluene, ethylbenzene and xylenes) analysis is presented. Determination of the repeatability of BTEX analyses resulted in relative standard deviations of 2.4–3.6%.

New method for aroma barrier testing

AbstractIn the above article (DOI: 10.1002/pts.791), reference to work published by Drs. Lindner‐Steinert, Piringer and Franz1–3 in which they had developed the method using polyethylene glycol (PEG 400) as a diluting agent in the source cell both for the single aromas and an aroma blend with seven compounds, and where the receiving cell is continuously flushed with nitrogen to transport the permeated aroma compounds to an adsorption trap was accidentally omitted.

Comparison of HC species from diesel combustion modes and characterization of a heat-up doc formulation

This study summarizes engine speed and load effects on HC species emissions from premixed charge compression ignition (PCI) and conventional diesel combustion, and it evaluates diesel oxidation catalyst (DOC) formulations on a gas flow reactor for the purpose of diesel particulate filter regeneration or lean NOx trap desulfation. HC emissions are sampled simultaneously by a Tedlar bag for light HC species and by a Tenax TA™ adsorption trap for semi-volatile HC species, and they are analyzed by gas chromatography with a flame ionization detector. The bulk temperature and residence time during combustion are key parameters that are important for understanding the effects of speed and load on engine-out HC emissions. The degree of post-flame oxidation is higher in PCI than in conventional combustion, and it is increased for PCI with a higher speed and load, as indicated by a lower fuel alkanes/THC ratio, a higher alkenes/fuel alkanes ratio, and a higher methane/THC ratio. Ethene and n-undecane are two representative HC species, and they are used as a surrogate mixture in the gas flow reactor to simulate PCI and conventional combustion with in-cylinder post fuel injection. Among the three DOC formulations tested, the catalyst with constituent precious metals of platinum and palladium (PtPd) showed the best light-off performance, followed by PtPd with an addition of cerium dioxide (PtPd+CeO2), and platinum (Pt), regardless of exhaust compositions. Conventional combustion exhaust composition shows a lower light-off temperature than that of PCI, regardless of catalyst formulation.

On-line purge and trap gas chromatography for monitoring of trihalomethanes in drinking water distribution systems

A method using an automated on-line purge and trap gas chromatograph with a dry electrolytic conductivity detector (DELCD) has been developed for monitoring four regulated trihalomethanes in drinking water distribution systems. This analyzer samples trihalomethanes from drinking water by pervaporation through a silicone capillary membrane contained within a gas extraction cell (GEC) followed by preconcentration using an adsorbent trap. Trihalomethanes are subsequently desorbed from the trap onto a capillary column, separated and detected. The analyzer operates in real-time, samples directly from the drinking water distribution system and is fully automated. The optimization, operation, and evaluation of the analyzer and method are discussed. Method detection limits (MDL) are less than 1.0 μg L −1 with acceptable estimates for accuracy, and precision. The results from two on-line monitoring studies in chlorinated and chloraminated distribution systems are presented. The performance of the method is compared directly to United Stated Environmental Protection Agency Method 502.2 and shows a very slight, but acceptable bias.

Growth kinetics and adsorption trapping of impurity during crystallization of NH4Cl in the NH4Cl-CuCl2-H2O-CONH3 system

The growth of NH4Cl crystals and their trapping of copper impurity in the NH4Cl-CuCl2-H2O-CONH3 quaternary system have been experimentally studied. The epitaxial adsorption of copper complexes on (100) faces leads to a sharp decrease in the growth rate in good correspondence with the Bliznakov-Chernov equation. The copper impurity enters the crystal composition in amounts up to 6.5 mol %. The impurity distribution coefficient nonlinearly changes with the copper concentration in the solution: it is much larger than unity at low concentrations and sharply decreases with an increase in supersaturation. Such behavior is indicative of the adsorption mechanism of copper trapping by NH4Cl crystals. Single-crystal X-ray study shows that the impurity is incorporated in NH4Cl crystals in the form of oriented intergrowths of different complex coppercontaining compounds. The concentration and variety of impurity phases increase with an increase in the copper content in the solution and decrease with an increase in supersaturation. Heterogeneous 2D isomorphous trapping of copper impurity by NH4Cl crystals induces high (up to 60 MPa) internal stresses in them, as a result of which anomalous birefringence and splitting of crystals occur.

