Analyte collection

After dissolving the sample in a beaker, remove any solid impurities by filtering a portion of the solution containing the analyte. Collect and discard the first several milliliters of solution before collecting a sample of approximately 5 mL for further analysis. 

The permeation dosimeter operates on the principle that the rate at which a gas permeates a given membrane is a fixed value, and the total mass of the gas that is transported through the membrane is a function of the concentration of the gas in the ambient atmosphere and the time of exposure. The quantity of analyte collected is given by equation (8.8)... 

Tybsre m is the total mass of analyte collected, D the molecular diffusion coefficient, A the area of the diffusion channel, L the diffusion path length, C the analyte concentration in the air, and Tt the sampling time. In deriving equation (8.7) it was assumed t. that the sorbent is effective sink for the analyte and,... 

Analyte collection/trapping scheme (packed bed or solvent trapping)... 

Analyte collection temperatures (restrictor, trap, elution)... 

Off-line SFE is inherently simpler for the novice to perform, since only the SFE (and analyte collection) step needs to be understood. In off-line SFE further cleanup or a pretreatment step can be employed to eliminate interferences. With off-line SFE, sensitivities are limited by the fact that only about 1 p,L of the collection solvent is generally injected into the GC. The daily sample throughput can be higher using offline SFE, since SFE-GC requires that the GC be used for a sample collection device (rather than performing chromatographic separations) during the SFE extraction, whereas several off-line extracts can be loaded into an autosampler for unattended GC analysis. 

Elimination of analyte collection, evaporation, reconstitution and injection... 

One of the requirements of this approach is that the analytes must be stable at the boiling point of the solvent, since the analytes collect in the flask. The solvent must show high solubility for the analyte and none for the sample matrix. Since this is one of the oldest methods of sample preparation, there are hundreds of published methods for all kinds of analytes in as many matrices. For example, XAD-2 resin (sty-rene-divinylbenzene) that was used to collect air samples to monitor current usage of pesticides in Iowa was Soxhlet-extracted for 24 h with hexane/acetone [22], This is common in environmental sample analysis, and one will see rows and rows of these systems in environmental laboratories. One disadvantage of Soxhlet extraction is the amount of solvent consumed, though modern approaches to solid sample extraction have tried to reduce the amount of solvent used. 

Small stationary phase coated fiber exposed to sample, then transferred to inlet Inert gas bubbles through sample vaporized analytes collected on trap and desorbed into GC Supercritical carbon dioxide extracts analytes from liquid and solid samples... 

The process can take one of two forms. In one, the sample and liquid are shaken (or otherwise agitated) together in the same container, the resultant mixture filtered, and the filtrate, which then contains the analyte, collected. In the other, fresh liquid is continuously cycled over a period of hours through the solid sample via a continuous evaporation-condensation process (that usually does not require an extra filtration step), and the liquid is collected. This latter method is known as a Soxhlet extraction. Soxhlet extraction will be discussed in more detail in Chapter 11. 

Extraction of semivolatile analytes collected using modified Method 5 (Method 0010) sampling train Accelerated solvent extraction (ASE) (3545A in update IVB) Ultrasonic extraction... 

CoxRD. 1983. Analytical collection and analytical techniques for volatile organics in air. Specialty conference on Measurement and monitoring of non-eriteria eontaminants in air, 101-112. 

Wang Ang 1990, first published in 1682 Analytic collection of medical formulas (Yi Fang Ji Jie . №). China Press of Traditional Chinese Medicine, Beijing... 

Application of SFE necessitates a CO2 source, a pump to pressurize the fluid, an oven containing the extraction vessel, a restrictor to maintain a high pressure in the extraction line, an analyte collection vessel, and an overall system controller. CO2 is drawn from the bottom of the tank with a dip tube because the liquid is the more dense of the two phases. The substantial vapor pressure of the CO2 at ambient temperature helps to displace the liquid into the pump. CO2 remains a liquid throughout the pumping or compression zones and passes through small-diameter metal tubing as it approaches the extraction vessel. A preheating zone in front of the extraction vessel allows supercritical temperature, pressure, and density conditions to be applied immediately to the analyte matrix in the vessel. 

In preconcentration, analyte collected from 150 mL was dissolved in 200 pL. The concentration increased by a factor of... 

Supercritical fluid extraction system - Hewlett Packard Model 7680A totally automated system with unlimited-capacity reciprocating pump, specially designed extraction chamber with safety interlocks, a variable restrictor nozzle and analyte collection trap. The operation of the extractor is controlled by a personal computer which is a Microsoft Windows-based system. An animated status screen provides real-time monitoring of the extraction process. Table II gives the SFE conditions for the HP extractor. 

The following basic procedures generally apply to all extractions performed. In cases where the extract did not undergo further analysis, steps related to analyte collection do not apply. 

Air analysis for carbamate pesticides may be performed by sampling air over 1 pm PTFE membrane. The analytes collected over the membrane are extracted with methylene chloride, exchanged into methanol, and analyzed by HPLC using postcolumn derivatization technique as described above. Certain pesticides may be analyzed too by the colorimetric method (see Part 3 under individual compounds). 

A new analyte collection method for off-line SFE based on mixing an expanding supercritical effluent with overheated organic solvent vapor.97... 

Vejrosta, J., P. Karasek, and J. Planeta. 1999. Analyte collection in off-line supercritical fluid extraction. Anal. Chem. 71 905-909. 

Utilization of an extraction membrane as analyte collecting medium in combination with thermal desorption Thermal Membrane Desorption Application - TMDA)... 

Utilization of passive dosimeters of permeation type of analyte collection stage and thermal desorption of their release... 

Data pipelining via enterprise server applications such as Pipeline Pilot (Accelrys/Scitegic), Inforsense, or the Talend (http //www.talend.com/) and KNIME (http //www.knime.org/) open source tools represent a powerful approach to integrate applications and develop custom functionality. As a specific application, Pipeline Pilot 7.0 includes a plate analytics collection for the development of complex plate-based data analysis and visualization protocols. 

Huopalahti and Henion " reported anabolic steroid extraction from bovine tissues. SFE was performed with CO2 at 60°C and 405 bar, with analytes collected in precooled methanol and quantitated using LC-MS analysis. Residues of 2-thiouradl, 6-methyl-2-thiouradl, 6-propyl-2-thiouracil, and 6-phenyl-2-thiouracil in bovine muscle tissues were extracted with SC CO2 and analyzed using GC-MS. ... 

As mentioned before, microdialysis is a sampling technique controlled by diffusion. Because a fluid continuously perfuses the probe, equilibrium conditions will not be reached, and only a fraction of the actual concentration of the analytes present in the medium surrounding the probe will be collected. The amount of analyte collected is normally defined as recovery . 

The development of new analyte collection methods using decreased amounts of solvent — and hence providing more concentrated extracts — is one other focus of current SFE research [43]. 

A typical supercritical fluid extractor includes a supercritical fluid (most often CO2 or CO2 with an organic modifier) source, a means of pressurizing the fluid, a pumping system (for the liquid CO2), an extraction thimble, a device to depressurize the supercritical fluid (flow restrictor), an analyte collection device, temperature-control systems for several zones, and an overall system controller. 

Analyte collection mode Solvent bubbling Sorption... 

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