Dynamic purge

Corwen [140] used dynamic purge and trap analysis to determine ketones and aldehydes (acetone, butyaldehyde, and 2-butanone) in seawater. 

Figure 21.5 Gas extraction. Also called the dynamic purge-and-trap method. Principle of a gas/solid extraction column. A chemical transformation used to detect an aldehyde hy deriva-tivization (testing polluted atmosphere, Supelco Inc.).

This relatively simple technique can provide sensitivity similar to the above dynamic purge-and-trap analysis. Headspace is a sampling device used in tandem with a GC installation (Figure 21.6). It is reserved for the analysis of volatile compounds present in a matrix, which cannot be itself directly analysed by... 

Purging Carrier and Makeup Gases Carrier-gas and makeup-gas systems require a static purge, followed by a dynamic purge, to ensure the desired purity levels. 

DYNAMIC PURGE After the last static purge, close the shutoff valves at the vent ends of the lines and bring the mainline pressure to 20 psig (1.4 bar). Choose a shutoff valve as far downstream from the cylinder as possible. Open this valve and adjust the valve to allow a 60 mL/min flow of gas. Purge for 24 hs. For this step an extra flow controller, installed after the opened shutoff valve, will make it easy to regulate the flow and will help minimize backdiffusion into the line. 

There are two methods of analysing the volatiles of a sample which have very different requirements concerning the instrumentation the static and dynamic (purge and trap, P T) headspace techniques. The areas of use overlap partially but the strengths of the two methods are demonstrated in the different types of applications. 

H. Ehret, V. Ducruet, A. Luciani, and A. Feigenbaum, Styrene and ethylbenzene migration from polystyrene into dairy products by dynamic purge and trap gas chromatography, J. Food Sci. 59 990 (1994). 

The labyrinth portion of the seal was designed to withstand the static and dynamic differential pressure (in the event of a major seal failure) while passing the minimum volume of purge gas. 

Gas phase stripping (purge-and-trap) techniques can iaq>rove the yield of organic volatiles from water or biological fluids by facilitating the transfer of volatiles from the liquid to the gas phase it is also more suitable than dynamic headspace sampling when the sample volume is restricted (320 23,347-351). Tbe technique is used routinely in many laboratorl B for the analysis... 

Haneda et al. [134,135] studied the formation and reaction of adsorbed species in NO reduction by propene over Ga203-Al203. IR transient reaction technique was employed to examine the reactivity and dynamic behaviour of surface species. The catalyst was first exposed to either C3H6/02/Ar or NO/Oz/Ar at 623 K for a long time to form and accumulate the surface species. The catalyst was further purged with pure Ar and the reaction gas then switched to various gas mixtures. Changes in the intensity of IR bands were measured with time on stream. The main surface species detected by IR during... 

In this method volatile organic matter in seawater is concentrated on a Tenax GC solid adsorbent trap and dry-ice trap in series. The trapped organic material is then desorbed and oxidised to carbon dioxide, which is measured with a non-dispersive infrared analyser. A dynamic headspace method was used for the extraction with the assistance of nitrogen purging. Dynamic headspace analysis [184] is an efficient extraction procedure. The efficiency of extraction... 

Blood, urine, adipose tissue Dynamic headspace purge cap. GC/FID Not reported 86-120 (blood) 48-110 (urine) 13-80 (adipose) for model compounds Michael et al. 1980... 

Dynamic headspace-extraction stripping and purge-and-trap methodology are used most often for determination of M-hcxanc in water and hazardous wastes. Dynamic headspace extraction techniques have been applied to water samples (Roberts and Burton 1994) and sediment (Bianchi et al. 1991). Detection limits of 0.5 g/L were reported for lake water (Roberts and Burton 1994) and 20 ng/kg (ppt) for sediment (Bianchi et al. 1991). Supercritical fluid extraction (SFE) is a relatively new technique that has been applied to -hcxane in soil (Yang et al. 1995). Membrane extraction of M-hexane from water samples has been developed to provide online, continuous monitoring (Wong et al. 1995 Xu and Mitra... 

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