The water used for the preparation of the standard solutions was prepared with a Milli-Q filtration system of Millipore.
To overcome the presence of volatile compound arising from the septa and the vials, these are heated for 1 h at 200°C. After cooling down, the septa are kept in an open box. This procedure does not completely eliminate the volatile substances, so that at low concentration the signal given by the septa and vials is the principal factor controlling the limit of quantification.
2.2. Apparatus
The measuring device (Fig. 1) can be seen as a gas chromatograph with a very short non separating column. It consists of an injector for wide bore column used for gas chromatography and a standard detector for gas chromatography. The detector and the injector are enclosed in a heating jacket and can be independently heated to the desired temperature. The injector is equipped with a septum and a glass liner of 2 mm i.d. The temperature of the injection port can be varied from 70 to 350°C; the capillary that links the injector to the detector is heated at the same temperature as the injector. A flow of helium drains the desorbed volatile substances from the injector to the detector. Both are linked with a short capillary of about 30 cm length and 0.32 mm i.d.
2.3. Procedure
For the tests described here, the measurement procedure is the following: 8 ml of the sample to be measured is pipetted into a 22 ml vial, the vial is then closed with a septum and heated at 35°C in the water bath. After an equilibration time, defined as the time necessary for the volatile substances of the solution reach equilibrium with the headspace, the SPME-fiber is inserted in a vial for the sampling process. After the sampling time (extraction time in the terminology of SPME), the SPME-fiber is immediately transferred to the apparatus, thermally desorbed and the volatiles are drained to the detector by the helium flow.
The water used for the preparation of the standard solutions was prepared with a Milli-Q filtration system of Millipore.
To overcome the presence of volatile compound arising from the septa and the vials, these are heated for 1 h at 200°C. After cooling down, the septa are kept in an open box. This procedure does not completely eliminate the volatile substances, so that at low concentration the signal given by the septa and vials is the principal factor controlling the limit of quantification.
2.2. Apparatus
The measuring device (Fig. 1) can be seen as a gas chromatograph with a very short non separating column. It consists of an injector for wide bore column used for gas chromatography and a standard detector for gas chromatography. The detector and the injector are enclosed in a heating jacket and can be independently heated to the desired temperature. The injector is equipped with a septum and a glass liner of 2 mm i.d. The temperature of the injection port can be varied from 70 to 350°C; the capillary that links the injector to the detector is heated at the same temperature as the injector. A flow of helium drains the desorbed volatile substances from the injector to the detector. Both are linked with a short capillary of about 30 cm length and 0.32 mm i.d.
2.3. Procedure
For the tests described here, the measurement procedure is the following: 8 ml of the sample to be measured is pipetted into a 22 ml vial, the vial is then closed with a septum and heated at 35°C in the water bath. After an equilibration time, defined as the time necessary for the volatile substances of the solution reach equilibrium with the headspace, the SPME-fiber is inserted in a vial for the sampling process. After the sampling time (extraction time in the terminology of SPME), the SPME-fiber is immediately transferred to the apparatus, thermally desorbed and the volatiles are drained to the detector by the helium flow.
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