Agriculture Reference
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Holland) down to a 10 cm depth. To obtain composite samples for each sampling point, soils
were collected by mixing five different components (four main directions of 2 m radius and
the center) within a 12.6 m 2 area. Approx. 1.5 kg of soil was taken at each site. Soil samples
were air-dried in a ventilated room until reaching constant weight, and bio-material (roots,
leaves) was manually removed. Then they were skived and sieved to < 0.25 mm. They were
refrigerated until analysis, within two weeks. The first survey as PCDD/Fs baseline was
conducted at April 2007, before this MWI started operation (May 2007). And soil samples
were collected every year (2008 to 2010) in the same sites as the first survey after this facility
operation began. During this period, fly ash and stack gas samples were collected from this
MWI.
2.3 Clean procedure and analysis technology
About 10 g (dry mass) of soil samples were used for PCDD/Fs analysis. A selective pressured
liquid extraction (SPLE) method was used for sample extraction by using a fully automated
ASE 300 system (Dionex, Sunnyvale, CA, USA) (Fig.3). The extraction condition and
procedure was referred to the SPLE method with a slight modification. Briefly, a 100-ml
extraction cell was used and the ratio of soil:alumina:copper was 5:5:1. Each sample was
spiked with a mixture of 13 C 12 -labelled PCDD/Fs compound stock solution (5 µl) and clean-up
standard (5 µl) before extraction. The extracts from ASE were subsequently followed by rotary
evaporation and multilayer silica gel column clean-up procedure following the Method of
USEPA 1613. The extracts were blow-down to 20 µl under a gentle stream of nitrogen (N 2 ),
and 5µl of 13 C 12 -labelled PCDD/Fs internal standard solution were added before sample were
subjected to PCDD/Fs analysis by using high-resolution gas chromatography with high-
resolution mass spectrometry (HRGC/HRMS) (JEOL JMS-800D) with a DB-5MS column (60 m
× 0.25 mm × 0.25 µm). The toxic 2,3,7,8-substituted PCDD/Fs (referred to as congeners) as well
as Tetra- to Octa-chlorinated homologues were identified based on isotope, and quantification
of PCDD/Fs was performed by an isotope dilution method using relative response factors
previously obtained from the five calibration standard solutions. In order to check the
duplicate results, two soil samples are analyzed twice each year survey. If there is a wide
variation in samples results, it also will be analyzed again. All isotope standards were
purchased from the Cambridge Isotope Laboratories, Inc. (USA).
Fig. 3. ASE 300 Schematic System.
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