Phase column type

Szabo, Z. et al. Analysis of nitrate ion in nettle (Urtica dioica L.) by ion-pair chromatographic method on a C30 stationary phase. J. Agr. Food Chem. 2006, 54, 4082-4086. Yokoyama, Y. et al. Optimum combination of reversed phase column type and mobile phase composition for gradient elution ion-pair chromatography of amino acids. Anal. Sci. 1997, 13, 963-967. 

In an excellent paper, Hearn and co-woikers [1306] reviewed 87 papers in which either a Cig (78 references), a Cg (5 references), or a C4 (4 references) column was used in conjunction with an acetonitrile/water (0.1% TFA) (80 references) or an acetonitrile/IPA/water (0.1% TFA) (7 references) gradient system. The retention contribution for each of 20 amino acid residues was presented graphically for each of 12 different mobile phase/column type combinations (e.g., acetonitrile/ IPA/water/TFA and Cig acetonitrile/water/TEA and Cg). Not only are the individual references within this paper valuable, but the initial choice of column type and mobile phase can be attempted if the amino acid composition of die peptide is known. 

Minimum allowable capacity of a column is determined by the need for effective dispersion and contacting of the phases. The types of plates differ in their ability to permit Tow flows of gas and liquid. A cross-flow sieve plate can operate at reduced gas flow down to a point where liquid drains through the perforations and gas dispersion is inadequate for good efficiency. Valve plates can be operated at veiy... 

This section discusses in detail the column types that are available for the size exclusion chromatography of both polar and nonpolar analytes. It first discusses the various columns available for standard nonaqueous size exclusion chromatography. It then reviews the columns available for general size exclusion chromatography using aqueous mobile phases. Finally, it examines the columns designed for size exclusion chromatography of proteins and peptides. 

Many racemic mixtures can be separated by ordinary reverse phase columns by adding a suitable chiral reagent to the mobile phase. If the material is adsorbed strongly on the stationary phase then selectivity will reside in the stationary phase, if the reagent is predominantly in the mobile phase then the chiral selectivity will remain in the mobile phase. Examples of some suitable additives are camphor sulphonic acid (10) and quinine (11). Chiral selectivity can also be achieved by bonding chirally selective compounds to silica in much the same way as a reverse phase. A example of this type of chiral stationary phase is afforded by the cyclodextrins. 

The pore structure of most cross-linked polystyrene resins are the so called macro-reticular type which can be produced with almost any desired pore size, ranging from 20A to 5,000A. They exhibit strong dispersive type interaction with solvents and solutes with some polarizability arising from the aromatic nuclei in the polymer. Consequently the untreated resin is finding use as an alternative to the C8 and Cl8 reverse phase columns based on silica. Their use for the separation of peptide and proteins at both high and low pH is well established. 

Column Type Length m Internal Diameter mm Film Thickness /tm Phase Ratio Capacity Factor lU mm opi cm/s Column Plate Count Plates Per Meter... 

In gas chromatography the value of the partition coefficient d ends only on the type of stationary phase and the column temperature. It is independent of column type and instrumental parameters. The proportionality factor in equation (l.ll) is called the phase ratio and is equal to the ratio of the volume of the gas (Vg) and liquid (V ) phases in the column. For gas-solid (adsorption) chromatography the phase ratio is given by the volume of the gas phase divided by the surface area of the stationary phase. 

The plate height, and thus the total number of theoretical or effective plates, depends on the average linear carrier gas velocity (van Deemter relationship) and, for a particular carrier gas, the efficiency will maximize at a particular flow rate. Only at the optimum carrier gas flow rate are n, N, and HETP Independent of the column length. The efficiency will also depend on the column diameter (see section 1.7.1) where typical values for n, N, and HETP for different column types can also be found. Values for n, N, and HETP are reasonably independent of temperature but may vary with the substance used for their determination, particularly if the test substance and statioKary phase are not compatible. 

There is a wide variety of commercially available chiral stationary phases and mobile phase additives.32 34 Preparative scale separations have been performed on the gram scale.32 Many stationary phases are based on chiral polymers such as cellulose or methacrylate, proteins such as human serum albumin or acid glycoprotein, Pirkle-type phases (often based on amino acids), or cyclodextrins. A typical application of a Pirkle phase column was the use of a N-(3,5-dinitrobenzyl)-a-amino phosphonate to synthesize several functionalized chiral stationary phases to separate enantiomers of... 

Some kinds of chromatography require relatively little optimization. In gel permeation chromatography, for example, once the pore size of the support and number of columns is selected, it is only rarely necessary to examine in depth factors such as solvent composition, temperature, and flow rate. Optimization of affinity chromatography is similarly straightforward. In RPLC or IEC, however, retention is a complex and sensitive function of mobile phase composition column type, efficiency, and length flow rate gradient rate and temperature. 

In practice, chromatography takes place on a layer or in a tube. Meyer [4] has compared analytical column-type chromatographic methods. A column can be an open capillary or a packed tube. In the first case the mobile phase is coated as a thin film on the inner wall of the capillary. In most cases GC is used as open-tubular... 

Analysis of reaction products - Liquid reaction products were analyzed by gas chromatography using a capillary column (type WCOT Fused Silica, stationary phase 5% phenyl-methyl-polysiloxane length - 50 m ID - 0.32 mm, OD - 0.45 mm film thickness - 0.25 pm). 

Other applications that utilize different types of reversed-phase columns in both dimensions have been advocated by Carr (Stoll et al., 2006) for metabolomics work in small-molecule separations. These stationary phases include a pentafluorophenyl-propyl stationary phase in the first dimension and a carbon-coated zirconia material stationary phase in the second dimension. A common mistake in 2D method development is to mismatch the solvent system the two solvent systems must be miscible as discussed below. 

Fused silica capillary columns of various internal bores and of lengths in the range 25 to 50 m are mainly employed for analytical separations. A variety of polar and non-polar column types are available including those open tubular types with simple wall coatings (WCOT), those with coatings dispersed on porous solid-supports to increase adsorbent surface area (SCOT) and porous layer open tubular (PLOT) columns. Important stationary phases include polyethylene glycol, dimethylpolysiloxane and different siloxane copolymers. Various sample introduction procedures are employed including ... 

A chiral GC column is able to separate enantiomers of epoxy pheromones in the Type II class, but the applications are very limited as follows a custom-made column packed with a p-cyclodextrin derivative as a liquid phase for the stereochemical identification of natural 3,4- and 6,7-epoxydienes [73, 74] and a commercialized column of an a-cyclodextrin type (Chiraldex A-PH) for the 3,4-epoxydiene [71] (See Table 3). The resolution abilities of chiral HPLC columns have been examined in detail, as shown in Table 7 and Fig. 14 [75,76, 179]. The Chiralpak AD column operated under a normal-phase condition separates well two enantiomers of 9,10-epoxydienes, 6,7-epoxymonoenes and 9,10-epoxymonoenes. Another normal-phase column, the Chiralpak AS column, is suitable for the resolution of the 3,4-epoxydienes. The Chiralcel OJ-R column operated under a reversed-phase condition sufficiently accomplishes enantiomeric separation of the 6,7-epoxydienes and 6,7-epoxymonoenes. 

The most common packing material in HPLC columns (Figure 13.4, C) is a solid with an organic group attached to it. For instance, the solid may have a hydrocarbon chain containing 18 carbons attached to it, making it hydrophobic. This type of column is called a C18 column or a reverse-phase column. Columns can be made with varying polarities and functionalities and thus can be used to carry out a wide variety of separations. 

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