Analytes semi- volatile

Fisk JF. 1986. Semi-volatile organic analytical methods - general description and quality control considerations. In Perket CL, ed. Quality control in remedial site investigation Hazardous and industrial solid waste testing, ASTM Spec Tech Publ 925. Vol. 5, American Society for Testing and Materials, 143-156. 

SFE-GC-MS is particularly useful for (semi)volatile analysis of thermo-labile compounds, which degrade at the higher temperatures used for HS-GC-MS. Vreuls et al. [303] have reported in-vial liquid-liquid extraction with subsequent large-volume on-column injection into GC-MS for the determination of organics in water samples. Automated in-vial LLE-GC-MS requires no sample preparation steps such as filtration or solvent evaporation. On-line SPE-GC-MS has been reported [304], Smart et al. [305] used thermal extraction-gas chromatography-ion trap mass spectrometry (TE-GC-MS) for direct analysis of TLC spots. Scraped-off material was gradually heated, and the analytes were thermally extracted. This thermal desorption method is milder than laser desorption, and allows analysis without extensive decomposition. 

SPME can be used to extract organic compounds from a solid matrix as long as target compounds can be released from the matrix into the headspace. For volatile compounds, the release of analytes into the headspace is relatively easy because analytes tend to vaporise once they are dissociated from their matrix. For semi-volatile compounds, the... 

An ELSD reduces the HPLC eluent into a particle stream and meas-nres the scattered radiation. It offers nniversal detection for non-volatiles or semi-volatiles and has higher sensitivity than the RI detector (low ng) in addition to being compatible with gradient analysis.It is routinely nsed in combinatorial screening. Response factors are less variable than those of other detectors. An ELSD consists of a nebnlizer eqnipped with a constant temperature drift tube where a counter-current of heated air or nitrogen reduces the HPLC eluent into a fine stream of analyte particles. A laser or a polychromatic beam intersects the particle stream and the scattered radiation is amplified by a photomultiplier. Manufacturers include Alltech, Polymer Laboratories, Shimadzu, Waters, Sedere and ESA. 

The advantage of headspace mode is that only volatile components that will not contaminate the GC are injected. InvolatUes do not partition into the headspace and so never enter the injector. Effectively, the analyte is decoupled from the influence of the drug (but see the discussion on validation below). However, many analytes that are amenable to GC by direct injection are not sufficiently volatile to give a high-enough vapour pressure to be detected by conventional headspace injection. These semi-volatile components can sometimes be successfully analysed using a variant of the headspace technique known as total vaporisation headspace injection. In this instance, a few microlitres of the sample solution are injected into the headspace vial, which is then incubated at a temperature that vaporises the solvent completely into the headspace. 

Target analyte range Formaldehyde and VOCs (n-hexane to n-hexadecane) Very volatile and semi-volatile organic compounds also considered... 

All fuel methods analyze GRO with a purge and trap sample introduction technique, whereas semi volatile diesel fuel and heavy, non-volatile motor oil (DRO and RRO) are first extracted from soil or water samples, and the extracts are injected into the analytical instrument. This distinction in sample preparation gave rise to the terms of total purgeable petroleum hydrocarbons (TPPH) or total volatile petroleum hydrocarbons (TVPH) and total extractable petroleum hydrocarbons (TEPH). A group of petroleum fuels with the carbon range of C7 to Cig may be analyzed with either technique. Common petroleum fuels and other petroleum products fall into these three categories as shown in Table 2.3. 

GC has been used extensively for the separation and determination of volatile organic molecules, and most aspects of this application area are fully documented in monographs on this technique. In the inorganic trace analysis area, however, fewer species possess the required volatility, and applications tend to be limited to the separation of volatile species of low molecular weight (such as methyl derivatives of As, Se, Sn, Hg) and the separation of semi-volatile organo-metals, metal halides, metal hydrides, metal carbonyls and metal chelates. For organo-metal species, the type of detection system required varies with the nature of the analyte, and the options include electron capture detection, flame photometric detection (sometimes ICP), AAS and MS. 

Determination of the optimum time for which the SPME sorbent will be in direct contact with the sample is made by constructing an extraction-time profile of each analyte(s) of interest. The sorption and desorption times are greater for semi volatile compounds than for volatile compounds. To prepare the extraction-time profile, samples composed of a pure matrix spiked with the analyte(s) of interest are extracted for progressively longer times. Constant temperature and sample convection must be controlled. Stirring the... 

For semi volatile compounds, inlet optimization is very simple. Classical splitless inlet conditions, followed by an initial column temperature cool enough to refocus the analyte peaks following the desorption, work well. Thus, a typical condition would be a temperature of about 250° C, a head pressure sufficient to maintain optimum GC column flow and an initial column temperature at least 100°C below the normal boiling point of the analyte. For semivolatile analytes, a classical splitless inlet liner can be used, as the cool column will refocus these peaks. The desorption time in the inlet must be determined by experimentation, but typically, runs between 1 and 5 minutes. 

Fig. 4.8. Custom-made set-up for the separation of potential semi-volatile interferences from volatile analytes. (Reproduced with permission of the American Chemical Society.)...

Based on available results, dynamic and static HS mode is complementary rather than competitive. The better choice in each case will depend on the sample-analyte interaction. Thus, the dynamic modes are better suited to semi-volatile compounds in water, while the static modes are to be preferred for solid and semi-solid samples. 

The desorption temperature usually ranges from 150 to 250°C for semi-volatile compounds. Usually, the optimum desorption temperature is roughly equal to the boiling point of the least volatile analyte [214]. In order to prevent broadening of the chromato-... 

This design affords shorter analysis times with minimal solvent consumption also, no preconcentration step is required as preconcentration is achieved simultaneously with distillation by retaining distilled analytes on the solid-phase material. This device features a broad range of uses in the analysis of semi-volatile compounds in solid samples with high moisture contents. 

There has been sustained interest in the development of analytical methods for realtime monitoring of environmental pollutants in recent years. Semi-volatile organic compounds tend to be adsorbed onto the surface of aerosol particles of respirable sizes and pose potential health hazards. Conventional methods used for the analysis of organic compounds that are present on the surface of aerosol particles are based on particle collection followed by extraction and chromatographic analysis of extracted species [90,91]. These methods require large amounts of sample and long analysis times. 

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