Adsorption Thermal Desorption Research Articles

Получение золь-гель методом и свойства аморфного железосодержащего алюмосиликата

The objective of the present study includes a modification of synthetic aluminosilicate with iron cations and an estimation of the modificator influence at structure and properties of the aluminosilicate. The iron-containing aluminosilicate (Si/Al = 4.72) with an Al/Fe molar ratio of 5:1 was prepared by the sol-gel method at pH = 1-2. Amorphous aluminosilicate (Si/Al = 4.72), which was synthesized by analogous procedure, was applied as a reference sample. By scanning electron microscopy, it was found that the powders had particles of 1-20 micrometers in size. The results of low-temperature adsorption-thermal desorption of nitrogen showed that the modification with Fe3+ ions affected the specific surface area and porosity of the material under study. The iron-containing sample has a higher specific surface area and pore volume comparing to the initial aluminosilicate. The Hammett indicator method was used to evaluate the surface centers of the samples. It was found that the materials under study were characterized by the presence of active sites with pKax values in the range from - 4.4 to 12.8 with a pronounced maximum at pKax = 1.02. For an iron-containing sample, the concentration of acid sites significantly decreases at pKax = 1.02, while at pKax 0.80, 1.03, 2.10, 2.50, 4.10, 5.00, 8.00, and 12.80, an increase in the number of acid sites is observed. The values of the Hammett function are practically the same for the studied samples and characterizes them as materials of medium acidity. For iron-containing aluminosilicate, the larger number of active sites was noted, it amounted to 313.5 mmol/g.

In-situ measurement of trace isoprene and dimethyl sulfide in seawater and oceanic atmosphere based on room temperature adsorption-thermal desorption

Abstact Aqueous biogenic gases play an important role in the global environment. Here, we describe a novel method developed to determine trace levels of biogenic gases (isoprene and dimethyl sulfide, DMS) in situ, based on room temperature enrichment-thermal desorption. The two gases from seawater (isoprene: 630 mL; DMS: 20 mL) and the marine atmosphere (1 L) were adsorbed into a funnel-shaped quartz tube at room temperature, then thermally desorbed (358 °C) and introduced into a gas chromatograph-flame ionization detector (GC-FID) using a portable curie-point injector. A suitable adsorbent material (Carbopack X) was added to the adsorption tube to trap two the target compounds in a gas stream for the first time. Good reproducibility (

Preparation of a Composite Material AC/Cu-BTC with Improved Water Stability and n-Hexane Vapor Adsorption

The Cu-BTC, a widely studied metal-organic framework (MOF), has been applied in various fields such as gas adsorption, separation, storage, and catalysis. However, the Cu-BTC collapses due to the replacement of the organic linker by water molecules under humid conditions, which limits its practical application in industries. In consideration of the undesirable water effect on the framework stability of Cu-BTC, a stable activated carbon (AC) was incorporated into it by the in situ method to yield a composite material AC/Cu-BTC with high water stability. XRD and SEM patterns proved that the AC7%/Cu-BTC successfully retains its crystal structure after being exposed to water molecules. The adsorption amount of n-hexane vapor of the AC7%/Cu-BTC after water vapor adsorption-thermal desorption is 307% of that of the Cu-BTC. The addition of the AC changes the adsorption active sites and reduces the strong affinity of the Cu-BTC to water molecules, resulting in the AC7%/Cu-BTC having a much lower adsorption rate for water vapor than the Cu-BTC. Therefore, the AC7%/Cu-BTC can be protected from a large amount of water molecules and avoid structural collapse caused by the disconnection between the copper center and the organic linker. The composite displays a potential value for stable applications of MOF-based materials under ambient conditions.

Emission characteristics and associated health risk assessment of volatile organic compounds from a typical coking wastewater treatment plant.

