Low-volatility compounds

Steam extraction has been used for gasoline and diesel fuel. High-molecular-weight components of the diesel fuel cannot be removed easily, although a total removal of up to 91% is possible. When used to remove low-volatility compounds in a soil with a high percentage of clay, performance is expected to be ca. 85%. The mobile in situ steam extraction system can reduce VOCs in soils by more than 50% of their initial level. Based on pilot studies, the stationary steam extraction system is expected to have a 90% removal efficiency.54... 

The Henry s law constant is an air-water partition coefficient, which can be determined by measurement of solute concentrations in both phases [11,58,59]. Some effort has been devoted to devising techniques in which concentrations are measured in only one phase and the other concentration is deduced by a mass balance. These methods are generally more accurate. The principal difficulty arises with hydrophobic, low volatility compounds which have only small... 

Rittfeldt, L. Determination of vapor pressure of low volatility compounds using a method to obtain saturated vapor with coated capillary columns, Anal Chem., 73(11) 2405-2411, 2001. 

Tesconi, M. and Yalkowsky, S.H. A novel thermogravimetric method for estimating the saturated vapor pressure of low-volatility compounds, J. Pharm. Sci., 87(12) 1512-1520, 1998. 

The mass spectrometer when used as a detector for liquid chromatography is a universal detector and in most instances has no influence on the chromatographic separation. LC/MS spectra obtained from both volatile and low- volatile compounds are similar to ordinary El spectra and may be interpreted by comparison with normal reference spectra collections. Interpretable mass spectra can also be obtained from nonvolatile compounds. 

For DNAPL vaporization to work, the soil material must be permeable enough for the vapor bubbles to rise to the top of the water table. DNAPL vaporization is not effective for some low-volatility compounds, such as dichlorobenzene, diesel fuel, naphthalene, phenol, trichlorobenzene, and trichloropropane, unless it is coupled with groundwater sparging. All information is from the vendor and has not been independently verified. 

One of the few properties all aroma compounds have in common is they must be volatile if they are not volatile, they cannot make a contribution to olfaction. With this said, there is a very broad range in volatility across aroma-active compounds so one obtains a disproportionately large proportion of very volatile compounds and lesser amounts of low-volatility compounds in all aroma isolates obtained based on this property. 

Quantitative Detection of Vapors from Low Volatility Compounds , USP 3883739 (1975) 105) L. Elias M. Krzymien, Methods of Evaluating the Sensitivity of Explosives Vapor Detectors , Lab Tech Rept LTR-VA, Natl Res Council, Canada (1975) 106) T. Kraziejko,... 

Particle induced desorption methods are commonly used to ionize low-volatility compounds. Cesium ion desorption (or cesium ion secondary ion mass spectrometry, SIMS) uses a primary beam of cesium ions to desorb and ionize a non-volatile sample. This technique has been used with FTMS to produce pseudomolecular ions of vitamin B12, ((812)2 + Cs - 2CN +, at m/z 2792 (24) and molecular ions of beta-cyclodextrin (m/z 1135) (92, 93). Detection limits of 10"13 mol for the peptide gramicidin S has been demonstrated using Cs+ SIMS with FTMS (25), and additional structural information was obtained using MS/MS processes. 

Spieksma, W., Luijk, R., Govers, H.A.J. (1994) Determination of the liquid vapour pressure of low-volatility compounds from the Kovats retention index. J. Chromatogr. A, 672, 141-148. 

A unique air-sampling probe shown in Figure 8 was developed to eliminate sampling problems. The absorption and concentration of low volatile compounds had been a particular problem due to the propensity of the materials to adhere to... 

Cholesterol is a low-volatile compound, but it is more volatile than the major triglycerides of milkfat. Superheated steam can be bubbled through the oil, heating it indirectly, which provides for the latent heat of vaporization of the distilling compounds and prevents steam condensation. Thus, the temperature and pressure can be varied independently. When the sum of the partial vapor pressures of water vapor and the distillates is equal to the total pressure, water vapor and the low-volatile components, such as cholesterol and free fatty acids, distill over. 

To make supercritical extraction processes more economic, separation of solute and solvent can be performed thanks to a membrane system. Sartorelli and Brunner [19] demonstrated that a membrane separation process can be proposed instead of the typical supercritical fluid cycle in the case of supercritical extraction to drastically reduce the energy losses. In fact, a stream of low volatile compounds (LVC) extracted by SC CO2 can be discharged of 80%-90% of LVC using a nanofiltration membrane with a drop of pressure equal to 2 MPa instead of about 20 MPa in the typical supercritical fluid cycle. 

