5.1 Saturated aliphatic halogen compounds
5.1.1 Natural waters
Murray and Riley [1, 2] described gas chromatographic methods for the determination of trichloroethylene, tetrachloroethylene, chloroform and carbon tetrachloride in natural waters. These substances were separated and determined on a glass column (4m x 4mm) packed with 3% of SE-52 on Chromosorb W (AW DMCS) (80-100 mesh) and operated at 35°C, with argon (30mL min-1) as carrier gas. An electron-capture detector was used, with argon-methane (9:1) as quench gas. Chlorinated hydrocarbons were stripped from water samples by passage of nitrogen and removed from solid samples by heating in a stream of nitrogen. In each case the compounds were transferred from the nitrogen to the carrier gas by trapping on a copper column (30cm x 6mm) packed with Chromosorb W (AW DMCS) (80-100 mesh) coated with 3% of SE-52 and cooled at -78°C, and subsequently sweeping on to the gas chromatographic column with the stream of argon. A limitation of this procedure is that compounds which boil considerably above 100°C could not be determined .
A different approach was to pass the water through a bed of activated carbon which was subsequently extracted exhaustively in a Soxhlet unit, and the extract was evaporated and analysed; this measured perchloroethylene and hexachloroethane, but the results are uncertain quantitatively . A method has been published by which the water sample was codistilled with cyclohexane and the organic phase was then injected into an electron-capture detector gas chromatograph . Extraction with n-pentane followed by gas chromatography has also been used  but although the extraction was easy and effective, the chromatographic conditions described were timeconsuming and unsuitable for compounds heavier than perchloroethylene.
Chlorinated normal paraffins up to C carbon number range are of low volatility and are thermally unstable, producing hydrogen chloride on decomposition; hence direct gas chromatography is not attractive. Zitko  has devised a method based on column chromatography followed by microcoulometric detection. The procedure is not specific. Zitko has also described  a confirmatory method in which the chloroparaffins are reduced to normal hydrocarbons which are then analysed by gas chromatography. Both methods lack sufficient sensitivity for trace (sub-ppm) analysis and the confirmatory method may be difficult to apply. Friedman and Lombardo  have described a gas chromatographic method applicable to chloroparaffins that are slightly volatile; the method is based on microcoulometric detection and photochemical elimination of chlorinated aromatic compounds that otherwise interfere.
Deetman et al.  have devised an electron-capture gas chromatographic technique, applicable to water, for the determination of down to 1ng L-1 of 1,1,1-trichloroethane, trichloroethylene, perchloroethylene, 1,1,1,2-tetrachloroethane, 1,1,2,2-tetrachloroethane, pentachloroethane, hexachloroethane, pentachlorobutadiene, hexachlorobutadiene, chloroform and carbon tetrachloride. These workers used extraction of the water samples with n-pentane as a means of isolating the chlorinated compounds from the sample. Recoveries of 95% were obtained in a single extraction. To dry the extract anhydrous sodium sulphate was found to be effective. Furthermore this drying agent could be freed from electron-capturing contaminants by heating  and did not absorb the chlorinated compounds. Under the specific conditions (i.e. using a temperature-programmed Dexsil-300 column) all the compounds are separated with the exception of carbon tetrachloride and 1,1,1-trichloroethane which are resolved only on the Apiezon-L column. This column is an alternative for the analysis of water with the proviso that it is not suitable for samples containing the less volatile compounds. If the water sample contains chlorobromomethanes which can interfere with the determination of chloroform and trichoroethylene, it is advisable to augment the analyses by repeating the chromatography with a column containing oxydipropionitrile packing which will separate the bromine compounds from the chlorinated solvents. To avoid contamination, use of a glove box is recommended for the preparation of water samples. In general, it is wise to exclude chlorinated solvents from the laboratory and if the ambient air is suspect, to blanket the inject port of the chromatograph with clean nitrogen.