Coking wastewater is a typical industrial wastewater and contains a number of toxic and harmful organic pollutants which threaten human health. However, emission of volatile organic compounds (VOCs) from coking wastewater treatment plants (WWTPs) is rarely studied. Here, the emission characteristics of VOCs were investigated in a full-scale coking WWTP composed of an anaerobic-oxic-oxic (A-O1-O2) treatment system. Furthermore, the potential health risks were assessed in this study. VOC emission rates were estimated at each unit of the coking WWTP and the influencing factors of emissions were discussed. Seventeen VOCs were identified in the air phase by gas chromatography-mass spectrometry combined with Tenax adsorption-thermal desorption method; benzene, toluene, and xylenes were predominant, and the concentration of total VOCs decreased gradually from the raw water tank (857.86 ± 131.30 μg m-3) to the effluent tank (28.56 ± 3.96 μg m-3). The total VOC emission rate from all units was 1773.42 g d-1, corresponding to an annual emission of 0.65 tons year-1. Since the treatment capacity of this coking WWTP was about 1500 m3 d-1, it was estimated that 1.18 g of VOCs are emitted during the treatment of 1 m3 wastewater. Influencing factors of VOC emission mainly include the background concentration of VOCs in wastewater, operational parameters of the treatment processes, and physicochemical properties of VOCs. The carcinogenic risk of VOCs for workers in this coking WWTP ranged from 3.0 × 10-5 to 7.8 × 10-4, which exceeded an acceptable level (1.0 × 10-6). The non-carcinogenic risk hazard ratio of benzene exceeded 1, indicating that benzene has an obvious non-carcinogenic risk. Understanding VOCs emission characteristics and emission rates can help to identify the adverse effects of coking WWTPs on human health and provide relevant information for policy-making.

Volatilizable Biogenic Organic Compounds (VBOCs) with two dimensional Gas Chromatography-Time of Flight Mass Spectrometry (GC <b>×</b> GC-TOFMS): sampling methods, VBOC complexity, and chromatographic retention data

Abstract. Two dimensional gas chromatography (GC × GC) with detection by time-of-flight mass spectrometry (TOFMS) was applied in the rapid analysis of air samples containing highly complex mixtures of volatilizable biogenic organic compounds (VBOCs). VBOC analytical methodologies are briefly reviewed, and optimal conditions are discussed for sampling with both adsorption/thermal desorption (ATD) cartridges and solid-phase microextraction (SPME) fibers. Air samples containing VBOC emissions from leaves of two tree species (Cedrus atlantica and Calycolpus moritzianus) were obtained by both ATD and SPME. The optimized gas chromatographic conditions utilized a 45 m, 0.25 mm I.D. low-polarity primary column (DB-VRX, 1.4 μm film) and a 1.5 m, 0.25 mm I.D. polar secondary column (StabilwaxTM, 0.25 μm film). Excellent separation was achieved in a 36 min temperature programmed GC × GC chromatogram. Thousands of VBOC peaks were present in the sample chromatograms; hundreds of tentative identifications by NIST mass spectral matching are provided. Very few of the tentatively identified compounds are currently available as authentic standards. Minimum detection limit values for a 5 l ATD sample were 3.5 pptv (10 ng m−3) for isoprene, methyl vinyl ketone, and methacrolein, and ~1.5 pptv (~10 ng m−3) for monoterpenes and sesquiterpenes. Kovats-type chromatographic retention index values on the primary column and relative retention time values on the secondary column are provided for 21 standard compounds and for 417 tentatively identified VBOCs. 19 of the 21 authentic standard compounds were found in one of the Cedrus atlantica SPME samples. In addition, easily quantifiable levels of at least 13 sesquiterpenes were found in an ATD sample obtained from a branch enclosure of Calycolpus moritzianus. Overall, the results obtained via GC × GC-TOFMS highlight an extreme, and largely uncharacterized diversity of VBOCs, consistent with the hypothesis that sesquiterpenes and other compounds beyond the current list of typically determined VBOC analytes may well be important contributors to global atmospheric levels of organic particulate matter.

Effect of fungicide residues on the aromatic composition of white wine inoculated with three Saccharomyces cerevisiae strains.

The effects of three fungicide residues (cyprodinil, fludioxonil, and pyrimethanil) on the aromatic composition (acids, alcohols, and esters) of Vitis vinifera white wines (var. Airén) inoculated with three Saccharomyces cerevisiae strains (syn. bayanus, cerevisiae, and syn. uvarum) are studied. The aromatic exponents were extracted and concentrated by adsorption-thermal desorption and were determined by gas chromatography using a mass selective detector. The addition of the three fungicides at different doses (1 and 5 mg/L) produces significant differences in the acidic fraction of the aroma, especially in the assays inoculated with S. cerevisiae, although the final contents do not exceed the perception thresholds. The lower quality wines, according to isomeric alcohol content [(Z)-3-hexen-1-ol and 3-(methylthio)propan-1-ol] are those obtained by inoculation with S. cerevisiae(syn. bayanus) and addition of cyprodinil. The addition of fungicides in the assays inoculated with S. cerevisiae (syn. bayanus) produces an increase in the ethyl acetate and isoamyl acetate contents, which causes a decrease in the sensorial quality of the wine obtained.

