Multiple column partition chromatography

CHAPTER 15 - DISPLACEMENT AND MULTIPLE COLUMN PARTITION CHROMATOGRAPHY... 

If a solid substance is extracted repeatedly with several portions of cold solvent, the operation is called maceration, if the same operation is carried out with hot solvent, it is called digestion and if the procedure has a countercurrent character, it is called percolation. So-called Soxhlet extractors, in which a solid substance is extracted with a solvent and the extract becomes more and more concentrated, function automatically. If a dissolved substance is extracted with one portion or more of an immiscible solvent, the operations is called simple extraction or multiple extraction, respectively. If the extraction is carried out by countercurrently-moving solvents, we deal with a countercurrent distribution technique. A continuous extraction of a liquid with another liquid immiscible with the first is called perforation continuous countercurrent extraction using two liquid phases is carried out in special countercurrent columns. If one of the phases is fixed on a carrier, partition chromatography is the name given to the operation. The choice of the given type of extraction method will depend on the character of the analyzed substances and on the required separation efficiency. 

Tan [71] devised a rapid simple sample preparation technique for analysing polyaromatic hydrocarbons in sediments. Polyaromatic hydrocarbons are removed from the sediment by ultrasonic extraction and isolated by solvent partition and silica gel column chromatography. The sulphur removal step is combined into the ultrasonic extraction procedure. Identification of polyaromatic hydrocarbon is carried by gas chromatography alone and in conjunction with mass spectrometry. Quantitative determination is achieved by addition of known amounts of standard compounds using flame ionization and multiple ion detectors. 

Headspace-GC-MS analysis is useful for the determination of volatile compounds in samples that are difficult to analyze by conventional chromatographic means, e.g., when the matrix is too complex or contains substances that seriously interfere with the analysis or even damage the column. Peak area for equilibrium headspace gas chromatography depends on, e.g., sample volume and the partition coefficient of the compound of interest between the gas phase and matrix. The need to include the partition coefficient and thus the sample matrix into the calibration procedure causes serious problems with certain sample types, for which no calibration sample can be prepared. These problems can, however, be handled with multiple headspace extraction (MHE) [118]. Headspace-GC-MS has been used for studying the volatile organic compounds in polymers [119]. The degradation products of starch/polyethylene blends [120] and PHB [121] have also been identified. 

In the case of acidic glycolipids the relative proton affinity of chemicals can shift the balance for negative ionisation in favor of co-eluted compounds. Pre-analytical separation under acidic conditions serves also to reduce as much as possible the dispersion in the MS spectrum of the metabolite into multiple m/ z representing the various adducts of counterions Na, K, NH4, organic amines, ... which improves sensitivity of the test. Sulfatides are lost during the partition between the hexane and the methanol/water phase. The analysis of sulfatides involves the isolation of the glycosphingolipid fraction and the subsequent separation of sulfatides from neutral lipids by chromatography on DEAE-sephadex or DEAE-cellulose column (the variety of methods are referenced in the website CyberLipid (http //www.cyberlipid.org/). 

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