In this method a 200mL sample of water is extracted with n-pentane and the extract is dried with anhydrous sodium sulphate. A portion of this solution is injected into the gas chromatograph fitted with a 1.5m (5mm i.d.) stainless steel or glass column packed with 15% Dexsil-300 on Diatomite-C (180-212^m) and a 63Ni electron-capture detector. The carrier gas is purified nitrogen at 50mL min-1. The oven is maintained at 65°C for 6min and then temperature programmed at 10°C min-1 up to 150°C and held until hexachlorobutadiene has eluted. The column is then purged at 250°C. The concentrations of the chlorinated hydrocarbons are determined by comparison of peak areas in the sample chromatogram with those of an external standard mixture. Figure 5.1 shows a typical chromatogram obtained by this method.
Hagenmaier et al.  have described a method for the quantitative gas chromatographic determination of volatile halogenated hydrocarbons in lake water samples. Sample enrichment is effected by liquid-liquid extraction with pentane, followed by separation on a capillary gas-liquid chromatographic column, with electron-capture detection. A 1:25 pentane/water ratio was employed in conjunction with a standard solution of a reference compound (1-bromobutane) for estimating extraction efficiency. The detection limit using split injection was about 0.005^g L-1 and could be increased to less than 1ng L-1 by on-column injection. The method was applied to samples of water
from Constance lake. The water contained appreciable amounts of trichloroethylene (8-20^g L-1) and tetrachloroethylene (2-5^g L-1).
Chiba and Haraguchi  determined halogenated organic compounds in natural water by gas chromatography-atmospheric-pressure-induced-helium-microwave-induced plasma emission spectrometry using a heated discharge tube for pyrolysis.
Kaiser and Oliver  have determined volatile halogenated hydrocarbons at the 0.1-10^g L-1 level in water by headspace and gas chromatography. Hrivnak et al.  determined chlorinated C -C hydrocarbons in water using capillary gas chromatography. For 1 the4 isolation of chlorinated hydrocarbons (w-butyl chloride, di-, tri- and tetrachloromethane, 1,2-dichloroethane, 1,2-dichloropropane and trichloroethylene), a stripping technique was used. The hydrocarbons were analysed in a capillary stainless steel column at 80°C. Using electron capture it is possible to determine down to 0.1^g L-1 of these substances.
Hellman  has applied the headspace technique to the determination of tetrachloromethane and trichloroethylene in river water. McLary and Barker  used headspace analysis to monitor levels of trichloromethane, 1:1:1 trichloroethylene and tetrachloroethylene in ground water samples. Biebier et al.  compared headspace and solvent extraction methods for the determination of halogenated hydrocarbons in natural waters. Yurteri et al.  studied the effects of salts, surfactants and humic material in clean and polluted water on the Henry's law constants governing headspace analysis.
Headspace analysis has been applied to the determination of volatile chlorinated hydrocarbons in water. Hellman  determined chloroform, carbon tetrachloride, trichloroethylene and perchloroethylene. Studies of the operating variables on the headspace technique are described including the effects of filling volume, bath temperature and duration of heating in the thermoblock. The method gave satisfactory and reproducible results, with detection limits of 0.05^g L-1 in all cases.
Mehran et al.  evaluated various gas chromatographic methods employing direct headspace and water injection into fused silica capillary columns for their ability to separate a model system composed of deionized water and trace amounts of 16 halocarbons. For headspace injection, both separation and detection sensitivity were affected by the lengths of solute bands and enhanced by focusing. Phase ratio focusing and distribution constant focusing were considered. Aqueous injection techniques required compromises when choosing detector temperatures and gas flow rates, with optimal values being system dependent.
Kirschen  analysed 17 halogenated organic compounds by a purge and trap method.
Prath and Pauliszyn  studied the gas extraction kinetics of volatile organic species, e.g. 1,1,1-trichloroethane from water using a hollow film membrane.
Lopez-Avila et al.  determined dichloromethane and aromatic compounds using photoionization and Hall electrolytic conductivity gas chromatography in which the gas chromatograph is connected in series to a purge and trap analyser.
