Environmental Engineering Reference
In-Depth Information
had been pre-extracted with dichloromethane, which was placed in a Soxhlet
extractor and extracted with 30 mL of dichloromethane for 12 h. After the extrac-
tion, the extract was reduced to about 10 mL on a water bath with the water bath
set at 38°C and the condenser water at 4°C. The reduced extract was transferred to
a 100 mL separating funnel and 20 mL of distilled water was added to the extract.
The mixture was washed with three 10 mL portions of 0.1 mol/L sodium carbonate.
The extraction was done in triplicate. The dried extract was reduced to 1 mL and
was cleaned up as described above for the water samples.
The dried extract from water and sediment samples was then reduced to about
1 mL and cleaned up in a glass column packed with about 25 g of silica gel (40 mm),
deactivated with 2% water (w/w), using n-hexane. Polycyclic aromatic hydrocar-
bons and other saturated compounds were eluted from the column successively
with 2 × 10 mL dichloromethane: hexane (85:15 v/v). The eluates were collected,
dried with Na2SO4 and evaporated using a rotary evaporator. The residues were
reconstituted with 1 mL of hexane for GC analysis. Quantization was done by
external standardization. High purity reagents were used in all the analyses to
reduce interfering peaks in chromatographic analysis. The following analytical
grade materials were used and were stored in tightly sealed containers:
•
Silica gel - particle size 0.040-0.063 mm for column chromatography
•
Dichloromethane (Aldrich);
n
-Hexane, 99.5% (Aldrich).
GC Conditions
Perkin Elmer Clarus 500 Gas Chromatograph, with FID detector and capillary
column (Perkin Elmer SA (Pty). The gas chromatograph had an auto-injection, dual
column system for both FID and ECD. The chromatograms were handled by a total
Chrom Work Station programmed temperature with He as carrier gas. The operating
conditions were: temperature programme; hold for 30 min. at 70°C, heat at 12°C/
min and hold at 330°C; column diameter, 250 mm, and a column packing of ELHE;
He carrier gas flow rate, 540 mL/min.
Results and Discussion
Results of the quality assurance studies are shown in Table
1
. Due to the low solu-
bility of PAHs in water and the subsequent low concentrations they are found in
aqueous media, most the methods developed so far for their analysis include an
extraction/concentration step, followed by elution with an appropriate solvent and
chromatographic analysis
[18]
. Some of these methods include liquid-liquid extrac-
tion (LLE), solid phase extraction and micro-sold phase extraction for water sam-
ples and Soxhlet extraction (SE), microwave-assisted extraction (MAE), micro-solid
phase extraction and ultrasonic extraction methods for solid samples
[8, 19-22]
.
