Carbohydrate analysis, normal-phase

Compared to refined vegetable oils, the compositions of crude vegetable oils and oil and fat products are more complicated. These samples contain proteins, carbohydrates, and minerals that interfere with HPLC separation and reduce the lifetime of the HPLC column. These compounds need to be largely eliminated from the extract before HPLC analysis. Saponification and heating are used to weaken sample matrices to allow the solvent to fully access all tocopherols and tocotrienols of the sample. Liquid/liquid extraction is used to remove these polar compounds from the organic solvent layer that contains tocopherols and tocotrienols. The normal-phase HPLC method is usually used for crude vegetable oils and vegetable oil products reversed-phase HPLC can be used for animal fat products. 

The retentivity of normal silica-based reversed-phase packings is barely enough to achieve retention of sugars. Also, not all C g bond phases are useful for carbohydrate analysis. A typical mobile phase is 100% water. In this mobile phase, well-endcapped packings often undergo hydrophobic collapse, namely, a sudden loss in retention. Nonendcapped Cjg bonded phases are therefore more suitable for carbohydrate separation by reversed-phase chromatography. 

Chemically bonded layers, with the exception of the amino-bonded silica gel, are also not popular or not suitable for carbohydrate analysis. There are no references on the use of diol- and cyano-mod-ified silica gel thin-layers for carbohydrate analysis. The similar polarities of these normal-phase bonded layers are inferior to the polarity of amino-modified silica (60). The retention of carbohydrates is lower and the separation can fail. The retention is sill lower on reversed-phase bonded layers. Therefore, these layers are less suitable for carbohydrate separation, but can be used for separation of some sugar derivatives. Silanized silica gel was used for thin-layer electromatography of some sugars (61,62), and reversed-phase bonded layers were used for separation of aminoglycoside antibiotics (46) and for separation of some sugar derivatives. 

This t) e of column was employed, for example, for the determination of several t) es of carbohydrates in vegetable and fruits, including oligo-, di-, and monosaccharides and polyols [1]. In the HILIC mode separations similar to those obtained in the normal-phase (NP) mode are obtained, although using reversed-phase (RP) compatible solvents for their elution. At present, new columns for ITILIC that could be interesting for carbohydrates analysis are under development, like columns based on immobilized secondary and tertiary amines. 

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