Effect of pesticide residues on the aromatic composition of red wines.

The influence of pesticide residues on the aromatic composition (major and minor volatiles) of red wines made from Vitis vinifera (Monastrell var.) was studied by comparing the concentration of aromas in wines made from grapes subjected (or not) to phytosanitary treatment with chlorpyrifos, fenarimol, mancozeb, metalaxyl, penconazole, and vinclozolin, according to the agricultural practice of the area. The analytical determination of the major volatiles was made by gas chromatography using a flame ionization detector, while the minor volatiles were determined by adsorption-thermal desorption gas chromatography using a mass selective detector. There were significant differences between the ethyl acetate, methanol, isobutanol, and diethylacetal levels of the control wine and that containing chlorpyrifos residues, although only the ethyl acetate exceeded the olfactory threshold. With regard to the minor volatiles, significant differences were detected in the concentrations of some esters, aldehydes, and acids. However, only isoamyl acetate exceeded the olfactory threshold in wines containing residues of chlorpyrifos, fenarimol, and vinclozolin.

Deuterium adsorption-desorption from diamond (100) single crystal surfaces studied by TPD

Due to the crucial role of hydrogen in diamond CVD process the adsorption-desorption of hydrogen on different diamond surface planes has been studied thoroughly in recent years. Contradictory results and explanations have been reported in the literature regarding the mechanisms and dynamics of the above system. Deuterium adsorption-desorption from a Di(100) surface was investigated by TPD and LEED. It was found that hydrogen plasma treatment results in a well-defined reconstructed Di(100)-(2 × 1):H surface for which a high quality LEED pattern was observed at primary electron beam energy as low as 28 eV. Annealing of the diamond (100) hydrogenated surface at 1200 C results in hydrogen desorption. The hydrogen-free Di(100)-(2 × 1) surface displays charging effects under low energy electron bombardment. Activated low-coverage deuterium adsorption on the Di(100) surface was performed in situ. The results show that deuterium desorbs from a single adsorption site, α 1 , on the (100) diamond surface. Desorption from these sites obeys first order kinetics. Simulation of the TPD spectra yields K = 10 13 s −1 and E act = 88 kcal/mol for the deuterium desorption from well-defined surface. Repeated deuterium adsorption-thermal desorption cycles cause surface degradation which results in additional peaks in the TPD spectrum. A possible mechanism to the first order desorption kinetics is suggested.

Comparison of Downhole and Surface Sampling for the Determination of Volatile Organic Compounds (VOCs) in Ground Water

AbstractThe relative precision and accuracy of sampling and analysis methods for the determination of trace concentrations of volatile organic compounds (VOCs) in ground water were compared. Samples were collected from a well containing nanogram‐per‐liter (ng/L) to microgram‐per‐liter (μg/L) levels of VOCs. A Keck helical rotor submersible pump was used to collect samples at the surface for analysis by purge and trap (P&T) and for analysis by adsorption/thermal desorption (ATD). Downhole samples were collected by passing water through an ATD cartridge. Although slight spontaneous bubble outgassing occurred when the water was brought to the surface, the relative precisions and comparabilities of the surface and downhole methods were generally found to be equivalent from a statistical point of view. A main conclusion of this study is that bringing sample water to the surface for placement in VOC vials (and subsequent analysis by P&T) can be done reliably under many circumstances. However, care must still be taken to prevent adsorption losses and cross contamination. Samples subject to strong bubble outgassing will need to be handled in a special fashion (e.g., by downhole ATD) to minimize volatilization losses. Additionally, the higher sensitivity of the ATD method allows lower detection limits than are possible with P&T. For example, several compounds present at the ng/L level could be determined with confidence by ATD, but not by P&T.