Cochran  used a Naflon tube drier in a purge-whole column cryotrapping method for selectively removing water from an analyte-containing purge stream during the analysis of volatile chlorinated and fluorinated hydrocarbons in natural water.
Chichester-Constable et al.  have developed an improved sparger for a purge and trap concentrator for the analysis of halocarbons in the 1-500^g L-1 range.
Mosesman et al.  have considered factors influencing the analysis of volatile pollutants by wide-bore capillary chromatography and a purge and trap system using five volatile gas mixtures -dichlorodifluoromethane, chloromethane, vinyl chloride, bromomethane and chloromethane. The factors studied were initial column temperature (10°C or 35°C), carrier gas (helium), flow rate, speed with which pollutants were desorbed from the trap and the type of detector used (flame ionization detector or electrolytic conductivity detector). After optimizing the analytical conditions for the gases, a mixture of 36 volatile pollutants was analysed. Resolution due to peak broadening was also done for the most volatile compounds. The remaining 30 compounds were refocused at the column inlet, producing sharp, well-resolved peaks. A carrier gas flow rate of 10mL min-1 and an initial column temperature of 10°C were the optimal conditions for purge and trap analysis of volatile priority pollutants from a VOCOL wide-bore capillary column.
Hollies et al.  have carried out a very extensive study of the determination of chlorinated long-chain normal paraffins (13-30 carbon atoms) in water.
Hollies et al.  found that choro-n-paraffins could be chromatographed on a silica gel plate from which an image of the chromatogram could be 'printed' on an aluminium oxide plate by heating the two face to face so that the high sensitivity of detection on aluminium oxide could be utilized.
In these methods the samples are cleaned up by liquid-solid adsorption chromatography, and thin-layer chromatography but those rich in lipids require preliminary solvent extraction. The methods distinguish between chloro-n-paraffins based on long carbon chains (C -C ) and those based on shorter chains (C -C ). The methods cover the
ranges 500ng L-1 to 8^g L-1 for water (i.e. from about the solubility limit upwards) and 50^g kg-1 to 16mg kg-1 for sediments and biota. The precision of the methods ranges from ±50% relative at the lowest concentrations to ±12% relative at the highest. Recoveries are about 90% for water, 80% for sediments, and between 80 and 90% for biota according to sample type.
For all samples, liquid adsorption chromatography clean-up was essential; a non-polar solvent (60/80 petroleum spirit) is used for separating mobile impurities from chloroparaffins (the adsorbate). The latter are then desorbed with a polar solvent, toluene or carbon tetrachloride. Aluminium oxide is used as a packing and the column can be prepared simply by dry packing. However, lipidous samples are cleaned up more effectively on silica gel which must be slurry-packed to achieve satisfactory efficiency. Furthermore, lipidous samples require pre-extraction based on solvent partition with dimethylformamide and 60/80 petroleum spirit. To get rid of any remaining impurities, which can spoil the subsequent thin-layer chromatographic stage by altering the chromatographic properties of the plate, a preliminary thin-layer chromatographic clean-up procedure is valuable; the impurities are separated from the chloroparaffin and then discarded by cutting off that half of the plate which contains them. Omission of this procedure leads to spots that are distorted and therefore difficult to quantify.
The final stage is to separate the chloroparaffins according to carbon chain length, Cereclor S45 and Cereclor 42 being used to calibrate the resulting chromatograms. These grades contain carbon chains in the ranges C -C and C -C respectively, and have chlorine contents of
45% and 42% (w/w) respectively. Using a densitometer a detection limit (50ng per spot) similar to the visible method is achievable, giving linear response up to 200^g of chloroparaffin.
Kummert et al.  has described a method for the trace determination (down to 0.06^mol) of tetrachloroethylene in natural waters using direct aqueous injection-high-pressure liquid chromatography. Stozek and Beumer  determined chlorinated degreasing solvents in water.
Renberg  has described a method utilizing XAD-4 microreticular resin for the determination of chloroethenes in water. Haloalkanes do not interfere in this procedure.
