Enrichment and Purification

One thing is common to all practicable methods of preparation they are not directed syntheses of single fuUerenes with defined sizes, but rather yield a mixture of different carbon cages. Consequently, the separation and purification of fuller-enes become necessary. As the concentration of and C70 is much higher than that of the larger homologs, the latter are much harder to isolate. 

In addition to the desired species, the fullerene soot contains a multitude of insoluble components like soot particles or graphitic fragments. Moreover, there may be polycyclic aromatic hydrocarbons also. The separation from insoluble contaminants may be affected by extraction because the fuUerenes, and most of all the small ones, exhibit significant solubility in some organic solvents (refer to Section 2.4.1.1). Toluene is most commonly used for this process. Other possible solvents include chlorinated aromahc species, carbon disulphide, benzene and hexane. As an alternative, the fullerene part of the raw material may be separated by sublimation. In any case a mixture of the generated fuUerenes is obtained which has to be resolved into its constituents. In most cases chromatography is used to this purpose. 

The separation of C o may further be attained by absorptive filtration on a mixture of charcoal powder and siUca gel. Pure toluene can be used here which distinctly increases the solubiUty, thus accelerating the process and markedly reducing the solvent consumption. Apart from Q,q, it has by now become possible to obtain C70 on a multigram scale as well as to make higher fullerenes available at least in amounts sufficient for physical examination. Highly purified materials can be produced by sublimation of the above substances. Chiral fullerenes (refer to Section 2.2.3) may be split into enantiomers by suitable methods, for example. 

HPLC on a stationary phase based on amylose. The latter has been successfully applied to Dr-Cye. 

Usually a synthesis of heterofuUerenes by simply reacting the carbonaceous starting material with a source of the respective heteroelement does not succeed. The reaction of graphite with boron nitride or cyanogen (CN)2, for example, does not yield the desired heterofullerene. Other methods starting from organic derivatives of fullerenes have to be considered instead. 

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Some reference odorants are commercially available some have to be synthesized in the laboratory. Sometimes or often, the concentration of an important odorant in a sample might be so low, that even after enrichment and purification,... 

M Fountoulakis, H Langen, C Gray, B Takacs. Enrichment and purification of proteins of Haemophilus influenzae by chromatofocusing. J Chromatogr 806 279-291, 1998. 

Sample clean-up can be done rapidly using a short LC column operated under gravity flow or under vacuum, centrifuge or syringe pressure. The most popular phases include silica and bonded phases. Disposable and inexpensive columns are available and can be found under the following trade names Sample Enrichment and Purification, PreSep Extraction, Bond-Elute, and solid-phase extraction. For example, purification of sulfamethazine in milk by SPE followed by quantitative analysis by TLC has been described earher... 

Guggjsberg, D., Risse, M., C., and Hadom, R., 2012. Determination of vitamin Bi2 in meat products by RP-HPLC after enrichment and purification on an immunoaffinity column. Meat Science. 90 279 283. 

In addition to particle manufacture, it is also possible to manipulate particles, thus enabling their movement between different chemical treatment zones [157,158] as well as sorting them by size [159-164]. Particle manipulation theories are not just useful in particle manufacture they can also be apphed to cell enrichment and purification procedures [165,166] or sample preparation [167] among others. 

For the enrichment and purification of unknown compound II, the hydrocarbons of about 20 kg of orange essence oil were removed by column chromatography on silica gel. Subsequently the compound occurring in fraction II was further purified by two-dimensional preparative capillary gas chromatography. Interpretation of the resulting mass spectra finally led to the identification of 8-tetradecenal. The mass spectrum is shown in Fig. 2. 

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