Adsorption/thermal desorption for the determination of volatile organic compounds in water

An adsorption/thermal desorption (ATD) method for volatile organic compounds is developed using small bed volume (0.68 cm 3) cartridges of the sorbent Tenax-TA. The method allows an ATD cartridge to be desorbed and analyzed with ca. 30 μl or residual water still on the cartridge. The method employs a water trap between the ATD thermal desorber and the capillary column. Results obtained indicate that (1) column plugging by ice can be avoided completely, (2) the water trap has a high transmission efficiency, (3) excellent chromatography can be obtained and (4) good comparability of results is obtainable between purge and trap and ATD for many volatile organic compounds at concentrations ranging for fractions of μg/1 to hundreds of μg/1.

Determination of Organic Contaminants in Residential Indoor Air Using an Adsorption-thermal Desorption Technique

This field study evaluated the ability of a multi-sorbent sampling tube/thermal desorption technique to identify and to provide quantitative data on volatile organic contaminants in indoor air. Air samples, from 12 Canadian homes, were collected on multilayer sorbent cartridges and analyzed using Adsorption/Thermal Desorption coupled with Gas Chromatography/Mass Spectrometry. The study included the identification and quantitation of 23 target compounds. Analysis of sorbent tubes fortified with these target compounds indicated that recoveries were greater than 70 percent and the precision was usually better than 15 percent. These organic compounds were found to be stable on the sorbent tubes for at least seven days. With some exceptions, the target compounds were usually detected at 1 to 10 micrograms/m3 in indoor air samples; other organics identified qualitatively were saturated hydrocarbons, unsaturated hydrocarbons, cyclic hydrocarbons, substituted aromatics, oxygenates, some halogenates and cyclic species such as camphenes/pinenes and carenes.

Adsorption/Thermal Desorption with Tenax‐GC for the Collection and Analysis of Polycyclic Aromatic Hydrocarbons and Chlorinated Compounds

AbstractA system for the determination of polycyclic aromatic hydrocarbons(PAHs) and chlorinated compounds in air by means of adsorption/thermal desorption(ATD) with small bed volume (0.1 g) Tenax cartridges, followed by cryogenic trap in a U‐shaped stainless steel tube with liquid nitrogen as an appropriate concentration method prior to capillary gas chromatography is described. Recoveries were determined for the complete ATD method. Desorption recoveries near 100% were found for a variety of chlorinated compounds and polycyclic aromatic hydrocarbons.

Adsorption/thermal desorption with small cartridges for the determination of trace aqueous semivolatile organic compounds

Adsorption/thermal desorption (ATD) with small bed volume (0.68 cm/sup 3/) Tenax cartridges and direct desorption to a fused-silica capillary gas chromatography column has been studied for the determination of a wide range of semivolatile compounds in water. Recoveries were determined for a 5 min, 250/sup 0/C desorption step alone, as well as for the complete ATD method. Desorption recoveries near 100% were found for a variety of phenols and other monocyclic aromatics, polycyclic aromatic hydrocarbons (PAHs) up to 1-methylphenanthrene, pesticides up to dieldrin, phthalates up to diethyl phthalate, and alkanes up to tricosane (C/sub 23/). Most phenols were not recovered will in the full ATD method studies. Virtually all other compounds studied, including nonphenolic monocyclic aromatics, PAHs, pesticides, and several alkanes were recovered well. Even compounds such as pyrene, butyl benzyl phthalate, and p,p'-DDE (1,1'-(dichloroethenylidene)bis(4-chlorobenzene)), which were not 100% recovered in the short 5-min desorption step alone, gave full ATD method recoveries near 100%; during the aqueous-phase sampling step, these compounds sorbed near the sample inlet end of the bed, facilitating recovery by thermal desorption.

A Tube and Cartridge Method for Down‐Hole Sampling for Trace Organic Compounds in Ground Water

ABSTRACTA small ground‐water sampling device has been developed which extends the down‐hole use of the adsorption/thermal desorption (ATD) analysis method for nonpolar organic compounds to very narrow piezometers (I.D. > 0.64 cm). The sampler consists of a sorbent cartridge, a flow restrictor, and a tube leading to the ground surface. The device is lowered down a piezometer, and water‐column pressure forces the sample through the cartridge. In the laboratory, the water is removed from the cartridge and the sorbed compounds are thermally desorbed to a gas chromatography (GC) column for analysis. Since the analytes are sorbed on the cartridge down‐hole, volatilization losses are avoided. Samples can be obtained without being influenced by the water column above the sampler or by tubing or pumps; many uncertainties associated with well purging and contamination from well casings and samplers can be minimized. The method was tested by sampling at a landfill. The coefficients of variation were in the 10‐18% range at the low μg/1 level. The limits of detection for several compounds were all under 0.1 μg/1, some being less than 1 ng/1. Sorption efficiencies of >93% were found for a variety of compounds. The method will be attractive when sensitivity and freedom from volatilization losses and sampler‐related contamination are required.