Simonov et al.  have described an ultraviolet spectrophotometric method for determining down to 1ppm of tetrachloroethylene, hexachloropropene, hexachlorobutadiene and hexachlorocyclopentadiene from their extinction at 202nm, 240nm, 255nm and 335nm respectively.
Dilling et al.  have studied the evaporation rates in aqueous solution of various polychlorinated compounds such as methylene dichloride, chloroform, 1,1,1-trichloroethane, trichloroethylene and tetrachloroethylene. The compounds were studied at concentrations of 1ppm in water. All the compounds examined had evaporated by 50% in less than 30min and by 90% in less than 90min when stirred in an open container at 25°C. The addition of salt, clay, limestone, sand, peat moss and kerosene to the water has relatively little effect on the rates of disappearance. These workers conclude that low-molecular-weight chlorinated hydrocarbons would not persist in agitated natural water bodies owing to evaporation.
Hellman  studied the behaviour of volatile chlorinated hydrocarbons in flowing waters in a series of model experiments designed to establish the relative importance of physical and biochemical processes in the degradation of these substances. The effects of turbulence, temperature, radiation, adsorption and remobilization were investigated, together with biochemical degradation over periods of about 9 days, corresponding to the transport time in the Rhine between Basle and the Dutch/German border. Release to the atmosphere was the principal dissipation route. Monitoring results for chlorinated hydrocarbons in Rhine water samples obtained under widely differing flow conditions are also discussed. For trichloromethane, the mass flow appeared to be almost independent of the hydrographic conditions, whereas for other compounds the mass flow appeared to increase as discharge increased. Possible explanations for such apparently anomalous behaviour are discussed.
Friedman et al.  studied the recovery of several volatile organic chlorocompounds from simulated water samples. Solutions of volatile organic compounds in organic free water and in 2% methanol were submitted to two US Geological Survey laboratories for volatile organic analysis by gas chromatographic separation and mass spectrometric detection. After 3 days, the analytical recovery of dilute concentrations of bromoform, dichlorobromomethane, ethylbenzene and 1,1,2,2-tetrachloroethane was not statistically different from the recovery of these compounds from methanol solutions which had been kept 100 times more concentrated until immediately prior to analysis. There was no significant difference between values reported by the two laboratories despite an altitude difference of 1.6km and the use of different instruments. Recovery efficiency was more than 80% in more than half the determinations. The recoveries of bromomethane and vinyl chloride were hindered by addition of 2% methanol to the storage containers. Recovery of 2-chlorovinylether from the 2% methanol was greater than from distilled water. However, recoveries from both decreased after 5 days. Recovery of dichloropropene from distilled water decreased after 11 days. There was no significant decrease in the recovery of bromomethane, chlorobenzene, chloroethane, dichlorobromomethane, ethylbenzene and vinyl chloride after 34 days.
Burguera and Burguera  have used the emissions from IrCl, IrBr and Irl, generated at an iridium-lined MECA cavity to determine organic halogen compounds separated on a gas chromatographic column. Emissions are measured, respectively at 360, 376 and 410nm. Linear calibration ranges are 5-60, 10-150 and 5-500mg for chloro, bromo and iodo alkanes respectively.
Martinsen et al.  preconcentrated organochlorine compounds on activated carbon and XAD-4 resin prior to determination by neutron activation analysis, thin-layer and gel permeation chromatography.
Pankow  showed that quantitative freeze trapping of mixtures of certain volatile chlorinated hydrocarbons can be done with a 30m fused silica capillary column kept at between -60 and -100°C throughout. The effect of using different trapping temperatures on the chromatograph peak profiles was examined for 1,1-dichloroethane, dichloromethane, chloroform, carbon tetrachloride, trichloroethene, 1,2-dichloropropane, 2-chloroethylvinylether, 1,1,2-trichloroethane, dibromochloromethane, tetrachloroethene and chlorobenzene. Trapping at -80°C appeared best, giving peak breadths of only 4-7s at 8°C min-1 and 110cm s-1 carrier gas speed.
