Purge and trap apparatus

Figure 4.3 Schematic of an off-line purge-and-trap apparatus. After Cole and Woolfenden [208a]. Reprinted with permission from LC.GC, Vol. 10, Number 2, February 1992, pp. 76-82. LC.GC is a copyrighted publication of Advanstar Communications Inc. All rights reserved...

Chromatographic methods have been applied with hydridization. Jackson et al. [98] used a commercial purge and trap apparatus fitted to a packed gas chromatographic column and flame photometric detector to achieve a O.lng detection. Purge and trap procedures followed by boiling point separations and detection by spectrophotometric methods yield detection limits in water of between 0.01 and lng. Detection of SnH emission by flame emission gives the greatest sensitivity. 

Figure 24-27 Purge and trap apparatus for extracting volatile substances from a liquid or solid by flowing gas. 

Residues. During failure analysis or as a process control, it is frequently of interest to determine whether residual solvents or potential offgassing/outgasslng products exist in coatings applied to components or assemblies. Application of a modified commercial purge and trap apparatus (Hewlett-Packard, Model 7675A) has proven effective for this type of investigation. 

Figure 33-6. A CDS Analytical Inc., model 6000 single unit purge and trap apparatus.

Figure 3.14. Schematic diagram of a purge-and-trap apparatus for gas extraction and cryogenic trapping of volatile organic compounds from water. (From ref. [142] Elsevier).

Figure 22-32 Purge and trap apparatus for extracting volatile substances from a liquid or solid by flowing gas. You need to establish the time and temperature required to purge 100% of the analyte from the sample in separate control experiments.

In general terss, the purge-and-trap technique is the nethod of choice Cor detemining organic volatiles in water because of its ease of operation. If greater sensitivity is required, the closed loop stripping apparatus should be used. 

Figure 8.27 A, apparatus for dynaaic headspace analysis of urine with sorbent trapping. B, gas phase stripping apparatus (purge-and-trap).

Because of the differences in the construction of various purge and trap devices, actual recoveries may vary significantly from those shown in Figure 3 and Table I. Therefore it is required that individual investigators determine recoveries of compounds to be measured as a function of flow rate with their apparatus. Operation in the optimum flow rate range will assure maximum sensitivity and precision for the compounds measured. 

The purge-and-trap method (see Section 6.4) is a common method to enrich volatile organic compounds from water samples. In your apparatus, you purge a 1 L water sample with a gas (air) volume flow of 1.5 L gas per minute at a temperature of 25°C. The compounds that you are interested in include tetrachloroethene, chlorobenzene and methyl-t-butylether (MTBE). Calculate the time required to purge 90% of each compound from the water. Any comments How much time would you save if you would increase the temperature from 25°C to 35°C What could be a problem when raising the temperature too much You can find all necessary data in Appendix C and in Table 6.3. 

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). 

Figure 2.23 Glass apparatus for the purge and trap technique (Tekmar). (a) U-tube with/without frit (5 and 25 mL sizes), (b) Needle sparger left single use vessels, middle glass needle with frits, right vessels with foam retention, 5, 20 and 25 mL volumes.

Set up an apparatus to purge out S02 with N2 from an acidified sample and trap the liberated gas in an absorbing solution, as shown below in Figure 2.31.1. 

If it is desired to carry out a chlorination, the apparatus is modified by replacing the dropping funnel and trap with a simple Y inlet tube attached directly to the reactor. One side of the Y is attached to the purge gas and the other to the chlorine source. If there is any question about the purity of the chlorine, it can be passed through a sulfuric acid wash. The chlorine flow rate during the reaction is about 300 ml./min. with no purge-gas flow. At the end of the reaction, the chlorine is purged from the system, and the product is removed as before. 

Peanut Oil/Cysteine and Peanut Oil/Methionine Systems. Peanut oil (100 g) and 10.0 g of cysteine or methionine were mixed and placed in a 500-mL two-neck round-bottom flask, which was interfaced to a simultaneous purging and solvent extraction (SPE) apparatus developed by Umano and Shibamoto 13). The mixture was heated at 200 C for 5 hr while stirring. The headspace volatiles were purged into 250 mL of deionized water by a purified nitrogen stream at a flow rate of 10 mL/min. The volatiles trapped by the water were continuously extracted with dichloromethane (50 mL) for 6 hr. The water temperature was kept at 10°C by a Brinkman RM6 constant-temperature water circulator. The dichloromethane extract was dried over anhydrous sodium sulfate, and the extract was then concentrated to 2.0 mL by fractional distillation with a Vigreux colunm at atmospheric pressure. The concentrated extract was placed in a vial and stored under argon at -4 C until tested for antioxidative activity. 

Dimethyl-2,3-dihydro-1,2-benzoisothiazolel,l-dioxide(60 g,0.304 mol)and NaF(16.8 g)in dry CHCI3 (500 mL) were cooled to — 40°C before the diluted mixture 10% F2/ N2 (w/ w) was introduced at a rate such that the flow in the second trap was about 15-25 mL min 1 (0.275 mol F2). After approximately 2 h, the contents of the second trap started to darken noticeably and the fluorination was discontinued. N2 was bubbled through the apparatus for about 1 h to purge the system of residual F2. The solvent was removed by rotary evaporation from the solution containing precipitate. After evaporation of the solvent, the crude mixture was purified by recrystallization from pentane (500 mL) at 0CC yield 42 g (64% from substrate, 71% from F2) mp 115-116.5 C. 

Fig. 1.2. Manifold for medium vacuum and inert gas. A low-temperature trap, on the right side of the figure, is used in the vacuum line to protect the pump from harmful vapors. When the apparatus is being filled with gas or purged with inert gas, the valve on the pressure release bubbler (which contains a check valve to prevent oil from backing up into the line) is opened to avoid excess pressure which would blow the apparatus apart. Often a mineral oil bubbler (not shown here) is connected in line with the inert-gas source to provide visual indication of the inert-gas flow.

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