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Purge sample introduction

For example, if gasoline is suspected to be the sole contaminant, the method will use purge-and-trap sample introduction. If higher-boiling petroleum fractions (diesel, middle distillates, motor oil) are the contaminants, the analysis will use direct injection and hotter oven temperatures. Mixtures or unknown contamination may require both volatile range and extractable range analyses. Alternatively, a single injection can be used to analyze the entire sample, but the extraction method must not use a solvent evaporation step. [Pg.193]

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. [Pg.60]

Much improved limits of detection can be obtained if either quartz or ceramic, flame-heated cells or graphite furnace atomisers are used (Szpunar et al., 1996). The effluent from the chromatograph is passed via a heated line either into the port provided for sample introduction (Radzuik et al., 1979) or the ports for the purge gases (De Jonghe et al., 1980). When the furnace atomiser is not coupled to a chromatograph, a temperature programme would be used to eliminate problems due to the matrix, but this cannot be used when coupled on-line and matrix interferences will occur. [Pg.69]

In an attempt to overcome the significant difficulties that the presence of water vapor poses to the analysis of very volatile compounds, purge-and-membrane extraction techniques have been developed that largely prevent the introduction of water into the analytical system. Typical implementations of this form of sample introduction have been called by its developers membrane extraction with a sorbent interface (MESI),97 or membrane introduction mass spectrometry (MIMS).98 " They are based on a silicone hollow-fiber membrane that is inserted into the sample to be monitored, and the passing of a certain volume of inert gas through the membrane. Volatile compounds permeate the membrane and are swept to the adsorbent trap from which they are desorbed into the GC. This method of sample introduction is particularly suited for field and process monitoring and for dirty samples, since it prevents any nonvolatile compounds from entering the analytical system.100... [Pg.320]

A chromatographic sample introduction technique in volatile components which are purged from a liquid medium by bubbling gas through it. The components are then concentrated by trapping them on a short intermediate column, which is subsequently heated to drive the components on to the analytical column for separation. [Pg.173]

For cold splitless injection, the sample is introduced into the vaporizing chamber at a temperature close to the solvent boiling point with the split vent closed. Shortly after sample introduction, the injector is rapidly heated to the temperature required to transfer the sample into the column, and the vaporization chamber purged of solvent residues by opening the split vent. Similar to hot splitless injection, cold trapping and solvent effects are employed as refocusing mechanisms. [Pg.1871]

Sample preparation was greatly simplified in the late 1990s by the introduction of commercial diamond attenuated total internal reflection (ATR) systems. These use a small diamond as a single-pass ATR element held in a metal plate. The sample is placed on the diamond, a plate is then brought down onto it and clamped in position. This ensures excellent contact between the ATR element and the sample, so immediately eliminates the problem of poor contact that made ATR so problematical for use with solids, particularly powders. The accessory can be permanently installed in the purged sample compartment of the spectrometer, so there is only a very short pathlength that is in the open air. This means that there is no need to wait for the sample compartment to purge to reduce the atmospheric water and carbon dioxide absorption. The result is that the sample can be placed in the accessory and scanned immediately. [Pg.2263]

Gas chromatography (GC) instruments may be equipped with various detectors to accomplish different analytical tasks. Flame ionization and thermal conductivity detectors are the most widely used detectors for routine analyses, nitrogen-phosphorus detectors are used for the trace analysis of nitrogen-containing compounds, and electron-capture detectors are used for halogen-containing compounds. GCs may also be equipped with peripheral accessories such as autosamplers, purge and trap systems, headspace samplers, or pyrolyzer probes for special needs in sample introduction. [Pg.16]

A capillary column, 30 m or longer, with a thick film of stationary phase, offers an alternative to cryogenic oven temperature control for solute-focusing purposes, which is especially attractive with auxiliary sample introduction techniques of purge and trap and thermal desorption. [Pg.141]

Figure 2.21 Possibilities for sample introduction in purge and trap, (a) U tube with/without frits (fritiess/frit sparger) for water sampies. (b) Sampie vessei (needie... Figure 2.21 Possibilities for sample introduction in purge and trap, (a) U tube with/without frits (fritiess/frit sparger) for water sampies. (b) Sampie vessei (needie...
Because the instrumentation requires the monitoring of several steps, valving, heating zones, and so on, purge-and-trap instrumentation is more complex, and may be more expensive to purchase, than other types of sample introduction. [Pg.30]

Hexachloroethane can be detected in tissues at levels as low as 0.001 pg/g (Nolan and Karbowski 1978) and recoveries range from 50 to 130%. Prior to analysis, hexachloroethane must be separated from the biological sample matrix and prepared for introduction into the analytical instrument. Separation may be effected by purging with an inert gas (helium), and trapping on an adsorbent cartridge (Tenax GC ), followed by... [Pg.136]

One method (EPA 8020) that is suitable for volatile aromatic compounds is often referred to as benzene-toluene-ethylbenzene-xylene analysis, although the method includes other volatile aromatics. The method is similar to most volatile organic gas chromatographic methods. Sample preparation and introduction is typically by purge-and-trap analysis (EPA 5030). Some oxygenates, such as methyl-f-butyl ether (MTBE), are also detected by a photoionization detector, as well as olefins, branched alkanes, and cycloalkanes. [Pg.202]


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See also in sourсe #XX -- [ Pg.39 ]




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