Chloromethanes have been preconcentrated on XAD-4 macroreticular resin .
5.1.2 Sea water
Dawson et al.  have described samplers for large-volume collection of sea water samples for chlorinated hydrocarbon analyses. The samplers use the macroreticular absorbent Amberlite XAD-2. Operation of the towed 'fish' type sampler causes minimal interruption to a ship's programme and allows a large area to be surveyed. The second type is a self-powered in situ pump which can be left unattended to extract large volumes of water at a fixed station.
5.1.3 Waste waters
Glaze et al.  used flame ionization, electron-capture and Coulson electrolytic detectors with gas chromatography to study the formation of chlorinated aliphatics during the chlorination of waste waters.
Lukacovic et al.  applied headspace gas chromatography to the determination down to 0.5mg L-1 of chlorinated hydrocarbons in waste waters. Techniques for enrichment and clean-up of the extract were devised, the preferred method consisting of liquid-liquid extraction with methylene chloride, followed by flash evaporation, clean-up of the concentrate by column chromatography on Florasil, a further evaporation step and subsequent gas chromatography with an electron-capture detector. Two gas chromatographic packings were compared for use with these haloethers, 3% SP-1000 on Supelcoport giving better results than Tenax-GC on account of better peak shape and resolution. The validity of the method was confirmed by application to samples of either municipal or industrial effluents spiked with known amounts of particular haloethers. Pfannhauser and Thaller  have described a gas chromatographic method for quantitatively estimating traces of 16 different halogenated solvents in waste water. The solvent residues were extracted using n-pentane on a column containing a mixture of deactivated Florasil with the ground sample. The elute was injected into a fused silica capillary column and the peaks recorded by electron-capture detection (Ni-63). The method could detect as little as 0.01^g L-1 of most halogenated short-chain aliphatic hydrocarbons.
An American Public Health Association method  has been published for the determination in waste water of the following aliphatic and aromatic chlorocompounds:
• Benzyl chloride
• Carbon tetrachloride
• Methylene chloride
A 3-10^L aliquot of the sample is injected into the gas chromatograph equipped with a halogen-specific detector. The resulting chromatogram is used to identify and quantitate specific components in the sample. Results are reported in micrograms per litre. Confirmation of qualitative identifications is made using two or more dissimilar columns.
The use of a halogen-specific detector minimizes the possibility of interference from compounds not containing chlorine, bromine or iodine. Compounds containing bromine or iodine will interfere with the determination of organochlorine compounds. The use of two dissimilar chromatographic columns helps to eliminate this interference and, in addition, this procedure helps to verify all qualitative identifications. When concentrations are sufficiently high, unequivocal identification can be made using infrared or mass spectroscopy. Though non-specific, the flame ionization detector may be used for known systems where interferences are not a problem.
5.1.4 Sewage effluents
Von Duzzeln et al.  and Henderson and Glaze  have discussed the gas chromatographic determination of chlorinated hydrocarbons in sewage. Henderson and Glaze used a gas chromatography-mass spectrometry computer program to manipulate the data to produce a limited cluster search; the resulting chromatogram indicates the peaks on the total ion chromatogram which possess a specific number of chlorine or bromine atoms.
HM Stationery Office (UK)  have described methods for the determination of chlorinated hydrocarbons, organochlorine pesticides and polychlorinated biphenyls in sewage sludge.
Rudolph and Koppke  described apparatus for the determination of trace organohalogen compounds (AOD) in municipal sewage.
5.1.5 Trade effluents
The application of gas chromatography to the determination of chlorinated hydrocarbons in water and effluents, with particular reference to the types of these compounds used in industry, has been reviewed by Hassler and Rippa .
Eklund et al. [48, 49] have developed a method for the determination of down to L-1 volatile organohalides in waters which combines the resolving power of the glass capillary column with the sensitivity of the electron-capture detector. The eluate from the column is mixed with purge gas of the detector to minimize band broadening due to dead volumes. This and low column bleeding give enhanced sensitivity. Ten different organohalides were quantified in industrial effluent from a pulp mill.
