Thermal desorption

An analytical methodology using Automatic Thermal Desorption (ATD) and GC/MS was developed for the determination of the pesticides alachlor, atrazine, captan, formothion, lindane and phosalone in atmospheric samples. This methodology was developed to evaluate the atmospheric contamination by pesticides during treatments and by post-application. Atmospheric samples were collected by using (4 i.d.×89 mm) stainless steel sampling tubes containing 125 mg

A new technique for analyzing the overall full range of volatile to semi-volatile organic compounds in high alcohol containing beverages using Vacuum Assisted Sorbent Extraction (VASE) in headspace paired with GCMS analysis is presented. 

A cartridge containing approximately 70mg of Tenax is placed into a sample vial containing either neat or diluted sample containing a high amount of alcohol. A vacuum tight interface allows the vial headspace to be evacuated to less than 0.01 atmospheres, or at least to the point where an aqueous mixture starts to boil at 25°C.  The vacuum is only applied for the time it takes to evacuate the vial, about 15-30 seconds depending on vial size. The vial remains under vacuum after removal of the vacuum source, creating a closed system where faster diffusion from the sample/headspace boundary layer to the adsorbent enhances rates of extraction for both low and higher volatility compounds.

Heavy volatile compounds with low vapor pressures which have little to no response by classical SPME are extracted 10-50x more efficiently. Unlike dynamic headspace, which uses an inert gas to sweep the volatiles of a sample through the adsorbent bed to concentrate and trap analytes, VASE is performed statically. VASE allows the sample and headspace to come to an equilibrium in a closed system, causing analytes to diffuse onto and collect at the very front of the adsorbent bed. Therefore, VASE achieves a much better recovery of heavier compounds while eliminating the common carryover issues.

Once placed under vacuum, the extraction time ranges from minutes to hours until equilibrium between the sample and headspace is reached to produce complete, reproducible extractions. This helps to prevent changes in extraction efficiency when small differences in the sample matrix occur. Additionally, using a packed adsorbent trap for VASE has the advantage of providing 100x more capacity than a GC capillary columns, allowing split injections of 50:1 or more to achieve rapid injection rates while still maximizing the amount that can be loaded onto capillary a GCMS systems for maximum sensitivity and optimum detection limits. In the case of alcoholic beverages, an increased phase ratio is extremely important in dealing with the high affinity of most odor and flavor compounds to the high alcohol containing matrix (up to 40% alcohol by volume).

Data is presented showing rum, whiskey, and wine samples analyzed using VASE, with and without the addition of water or a saturated sodium sulfate solution to determine the optimum approach for recovering volatile to semi-volatile compounds in the sample. Calibration curves of trace level contaminants in wine are also presented showing calibrations from 0.1 to 20 ng/L for Trichloroanisoles, Tribromoanisole,  Geosmin, and 2-Methylisoborneol, using Geosmin-d3 as the internal standard.  Consistent recovery of these compounds in spiked and non-spiked drinking water and wine demonstrated the ability to perform measurements in matrices with varied complexity and affinity for the target analytes. The results show the extensive range of compounds extracted using VASE. This demonstrates its potential as a sensitive and routine method for examining aroma compounds relating to flavor analysis and regulated contaminants such as trichloroanisoles and phthalates in alcoholic beverages.

Hydrogen sulphide is an environmentally hazardous gas which is present in many gas streams associated with oil and gas industry. Oxidation of H 2S to sulphur in air produces no bulky or waste material and requires no further purification. Activated carbon is known as a catalyst for this reaction. In this research, a coal-based precursor (luscar char) and a biomass-based precursor (biochar) were used for production of activated carbons by two common methods of activation: physical and chemical activation in which steam and potassium hydroxide (KOH), respectively, were used. Experiments were designed by the statistical central composite design method. Two models were developed for the BET surface area and reaction yield of each activation process. These models showed the effects of operating conditions, such as activation temperature, mass ratio of activating agent to precursor, activation time, and nitrogen flowrate on the BET surface area and reaction yield for each activation method for each precursor. The optimum operating conditions were calculated using these models to produce activated carbons with relatively large BET surface area (> 500 m2/g) and high reaction yield (> 50 wt %). The BET surface area and reaction yield for activated carbons produced at optimum operating conditions showed maximum 7 and 7.4% difference, respectively, comparing to the values predicted by models. The activated carbons produced at optimum operating conditions were used as the base catalysts for the direct oxidation of 1 mol % hydrogen sulphide in nitrogen to sulphur at the temperature range of 160-205°C and pressure of 700 kPa. Originally activated carbons showed a good potential for oxidation of hydrogen sulphide by their selectivity for sulphur product and low amount of sulphur dioxide production. To improve the performance of steam-activated carbons, the catalysts were modified by acid-treatment followed by thermal desorption. This method increased the break-through times for coal-based and biomass-based catalysts to 115 and 141 minutes, respectively. The average amounts of sulphur dioxide produced during the reaction time were 0.14 and 0.03% (as % of hydrogen sulphide fed to the reactor) for modified activated carbons prepared from biochar and luscar char, respectively. The effects of porous structure, surface chemistry, and ash content on the performances of these activated carbon catalysts were investigated for the direct oxidation reaction of hydrogen sulphide. The acid-treatment followed by thermal desorption of activated carbons developed the porosity which produced more surface area for active sites and in addition, provided more space for sulphur product storage resulting in higher life time for catalyst. Boehm titration and temperature program desorption showed that the modification method increased basic character of carbon surface after thermal desorption in comparison to acid-treated sample. In addition, the effects of impregnating agents (potassium iodide and manganese nitrate) and two solvents for impregnation process were studied on the performance of the activated carbon catalysts for the direct oxidation of H2S to sulphur. Sulphur L-edge X-ray near edge structure (XANES) showed that the elemental sulphur was the dominant sulphur species in the product. The kinetic study for oxidation reaction of H2S over LusAC-O-D(650) was performed for temperature range of 160-190°C, oxygen to hydrogen sulphide molar ratio of 1-3, and H2S concentration of 6000-10000 ppm at 200 kPa. The values of activation energy were 26.6 and 29.3 kJ.gmol-1 for Eley-Rideal and Langmuir-Hinshelwood mechanisms, respectively.

This study reports a general assessment of the organic composition of the PM(2.5) samples collected in the city of Augsburg, Germany in a summer (August-September 2007) and a winter (February-March 2008) campaign of 36 and 30 days, respectively. The samples were directly submitted to in-situ derivatisation thermal desorption gas chromatography coupled with time of flight mass spectrometry (IDTD-GC-TOFMS) to simultaneously determine the concentrations of many classes of molecular markers, such as n-alkanes, iso- and anteiso-alkanes, polycyclic aromatic hydrocarbons (PAHs), oxidized PAHs, n-alkanoic acids, alcohols, saccharides and others. The PCA analysis of the data identified the contributions of three emission sources, i.e., combustion sources, including fossil fuel emissions and biomass burning, vegetative detritus, and oxidized PAHs. The PM chemical composition shows seasonal trend: winter is characterized by high contribution of petroleum/wood combustion while the vegetative component and atmospheric photochemical reactions are predominant in the hot season.

Two methods for determining fuel contamination in groundwaters are compared. The first is based on headspace extraction, while the other utilizes purge and trap. Analyses, in both cases, are made by gas chromatography/flame ionization detection, with benzene, toluene, and xylene isomers as monitoring agents for fuel leaks. When compared, results show satisfactory agreement if we take into account the high