Liquid extraction, soil cleanup

Figure 3 Experimental design for continuous MAE, liquid-liquid extraction, sorption/cleanup of phenol compounds in soil samples. IV, injection valve PS, membrane phase separator o.p. and a.p., organic and aqueous phases W, waste. (Reproduced with permission from Ericsson M and Colmsjo A (2000) Dynamic microwave-assisted extraction. Journal of Chromatography 877 141 Elsevier.)...

Soil, sediment, and dust samples were prepared in a similar way before analysis. After the pre-cleanup steps and homogenization, FRs were extracted from samples using different solid-liquid extraction techniques. The most commonly used technique was accelerated solvent extraction (ASE), which enables the fast extraction of samples using different solvents such as hexane and dichloromethane [98-100]. Other commonly used techniques for these samples were ultrawave-assisted extraction (UAE) [97], which also enabled quick extraction, and the more time-consuming but very efficient technique, Soxhlet extraction [96]. Some authors have also described less common techniques such as microSPE [95]. There is also information that many FRs that are no longer produced (mainly PCBs and PBDEs) are present in dusts, soils, and sediments in very high amounts, even 390 pg/g [98]. 

PAHs can be eluted as a separate band although they may still coelute with chlorinated aromatics, pesticides, and nitroaromatics, thus necessitating another cleanup step prior to analysis. Another strategy is to separate the organic acids and phenols from soil/sediment extracts by performing a liquid-liquid extraction with 10 N NaOH. ° The solvent extract is shaken in a separatory funnel with three aliquots of concentrated NaOH. The combined extracts containing the acids and phenols is discarded while the extract, in DCM, is dried and concentrated for GC analysis or solvent exchanged for another analysis method. 

Solid-liquid extraction can be performed with Soxhlet equipment, but simpler processes with equally convincing results are available. These include mechanical shaking of a mixture consisting of correctly dried and pulverized soil and about 10 times as much solvent, and conventional operations involving cleanup and possibly concentration. 

Residue analytical methods for neonicotinoids in crops, soil and water samples have been developed. The basic principle of these methods consists of the following steps extraction of the crop and/or soil samples with acetone or the other organic solvent, cleanup by liquid-liquid partition or column chromatography, and quantitative analysis by high-performance liquid chromatography with ultraviolet detection (HPLC/UV). Simple column cleanup procedures are used to improve the accuracy and sensitivity of these methods. 

This procedure ( ) has been used since 1982 by EPA for routine investigations. The analytical protocol requires complete extraction of the sample followed by liquid chromatographic cleanup and isomer-specific 2,3,7,8-TCDD analysis by high resolution gas chromatography/low resolution mass spectrometry. The extraction begins with ten grams of soil which is spiked with internal surrogate CI4-2378-... 

Another example is the use of the EPA 418.1 method to determine TPH content. The EPA 418.1 method, based on measuring the absorption of C-H bond in the 3200 to 2700 wave number range, was originally intended for use only with liquid waste but had been one of the most widely used methods for the determination of TPH in soils before its demise because of the use of a chloro-fluoro carbon extracting. For some site assessments. Method 418.1 was the sole criterion for verihcation of site cleanup. However, there were some problems associated with this method such as inherent inaccuracy in the method (i.e., positive or negative biases caused by various factors) and the lack of effective reference standards when working with an unknown. 

Terra-Vac, Inc., developed the In-Situ Vacuum Extraction process, which removes volatile organic constituents (VOCs) from the unsaturated zone of soils through extraction wells. The extracted gases and water proceed to a vapor-liquid separator and an emission control system. The process has been employed at over 60 sites. Four case studies, including three Superfund sites, have been documented. The process represents a viable technology to fully remediate sites contaminated with volatile organics. Considerations for use include contaminent volatility, site-specific cleanup level, and soil properties. The process works well with most soil types. The air-filled porosity of a soil is an important criterion to indicate whether vacuum extraction will work. Soils with low permeability but with... 

---