5.2 Unsaturated aliphatic halogen compounds
5.2.1 Natural Waters
Alberti and Jonke  describe a gas chromatographic method for its determination using a flame ionization detector and a Poropak Q or Chromosorb 101 column for the determination of vinyl chloride in surface waters. The detection limit is 0.3mg L-1 and samples of waste waters from vinyl chloride or PVC factories can be injected direct into the gas chromatograph, while water samples with lower concentrations require preliminary enrichment for which a gradient-tube method is described.
Burgasser and Calaruotolo  have described a gas chromatogra-phic method for determining semi- or non-volatile chlorinated organics such as hexachlorobutadiene, hexachlorocyclopentadiene, octachlorocy-clopentene and hexachlorobenzene in amounts down to 0.1^g L-1 in natural waters. These compounds fall into the category of those which are preferentially soluble in non-aqueous solvents. These workers used a
Brinkmann Polytron homogenizer to perform the extraction and a Sorval refrigerated centrifuge to speed up the phase separation process. The extraction of chlorinated organic compounds from water can be carried out in a single vessel in one step, taking only 10min to complete.
In the direct gas chromatographic method  vinyl chloride, arenes and other volatile halogen compounds are separated from the water sample by stripping them in a closed system. The stripped compounds were absorbed on Poropak N in a glass tube within the closed system and eluted with methanol. They were then separated by gas chromatography on a 3m Chromosorb 102 column. The solvent is compatible with either electron capture or photoionization detectors. Using photoionization detectors both arenes and vinyl chloride were determined with detection limits of 1^g L-1. The procedure was made semi-automatic by the use of autosamplers on the gas chromatograph, enabling 25 samples a day to be analysed.
126.96.36.199 Gas chromatography—mass spectrometry
Fujii  has combined mass spectrometry with gas chromatography for the direct determination of sub-microgram per litre amounts of vinyl chloride in potable and river waters. The method is based on mass fragmentography followed by chromatography-mass spectrometry by simultaneously recording m/e 62 and 64.
Analyses were performed on a Finnigan 2300F gas chromatograph-quadrupole mass spectrometer equipped with a multiple-ion detector, by which mass fragmentography can be carried out. The interface between the gas chromatograph and the mass spectrometer was an all-glass jet-type enrichment device. The mass spectrometer was set to unit resolution (10% valley between adjacent nominal masses). The resulting ion currents were recorded on a multichannel strip chart recorder. The instrument was operated in the electron-impact mode. Other conditions held constant throughout the analysis were: helium carrier gas at a flow rate of 34mL min-1; temperature of the gas chromatograph injection port at 200°C; pressure in the mass spectrometer of 1 x 10-5 torr; ionization voltage of 70eV; emission current of 490^A.
Rivera et al.  have also described a direct mass spectrometric method for determining volatile chlorinated hydrocarbons, including vinyl chloride, in water. They give details of a highly sensitive technique for the determination of aliphatic chlorinated hydrocarbons, based on concentration by adsorption by stripping on a charcoal filter and quantitation by a mass spectrometric integrated ion-current procedure, with desorption from the charcoal inside a temperature-programmed inlet probe.
The charcoal filter was quantitatively transferred to the previously cooled direct inlet probe of an MS-902S AEI high-resolution mass spectrometer that could be temperature programmed from -150 to +350°C. Vinyl chloride desorption took place in the range of -30 to +100°C. In this temperature interval and with the use of the peak matching technique (resolution 1000), the signals at m/e 62 and 64, corresponding to the molecular ions C H 35Cl and C H 37Cl, were
Quantitative measurements of vinyl chloride in water were made by interpolating measured curve areas on a linear plot obtained by running standard water samples in the 0.05-10.0ppb range. Standard deviation was 9%. Quantitation became difficult below 0.05ppt.
188.8.131.52 Headspace analysis
Headspace analysis with a photoionization detector  has been used to determine vinyl chloride in a natural water.
