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Chromatografy Methods for Environmental - Ando D.J.

Ando D.J. Chromatografy Methods for Environmental - Wiley publishing , 2003. - 265 p.
Download (direct link): chromatography2003.pdf
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Solids
133
7.7.2 Example 7.6: Pressurized Fluid Extraction of DDT, DDD and DDE from Contaminated Soil
7.7.2.1 Extraction Conditions These were as follows:
• Sample: 2 g
• PFE conditions: pressure, 2000 psi, temperature, 100°C; static extraction time, 10 min; three static/flush cycles.
Comments Sample placed in stainless-steel extraction cell on top of a filter to prevent cell-frit blockage. ‘Hydromatix’ was used to fill the headspace in order to reduce solvent consumption.
7.7.2.2 Analysis by GC-MS
Separation and identification of DDT, DDD and DDE was carried out on an HP 5890 Series II Plus gas chromatograph, fitted to an HP 5972A mass spectrometer. A 30 m x 0.25 mm id x 0.25 ^m film thickness DB-5ms capillary column was used, with temperature programming from an initial temperature held at 120°C for 2 min before commencing a 5°Cmin-1 rise to 290°C, with a final time of 2 min. The split/splitless injector was held at 280°C and operated in the splitless mode. The mass spectrometer transfer line was maintained at 280°C. Electron impact ionization at 70 eV, with the electron multiplier voltage set at 1500 V, was used, while operating in the single-ion monitoring (SIM) mode.
7.7.2.3 Typical Results
These are shown in Figure 7.17 [6].
U)
c
o
§•§.
O
600 -400 -200 -
Figure 7.17 Results obtained for the pressurized fluid extraction of DDT, DDD and DDE from contaminated soil, and comparison with those obtained from Soxhlet extraction: ?, Soxhlet; EH, PFE: 1, DDT; 2, DDD; 3, DDE [6] (cf. DQ 7.13).
0
f Note that the commercial organochlorine pesticide known as ‘DDT’ is not a single chemical compound. Its major active component (70-80% of the total content) is p,p;-dichlorodiphenyl trichloroethene (p,p;-DDT), along with smaller quantities of the related compounds, p,p'-dichlorodiphenyl dichloroethene (p,p;-DDD) and p,p;-dichlorodiphenyl dichloroethene (p,p;-DDE).
134
Methods for Environmental Trace Analysis
DQ 7.13
Comment on the results obtained in this study (see Figure 7.17).
Answer
It is found that the recoveries of DDT and its metabolites from soil are similar, irrespective of the extraction method being used.
7.8 Matrix Solid-Phase Dispersion
Matrix solid-phase dispersion (MSPD) is analogous to solid-phase extraction (SPE), as described later in Chapter 8. The main difference being that MSPD is used for solid samples. In MSPD, the sample is mixed with an SPE sorbent, e.g. C18 (octadecylsilane (ODS)) from the cartridge. After returning the sorbent-sample mixture to the cartridge, it is eluted as in SPE. The main purpose of the C18 sorbent is to act as an abrasive, thus disrupting the sample’s structure, and hence promoting its dispersion within the sorbent and creating a large surface area for solvent interaction. The best ratio of sample to sorbent is 1:4. In practice, it should be possible to adapt the type of sorbent for a particular sample, thereby providing a tailored extraction procedure. A typical scheme for matrix solid-phase dispersion extraction is shown in Figure 7.18.
Figure 7.18 Typical procedure used for the matrix solid-phase dispersion of solids.
Solids
135
7.8.1 Example 7.7: Matrix Solid-Phase Dispersion of an Alcohol Ethoxylate (Lutensol, C13 and C15, with an Average Ethoxy Chain of EO7), Spiked onto an Homogenized Fish Tissue
7.8.1.1 Extraction Conditions These were as follows:
• Sample: 1 g
• MSPD conditions. SPE cartridge washed with 20 ml of hexane, which was then discarded. Elution of the alcohol ethoxylate (AE) was carried out using several solvent systems: (1) 20 ml of methanol followed by 20 ml of acetonitrile, (2) 20 ml of dichloromethane/acetonitrile (1:1 (vol/vol)), followed by 20 ml of methanol, and (3) 20 ml of dichloromethane/acetone (1:1 (vol/vol)). The eluents were taken to 1 ml at 60°C under a gentle stream of nitrogen, and to dryness under nitrogen and in ice.
Comments Sample mixed with 1 ml of methanol, octadecylsilane (ODS, C18) was added (4 g), and the resultant mixture ground until a free-flowing powder was obtained. The mixture was then placed in an empty SPE extraction cartridge with filters at either end.
7.8.1.2 Extract Clean-Up
This was carried out by using two Al-N cartridges. The first of these was conditioned with 20 ml of dichloromethane/methanol (100:5 (vol/vol)) at a flow rate of 2-3 mlmin-1. The dried residue from the MSPD step was resolvated in 5 ml dichloromethane/methanol (100:5 (vol/vol)), and this was then passed through the Al-N cartridge and collected in a glass vial. The sample container was washed with another 2 x 5 ml of dichloromethane/methanol (100:5 (vol/vol)); these were also passed through the cartridge, which was then washed with a further 5 ml of dichloromethane/methanol (100:5 (vol/vol)). All eluents were collected, taken to 1 ml at 60°C, and to dryness under ice, under a gentle stream of nitrogen.
The second Al-N cartridge was conditioned with 20 ml of cyclohexane at a flow rate of 2-3 mlmin-1. Then, the dried extract was resolvated in 3 ml of cyclohexane, using a sonic bath. This solution was then transferred to the Al-N cartridge. The vial containing the extract was rinsed with 2 x 5 ml of cyclohexane, and then transferred to the cartridge. The eluate was discarded and the AE eluted with 20 ml of dichloromethane/methanol (100:5 (vol/vol)). This extract was taken to 1 ml at 60°C and to dryness under ice, again under nitrogen.
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