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Source: Reprinted with permission from Kirschen [154]. Copyright (1980) Varian AG, Zug, Switzerland.

Source: Reprinted with permission from Kirschen [154]. Copyright (1980) Varian AG, Zug, Switzerland.

Ion exchange resin adsorption—gas chromatography

Renberg [31] has reported a resin adsorption method for the determination of trihalomethanes and choroethanes and dichloroethane in water. In this method halogenated hydrocarbons are determined by adsorption on to XAD-4 polystyrene resin and eluted with ethanol. The extract is analysed by gas chromatography and is sufficiently enriched in hydrocarbon to be suitable for other chemical analysis or biological tests. Volatile hydrocarbons yielded recoveries of 60-95%. By using two series-connected columns Renberg [31] was able to study the degree of adsorption and the choroethane was found to be more strongly adsorbed than the haloalkanes. To study the adsorption character of substances described here, as well as other compounds, Renberg [31] connected two columns in a series and after the passage of the water sample the columns were eluted separately. The recovery of the substances of the second column, compared to those of the first one, will indicate the leakage of substances which is dependent on, for example, water flow rate and polarity of the substances. The ratio (a / a ) of the amounts found in the second (a ) and the first (a ) column re1 spectively, will predict the degree of 2adsorption, whic1h can be regarded as a measurement of the lipophilicity of the substances studied. The values of the ratios found in the recovery experiments, shown in Table 5.11, indicate tetrachloroethane and 1,2-dichloroethane as the most and the least lipophilic of the substances tested.

Capillary column gas chromatography

Use of a capillary column in the place of a conventional packed column improves resolution in the separation of halomethanes (Table 5.12).

Eklund et al. [49, 142] have developed a method for the determination of down to 1^g 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 potable water. A chromatogram of a standard pentane solution of various volatile organochlorine compounds including trihaloforms is shown in Fig. 5.9. Retention times were measured on two columns with different stationary phases, i.e. SE-52 and Carbowax 400.

Kissinger [162] has reported a high-resolution capillary column gas chromatographic procedure for the determination of trihaloforms in potable water. The trihaloforms were determined by sorption on to columns of acetylated XAD-2 resin after the removal

Table 5.11 Results of recovery experiments from five spiked samples

Table 5.11 Results of recovery experiments from five spiked samples

Source: Reprinted with permission from Renberg [31]. Copyright (1978) American Chemical Society.

Notes a Sum of the amounts, found in the two series-connected columns (a1 ± a2).

b Ratio of the amounts found in the second and first column, respectively.

To prepare solutions purified water (250mL) was transferred to a 250mL separatory funnel and 250DL of an ethanol solution containing chloroform, bromodichloromethane, chlorodibromomethane, 1,2-dichloroethane, and tri- and tetrachloroethane was added. The funnel was shaken and the spiked water allowed to pass the columns. The flow was stopped when the level just reached the top of the upper bed. In order to rinse the glass walls from substances adsorbed, additional water (3 x 250mL) was passed through the funnel columns and the columns were eluted as described. The separatory funnel was shaken with ethanol (25mL) for the determination of substances adsorbed on the glass walls.

Table 5.12 Determination of halofoms in potable water, capillary column gas chromatography

Extraction GC Pocking Haloform Detection Recovery Reference solvent detection limit {%)

Table 5.12 Determination of halofoms in potable water, capillary column gas chromatography

n-Pentane

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