Trace organic compounds in rain. 1. Sampler design and analysis by adsorption/thermal desorption (ATD)

The design and sue of a rain sampler with a 0.89-m/sup 2/ collection surface area are described. The sampler is controlled electronically, provides for the in situ filtration of the sample, and carries out the preconcentration of nonpolar organic compounds by means of cartridges of the sorbent Tenax-GC. Analytical results were obtained for 27 compounds by fused silica capillary column gas chromatography with detection by mass spectrometry for four rain events sampled 12 km southwest of Portland, Or, at the Oregon Graduate Center (OGC), and for five rain events sampled in southeast Portland. Mean dissolved rain concentrations for ..cap alpha..-hexachlorocyclohexane (..cap alpha..-HCH), naphthalene, acenaphthylene, fluorene, and phenanthrene were 5.9, 11, 4.7, 3.2, and 24 ng/L, respectively, at OGC. The mean values for the Portland events were 47, 72, 55, 43, and 140 ng/L, respectively. Since dissolved concentrations were measured, the data were also used in conjunction with available Henry's law constants to estimate the concurrent, local atmospheric levels of these compounds at these sites. Many of the H values of interest are available only near T = 298 K. Therefore, the further understanding of the wet deposition of toxic organic compounds will be facilitated by the direct study of wetmore » deposition as well as by the determination of the temperature dependence of the H values of environmentally interesting compounds. 36 references.« less

Effects of flow rate and temperature on the thermal desorbability of polycyclic aromatic hydrocarbons and pesticides from Tenax-GC

One factor limiting adsorption/thermal desorption (ATD) preconcentration techniques is the thermal desorbability of the analyte compounds. The behavior of a set of compounds including polynuclear aromatic hydrocarbons (PAH) and several pesticides on 0.110 g of the sorbent Tenax-GC was investigated as a function of desorption temperature and carrier gas flow rate. The recoveries obtained with helium at 11.2 mL/min are as follows: naphthalene, 99 +/- 1; fluorene, 70 +/- 1; ..cap alpha..-BHC, 97 +/- 8; heptachlor, 26 +/- 5; fluoranthene, 99 +/- 1; pyrene, 93 +/- 1; dieldrin, 120 +/- 3; DDD, 60 +/- 2;DDT 20 +/- 1; benzo(k)fluoranthene, 93 +/- 3; perylene, 89 +/- 2; and benzo(ghi)perylene, 88 +/- 5. The desorbing compounds were trapped on a fused silica capillary column at -30/sup 0/C. Excellent resolution and separation number performance was maintained despite the use of high desorption carrier gas flow rates. Estimates were made of the retention volume and desorbing peak width characteristics of several of the compounds on Tenax-GC at the desorption temperatures studied. 5 figures, 3 tables.

Adsorption-thermal desorption as a method for the determination of low levels of aqueous organics

Adsorption followed by thermal desorption (ATD) with Tenax GC is an effective analytical tool for the preconcentration-analysis of water samples containing μ/kg quantities of the three United States Environmental Protection Agency (U.S. EPA) “Priority Pollutants” p-dichlorobenzene, hexachloro-1,3-butadiene, and 2-chloronaphthalene. A centrifugation method allows the removal of all but 80 μl of water from a glass cartridge packed with 0.75 g Tenax GC. A 10-min follow-up vacuum-desiccation step will reduce the residual water to ≈ 5 μl. A new procedure is presented for conducting recovery tests with sparingly soluble compounds and for the desorption of loaded cartridges. The recovery efficiencies for the tree compounds showed little dependence upon the sample flow-rate in the range 0.25–2.0 ml/sec. One cartridge absorbed ≈ 80% of these compounds at all flow-rates, and a second cartridge in series recovered the remaining ≈ 20%.