Volatile profiles of sparkling wines obtained by three extraction methods and gas chromatography–mass spectrometry (GC–MS) analysis

Simultaneous distillation extraction (SDE) and closed-loop stripping analysis (CLSA) show great capacity for organic compound extraction. Here we used these techniques to obtain and characterize a wide range of volatile compounds from aged cava sparkling wine. We also explored the potential application of head space-solid phase micro extraction (HS-SPME) to determine the distinctive volatile compounds of aged cava as this technique is a common extraction method in quality flavour control. For SDE, 50 mL of cava were extracted with pentane/dichloromethane during 4 h in a Likens–Nickerson (LN) extraction apparatus; while for CLSA, 25 mL of cava were stirred during 1 h into a CLSA apparatus with an adsorbent trap of granulated activated carbon. HS-SPME was performed at 35 °C using 2 ml of sample for 30 min. The 20-mm SPME fibber was coated with a 50/30-μm layer of divinylbenzene–carboxen–polydimethylsiloxane (DVB–CAR–PDMS). All the extraction methods were followed by gas chromatography–mass spectrometry (GC–MS) analysis. SDE and CLSA allowed the identification of 84 volatile compounds. Almost 40% of the volatiles from these two techniques were obtained by HS-SPME. Moreover, here we provide the first description of several tentatively identified compounds such as lilial, octanal, 2-octanone, isopropyl disulfide, methylthiophen-3-one, α-amyl-cinnamaldehyde, ethyl 2-furancarboxylate, 2-acetylfuran, and 5-methylfurfural in cava.

Static headspace--gas chromatography: theory and practice

Static headspace--gas chromatography: theory and practice

A Comparison of SnifProbe and SPME for Aroma Sampling

The popular solid phase micro extraction (SPME) device and method is compared with SnifProbe (Gordin and Amirav in J Chromatogr A 903:155–172, 2000) in their application for coffee aroma sampling for its analysis. The main difference between SPME and SnifProbe is in the relative motion of the sampled air. While SPME is based on static air sampling and the achievement of equilibrium, SnifProbe is based on active air pumping through the adsorption trap. A second important difference concerns the sample introduction into the GC injector for its intra injector thermal desorption. SPME is based on the use of a special syringe for sample introduction without any change to the injector, while SnifProbe requires a ChromatoProbe for sample introduction. We found that as a result of these differences, while SnifProbe provides a more faithful (representative) headspace and aroma sample collection, SPME is characterized by major compound dependent sample bias. In addition, SnifProbe enabled much faster sample collection than SPME. Since SnifProbe uses the ChromatoProbe for sample introduction into the GC, bigger sample collection/trapping devices such as silicone tubing can be used, and as a result, over ten times superior SnifProbe sensitivity (versus SPME) was demonstrated. Additional SnifProbe and SPME features are compared and discussed.

AI-700 pharmacokinetics, tissue distribution and exhaled elimination kinetics in rats

