Unmodified packings

Zorbax PSM packings are produced in three forms unmodified, trimethyl-silane modified, and diol modified. Modified Zorbax PSM packings are produced by chemically bonding a layer on the silica surface through siloxane bonds (Table 3.1). Silanized Zorbax PSM packings suppress adsorption effects and are the preferred choice when the mobile phase contains organic solvents. Unsilanized and diol modified Zorbax PSM packings should be used when the mobile phase consists of aqueous solvents. 

S mg), dimer (peak I) and monomer (peak 2), ovalbumin (S mg) (peak 3), and cytochrome c (3 mg) (peak 4) was loaded onto a Fractogel EMD BioSEC column (600 X 16 mm) with a bed height of 600 mm. PBS (pH 7.2) was used as the eluent at a flow rate of I ml/min the sample volume was O.S ml. (B) The same protein sample as in A was injected onto a column of identical dimensions packed with unmodified Fractogel HW 6S. Without the tentacle modification the base matrix displays only a poor resolution of the test mixture. 

Using acetic acid, starch acetates are formed, which are used as film-forming polymers for pharmaceutical products, and as the polymer in biodegradable packing-foam peanuts. Starch acetates have a lower tendency to create gels than unmodified starch. 

Although open tubular columns have been used for RPLC,42 most applications use packed columns. The most widely used column packings are formed by chemically bonding butyl (C4), octyl (C8), or octadecyl (C18) chains to a silica surface. Phenyl (Ph), cyano (CN), and amino (NH2) functionalities are also used. Polymeric packings which are finding broad acceptance include alkyl-grafted poly(methylmethacrylate) and alkyl-grafted or unmodified... 

Fig. 3.1b lists some of the properties of two commercially available microparticulate packings. The first is a 5 /im unmodified silica, the second a 3 fim silica, chemically modified with octadecylsilane (ODS, C-18). 

Both capillary and packed columns are available for use. Much of recent interest in SFC is based on the stability and high efficiencies capillary columns. Because these columns are deactivated, the elution analytes with unmodified carbon dioxide is possible. Some of the comm stationary phases available as capillary columns are as follows ... 

Heaton et al. have reported the supercritical fluid chromatography of taxicin I and taxicin II extracted by supercritical fluid extraction of Taxu baccata, the English yew tree [41]. They compared capillary- and packed- column SFC and concluded that packed-column SFC was better than capil4 lary-column SFC for quantitative analysis of these compounds. Capillary SFC was done on either a biphenyl or carbowax column with unmodified carbon dioxide as the mobile phase. The packed-column SFC was performed on a nitrile column with a mobile phase consisting of a methanol gradient with carbon dioxide. 

Open tubular Gel Monolith Packed SEC Packed unmodified IPacked modified I ... 

CEC packed unmodified Silica gel Size, charge, adsorption "reverse phase", ion-exchange... 

One of the main reasons for the widespread use of silica as an HPLC packing material is that it may be used either unmodified or after chemical derivatisation of the silanol groups, allowing the surface chemistry to be altered to suit different modes of chromatography. 

Porous graphitic carbon (PGC) has a rigid structure, is chemically stable and has a very hydrophobic surface. It can therefore be used for reversed-phased HPLC, where it displays a similar or greater degree of retention to ODS. It has excellent pH stability and hence ion suppression of either acidic or basic drugs is easily carried out on this material. It displays different selectivity to silica based packings, allowing isomeric separations more typical of unmodified silica to be carried out (Bassler, 1989). 

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