Diol phase

The reagent can be used, for example, on silica gel, kieselguhr and Si 50000 layers as well as on RP, CN, NH2 and DIOL phases. Cellulose and polyamide 11 layers char on heating. 

The reagent can, for instance, be employed on silica gel, kieselguhr. Si 50000, cellulose and NH2 layers the reaction is appreciably less sensitive on RP 18, CN and Diol phases, neither is there any color differentiation of the purine derivatives [8J. Cellulose and polyamide layers are not suitable, since the whole layer background is colored dark brown [8]. 

Hydrophilic interaction chromatography (HB IC) or aqueous normal-phase chromatography (ANP) refers to the use of polar stationary phases (e.g., bare silica, silica, or polymeric phases with bonded zwitterionic ligands, diol phases) in combination with a mobile phase rich in organic solvent but containing a significant amount of water (typically at least 3%). Bell [97] summarized the advantages of this technique as follows ... 

Table 8.3 Binary gradient for Diol-phase column. ...

In summary, the diol-phase column had better separation resolution for procyanidin oligomers than the silica column. Limits of quantitation in the diol-phase method were significantly lower than those in the silica... 

By LSC we include separations on any polar, nonionic phase, e.g., alumina, silica, or bonded-phase packings such as cyanopropyl, aminopropyl, and diol-phase. 

The diol phases are usually prepared from trimethoxy-glycidoxypropyl or triethoxyglycidoxypropyl silane, followed by hydrolysis of the epoxy group to form the diol functionality. The most widely used diol phase is the 1,2-dihydroxypropyl propyl ether phase. 

Normal phase systems consist of a polar adsorbent and a less polar mobile phase. Because these were the first available chromatographic systems they were named normal phase systems. They are for instance silica gels or other oxides in conjunction with a non-polar solvent such as heptane, hexane or some slightly polar solvents like dioxane. Semi-polar adsorbents such as cyano or diol phases can be operated in the normal phase mode as well. The combination of water and silica is not recommended due to the strong interaction between water and adsorbent. Furthermore silica is slightly soluble in water, which results in a shortened lifetime of the adsorbent. Normal phase systems are limited to organic solvents and thus the solutes have to be soluble in these solvents. 

If the retention time is much higher than the time of the initial gradient (retention factor 10) the substances seem to be too lipophilic for RP separation on the initial adsorbent. The polarity of the adsorbent should be increased by the use of amino or diol phases. If the adsorbent is already polar the phase system must be changed to NP-chromatography (Section 4.3.2). 

Figure 11.1 Separation of a nonionic surfactant on a diol phase (reproduced with permission of Supelco). Conditions sample, Triton X-100 with average / = 10 column, 25cm x 4.6mm i.d. stationary phase, Supelcosil LC-Diol, 5 j,m mobilephase 1 mlmin nonlineargradientfrom 15.5%dichloromethane -I- 3% methanol in hexane to 40% dichloromethane + 10% methanol in hexane in 35 min temperature, 35 C UV detector, 280 nm.

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