Solvent trapping

While partially concurrent eluent evaporation is easier to use, and is preferred for the transfer of normal phase solvents, concurrent eluent evaporation with co-solvent trapping is the technique of choice for transfer of water-containing solvents, because wettability is not required. 

Figure 2.7 (11) shows a gas chromatogram obtained by co-solvent trapping and concurrent eluent evaporation after injecting 500 p.1 of diluted gasoline. The main solvent was -pentane with 5% of -heptane as co-solvent. It is noteworthy that without the co-solvent, higher-boiling compounds could be lost. 

In order to ascertain that the NDELA formation does not occur as a result of trapping of the smoke or during the analysis, we added diethanolamine to tobacco prior to extraction with ethyl acetate in the presence of ascorbic acid. The control value for NDELA was 121 ppb and the experiment with 5.5 iqg diethanolamine addition yielded 113 ppb NDELA. For control of the smoke analysis we added 5.5 mg of DELA in the solvent trap and smoked cigarettes known to be free of DELA. Analysis of the trapped material showed no significant quantities of NDELA, so that artifactual formation of this nitrosamine during smoke collection and analysis can be ruled out. 

Figure 3.6 Different peak distortion problems due to band broadening in time and band broadening in space observed during hot splitless injection. Band broadening in space is characterized by a broadening which grows proportionally with retention time and may result in peak splitting that is poorly reproducible. Band broadening in time is characterized by a constant broadening of all peaks. Partial solvent trapping results in characteristic chair and stool shaped peaks. (Adapted with permission from ref.

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

A clogged solvent trap resulting in loss of vacuum should be guarded against, t Depending on the temperature of the tap water and the rate of flow, the product may tend to solidify in the distillation head. 

As noted above, formation of a furan [4 + 3]-cycloadduct during irradiation of a 4-pyrone was advanced as evidence for the zwitterionic intermediate. This process can be moderately efficient (equation 4)68, and can be envisioned as an approach to substituted cyclooctanoids. Besides the formation of three new carbon-carbon bonds, an additional attractive feature is the complete diastereoselectivity, arising from a compact [4 + 3]-cycloaddition transition state with approach from the face opposite the epoxide. However, the generality of the intermolecular reaction is limited, as competing [2 + 21-photodimerization, solvent trapping and rearrangement often predominate58. 

Substrates in which the furan was tethered at C-3 have also been examined107. These cases typically possessed ring-oxygenation at C-4, and the nature of this substituent proved to be important (Scheme 50). Examples with a free hydroxyl or a methyl ether at this position led to low yields of cycloadducts 221-224 and substantial amounts of polar by-products, possibly via competing solvent trapping pathways which ultimately lead to... 

Yang Yu, Hawthorne B, Miller DJ. 1995. Comparison of sorbent and solvent trapping after supercritical fluid extraction of volatile petroleum hydrocarbons from soil. J Chromatogr A 699 265-276. 

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. 

Finally, extractions from solids can be performed by heating followed by solvent trapping. Such a procedure is known as thermal extraction. 

DR. SIDERS The data of Beitz and Miller are very interesting but I feel uncertain about their correct interpretation because the measurements were for transfer of an electron from a solvent trap rather than from a molecule. Also, there s lot of scatter in the data, although they do seem to show inversion. Finally, the data were obtained in a 2-methyl-tetrahydrofuran glass at 77°K, which may differ significantly from water at room temperature. 

CHEMICAL KINETICS SOLVENT-TRAPPED INTERMEDIATES SOLVENT ISOTOPE EFFECT KINETIC ISOTOPE EFFECT Solvent parameter,... 

Remove the reflux head, hook up a vacuum Hource with solvent trap and evaporate the solvent under reduced pressure. Warning - The product is now crude Sarin and must be handled accordingly. 

A similar solvent trapping mechanism has been proposed to account for formation of 5-indanol from acid-catalyzed isomerization of the arene oxide tautomer of oxepin (22) (73JA60641). 

For solvent trapping, sample should contain 10 times as much solvent as analyte and column temperature should be 40 C below the solvent s boiling point. 

Splitless injection is required for very dilute solutions. It offers high resolution but is poor for quantitative analysis because less volatile compounds can be lost during injection. It is better than split injection for compounds of moderate thermal stability because the injection temperature is lower. Splitless injection introduces sample onto the column slowly, so solvent trapping or cold trapping is required. Therefore, splitless injection cannot be used for isothermal chromatography. Samples containing less than 100 ppm of each analyte can be analyzed with a column fdm thickness < 1 p.m with splitless injection. Samples containing 100-1 000 ppm of each analyte require a column film thickness 1 p.m. 

---