Bonded phases microparticulate

In NPLC, which refers to the use of adsorption, i.e. liquid-solid chromatography (LSC), the surface of microparticulate silica (or other adsorbent) constitutes the most commonly used polar stationary phase normal bonded-phase chromatography (N-BPC) is typified by nitrile- or amino-bonded stationary phases. Silica columns with a broad range of properties are commercially available (with standard particle sizes of 3, 5 and 10 im, and pore sizes of about 6-15nm). A typical HPLC column is packed with a stationary phase of a pore size of 10 nm and contains a surface area of between 100 and 150m2 mL-1 of mobile phase volume. 

Microparticulate silica can be used in a number of modes for hplc of these, reverse phase chromatography using bonded phases is the most widely used. In normal and reverse phase chromatography the retention times and selectivities of solutes can be altered by adjustment of the nature and composition of the mobile phase. 

A number of specialised stationary phases have been developed for the separation of chiral compounds. They are known as chiral stationary phases (CSPs) and consist of chiral molecules, usually bonded to microparticulate silica. The mechanism by which such CSPs discriminate between enantiomers (their chiral recognition, or enantioselectivity) is a matter of some debate, but it is known that a number of competing interactions can be involved. Columns packed with CSPs have recently become available commercially. They are some three to five times more expensive than conventional hplc columns, and some types can be used only with a restricted range of mobile phases. Some examples of CSPs are given below ... 

The surface of microparticulate silica can be modified by the attachment of different groups to produce bonded phases. Reverse phase chromatography using bonded phases is generally faster and easier than other modes, and consequently has achieved very wide popularity. 

Ionic solutes can be separated by ion-exchange chromatography using microparticulate resins or bonded ion-exchangers based on microparticulate silica. Such separations are often achieved more easily by ion-suppression or ion-pairing techniques, which use bonded phase columns in the reverse phase mode. 

When such microparticulate-bonded-phases are packed compactly into a column by means of a suitable device, the small size of these particles offers a significant resistance to solvent flow therefore, the mobile phase has to be pumped through the column under a high positive pressure. For an analytical HPLC, the mobile-phase is pumped through the column at a flow rate of 1-5 cm3, min-1. 

Subsequently, Majors (40) popularized microparticulate bonded phases... 

The present popularity of RPC, however, is due to the deyelopment of hydrocarbonaceous bonded phases in microparticulate fond which yield columns particularly suitable for use in sophisticated HPL uipment. Although the column constitutes only a small part of an an ytical liquid chromatograph, both in dimension and price, it occupies a supremely important position. First of all, the chromatographic process tjdces place in... 

As an alternative to pellicular materials, microparticulate stationary phases may be used. These are either based on organic resins or on inorganic oxides. The latter class contains bare oxides, as well as chemically bonded phases, which may be synthesized in a way similar to that described in section 3.2.2.1, but the functional end group is now an ionic one. 

Besides chemically bonded phases on silica gel supports microparticulate macroporous polymer resins also have been used in the analysis of alkaloids (see Chapters 7 and 8). A disadvantage of macroporous polymer resins is that they are not as rigid as the reversed-phase materials based on silica gel. In addition they may shrink or swell slightly - depending on the composition of the mobile phase. On the other hand they are more stable than chemically... 

Matthews et al. (109) were the first to report LC of vitamin D metabolites using the pellicular packing ODS-Permaphase and a gradient of methanol and water. With the advent of the microparticulate bonded phases, such as p.Bonda-... 

Solid-phase extraction (SPE). In solid-phase extraction, the analytes are retained on short, disposable cartridges packed with microparticulate adsorbents or bonded phases. After sample application, the minicolumns are washed with a solvent to remove poorly retained matrix components, followed by displacement of the analyte(s) with a strong solvent. SPE may be used as a cleanup... 

Stationary phase (pacidng) Porous, microparticulate silica, chemically-modified silica (bonded phases) or styrene/divinyl benzene co-polymers Stationary phase (pacidng) Porous, microparticulate silica, chemically-modified silica (bonded phases) or styrene/divinyl benzene co-polymers... 

Ion-exchange chromatography (lEC). Stationary phases for the separation of mixtures of ionic solutes, such as inorganic cations and anions, amino acids and proteins, are based either on microparticulate ion-exchange resins, which are crosslinked co-polymers of st)U ene and divinyl benzene, or on bonded phase silicas. Both types have either sulfonic acid cation-exchange sites (-SO3 H ) or quaternary ammonium anion-exchange sites (-N RjOH") incorporated into their structures. 

The herbicides are extracted from soil samples with methanol. They are chromatographed on microparticulate silica bonded with octadecyltrichlorosilane using a mixture of methanol, water and ammonia as mobile phase and an ultraviolet spectrophotometric detector. 

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