A

aHCH, hexachlorocyclohexane; HCB, hexachlorobenzene; PCB, polychlorinated biphenyl congener.

bRef. [14] (value at 25°C linear interpolated from the data).

aHCH, hexachlorocyclohexane; HCB, hexachlorobenzene; PCB, polychlorinated biphenyl congener.

bRef. [14] (value at 25°C linear interpolated from the data).

filled into a glass column. An air flow was passed through the sand bed maintained at a temperature of 12°C. This contaminated air was mixed in the exposure chamber with a flow of purified air. The average temperature in the exposure chamber was 19°C and the air humidity was about 50%. In order to analyze the semi-volatile organic compound concentrations in the exposure chamber, a desorption tube filled with TenaxTM TA sorbent was integrated in a bypass of the exhaust air flow of the exposure chamber. The loaded desorption tubes were stored in tube containers at 4°C in the dark until analysis using thermodesorption/ GC-MS.

The system used for the calibration of the sampler types B1 and B2 was as described by Larsen et al. [9]. This system is easier to handle because no expensive conditioning is necessary. The standard gas mixtures were generated dynamically in a generator column (Fig. 5.3). Sea sand loaded with the test chemicals was placed in the flow-through cell. The procedure to prepare the sand was also performed according to the method of Hauk [8]. A U-formed glass tube (d) filled with 100g contaminant loaded sea sand was placed in a thermostatic water bath with a temperature of 10°C. Approximately 22 mg of each component

Fig. 5.3. Calibration device: FC, flow control; PC, pressure control; TC, temperature control; a, compressed air; b, purification system for air; c, washing bottle; d, glass column; e, mixing chamber; f, calibration chamber; g, stainless steel lattice; h, measure for humidity; i, TenaxTM TA tube; k, glass column filled with blue silica-gel.

Fig. 5.3. Calibration device: FC, flow control; PC, pressure control; TC, temperature control; a, compressed air; b, purification system for air; c, washing bottle; d, glass column; e, mixing chamber; f, calibration chamber; g, stainless steel lattice; h, measure for humidity; i, TenaxTM TA tube; k, glass column filled with blue silica-gel.

was adsorbed on the sand surface in the generator column. A purified compressed air flow (12 mL min-1) was passed through the sand bed, purging the substances into the mixing chamber (e), where further dilution took place with the aid of an additional clean air flow of 15 L min-1. Before reaching the mixing chamber, the dilution air was moisturized by continuously passing it through a temperature-controlled washing bottle (c) (12°C) filled with double distilled water.

A desiccator (volume 21.5 L) was used as calibration chamber (f). After the mixing step, the standard gas mixture was transferred to the bottom of the calibration chamber. A stainless steel lattice (g) was positioned inside the calibration desiccator at a height of 25 cm from the bottom, where the passive samplers were horizontally placed during exposure. Glass tubes were used for the connections between generator column, mixing chamber and exposure chamber.

The contaminated air in the calibration chamber flows out through an opening in the desiccator lid. The humidity in the exhaust air stream was measured with a Q hygrotemp 80 (Merck, Darmstadt, Germany)

(h). A desorption tube filled with TenaxTM TA (i) was installed in a bypass of the exhaust air flow to determine analyte concentrations in the gas mixture. The analytes were accumulated from contaminated air flowing at 30-40 mL min—1. The adsorption tubes were exposed for 6h before the passive samplers were removed. After accumulation, the tubes were stored frozen at -18°C in a container wrapped with aluminium foil until thermodesorption/GC-MS analysis. The concentrations of the semi-volatile components in the chamber during exposure are shown in Table 5.2.

For the determination of sampling rates, the permeation samplers were positioned perpendicular to the flow direction in the calibration chamber. The average air humidity was 50.6%. The calibration device was installed in a room with a mean temperature of 28°C. After 72,144, 216, 312 and 383 h two samplers of either type were removed, wrapped in aluminium foil and stored as described above.

5.3.4 Thermodesorption/GC-MS analysis

The semi-volatile compounds sorbed in the receiving phase of the samplers and enriched on TenaxTM TA-filled desorption tubes were analysed using thermodesorption/GC-MS. The system used consisted of an Agilent Technologies 6890/5973N GC-MS system (Palo Alto, CA, USA) connected to a Gerstel TDSA thermodesorption device. The TDSA was operated under the following conditions: desorption temperature, 250°C; desorption time, 10min; splitless (solvent vent mode); and helium flux, 100 mL min—1. The temperatures of the two transfer lines (between the TDSA device and the cold injection system (CIS 4) and from the GC and MS ion source) were set at 250°C. The CIS was equipped with an empty liner to cryo-focus the analytes prior to transfer to the capillary column, and was cooled with nitrogen during thermodesorption. The following conditions were used for the cold injection system: during thermodesorption, temperature was set to -150°C, raised at 12°C s—1 to 250°C and held for 5min; the injector was used in splitless mode with a time of 1.5 min. An HP-5 MS capillary column (30 m; 0.25mm i.d.; 0.25 mm film thickness) (Agilent Technologies) was used with the following temperature programme: 50°C, 3 min isothermal, raised to 160°C at 15°C min—1, raised at 3°C min—1 to 235°C, and then raised at 30°C min—1 to the final temperature of 280°C, held for 8 min. Helium was used as carrier gas with a linear velocity of 40 cm s—1 in constant flow mode. The single ion-monitoring (SIM) mode was selected for the detection of the analytes. Two characteristic target ions were chosen for each compound under consideration.

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