Workers at the National Environment Research Centre, US Environmental Protection Agency  have described a purge and trap method for determining vinyl chloride at the microgram per litre level in water. An inert gas is bubbled through the sample to transfer vinyl chloride to the gas phase, and the vinyl chloride is then concentrated on silica gel or Carbosieve B under non-cryogenic conditions, and determined by gas chromatography with a halogen-specific detector. Gas chromatography-mass spectrometric methods were used to provide confirmatory identification of vinyl chloride.
Bellar et al.  used a computer to scan the data and construct a selected ion current profile consisting of peaks that produce an m/e 62 ion. Other compounds likely to be present in the water sample which produce m/e 62 ions are easily resolved using the gas chromatographic conditions recommended by these workers, so, in this sense, the method is specific for vinyl chloride.
Data obtained by Bellar et al.  showed in their technique that a quantitative recovery of vinyl chloride is obtained on silica gel and Carbosieve B with purge volumes of 150-400mL at 20mL min-1.
To determine the effect of sample collection and storage on the accuracy of the method, a 1L sample of river water contained in a 1L separately funnel was dosed with vinyl chloride at 20^g L-1. This mixture was then used to fill several 50mL glass-stoppered bottles.
The bottles were then stored under ambient conditions. Seven of the samples, having no headspace, were randomly selected and analysed over a period of 93h. The data show that the recoveries were constant over the period of study. The average recovery was 15.1 ± 0.4^g L-1. The initial 25% loss is attributed to the headspace above the dosed sample while it was contained in the separately funnel. Losses due to headspace or exposure to the atmosphere are further illustrated below.
The time zero sample from the above experiment, now containing 5mL of headspace, was reanalysed at 15min and again at four additional times over a period of 300min (Fig. 5.2). Each time 5mL of sample was withdrawn leaving an additional 5mL of headspace. Care was taken not to agitate the sample during the storage period. The results show that as the headspace increases, the recovery of vinyl chloride decreases. The total loss over the time period was about 50% or about 10% h-1. These observations indicate the extreme care that is essential when dealing with the analysis of volatile organics in water samples.
The loss of vinyl chloride from water in an open narrow neck container at ambient temperature was observed by dosing 50mL of tap water in a 50mL volumetric flask with 10mg L-1 of vinyl chloride and 20mg L-1 chlorobenzene. Chlorobenzene is relatively non-volatile and was used as an internal standard. These analyses were done by direct aqueous injection gas chromatography, not by the purge and trap technique. The recovery of vinyl chloride relative to the chlorobenzene is
shown in Fig. 5.3. The loss of vinyl chloride was linear throughout the time period with a total loss of 35% or about 17% h-1. The recovery of chlorobenzene was constant throughout the study. To test the procedure over a wide concentration range, a standard curve was prepared by injecting known amounts of a 10ng ^L-1 vinyl chloride-in-acetone solution into the purging device containing 5.0mL of organic-free water. Each mixture was then purged and analysed. The response obtained by microcoulometric titration gas chromatography was linear over a concentration range of 4-40^g L-1 (Fig. 5.4). Based on data collected for similar halogenated hydrocarbons, the method may be useful up to 2500^g L"1.
Kummert et al.  have described a method for the trace determination (down to 0.06^mol) of tetrachloroethylene in natural waters using direct aqueous injection-high-performance liquid chromatography.
184.108.40.206 Purge and trap analysis
The Bellar  purge and trap method described in Section 220.127.116.11 has been applied to the determination of vinyl chloride in sea water. Figure 5.5 represents the chromatogram obtained from a sea water sample dosed with vinyl chloride and other organohalides. Using the Hall electrolytic conductivity detector, no response was obtained for the acetone used to prepare the vinyl chloride standard solution.
The combined mass spectrometry-gas chromatography method , discussed in Section 18.104.22.168 for the determination of vinyl chloride in natural waters, has also been applied to sea waters.
Fig. 5.5 Electrolytic conductivity gas chromatogram of organohalides recovered from dosed sea water (full-scale response, 160 □mhos). (Reprinted with permission from Bellar et al. . Copyright (1976) American Chemical Society.)
