Column Characterisation

Column Characterisation- the Degree of Difficulty of Separation Referring to Figure 3.1 for a binary mixture and given ... 

Lipoproteins (from human plasma). Individual human plasma lipid peaks were removed from plasma by ultracentrifugation, then separated and purified by agarose-column chromatography. Fractions were characterised immunologically, chemically, electrophoretically and by electron microscopy. [Rudel et al. Biochem J 13 89 1974.]... 

Meehan, E., and O Donohue, S. J. (1992). The Role of Column and Media Design in the SEC Characterisation of High Molecular Weight Polymers. Presented at ISPAC 5, Inuyama, Japan. 

Table 1. Characterisation data and viscosities, ri0, of polystyrene (molar mass distribution Mw/Mn<1.3) in toluene at 25 °C. Theoretical viscosities, ri0(theor), were calculated from Eq. (14). In the last column A represents the relative deviation of ri0(theor) from T 0(exp) ...

Berger [340] has examined the use of pSFC in polymer/additive analysis. As many polymer additives are moderately polar and nonvolatile SFC is an appropriate separation technique at temperatures well below those at which additives decompose [300,341,342], SFC is also a method of choice for additives which hydrolyse easily. Consequently, Raynor et al. [343] and others [284,344] consider that SFC (especially in combination with SFE) is the method of choice for analysing polymer additives as a relatively fast and efficient sample preparation method. Characterisation of product mixtures of nonpolar to moderately polar components encompassing a wide range of molecular masses can be accomplished by cSFC-FID. Unknown polymer additives may be identified quite adequately by means of cSFC-FID by comparison with retention times of standards [343], However, identification by this method tends to be time-consuming and requires that all the candidate compounds are on hand. SFC-FID of some low-to-medium polarity additives on reversed-phase packed columns... 

HPLC has also been used for analysing fatty acid mixtures [708] and for the characterisation of fatty acids and their derivatives [709]. Fatty acids are commonly analysed on polymeric RPLC columns. Only multiple unsaturated fatty acids can be detected by UV in HPLC the others require derivatisation into UV-absorbing or fluorescing derivatives. Simultaneous determination of saturated and unsaturated fatty acids (C12-C24) by means of RPLC has been reported [710]. Derivatisation is necessary. 

The most spectacular results with temperature-programmed LC have been obtained for some notoriously difficult polymeric additives. Characterisation of the oligomeric HALS stabiliser poly [[6-[(l,l,3,3-te-tramethylbutyl) amino]-l,3,5-triazine-2,4-diyl][(2,2,6,6-tetramethyl-4-piperidyl)imino]-l,6-hexanediyl [(2,2,6,6-tetramethyl-4-piperidyl)imino]] (I) (Figure 4.12) is difficult for several reasons it has a broad MWD, may contain isomers, and has several amino groups that promote almost irreversible adsorption to silica based column packings in LC. 

Several reviews [767,768] and books [51,757,767, 769] deal with SEC in relation to the molecular weight characterisation of synthetic polymers (see also Bibliography). Trends in the development of column technology, detectors and data handling for SEC have recently been discussed [770,771]. The field produces some 1200 papers per year. 

A recent extension of the scope of SPE-GC and SPE-GC-MS concerns the use of AED detection with its multielement detection capability and unusually high selectivity. Hankemeier [67] has described on-line SPE-GC-AED with an on-column interface to transfer 100 iL of desorbing solvent to the GC. The fully on-line set-up is characterised by detection limits of 5-20 ngL because of quantitative transfer of the analytes from the SPE to the GC module. On-line coupling of SPE with GC is more delicate than SPE-LC, because of the inherent incompatibility between the aqueous part of the SPE step and the dry part of the GC system. 

Various authors have described on-line LC-SFC coupling [947,948]. Coupling of LC to SFC with conventional-size LC columns, where only a small fraction of the peak of interest is transferred to the SFC, allows only for qualitative results, and does not address the need for improved sensitivity in cSFC. Cortes et al. [948] have described relatively large-volume sample introductions (>10 xL) into cSFC, using microcolumn LC in the first dimension. LVI-LC-cSFC provides enhanced sensitivity compared with conventional cSFC injection techniques. LC-cSFC is expected to be of utility in the characterisation of complex samples, and in the determination of components which are thermally labile do not contain significant chromophores or do not have sufficient volatility to be analysed by GC. 

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