The purpose of these studies was to determine the pharmacokinetics, tissue distribution, and exhaled elimination kinetics in rats for intravenously administered AI-700, which consists of porous microspheres containing decafluorobutane (DFB), for use as an ultrasound contrast agent. [Pd]-AI-700 was administered intravenously to rats (10 mg microspheres/kg). Blood and tissue samples collected at specified times were analyzed for palladium by inductively coupled plasma-mass spectrometry (ICP-MS). AI-700 was also administered intravenously to rats (40 mg microspheres/kg) and expired air was collected over time. Expired air samples were analyzed for DFB by validated adsorbent trapping–thermal desorption–gas chromatography–mass spectrometry methodology. Pd from [Pd]-AI-700 was cleared from blood with a ca. 50–85% decline from peak concentration within 5 min. At 1440 min post-dose, 52–72% of the Pd dose was recovered from organs of the reticuloendothelial system. Approximately 77% of the intravenously injected DFB was found in expired air within 3 h after dosing, with most of the DFB dose (61 ± 6%) expired within the first 10 min after dosing. As expected, the microspheres were cleared through the reticuloendothelial system, and the DFB was eliminated in expired air, with more than half of the DFB eliminated within the first 10 min after dosing.

Attraction to Ornamental Peony (Paeonia lactiflora, Paeoniaceae) by Polistes dominulus Christ (Hymenoptera: Vespidae) Demonstrated Using Olfactometers

Observations were made of Polistes dominulus Christ (Hymenoptera: Vespidae) on budding Paeonia lactiflora plants (Paeoniaceae). Y-tube and parallel tube olfactometer experiments were performed on field-collected queens and workers to determine if peony odor is attractive to P. dominulus. In Y-tube olfactometer experiments, the wasps showed a significant orientation response toward peony bud odor but they did not show a significant response toward peony foliage odor, when compared to the control. Peony bud volatiles were collected in an adsorbent trap and tested in a parallel tube olfactometer for attractiveness to P. dominulus females. The wasp took significantly less time to travel upwind in the peony bud volatile tube compared to the control tube. Chemicals that produce peony bud odor could serve as a feeding attractant lure for trapping P. dominulus.

Comparison of Needle Concentrator with SPME for GC Determination of Benzene, Toluene, Ethylbenzene, and Xylenes in Aqueous Samples

A method of solventless extraction of volatile organic compounds from aqueous samples has been developed and validated. A new arrangement in which the internal volume of a needle capillary adsorption trap is completely filled with Porapak Q, as adsorbent material, and wet alumina, as a source of desorptive water vapor flow, is presented. The device has been used for head-space sampling of benzene, toluene, ethylbenzene, and xylenes (BTEX) from water samples and compared with solid-phase microextraction. Under the same sampling conditions the analytical characteristics of the device for the BTEX compounds are better than those of solid-phase microextraction. Limits of detection and quantification are below 0.5 μ g L−1.

Gas chromatography system for the automated, unattended, and cryogen-free monitoring of C2 to C6 non-methane hydrocarbons in the remote troposphere

An unattended, automated, on-line, cryogen-free, remotely controlled gas chromatography (GC) system was developed and has been deployed for more than 1 year for the continuous determination of C 2 to C 6 hydrocarbons at an observatory located at 2225 m elevation, on the summit caldera of an inactive volcano on the island of Pico, Azores. The GC instrument is tailored to the measurement challenges at this remote and high altitude site. All consumable gases are prepared in situ. Total power use remains below 700 W at all times. Sample collection and analysis is performed without use of cryogen. Hydrocarbons are concentrated on a one-stage trapping/injection system consisting of a Peltier-cooled multi-bed solid adsorbent trap. Analytes are detected after thermal desorption and separation on an alumina-PLOT (porous-layer open tubular) column by flame ionization detection (FID). Sample focusing, desorption, separation and detection parameters were thoroughly investigated to ensure quantitative collection and subsequent injection onto the GC system. GC operation is controlled remotely and data are downloaded daily. Sample volumes (600 and 3000 ml) are alternated for analysis of C 2 to C 3 and C 3 to C 6 hydrocarbons, respectively. Detection limits are in the low parts per trillion by volume (pptv) range, sufficient for quantification of the compounds of interest at their central North Atlantic lower free troposphere background concentrations.

