Purge-and-trap system

Schematic diagram of a purge-and-trap system. Anaiyte is coiiected in the primary adsorption trap. The secondary adsorption trap is monitored for evidence of breakthrough.

Chloroform was determined on the 500 1 concentrate by using a Tracor 550 gas chromatograph with a 310 Hall electroconductivity detector in the halogen mode, connected to a Tekmar LSC-2 purge and trap system. The column was an 8-ft 1% SP-1000 on 60-80-mesh Carbopack B. An oven temperature gradient of 80-220 °C at 8 °C/min after an initial hold of 2 min was used. Fifty microliters of the acetonitrile concentrate was diluted to 5 mL with organic-free water in the purging vessel for the analysis. 

Nerin, C. Rubio, C. Cacho, J Salat ranca, J. 1996. Determination of Styrene in Yogurt by an Automatic Purge and Trap System Coupled to GC-MS. Presented at ILSI International Symposium Food Packaging Ensuring the Safety and Quality of Foods Budapest, Hungary. 11-13 September. 

After a certain purging period, a six-way valve allows switching of the flow through the system as shown in the simplified diagram of a purge-and-trap system given in Figure... 

Figure 5.2.14. Simplified diagram of a purge-and-trap system with an on-line pyrolyser connected to a GC.

The principle of the purge-and trap system is based on the partition of compounds between a gas and a solid adsorbing phase. The apparent volume of the absorbing solid can be measured and is defined by... 

Rel, (47) gives the relation between the initial concentration of an analyte Co in a solid phase and its concentration in the gas phase Cg, assuming equilibrium conditions. The same equation can be applied for the desorption of the analyte from the sample and for the absorption and desorption of the analytes from the trap. The equilibrium conditions are not commonly fulfilled in purge-and-trap systems, the amount of analyte in the gas phase (Cg Vg) being in general lower than the one given by rel. (46). 

Pyrolysates can be analyzed off-line in a purge-and-trap system if only the volatiles are of interest in an analysis. 

Purge-and-trap systems for water and sediment samples followed by sorption and desorption. Both open- and closed-loop stripping have been used. 

FIGU RE 14.1 Schematic drawing of a modern online purge and trap system. (From Valor, I., In Handbook of Water Analysis, Nollet, Leo, M. L., Ed., Marcel Dekker, New York, 2000. With permission.)... 

Figure 3.3a shows a schematic of a purge-and-trap system for the collection of volatiles contained in an aqueous sample. Clean air is bubbled through the water sample to purge the water of the volatiles and then carry the volatiles into the IMS. If the concentrations of the analytes are too low for direct detection, a trap (preconcentrator) device is inserted between the purged water sample and the IMS. Figure 3.3b is a schematic of an exponential dilution system used to calibrate IMS instruments for... 

Figure 2 shows a schematic diagram of a typical purge-and-trap system. It consists of two major components a purging device and a sorbent trap. The two parts are connected with each other and to the analytical instrument through transfer lines, with a six-port switching valve controlling the flow path. 

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. 

The reported performance characteristics of the earlier methods for dissolved DMS indicate that similar analytical precision can be obtained with different purge and trap systems, and that major analytical problems are associated with sample handling and storage (see Section 24.8). Unlike the inter-comparison of aircraft instrumentation for atmospheric DMS (Gregory et al., 1993), no such comprehensive inter-calibration of malytical procedures for dissolved DMS has been carried out. Therefore, the choice of a particular method may reflect the personal experience of the author. Here, a semi-automated method modified from Andreae and Barnard (1983) is described. It provides adequate precision (better than... 

Ho, J.S. Hodakievic, P. and Bellar, T.A. A fully automated purge-and-trap system for analyzing volatile organics in drinking water. American Laboratory 1989, July, 40-51. 

Schnable, J.G. Capangpangan, M.B. and Suffet, I.H. Continuous automatic monitoring of volatile organic compounds in aquesous streams by a modified purge and trap system. Journal of Chromatography 1991,549, 335-344. 

Fig. 5.9. Apparatus for the gas chromatography-olfactometry of static headspace samples. 1 Sample in ther-mostated glass vessel, 2 septum, 3 gastight syringe, 4 injector, 5 hydrophobed glass tube, 6 carrier gas, e. g, helium, 7 purge and trap system, 8 cold trap, 9 gas chromatograph with capillary column, 10 sniffing port, 11 flame ionization detector (according to Guth and Grosch, 1993)...

The choice of inlet type and injection technique depends on if the sample is in liquid, gas, adsorbed, or solid form, and on whether a solvent matrix is present that has to be vaporized. Dissolved samples can be introduced directly onto the column via a COC injector, if the conditions are well known if a solvent matrix has to be vaporized and partially removed, a S/SL injector is used (most common injection technique) gaseous samples (e g., air cylinders) are usually injected using a gas switching valve system adsorbed samples (e g., on adsorbent tubes) are introduced using either an external (online or off-line) desorption apparatus such as a purge-and-trap system, or are desorbed in the S/SL injector (SPME applications). 

Purge and Trap System 0.1 Analytical Eclipse model 4660... 

Sample preparation Purge and Trap Tekmar purge and trap system LSC 2000 ... 

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