Since membrane distillation exhibits high abihty of concentration of aqueous solutions with high retention of acids, salts, and other low-volatile compounds, it can be used for concentration of different radioactive waste streams with high volume reduction and high retention factors [97-99]. 

The derivatization is commonly done for medium and low volatility compounds. The volatile compounds are more frequently analyzed by on-line techniques without derivatization, although on-line derivatization is occasionally utilized (such procedures were discussed in Section 2.7). When the off-line derivatization is done for the pyrolysate generated in a furnace, no particular precautions are recommended. For Curie-point or filament type pyrolysers, the pyrolysate can be collected in a deactivated piece of capillary column connected to the pyrolyser and cooled either in an ice bath or at lower temperatures needed for capturing more volatile compounds. 

An environmental application of liquid extraction is the removal of trace organics from water. Examples are the separation of acetic acid-water mixtures and removal of solvents, insecticides, pesticides, etc., from water. It can also be applied to the separation of liquids with close boiling points or those that form azeotropes, such that distillation is not useful. In addition, zero- or low-volatility compounds, such as metals and organometallic derivatives, can be separated by liquid extraction as can mixtures of water-hydrogen bonded compounds, such as formaldehyde. Solid extraction (leaching) can be used to remove organics or heavy metals from contaminated soils, sludges or contaminated equipment. 

The detailed test protocols are recommended for those compounds falling in the class of high or intermediate volatility. For low volatility compounds, the detailed test protocol is recommended if the screening study suggests that other processes, such as photolysis and biodegradation, are slow. 

Impurities Concentration of impurities by using chemical absorbers, which form low-volatility compounds with impurity after concentration (sometimes after regeneration) gas chromatographic impurity analysis is carried out 123-124... 

In chemical transport, non-volatile or low volatility compounds are transformed by the influence of a reagent to a volatile species, which is transported and deposited by deeomposition on the substrate. Therefore, the deposition process can be described as ehemical deposition. 

Although 100 fim polydimethylsiloxane (PDMS) film seems to be the most suitable and widely used for the analysis of BTEX, 75 /rm Carboxen-PDMS seems have higher extraction efficiencies for low volatility compounds.Figure 14.2 shows higher responses for Carboxen-PDMS than for PDMS fiber, but it is also seen how the response of the former depends too much on the total concentration of analytes, probably because an adsorption or condensation mechanism also takes place in the extraction process. Thus, the repeatability for the 75 /rm Carboxen-PDMS is lower than for 100 /rm PDMS. 

In another case study, Zellweger et al., (1997e) studied the emission of hexanal fi om linoleum in an office. SER measured with the FLEC (both on-site and in-lab) correlated well with the area-specific emission rates (SER ) calculated on ventilation rate and room air concentrations. The FLEC measurements also revealed that low-volatility compounds such as glycol ethers from the room air had absorbed on the linoleum, although the linoleum initially did not emit any glycols. Relatively often, low-volatility VOCs are subject to sink effects. 

The enthalpies of phase changes of low-volatility compounds are not generally determined directly, but are derived fi om die measured relation between vapour pressure and temperature with the help of the Clausius-Clapeyron equation (13). 

For illustrative purposes, vapour pressure may be portrayed as solubility in air. This parameter is strongly dependent on the ambient temperature if measured at different temperatures, the logarithm of can be linearly related to the reciprocal temperatures (K). For most liquids, vapour pressure ranges between 10 and 4 x 10 Pa at room temperature. It is experimentally accessible using a (mercury) manometer to measure the pressure established in the gas phase above the pure compound at defined temperatures. For volatile chemicals p > 100 Pa), measured data are generally accurate, whereas for low-volatility compounds (p < 100 Pa), the experimental results may scatter by one order of magnitude (Schwarzenbach, Geschwend and Imboden, 1993). 

Seven reductive sulfur compounds, out of fourteen that could be analysed using the GC-MS procedure, were found in the Cabernet Sauvignon wine, and their concentrations were monitored at the beginning and the end of the trial. The highly volatile sulfur compounds (boiling point less than 90 °C) foimd to be present were methanethiol (MeSH) and dimethyl sulfide (DMS). The wine also contained five low volatile compounds (boiling point above 90 °C), including dimethyl disulfide (DMDS), methyl thioacetate (MTA), S-ethyl thioacetate (ETA), 2-(methylthio)-l-ethanol (MTE) and 3-(methylthio)-l-propanol (MTP) (methionol). 

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