Zeolite‐Based Adsorbers for Reducing Light Hydrocarbon Emissions from Engine Exhaust

Adsorption of light hydrocarbons, such as ethane, ethylene, n‐butane, isobutane, and isobutene, on zeolites 5A [LTA] and H‐Beta [BEA] was investigated, in order to evaluate the possible use of these zeolites as adsorbents for reducing cold start emissions at engine exhaust. Equilibrium isotherms at 25°C were determined and analyzed by Langmuir and virial equations to estimate adsorption capacities at saturation and adsorption affinity for single hydrocarbons at low pressure. Good affinities of zeolites 5A and H‐Beta for the tested light hydrocarbons were found either at saturation or at low pressure. Flow measurements were also carried out with a fixed‐bed microreactor using a real engine exhaust gas. Reasonable performances of zeolite H‐Beta in trapping hydrocarbons present in the emission at engine exhaust were obtained. Poor performances, obtained, on the contrary, with zeolite 5A, were interpreted as due to the preferential adsorption of water vapor, compared to hydrocarbons. On the basis of the present and of previously collected data, the possibility of use of zeolite H‐Beta, coupled to zeolite H‐Y or zeolite H‐ZSM5, to realize a hydrocarbon adsorbent trap for reducing cold start emission is, at last, envisaged.

Combining Preconcentration of Air Samples with Cavity Ring-Down Spectroscopy for Detection of Trace Volatile Organic Compounds in the Atmosphere

Quantitative detection of small volatile organic compounds in ambient air is demonstrated using a combination of continuous wave cavity ring-down spectroscopy (cw-CRDS) and the preconcentration of air samples with an adsorbent trap. The trap consists of a zeolite molecular sieve, selected for efficient trapping of the test compounds ethene (ethylene) and ethyne (acetylene). Upon heating of the trap, these organic compounds desorb into a small-volume ring-down cavity, and absolute concentrations are measured by CRDS at 6150.30 cm(-1) (ethene) and 6512.99 cm(-1) (ethyne) without the need for calibration. The efficiency of the trapping and desorption was tested using commercial standard gas mixtures and shown to be 100% in the case of ethene, whereas some ethyne is retained under the current operating conditions. Samples of indoor and outdoor air were analyzed for ethene content, and measurements were made of mixing ratios as low as 6 ppbv. Removal of water vapor and CO(2) from the air samples prior to trapping was unnecessary, and the selectivity of the trapping, desorption, and spectroscopic detection steps eliminates the need for gas chromatographic separation prior to analysis. With anticipated improvements to the design, measurements of these and other trace atmospheric constituents should be possible on time scales of a few minutes.

Automated measurement and calibration of reactive volatile halogenated organic compounds in the atmosphere.

The automated calibration and analysis of very low mixing ratios of the reactive volatile organic halocarbons CH(3)I, CHCl(3), C(2)H(5)I, 2-C(3)H(7)I, CH(2)Br(2), CH(2)ClI, CHBr(2)Cl, 1-C(3)H(7)I, CH(2)BrI, CHBr(3) and CH(2)I(2) for long term atmospheric field measurements are described. Analytes were pre-concentrated from 3 l of air onto an adsorbent trap cooled to -10 [degree]C using Peltier plates, and rapidly transferred to a gas chromatograph (GC) by resistive heating. A two stage Carboxen 1016/Carbotrap C adsorbent trap allowed good analyte recovery and rapid desorption without the need for post-desorption cryofocussing. Halocarbons were detected using a mass spectrometer (MS) in selective ion mode. Detection limits were between 0.02 and 0.12 pptv (parts per trillion by volume) for approximately hourly samples of CHCl(3), CH(3)I, C(2)H(5)I, 1-C(3)H(7)I, 2-C(3)H(7)I, CH(2)ClI, CH(2)Br(2), CHBr(2)Cl, CH(2)BrI, CHBr(3) and CH(2)I(2) with a precision of 3-8%. A novel calibration system was constructed which utilised fixed volume (50 [micro sign]l) injections of the output of thermostatted permeation tubes into a stream of nitrogen gas in order to dilute parts per million by volume (ppmv) mixing ratios into pptv. The calibration was completely automated, allowing multi-point calibrations during routine operation. The overall accuracy of the measurements is estimated to be +/-15%. The instrument was used continuously for automated atmospheric measurements during a 4-month research cruise from Germany to Antarctica, and a 6 week field campaign at Mace Head, Ireland. The results for CHCl(3) during the latter campaign were within 13% of measurements made by a GC-MS operating continuously at the site within the long term Advanced Global Atmospherics Gases Experiment.

