2.3. HS-SPME procedure
HS-SPME extraction was performed using a Supelco (Bellefonte,
USA) manual holder containing a fiber assembly with a 100 μm polydimethylsiloxane
(PDMS) coating. The fiber was conditioned in the injection
port of a gas chromatograph at 250 °C for 30 min prior to use and
blank desorption was performed. 2 mL of aqueous sample (standard
or real) was placed in 4 mL glass vial with PTFE/silicone septa, which
contained 10% (w/v) sodium chloride salt. The fiber was exposed to
the headspace of a sample, kept at a selected temperature for a set
time, retracted into a needle, and introduced into the injection port of
gas chromatograph. Extraction was supported by magnetic stirring at
the highest possible level. A fiber blank experiment was performed to
ensure that there were no contaminants on the fiber.
For optimization of HS-SPME process, the factors affecting extraction
efficiency (headspace volume, extraction time, temperature,
sample ionic strength and agitation speed) were investigated.
2.4. Gas chromatography flame-ionization detector (GC–FID)
HP5890 series II gas chromatograph equipped with a split/splitless
injector coupled with a flame-ionization detector connected to an
Agilent 3396 series 3 integrator was used. Analytes were desorbed
fromthe fiber in a gas chromatograph splitless injection port. The injection
port was fitted with a 0.75 mm i.d. injection liner (Supelco) with
the split–splitless purge valve opened at 1 min after injection. The desorption
temperature and time of analytes were optimized. The depth
of the SPME needle in the injection port was also selected (3 cm) and
controlled. The injector temperature was 260 °C. The chromatographic
column used was Zebron ZB-5 (30 m×0.25 mm×0.25 μm
of 5% phenyl–95% dimethylpolysiloxane) supplied by Phenomenex
(USA). Helium (CP grade, 99.999%) was used as a carrier gas and was
supplied by BOC Gases Europe (Guildford, UK). The flow of carrier gas
was 1 mL min−1, with constant flow conditions being observed
throughout. The temperature program was as follows: 40 °C (hold
2 min), 10 °Cmin−1 to 70 °C, 5 °C min−1 to 90 °C, then 25 °C min−1
to 270 °C (hold 1 min). The detector temperaturewas 300 °C. For confirmation
of the developed analytical methodology a second fused silica
column was also used: Equity™-1 capillary column (30 m×0.25 mm×
0.25 μm film thickness) supplied by Supelco.