Headspace gas

In order to maintain reproducibility it is important to measure all volumes accurately. In a typical operation using 500 ml (one pint) cans, the procedure is to place 300 ml of degassed salt-water brine into the 500 ml can and add sediment until the can is filled to the brim, giving 200 ml of sediment and 300 ml of brine. The can is sealed and then zero-grade nitrogen is injected through a prepared septum to displace 100 ml of brine and leaving the can with a 2 2 1 mixture of 200 ml brine, 200 ml sediment, and 100 ml headspace. 

One of the drawbacks of using this technique is the need to freeze the canned samples if they cannot be analysed within one or two weeks of their collection. Failure to follow this procedure can create problems because of the generation of biogenic gas in the cans or the bacterial oxidation of the hydrocarbon gases to carbon dioxide. 

Hydrocarbon concentration values are reported in terms of ppm by volume in the nitrogen headspace or as ppm or ppb by weight, normalised to the weight of sediment. Gases concentrations reported by weight are not truly representative of the actual gas migrating from depth because some of the free gas has been allowed to escape during collection and sample preparation. Furthermore, the sorbed gas is never completely extracted into the headspace, and may not always reflect the true gas content of the soil. 

The headspace sampling technique can yield useful results if sufficient numbers of samples can be collected to use statistical populations to suggest anomalous areas. One should always exercise caution, however, with respect to characterisation of gas composition, since evaporation during the collection stage always occurs, resulting in the relative depletion of the lighter gases. 

The device used in this technique is a small stainless steel ball-mill containing two stainless steel or ceramic balls which crush and disaggregate the sample when the ball-mill is shaken (Fig. 5-25). This approach concentrates the loosely-bound adsorbed gases into the headspace of the ball-mill. Because of the equilibrium problem mentioned above under headspace techniques, this sampler was adapted by Whelan (1979) and Whelan et al. (1980) to ensure that lithified sediments and cuttings are completely broken up during analysis. 

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Static headspace GC/MS. The partitioning of volatile and semivolatile compounds between two phases in a sealed container. An aliquot of the headspace gas generated is injected onto a gas chromatographic column. This is followed by mass spectrometric analysis of compounds eluting from the gas chromatograph. 

Blood and urine are most often analyzed for alcohol by headspace gas chromatography (qv) using an internal standard, eg, 1-propanol. Assays are straightforward and lend themselves to automation (see Automated instrumentation). Urine samples are collected as a voided specimen, ie, subjects must void their bladders, wait about 20 minutes, and then provide the urine sample. Voided urine samples provide the most accurate deterrnination of blood alcohol concentrations. Voided urine alcohol concentrations are divided by a factor of 1.3 to determine the equivalent blood alcohol concentration. The 1.3 value is used because urine has approximately one-third more water in it than blood and, at equiUbrium, there is about one-third more alcohol in the urine as in the blood. 

Principle. The content of 1,4-dioxane in ether sulfates is determined by headspace gas chromatography according to the standard additions method. The method is suitable for all ether sulfates and gives reliable results independent of chain length distribution and water content. 

Blood Digested with H2SO4 dimethylsulfate at 60°C for 4 hours headspace gas injected into GC GC/ECD (trichloroethylene, trichloro-ethanol, and trichloroacetic acid) 3 ppb (trichloroethylene) 60 ppb (trichloro-ethanol) 30 ppb trichloroacetic acid) NR Monster and Boersma 1975... 

Enzyme hydrolysis of sample decarboxylation of trichloroacetic acid headspace gas analyzed... 

Tissue Mixed with a proteolytic enzyme incubated at 65 °C headspace gas analyzed GC/ECD NR NR Ramsey and Flanagan 1982... 

Tissue Homogenized with saline and isooctane at 4°C headspace gas analyzed GC/ECD 8.4 ppb 86-91 Chenetal. 1993... 

Water Equilibrated in sealed vial at room temperature headspace gas injected into GC GC/ECD. 04 ppb 105 Dietz and Singley 19... 

Liquid and solid waste Equilibrated in sealed vial headspace gas injected into GC GC/HSD 0.03 ppb 106 EPA1982c... 

Christensen JM, Rasmussen K, Koppen B. 1988. Automatic headspace gas chromatographic method for the simultaneous determination of trichloroethylene and metabolites in blood and urine. J Chromatogr 442 317-323. 