Needle concentrator for gas chromatographic determination of BTEX in aqueous samples

A simple method of solventless extraction of volatile organic compounds (BTEX) from aqueous samples was developed and validated. A new arrangement of the full volume inside needle capillary adsorption trap (INCAT) device with Porapak Q as a sorbent material and wet alumina as a source of desorptive water vapour flow in a closed analytical system is presented. The analytical characteristics of developed device and of compared purge-and-trap (PTI) device for BTEX compounds are similar; the limits of detection as well as quantification are lower than 1 μg l −1.

Fast volatile organic compound recovery from soil standards for analysis by thermal desorption gas chromatography.

The development of high-throughput environmental screening assays are needed to meet high-specification data quality objectives (DQOs) that require large numbers of samples to be taken and analysed rapidly. The acquisition and stabilisation of the sample is a key technical and operational challenge in analytical sequences associated with the determination of volatile organic compound (VOC) contamination of soils. Further the development of miniaturised and embedded analytical systems for environmental conditioning monitoring requires the development of new sampling techniques. A proof-of-concept study is described that shows how pressurised gas, in this case carbon dioxide, may be used to recover reversibly-bound VOCs from soil into an adsorbent sampler, and then analysed by thermal desorption-gas chromatography. The effects of the volume of the pressurised gas, the gas flow rate and the mass of the soil sample on the recovery efficiency and breakthrough from the adsorbent trap were investigated in a preliminary characterisation study. Two distinct approaches were identified. The first involved ventilation of the voids within the soil matrix to displace the soil-gas headspace, a rapid screening approach. The second involved a more prolonged purge of the matrix to strip reversibly bound species into the gas phase and hence pass them into the adsorbent trap, a purge and trap approach. The shortest possible sample processing time required to yield analytically useful responses was 5 s with the use of the headspace approach. In this case n-octane, benzene and toluene were recovered from conditioned spiked soil samples at concentrations in the range 42 to 1690 mg kg(-1). The limit of detection for the system was estimated to be no greater than 1.2 mg kg(-1). Using the purge and trap variant enabled recovery efficiencies greater than 93% to be achieved with liquid spikes of n-octane onto soil samples. These preliminary studies showed that a system based on this approach would need to balance recovery efficiency, time and analyte breakthrough from the adsorbent trap.

A two-column method for long-term monitoring of non-methane hydrocarbons (NMHCs) and oxygenated volatile organic compounds (o-VOCs).

A method has been developed for concurrent analysis of C2-C7 hydrocarbons and C2-C5 oxygenated volatile organic compounds (o-VOCs) including alcohols, aldehydes, ketones and ethers. A multi-bed, Peltier-cooled adsorbent trap, consisting of Carboxen 1000 and Carbopack B, was used to acquire one sample per hour. Upon injection the sample was split in an approximately 50:50 ratio between a 50 m aluminium oxide (Al2O3) porous layer open tubular (PLOT) column and a 10 m LOWOX column. Eluents from each column were then analysed using flame ionisation detection (FID). Regular calibration of the system was performed using a standard cylinder mixture at the parts per billion by volume (ppbV) level for non-methane hydrocarbons (NMHCs) and a permeation tube method for the oxygenated species. The system is fully automated with NMHC detection limits between 1 and 10 parts per trillion by volume (pptV) and o-VOC detection limits between 10 and 40 pptV.