Separator silica, underivatized

The separation of underivatized VFA is now commonly accomplished on specialty capillary GC columns. These have replaced packed GC columns which were frequently used in the Capillary fused silica columns designed for organic acid separation are of... 

This material is synthesized from 4-(3,5-dinitrobenzamido)-tetrahydro-phenanthrene which is also covalently bonded to silica particles 5 pm in diameter. It is used to separate the underivatized isomers of drugs such as Ibuprofen and Naproxen. It is a fairly stable phase and is available in both enantiomeric forms allowing elution order reversal if so desired. 

Their advantage for carbohydrate separations over underivatized silica is an increased rate of mutarotation, which prevents the formation of double peaks... 

Note The dipping solution may also be used as a spray solution [2]. Catecholamines are only separable on silica gel layers as their triacetyl derivatives but they can be separated underivatized on cellulose layers [4]. 

Many of the chiral molecules containing amide groups were bonded to a solid support for the preparation of CSPs [16-19]. The racemic compounds resolved on these CSPs include a-hydroxycarbonyls, /i-hydroxycarbonyls, amino acids, amino alcohols, amine, and derivatized and underivatized diols. The preliminary chiral diamide phase [(/V-foriuyl-L-valyl)aminopropyl)silica gel] has sufficient separability for racemic /Y-acylatcd a-amino acid esters but not in other types of enantiomer [16]. Most of the eluents used with these CSPs are of normal phase mode, including w-hcxanc, 2-propanol, chlorinated organic solvents, and acetonitrile. 

There are also stationary phases that effectively partition solutes in either reversed-phase or normal-phase mode. These stationary phases are typically silica particles derivatized with cyano, diol, or amino functional groups. Particles with a cyano-functionality separate based on polarity utilizing nitrile interactions between the stationary phase and the solute. The amino group of typical amino stationary phases interacts primarily with anionic and organic acid portions of the solute. Diols utilize hydroxyl interactions similar to underivatized silica but offer a slightly different selectivity. These and other bonded-silica phases offer alternatives to underivatized silica, but they are used much less frequently. The mobile phases employed with these stationary phases are the same as used in standard reversed-phase or normal-phase chromatography. 

Simmons, B.R. Stewart, J.T. HPLC separation of selected cardiovascular agents on underivatized silica using an aqueous organic mobile phase. J.Liq.Chromatogr., 1994, 17, 2675-2690... 

Micropacked columns are available with most of the bonded-phase packings used in HPLC. Porous and non-porous silica particles are optionally functionalized with covalently ound silanes or other strongly adsorbed materials. ALkyl-bonded silicas produce separations, generally based on solute volatility, but with the potential for selectivity differences based on interaction with silanol groups. Underivatized silica is popular for petroleum separations of aliphatic and aromatic hydrocarbons. Silver-ion-containing silica columns are selective for olefin separations. Huoroalkyl-bonded... 

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