Water samples purging

Drinking Heat water sample purge-and-trap GC/MS Not No data Barkley et al. ... 

Water (TAL) Purging of sample with gas followed by cryogenically trapping volatile species onto solid sorbent GC column GC/AAS 0.5 ng/g No data Chau et al. 1980... 

They describe the development of a system employing a Tenax GC filled purge and trap sampler, which collects and concentrates volatile organotins from water samples (and species volatilised by hydrodisation with sodium borohydride), coupled automatically to a gas chromatograph equipped with... 

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... 

In the purge-and-trap procedure, vials filled to the brim with the water samples are loaded into an auto-sampler, and then when the unit is operating, samples are drawn, one by one, into a tube where helium sparging occurs. Because the THMs are volatile, the helium sparging draws them out of the samples. The helium-THM gaseous mixture then flows through a trap in which the THMs are adsorbed and concentrated. This is followed by a desorption step in which the desorbed THMs are guided to the GC column. A Hall detector is used. 

Periodic monitoring points should include extraction, injection, and monitoring points. When sampling injection wells, the injection system should be shut down for approximately 24 h to allow ambient conditions to be reestablished. Monitoring wells should be purged and sampled according to standard procedures. Extracted fluid material (pumped water) can be sampled by the same procedures as collecting a surface water sample. 

Soxhlet, sonication, supercritical fluid, subcritical or accelerated solvent, and purge-and-trap extraction have been introduced into a variety of methods for the extraction of contaminated soil. Headspace is recommended as a screening method. Shaking/vortexing is adequate for the extraction of petroleum hydrocarbons in most environmental samples. For these extraction methods, the ability to extract petroleum hydrocarbons from soil and water samples depends on the solvent and the sample matrix. Surrogates (compounds of known identity and quantity) are frequently added to monitor extraction efficiency. Environmental laboratories also generally perform matrix spikes (addition of target analytes) to determine if the soil or water matrix retains analytes. 

The balance of this paper is concerned with a presentation of the details of the gas purging and adsorbent trapping method for the analysis of very volatile compounds in water samples. A number of method variables have been studied during the last five years, and the method has been applied to a wide variety of sample types. There have been a number of publications which are cited and may be consulted for additional information (B-12). 

Table I contains a list of some of the compounds that have been submitted to this type of analysis. The recovery data is intended to be illustrative only since recoveries depend strongly on several important method variables. Recoveries are expressed as a percentage of the amount added to organic free water. The purge time was 11-15 minutes with helium or nitrogen, the purge rate was 20 ml/minute at ambient temperature, and the trap was Tenax followed by Silica Gel. Data from the 5 ml sample was obtained with a custom made purging device and either flame ionization, microcoulo-metric, or electrolytic conductivity GC detectors. Data from the 25 ml sample was obtained with a Tekmar commercial liquid sample concentrator and a mass spectrometer GC detector using CRMS.

All the experiments summarized in Table I were conducted with the water sample at ambient temperature, about 22°C. Purging at elevated temperatures has been investigated and clearly affects recoveries of some compounds. However,... 

Water, environmental Purge, cryogenic trap samples... 

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. 

A measured volume of sample purged with an inert gas styrene purged out from water absorbed on a sorbent trap trap heated and back flushed with He analyte transported into the GC column separated from other volatiles determined on a PID, FID or a mass spectrometer. 

Solid samples mixed with methanol an aliquot of methanol extract spiked into a measured volume of water in purging vessel and subjected to purge and trap concentration and analyzed as above. 

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. 

VOCs are purged from soil and water samples with a flow of an inert gas and concentrated in a trap kept at ambient temperature. After the purging has been completed, the trap is heated, and a reverse flow of inert gas flushes the VOCs from the trap onto the top of the column. 

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