Stationary phase Bonded phases

These developments have been fuelled in part by the apparently unrelenting increase in microcomputing power, bringing with it improved control and data acquisition and processing capabilities and partly by the improved technologies for the preparation of chromatographic media and packings in GC and LC, for example, chiral stationary phases, bonded phase capillary GC and narrow bore HPLC. 

Sentell, K.B. and Dorsey, J.G, Retention mechanisms in reversed-phase chromatography. Stationary-phase bonding density and solute selectivity, J. Chromatogr., 461, 193, 1989. 

K. Kovacs-Hadady and J. Szilagyi, Separation of minoxidil and its intermediates by over pressured layer chromatography using a stationary phase bonded with 1-methyl-ammoniun chloride, J. Chromatogr., 553 459 (1991). 

The growing popularity of reversed phase chromatography in particular has prompted polymer manufacturers to investigate the use of polymeric media for this mode of operation. Macroporous copolymers of styrene and divinylbenzene have similar properties to silica based stationary phases bonded with alkyl chains. However, the absence of leachables and stability at high pH can offer advantages under certain circumstances. High quality, mechanically stable macroporous polymeries are now manufactured at much larger scales than the... 

Adsorption of analytes on ion-exchange sorbents is based on electrostatic interactions between charged functional group in the compounds of interest and the positively or negatively charged groups on the stationary phase (bonded to the silica surface). 

KB Sentell, JG Dorsey. Retention mechanisms in reversed-phase liquid chromatography stationary-phase bonding density and partitioning. Anal Chem 61 930-934, 1989. 

Normal-phase, bonded-phase columns are likely underutilized for separations where they should be the method of choice. This is due both to the ease of use of reversed-phase, bonded-phase columns, discussed next, and also to the many problems inherent in the use of bare silica and alumina. Very straightforward method development in normal-phase chromatography can be performed by combining the solvent and stationary-phase selectivity triangles. The three columns, each used with the three recommended modifiers, should provide the maximum difference in selectivity available. These nine experiments, used in conjunction with chemometric optimization schemes, should then provide a ratio-... 

Capillary column gas chromatography gas chromatography using columns 10-100 m long with an internal diameter of 0.1-0.7 mm, usually with the stationary phase bonded to the internal wall (WCOT). Capillary columns have high efficiencies ( eir) and give rapid analysis times. The A term in the van Deemter equation is zero as the column does not contain stationary phase particles or packing. 

Gas chromatography columns for interplanetary exploration should be very efficient, due to the stringent demands imposed on payload. Porous-layer open tubular (PLOT) columns loaded with a styrene-divinyl benzene copolymer showed better performance than Cromosorb 103 or Porapak Q columns in the analysis of low molecular weight hydrocarbons and nitriles. Potassium chloride-deactivated alumina PLOT columns, on the other hand, were not good for the intended purpose, because low molecular weight nitriles were difficult to elute. Wall coated open tubular (WCOT) columns with a stationary chemically bonded phase of dimethyl siloxane have the mechanical resilience to endure the conditions of extraterrestrial exploration and separated efficiently C1-C4 nitriles. Permanent gases were analysed in the presence of hydrocarbons and nitriles with a PLOT capillary column. The equilibrium constant for the interaction of nitrile groups with various solutes was determined by GLC. ... 

Before the development of reversed-phase bonded phases, normal-phase chromatography was the most popular separation technique. It relies on the interaction of analytes with polar functional groups on the surfooe of the stationary phase, which is strongest when nonpolar solvents are used as mobile phase. Previously, it was also called adsorption chromatography. However, the technique has expanded from the exclusive application of metal oxide adsorbents such as silica and alumina as stationary phases to the use of polar bonded phases. Thus the name adsorption chromatography has become too narrow. 

The chip described by Kutter et al. has limited sample trapping capacity. The phase ratio of the stationary phase bonded to the inner wall is low, and not all of the sample may be extracted using... 

The separation was carried out using the CSP-2 stationary phase bonded to silica gel having a particle size of 5 pm. The stationary phase was packed into a column 25 cm long, 4.6 mm ID. and operated at ambient temperature. The mobile phase consisted of in -hexane/2-propanol... 

Bleeding of a separation column being either old or unsuitable for MS detection results in an increased elution of the stationary phase bonding, which is split off the carrier material surface and leads to an increased noise in the LC/MS chromatogram. 

Despite the fact that, in some cases, small differences in AH and A5 can be observed (for various solutes, but on the same column with the same mobile phase), these differences could be found to be essentially insignificant when compared to a change in stationary-phase bonding density using enthalpy-entropy compensation. Enthalpy-entropy compensation is a term used to describe a compensation temperature, which is system independent for a class of similar experimental systems.Melander et have used the enthalpy-entropy compensation method in studies of hydrophobic interactions and separation mechanisms in reversed phase HPLC. Mathematically, enthalpy-entropy compensation can be expressed by the formula 9 ... 

Unlike a UHPLC system, in the HPLC system, both the reversed-phase [46,47] and the normal-phase [29,48-50] mode have reportedly been used to determine procyanidins and alkaloids in cocoa samples. This is explained because, until now, no UHPLC columns with polar stationary phase (normal-phase mode) with sub-2 pm have been developed. Initial reports for the determination of procyanidins and alkaloids in cocoa samples by HPLC technique were based on the normal-phase mode, and monomer procyanidins through decamer procyanidins were resolved. In this normal phase, two different stationary phases were reported, an unmodified silica column [29,50] and a dihydroxypropyl-bonded silica [48,49]. 

In the most common application of this separation mode, components are separated according to the number and nature of the polar functional groups (e.g., ester bonds, phosphate, hydroxyl, and amine groups) in lipid molecules. Since the head group of an individual lipid class predominantly determines the polar interactions with stationary phase, normal-phase HPLC separates a lipid extract solution into the lipid classes rather than into molecular species. 

Hence, this NMR technique allows us to record the NMR spectrum of a dissolved analyte in the presence of a chromatographic sorbent, and therefore mimic a static chromatographic situation. In the suspended-state HR/MAS NMR experiment, the resolution of the signals of the dissolved analyte will be comparable to that in a solution-state NMR experiment. HR/MAS NMR spectroscopy also allows the acquisition of H NMR spectra of stationary phases bonded to silica supports with high resolution compared to the corresponding solid-state NMR spectra. The HR/MAS H NMR spectrum of a (tert-butylcarbamoyl)quinine selector covalently bonded to silica, suspended in [DJmethanol, shows that a full structure elucidation of the selector is possible (see Fig. 4). 

Another common practice in HPLC enantioseparation is the use of organic solvents of low polarity as mobile phase components. Although, from the point of view of lipophilic-ity, the organic material bonded or coated onto the chromatographic matrix makes CSPs similar to C8, C18, or phenyl standard stationary phases, normal phase mode is often preferred over reversed-phase conditions. The use of a lipophilic solvent in a lipophilic environment favors dipolar interactions such as hydrogen bonding, dipole-dipole interactions, and ir-stacking, while nonselective van der Waals interactions are minimized. As a result, the selective association CS-enantiomer is favored. 

Another approach to improving resolution is to use thin films of stationary phase. Capillary columns used in gas chromatography and the bonded phases commonly used in HPLC provide a significant decrease in plate height due to the reduction of the Hs term in equation 12.27. 

An important problem with all liquid stationary phases is their tendency to bleed from the column. The temperature limits listed in Table 12.2 are those that minimize the loss of stationary phase. When operated above these limits, a column s useful lifetime is significantly shortened. Capillary columns with bonded or... 

A liquid stationary phase that is chemically bonded to a particulate packing material. 

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