Some other stationary phases

This must be used with caution as aromatics, amines, esters and many others may be chemisorbed. 

This is hexagonally crystallized calcium phosphate, Caio(P04)6(OH)2. It can be prepared in pressure-stable form (up to 150 bar) and is suitable for the separation of proteins and other biopolymers. 

Agarose is a cross-linked polysaccharide and is stable over the whole pH range 1-14. It can be derivatized to give, for example, stationary phases for affinity chromatography. 

Titania is crystalline TiO2 with basic OH groups on its surface (this is in contrast to silica) therefore it is stable at high pH. It can be used in both the normal-phase and the reversed-phase mode. 

Zirconia ZrO2 has similar properties as titania but can also interact with the analytes by ligand exchange because it is a Lewis acid. Chemical derivatization is possible. Coating with polybutadiene or polystyrene gives phases which are stable over a pH range of at least 1-13 and at temperatures higher than 200 °C. 

The large number of OH groups make this product very polar and it can be used for gel filtration on its own and for affinity chromatography in derivative form. The hydroxyalkyl residue can be derived from glycol or glycerine. 

This is a fully porous, spherical stationary phase with unique reversed-phase properties but it can also be used in the normal-phase mode. PGC has a crystalline graphite surface. It is chemically stable from lOM acid to 10 M alkali and can withstand high temperatures. The selectivity (i.e. the elution order) is different from silica-based reversed phases. PGC is recommended for the separation of highly polar and ionized compounds as well as of 

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Change column to one with some other stationary phase, perhaps one suggested by your instructor. Set the column temperature to 100°C and the carrier gas flow rate to 20 mL/min. Inject 1.0 pL of the mixture. Assuming good resolution, observe the order of elution. Is it different from that observed with the former stationary phase If so, explain how that could be. If not, compare the resolution here with that of a previous injection in which all the parameters were equal. Comment on the difference. 

You need to adjust your gas chromatograph to the proper conditions for the analysis. We recommend that you prepare and analyze the reference mixture listed in the Procedure section. Most chromatographs will be able to separate this mixture cleanly with the possible exception of the xylenes. One possible set of conditions for a Gow-Mac model 69-350 chromatograph is the following coliunn temperature, 110-115°C injection port temperature, 110-115°C carrier gas flow rate, 40-50 mL/min column length, approximately 12 ft. The column should be packed with a nonpolar stationary phase similar to silicone oil (SE-30) on Chromosorb W or with some other stationary phase that separates components principally according to boiling point. 

For the separation of ofloxacin enantiomers by TLC, some other stationary phases were used such as cellulose fra(4-methylbenzoate), cellulose tm(4-nitrobenzoate) [12], and cellulose (3,5-dinitrobenzoate) [13]. 

In this case study, two different Cl 8 columns from different manufacturers were used. Alternatively, other stationary phase types could also be used such as a polar embedded phase and a Cl 8 phase. Some systems come also equipped with a six-column switcher and in that case, two different types of polar embedded phases, phenyl phase, pentafluorophenyl phases, two different Cl 8 phases (of different bonding density) and an alternate C8 phase could be used. 

One of the problems encountered in gas chromatographic separation even with capillary columns is the coelution of some components by one or the other stationary phase. In an experiment studying the mixture shown in Table 3 a 30 m X 0.32 mm ID column coated with I.O fim DB-I (J W) could not separate compounds 8 and 9 whereas they were separated by a DB-I70I (J W)... 

The packing materials described above separate chemical entities by exploiting chemical differences, e.g., hydrophobicity. Another class of stationary phases separates molecules based on chirality this is accomplished using a silica particle derivatized with a chiral moiety. There are several classes of chiral stationary phases including helical polymers, brushlike functional groups, protein/peptides, and inclusion complexes. Each of these is described in more detail below. Some manufacturers produce chiral stationary phases that operate either in reversed-phase or normal-phase mode, and some chiral stationary phases can be used in both modes. As with other stationary phases, there are numerous manufacturers of chiral stationary phases. However, contrary to Cl 8 and other achiral packing materials, each manufacturer of chiral stationary phases typically offers unique phases with completely separate selectivities. 

If an adequate separation is not obtained by the use of either the reversed-phase analytical method or the silica method, then other stationary phases are scanned for their separation capability (CN, C8, C4, phenyl, chiral, etc.). Often a scouting gradient can be employed to screen columns by HPLC.7 For reversed-phase systems (aliphatic and CN columns), a gradient of acetonitrile and water can be set up, beginning with 100% water and ending with 100% acetonitrile over approximately 30 column volumes. Of the columns that show some peak separation, the gradient can usually be... 

There are a large number of possible derivatives that can be prepared and almost every one will probably possess some unique property that will enhance the separation of certain enantiomeric pairs. The examples given in figure 8.18 are those selected by the chiral stationary phase manufacturer ASTEC as those more broadly useful for chiral separations. Other stationary phase manufacturers may well select other types of derivatives for optimal use. 

Synthetic chiral adsorbents are usually prepared by tethering a chiral molecule to a silica surface. The attachment to the silica is through alkylsiloxy bonds. A study which demonstrates the technique reports the resolution of a number of aromatic compoimds on a 1- to 8-g scale. The adsorbent is a silica that has been derivatized with a chiral reagent. Specifically, hydroxyl groups on the silica surface are covalently boimd to a derivative of f -phenylglycine. A medium-pressure chromatography apparatus is used. The racemic mixture is passed through the column, and, when resolution is successful, the separated enantiomers are isolated as completely resolved fiactions. Scheme 2.5 shows some other examples of chiral stationary phases. 

Silica gel and aluminium oxide layers are highly active stationary phases with large surface areas which can, for example, — on heating — directly dehydrate, degrade and, in the presence of oxygen, oxidize substances in the layer This effect is brought about by acidic silanol groups [93] or is based on the adsorption forces (proton acceptor or donor effects, dipole interactions etc) The traces of iron in the adsorbent can also catalyze some reactions In the case of testosterone and other d -3-ketosteroids stable and quantifiable fluorescent products are formed on layers of basic aluminium oxide [176,195]... 

YHiile THF is the solvent of choice for ordinary acrylate ester polymers, there are numerous monomers that can be incorporated into those acrylic polymers that cause problems either with solubility or with adsorption onto the stationary phase. In some cases, these problems can be overcome by switching to a solvent other than THF. 

Popova and colleagues47 carried out TLC of oxidation products of 4,4 -dinitrodiphenyl sulphide (the sulphoxide and sulphone) on silica gel + a fluorescent indicator, using hexane-acetone-benzene-methanol(60 36 10 l) as solvent mixture. Morris130 performed GLC and TLC of dimethyl sulphoxide. For the latter, he applied a 6% solution of the sample in methanol to silica gel and developed with methanol-ammonia solution(200 3), visualizing with 2% aqueous Co11 thiocyanate-methanol(2 1). HPLC separations of chiral mixtures of sulphoxides have been carried out. Thus Pirkle and coworkers131-132 reported separations of alkyl 2,4-dinitrophenyl sulphoxides and some others on a silica-gel (Porosil)-bonded chiral fluoroalcoholic stationary phase, with the structure ... 

It should be recalled that all substances that are used as stationary phases, or as supports for bonded phases, that have pores commensurate with the size of the molecules being separated, will exhibit exclusion properties. Thus, even if the solutes are retained largely as a result of the interactions of the solute molecules and those of the two phases if, due to their size, some molecules can interact with more stationary phase than others, then the retention will also be controlled to some extent by exclusion. The term exclusion chromatography is, therefore, usually confined to those separations where retention is controlled... 

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