Fig. 5.5 Electrolytic conductivity gas chromatogram of organohalides recovered from dosed sea water (full-scale response, 160 □mhos). (Reprinted with permission from Bellar et al. . Copyright (1976) American Chemical Society.)
5.2.3 Potable waters
Benoit and Williams  give details of a solvent extraction procedure for concentration of trace amounts of hexachlorocyclopentadiene from potable water prior to determination by gas chromatography.
22.214.171.124 Gas chromatography—mass spectrometry
The combined mass spectrometry-gas chromatography method, discussed in Section 126.96.36.199 , for the determination of vinyl chloride in natural waters has also been applied to potable waters.
Rivera et al.  have described a direct mass spectrometric method for determining volatile chlorinated hydrocarbons, including vinyl chloride, in portable water. They give details of a highly sensitive technique for the determination of aliphatic chlorinated hydrocarbons, based on concentration by adsorption by stripping on a charcoal filter and quantitation by a mass spectrometric integrated ion-current procedure, with desorption from the charcoal inside a temperature-programmed inlet probe.
The Bellar  purge and trap method described in Section 188.8.131.52 has been applied to the determination of vinyl chloride in potable water. Figure 5.6 represents a typical gas chromatogram obtained from chlorinated tap water which has been dosed with vinyl chloride. The chloroform, bromidichloromethane and dibromochloromethane are common to chlorinated drinking waters and result from the chlorination process. Low levels of methylene chloride are often observed in samples analysed by this technique. These are attributed to method background.
Ando and Sayato  carried out studies on the migration of vinyl chloride migrating into potable water from PVC pipes.
5.2.4 Trade effluents 184.108.40.206 Gas chromatography
Direct aqueous injection gas chromatography using flame ionization, microcoulometry, electrolytic conductivity and mass spectrometry for
detection has been used for the identification and measurement of vinyl chloride in industrial effluents . The reported lower limits of detection vary but 100^g L-1 appears to be conservative for vinyl chloride using a flame ionization detector. Halogen-specific detectors, for example for the microcoulometric and electrolytic conductivity, are less sensitive (approximately 1000^g L-1). However, they do improve the qualitative accuracy of the determination. As much as 500mL of water is extracted with 1mL of carbon tetrachloride. One microlitre of the extract is analysed by gas chromatography. Extraction efficiencies for vinyl chloride are reported to be about 77% at 1-10^g L-1 and near 100% at 0.2-3mg L-1.
Burgasser and Calaruotolo  have described a gas chromatographic method for determining semi- or non-volatile chlorinated organics such as hexachlorobutadiene, hexachlorocyclop-entadiene, octachlorocyclopentene and hexachlorobenzene in amounts down to 0.1ppb in plant effluents and ground waters. These compounds fall into the category of those which are capable of being analysed by purge and trap techniques but which are preferentially soluble in non-aqueous solvents. These workers used a Brinkmann Polytron homogenizer to perform the extraction and a Sorval refrigerated centrifuge to speed up the phase separation process. The extraction of chlorinated organic compounds from water can be carried out in a single vessel in one step, taking only 10min to complete.
Extraction efficiencies are 90-100% following a single 30s extraction. By using hexane, hexane-benzene, or hexane-toluene instead of hexane- methylene chloride, the concentration step can be eliminated except for gas chromatographic-mass spectrometric analysis where only concentration by nitrogen purge would be required. For compounds with less favourable distribution coefficients, pH adjustments and multiple extractions might be necessary and these factors should be examined for individual cases.
Because of the very short extraction time and the design of the Polytron homogenizer, essentially no heat is transferred to the sample during the extraction process. This eliminates the potential for thermal degradation or evaporation loss of the compounds of interest, an effect occasionally observed when ultrasonic extraction techniques are used.
Table 5.1 is a summary of the statistical analysis of the data. The percentage recovery and standard deviation at each concentration level and the correlation coefficients for the linearity of each compound over the range studied are given. This demonstrates that the procedure
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