Sorbent trapping

Headspace methods provide an indirect method of sample analysis suitable for the determination of organic volatiles [11,318-323]. The gas diase in contact with the sample and not the sample matrix itself is taken for analysis. If the sample is in thermodynamic equilibrium with the gas phase in a closed thermostated vessel, then this method of analysis is referred to as static headspace. If a carrier gas is passed over the sample and the sample volatiles accumulated in a cryogenic or sorbent trap, then the method is generally referred to as dynamic headspace. If the carrier gas is introduced below the surface of... 

Flg ire 8.29 Apparatus for siunpling airborne organic samples. A, trapping of organic volatiles in air using a sorbent trap B, thermal desorption chamber C, high-volume sampler for air particulates. 

Figure 8.27 A, apparatus for dynaaic headspace analysis of urine with sorbent trapping. B, gas phase stripping apparatus (purge-and-trap).

Purge, trap on soil sorbent trap, heat and desorb, backflush to GC... 

This is an alternative technique to headspace analysis for the identification and determination of volatile organic compounds in water. The sample is purged with an inert gas for a fixed period of time. Volatile compounds are sparged from the sample and collected on a solid sorbent trap—usually activated carbon. The trap is then rapidly heated and the compounds collected and transferred as a plug under a reversed flow of inert gas to an external gas chromatograph. Chromatographic techniques are then used to quantify and identify sample components. 

Yang et al. [2] have compared sorbent trapping with solvent trapping after the supercritical fluid extraction of volatile petroleum hydrocarbons in soil. Sorbent trapping yielded quantitative collections of n-alkanes as volatile as n-hexane, while solvent trapping effectively collected w-alkanes as volatile as n-octane. 

Water Purge with Inert gas, trap on sorbent trap, desorb thermally GC/HSD Approx. 0.5 ig/L No data APHA 1985a... 

Air-emission sources VOST sampling train (sorbent traps) thermal desorption GC/MS No data No data Method 0030 EPA1994h... 

Agricultural processing will still incorporate solvents. As an example, soybean flakes were extracted with supercritical carbon dioxide to produce a solvent-free, good-quality soybean oil. During the SFE process, volatile compounds were trapped on a porous polymer trap attached at the exhaust port of the SFE apparatus. The volatile profile obtained from the sorbent trap was found to be similar to the headspace profile from the SFE/soybean oil removed during the same extraction. In addition, crude soybean oil was heated in a stirred reactor and the volatiles, which were stripped by supercritical carbon dioxide in an attempt to improve oil properties, were collected on sorbent traps and analyzed by the above method for comparison. The described methodology permits the characterization of volatiles and semivolatUes in SEE soybean oil and can be used to monitor the extraction and quality of the resultant oil (Snyder and King, 1994). 

Three purge and trap methods are used to determine 29 halocarbons (Method 601), seven aromatics (Method 602, including four of the halo-carbons), and acrolein and acrylonitrile (Method 603). The three methods are distinctly different in the sorbent trap materials, GC columns, and... 

EPA Method No. Parameters Purge Temp. Sorbent Trap Column Packing GC Temp. (°C) Detectora... 

Method 624 for Purgeable Volatiles. This method, similar to Methods 601 and 602, simultaneously determines the chlorinated aliphatic and aromatic purgeable priority pollutants. The sorbent trap employed here consists of 1 cm of 3% OV-1 coated solid support, 15 cm of Tenax-GC, and 8 cm of silica gel. The GC column is 6-ft X 0.1-in. i.d. packed with 1% SP-1000 Carbopack B (60-80 mesh) operated under the following oven temperature conditions initial temperature of 45 °C for 3 min, then programmed at 8 °C/min to 220 °C. 

Determinand Subcritical water extractant Sorbent trap Analytical finish Reference... 

Petroleum hydrocarbons co2 Comparison of sorbent trapping with solvent trapping Gas chromatography [149]... 

In general, supercritical fluid extractions can be performed in either an on-line extraction mode or an off-line extraction mode. Off-line supercritical fluid extraction is the most common mode and involves extracting the analytes from the matrix and collecting them in either a sorbent trap or a collection solvent [11]. Following the collection step, the analytes are determined on a separate instrument (for example, on a chromatograph or an infrared spectrometer). In the on-line supercritical fluid extraction experiment, the outlet of the supercritical fluid extraction system is connected to a second analytical... 

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