Microwave extract

Microwave extraction realized at 120 °C for 30 min with Hexane -Acetone (3 2 V/V) as the extraction solvent was identified as the most effective extraction procedure for isolation of TPH from biotic matrices. The aim of this research is to develop a silica gel and alumina fractionation procedure for plant sample extraction. Column chromatography with two solvents (chloroform and hexane dichloromethane) as a mobile phase were used for clean-up of extract. In this research the efficiency of recovery received from chloroform as a mobile phase. 

Specifically for triazines in water, multi-residue methods incorporating SPE and LC/MS/MS will soon be available that are capable of measuring numerous parent compounds and all their relevant degradates (including the hydroxytriazines) in one analysis. Continued increases in liquid chromatography/atmospheric pressure ionization tandem mass spectrometry (LC/API-MS/MS) sensitivity will lead to methods requiring no aqueous sample preparation at all, and portions of water samples will be injected directly into the LC column. The use of SPE and GC or LC coupled with MS and MS/MS systems will also be applied routinely to the analysis of more complex sample matrices such as soil and crop and animal tissues. However, the analyte(s) must first be removed from the sample matrix, and additional research is needed to develop more efficient extraction procedures. Increased selectivity during extraction also simplifies the sample purification requirements prior to injection. Certainly, miniaturization of all aspects of the analysis (sample extraction, purification, and instrumentation) will continue, and some of this may involve SEE, subcritical and microwave extraction, sonication, others or even combinations of these techniques for the initial isolation of the analyte(s) from the bulk of the sample matrix. 

For polymer/additive analysis complete dissolution is not a prerequisite. Rather, the solvent should at least swell the polymer by diffusion, which allows the physically blended additives to dissolve. True dissolution occurs predominantly when polymer chain lengths are small, on the order of 5000-10 000 Da. Solvent choice for dissolution or extraction should take into account restrictions imposed by further analysis steps (compatibility with chromatographic and/or spectroscopic requirements). When microwave extraction of additives from a polymer is followed by HPLC analysis, the solvent must be compatible with the HPLC mobile phase so that solvent exchange is not required before analysis. 

Costley et al. [113] have evaluated the use of a range of organic solvents (dichloromethane, water, acetone, hexane, xylene) in the microwave extraction of oligomers from PET and have compared MAE to alternative extraction approaches (Soxhlet, Pan-bomb). 

Table 3.4 contains a comparison of microwave extraction with other sample preparation procedures. MAE compares favourably with Soxhlet/Soxtec and... 

The popularity of MAE methods for in-polymer additive analysis is reflected in a limited list of reported applications. This is both on account of the former lack of dedicated microwave equipment designed specially for small analytical samples and the relatively recent commercial introduction of the technique. Microwave extraction for analytical purposes is a relatively new growth area [441]. 

In order to perform extraction of additives or dissolution of polymers, solvents that absorb microwave energy are necessary. This is more important than direct absorption of microwave energy by the polymer or additives. When microwave extraction of additives... 

Figure 3.14 Microwave extraction of 0.1 % Irganox 1010 from ground (20 mesh) polyolefins ( , PP O, LDPE +, HDPE) with 1,1,1-trichloroethane. After Freitag and John [96]. From W. Freitag and O. John, Angewandte Macromoleculare Chemie, 175, 181-185 (1990). Wiley-VCH, 1990. Reproduced by permission of Wiley-VCH...

Figure 3.16 Influence of time on microwave-extraction efficiencies for additives in HDPE. After Jassie et al. [454]. Reprinted with permission from L. Jassie et al., in Microwave-Enhanced Chemistry (H.M. Kingston and S.J. Haswefl, eds), American Chemical Society, Washington, DC (1997), pp. 569-609. Copyright (1997) American Chemical Society...

The advantages associated with the MAP technology as compared to conventional and automatic Soxhlet methods are considerable (Table 3.33). In MAP high sensitivity and selectivity by fractionation are achieved using different extraction media with similar, or better, linearity and reproducibility parameters. One of the principle features of the process is the lower temperatures observed in the microwave-extracted materials in contrast to volumetric heating usually experienced in traditional solvent procedures. These lower temperatures... 

SFE has now been available long enough to allow an evaluation of its prospects for polymer/additive extraction. SFE is still around, but EPA and FDA approved SFE methods are still wanting. The main problem is strong matrix effects. SFE is not a cookbook method for one s matrix. Not unlike microwave extraction, SFE requires that a specific method be developed to optimise the recovery for each polymer/additive system. Therefore, the success of SFE depends on the polymer... 

Freitag and John [96] studied rapid separation of stabilisers from plastics. Fairly quantitative extraction (>90% of the expected content) of stabilisers from a powdered polymer was achieved by MAE within 3 to 6 min, as compared to 16 h of Soxhlet extraction for the same recovery. MAE and Soxhlet extraction have also been compared in the analysis of cyclic trimer in PET [113]. On the other hand, Ganzler et al. [128] compared the extraction yields for various types of compounds from nonpolymeric matrices for microwave irradiation with those obtained by the traditional Soxhlet or shake-flask extraction methods. Microwave extraction was more effective than the conventional methods, in particular in the case of polar compounds. As expected, the efficiency of the former is high especially when the extraction solvents contain water. With the high dipole moment of water, microwave heating is more... 

During extraction, both the temperature and pressure in the extraction container increase, and thus care must be taken. The container must be able to withstand the temperatures and pressures and must be compatible with the extractant used. When the microwave extraction time is complete, the digestion container is removed and the digestate is handled and analyzed in the same way as a nonmicrowaved sample [15]. An example of a microwave extraction is given in Procedure 11.9 ... 

Microwave extractions can be carried out by any of the above-mentioned extractions resulting in the extraction of the same components. The advantage is that microwave extraction is typically much faster. 

Microwave extractions such as that illustrated in Procedure 12.4 have been used to extract chlorinated biphenyls, phenols, sulfonylurea herbicides, and triazines from soil [7,9,13,15],... 

In Procedure 12.4, sample and solvent are added to the extraction vessel at room temperature and are heated to 130°C during the extraction process [9], The extraction time is short when compared to other extractions procedures, being only 10 minutes. Microwave extraction is used when a rapid analysis is desired and the analyte of interest is not affected by high temperature and pressure. 

Two examples of other extraction methods of APEO from solid matrices that have been studied include solid-phase microextraction (SPME) [50] and microwave extraction [46],... 

The microwave extraction was performed with 25 mL methanol at 150°C, 10 atm and 20 min extraction time. Large variations in recovery were obtained between 31 and 85% for different sediments [46]. 

Heise and Litz [26] investigated the extraction behaviour of surfactants (LAS, NPEO and cationics) from sand comparing Soxhlet extraction, accelerated solvent extraction (ASE) and microwave-assisted extraction. Fractionation of the three surfactant types anionic, non-ionic and cationic, was accomplished by column chromatography with aluminium oxide. Soxhlet extraction and ASE of spiked sand with methanol—stored during 7 days prior to extraction—gave similar recoveries for both LAS and NPEO with values between 88 and 116%. Less efficient extraction was achieved by microwave extraction (79% for NPEO). 

LAS Sludge-amended soil Microwave extraction (acidic methanol) SAX + RP-C8 HPLC-FL [Pg.833]

---