Polar embedded phases commercially available

The development of reversed-phase chromatographic media has intensified during the last decade. Now, many manufacturers pride themselves on their high degree of the batch to batch reproducibility, both with respect to the retention properties of the stationary phase and also in regards to the quality of the packed bed. Recent years have seen the development of a variety of polar embedded and polar endcapped reveresed-phase materials. There is in reality no limitation placed on the type of reversed-phase material that could be used for reversed-phase applications, other than commercial availability. Therefore expansion of the available reversed-phase media that enter the market place continues, as chromatographers continually seek new ways to gain selectivity. 

Type IV materials exhibit unique ion-exchange properties supplemented by RP characteristics, so that they may be considered as RP-modified ion-exchange materials. Lammerhofer et al. [59] have developed a number of RP/weak anion exchanger (WAX) materials consisting of a selector immobilized onto thiol-modified silica. In these phases, the WAX site is located at the top of the lipophilic layer and is linked to the silica support via a lipophihe spacer with polar-embedded amide or sulfide groups. These columns, however, are not commercially available. 

Recently, there has been an increase in the number of commercially available phases which the manufacturers claim to be suitable for chromatography using purely aqueous mobile phases. These have been further classified, by the manufacturers, as polar embedded, enhanced polar selectivity, and Aqua phases. Some of the phases in the latter two classifications have been further described by the manufacturers as polar/hydrophilic endcapped phases, depending on the bonding technology employed. Unfortunately, there is a dearth of information regarding the bonding chemistry employed [2]. 

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