Dietz EA Jr, Singley KF. 1979. Determination of chlorinated hydrocarbons in water by headspace gas chromatography. Anal Chem 51 1809-1814. 

Entz RC, Hollifield HC. 1982. Headspace gas chromatographic analysis of foods for volatile halocarbons. 

Entz RC, Thomas KW, Diachenko GW. 1982. Residues of volatile halocarbons in foods using headspace gas chromatography. J Agric Food Chem 30 846-849. 

Ramsey JD, Flanagan RJ. 1982. Detection and identification of volatile organic compounds in blood by headspace gas chromatography as an aide to the diagnosis of solvent abuse. J Chromatogr 240 423-444. 

Miettinen, S.M. et al.. Effect of emulsion characteristics on the release of aroma as detected by sensory evaluation, static headspace gas chromatography, and electronic nose, J. Agric. Food Chem., 50, 4232, 2002. 

Ulberth F (1998) A rapid headspace gas chromatographic method for the determination of the butyric acid content in edible fats. Z Lebensm Unters Forsch 2o6A 305-3oy. 

Figure 8.26(A) is an example of a valve type interface [329]. Helium carrier gas is provided to the headspace saiq)ler and is split into two flow paths. One path is flow-controlled and provides a constant flow of carrier gas which passes from the headspace unit through the heated transfer line to the gas chromatograph. The second flow path is pressure-regulated and, in the standby mode, the seunple loop and seuapling needle are flushed continuously by the helium flow. At a time determined by the operator, the sampling needle pierces the septum and helium pressurizes the headspace vial to any desired pressure. The headspace gas is then allowed to vent through the sample loop. Once filled, the sample loop is placed in series with the normal carrier gas flow and its contents are driv Bbhrough the heated...

B. Kolb, "Applied Headspace Gas Chromatography", Heyden, London, UK, 1980. 

B. Kolb and L.S. Ettre, Static Headspace-Gas Chromatography. Theory and Practice, Wiley-VCH, New York, NY (1997). 

H. Hachenberg and K. Beringer, Die Headspace-Gas-chromatographie als Analysen- und Messmethode, Springer-Verlag, Berlin (1996). 

The purpose of in-use stability studies is to establish the period for which a product intended to be used on more than one occasion may be used after reconstitution or dilution or the withdrawal of the first dose from the container without adversely affecting the integrity of the product and with the product retaining acceptable quality characteristics. This type of test can be applied to any multiple use product (e.g., sterile products in multiple-use containers, powders or granules including those used to produce oral solutions or suspensions) but is likely to be of particular importance in the case of products that are manufactured with an inert headspace gas, for products containing antioxidants to protect an active ingredient that is liable to oxidative decomposition, and for products that contain a volatile antimicrobial preservative. 

Either static or dynamic headspace gas GC is used to examine residual solvents in polymeric materials. Figure 43 shows the complex volatiles liberated from a printed multi-layer salad wrap, heated at 300°C under nitrogen. 

Part 22 Determination of ethylene oxide and propylene oxide in plastics Headspace gas chromatography with diethyl ether as internal standard... 

Page BD. 1985. Determination of acrylonitrile in foods by headspace-gas chromatography with nitrogen-sensitive detection Collaborative study. J Assoc Off Anal Chem 68 776-782. 

Hussam, A., Carr, P. W. (1985) A study of a rapid and precise methodology for the measurement of vapor-liquid equilibria by headspace gas chromatography. Anal. Chem. 57, 793-801. 

Bakierowska, A.-M., Trzeszqzynski, J. (2003) Graphical method for the determination of water/gas partition coefficients of volatile organic compounds by a headspace gas chromatography technique. Fluid Phase Equil. 213, 139-146. 

Kolb, B., Welter, C., Bichler, C. (1992) Determination of partition coefficients by automatic equilibrium headspace gas chromatography by vapor phase calibration. Chromatographia 34, 235-240. 

Schoene, S., Steinhanses, J. (1985) Determination of Henry s law constant by automated headspace gas chromatography determination of dissolved gases. Fresenius Z. Anal. Chem. 321, 538-543. 

Neill et al. [22] have described a headspace gas chromatographic method for the determination of carbon dioxide (fugacity) in seawater. This method requires a small water sample (60 ml), and provides for rapid analysis (2 min). 

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