Chromatographic separation carbohydrates

The above chemicals can be obtained by fermentation (qv) of other sugars. However, some compounds require sucrose as a unique feedstock. Examples are the polysaccharides dextran, alteman, andlevan, which are produced by specific strains of bacteria (48,54—56). Dextrans are used to make chromatographic separation media, and sulfated dextran derivatives are used as plasma extenders (41). Levans show promise as sweetness potentiators and, along with alteman, have potential as food thickeners and bulking agents in reduced-caloric foods (55,56) (see Carbohydrates). 

RI detectors measure this deflection, and are sensitive to all analytes that have a different R1 than the mobile phase. There are two major limitations First, Rl detectors are very sensitive to changes in the temperature, pressure, and flow rate of the mobile phase, and so these measurement conditions must be kept stable in order to obtain low background levels. Second, Rl detectors are incompatible with chromatographic separations using gradient elution. Furthermore, because Rl detectors are nonselective, they must be used in conjunction with other detection methods if specificity is required. Nevertheless, they have found wide application in isocratic chromatographic analysis for analytes that do not have absorptive, fluorescent, or ionic properties, such as polymers and carbohydrates. 

Because nuclear magnetic resonance (NMR) is particularly advantageous for carbohydrates, protecting group routes may often be shortened by the use of partial substitution reactions [4-6], followed by chromatographic separations and characterization by means of NMR. 

In spite of the fact that this chromatographic technique is not generally associated with carbohydrate analysis, some applications are found in the literature where silica gel has been employed either directly or indirectly (after modification of the phase or the analytes). The use of silica gel for this purpose involves a polar eluent such as ethylformate/EtOH/H20 (6 2 1, v/v/v) and has been applied to the chromatographic separation of some mono- and disaccharides. 

Niederhauser, T. L., Hailing, J., Poison, N. A., and Lamb, J. D. (1998) High-performance Anion-exchange Chromatographic Separations of Carbohydrates on a Macrocycle-based Stationary Phase with Eluents of Relatively Low pH and Concentration, J. Chromatogr. A 804, 69-77. 

In fact, boronic acids have been extensively used in carbohydrate chemistry, for example in chromatographic separations since the early 1970s. However, WulfF and coworkers were the first to employ boronic esters in imprinted polymer carbohydrate receptors (a) G. Wulff, Pure Appl. Chem. 1982, 54, 2093-2102 ... 

The possible development of LA into a cross-over chemical between carbohydrates and petrochemicals has recently spurred the development of more efficient procedures for its production. Most start from cheap starting materials such as lignocellulose residues and waste paper in acidic medium at approx. 200 °C the theoretical yield of such a procedure is 0.71 kg kg-1 (see Fig. 8.36). In a patent application for a two-stage procedure the claimed yields were 62-87% of the theory, depending on the raw material [195]. A much simpler, extrusion-based procedure has been described but even when fitted with a second stage the yield was not better than 66% of the theory [196]. Efficient DSP is not trivial and the chromatographic separation that has been described [197] is obviously not compatible with the aimed-for commodity status of LA. Alternatively, the LA can be esterified in situ [197]. 

In spite of the stability of THP ethers, its use in carbohydrate chemistry is currently limited due to the resulting diastereomeric mixtures obtained by the introduction of an additional stereocenter. This fact makes chromatographic separation and characterization of the products difficult and therefore their use will probably decrease in the future. 

A successful technique applied for the analysis of humin and humic acids was the pyrolysis with on line methylation followed by GC/MS analysis [6,9]. In one such study [9] humin deashed by treatment with HCI and FIF was pyrolysed and compared to humic acid obtained from the same soil, showing that humin contains larger amounts of carbohydrates and aliphatic compounds. This type of study also revealed the presence in the humin and humic acid pyrolysates of monocarboxylic acids with up to 32 carbon atoms, dicarboxylic acids, methoxymonocarboxylic acids with up to 26 carbon atoms, triterpenoid acids, etc. These compounds were not reported in other studies (e g. [2]) where the chromatographic separation did not allow the detection of compounds difficult to elute due to their high boiling point and polarity. 

The GC and HPLC methods were developed for the chromatographic separation of carbohydrates. Gas chromatographic methods are very time consuming, because carbohydrates, owing to their non-volatile character, have to be derivatized prior to the determination [97], On the other hand, the LC method using strong-acid cation exchangers in the calcium form and de-ionized water as the eluent [98] is widespread, but has several drawbacks ... 

S. Hughes and D. C. Johnson, High-performance liquid chromatographic separation with triplepulse amperometric detection of carbohydrates in beverages,/ Agric. Food Chem., 30.712,1982. 

The principles of the PAD were discussed in Chapter 4. Perhaps the major use of the PAD in anion chromatrography has been for the detection of carbohydrates. At pH around 11 or higher sugars become anionic and can be separated by anion chromatography. For many years a somewhat awkward post-column derivatization reaction was used for detection of carbohydrates after a chromatographic separation, but the use of a PAD now provides a simple and direct detection method. 

Kdnig WA, Benecke I, Bretting H (1981) Gas Chromatographic Separation of Carbohydrate Enantiomers on a New Chiral Stationary Phase. Angew Chem Int Ed Engl 20 693... 

A general essay on column chromatography of carbohydrates was written by Capek and Stanek [123], the same authors [224] reviewed polysaccharides, and Juficova and Deyl [225] summarized chromatographic separation of polysaccharide-protein complexes. Reviews specialized on ion exchange chromatography of oligosaccharides... 

Derenbach (1970) made a distinction between soluble and combined RNA of planktonic material from the different behaviour of these compounds after different extraction procedures. He and others (see Derenbach, 1970 for references), employed the orcinol/hydrochloric acid reagent according to Ceriotti (1955). Since a variety of other sugars may interfere (see section 3.1 orcinol/sulphuric acid has also been used as a reagent for total carbohydrate determinations) correction factors or preferably chromatographic separations of the extracts are required for quantitative results. 

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