Liquid chromatography packed columns

packed columns are used for practical separations. Eqn.(7.6) shows the speed of analysis to be proportional to the required number of plates and to the square of the (particle) diameter. We used this equation in chapter 4 to derive an expression for the required retention time under conditions of constant flow rate and particle size (tne fiC i eqn.4.48). However, eqn.(7.6) suggests that the speed of analysis may always be increased by decreasing the particle size. In other words, it suggests that the smallest available particles should always be used in packed columns. This interpretation is too simple. 

In LC (and to a lesser extent also in GC) the limiting factor is the maximum allowable pressure drop over the column. As an example, we will look at the dimensions of packed columns for LC when the operating pressure (Ap) is fixed at the maximum value allowed by the instrumentation [704]. 

The pressure drop is given by Darcy s law (eqn.7.1). Optimum flow rates on columns with different particle sizes can be related by using the same reduced velocity (v, eqn.7.4) for each column. Since the diffusion coefficient Dm is a constant, we find for the ratio of the linear velocities on two columns (1 and 2) 

If the reduced velocities on the two columns are equal, then the reduced plate height (h eqn.7.3) may also be expected to be equal, and, hence, the column length varies according to 

All parameters on the right-hand side of eqn.(7.9) are constants, and therefore the optimum particle size for a given separation is proportional to the square root of the number of plates required. 

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Reversed-phase high-performance liquid chromatography (HPLC) column 50 mm x 3.2-mm i.d. with Kromasil 5- um Gig packing High-performance liquid chromatograph coupled to a triple-quadrupole mass spectrometer with an atmospheric pressure chemical ionization (APCI) source Gel permeation chromatograph with a 60 mm x 25-mm i.d. column packed with Bio-Beads SX-3 (50-g)... 

For enhanced throughput, fast RPLC methods using monolithic silica columns [238], small size particles (3 pm) packed columns [173, 195, 226, 235-237, 239, 240], ultra high pressure liquid chromatography (UHPLC) columns packed with sub-2 pm particles [145,196, 227, 245, 247] and 2.6 pm core-shell particles HPLC columns [246] have been proposed for the high-throughput separation and quantification of tamoxifen/metabolites. 

The earliest of GC analyses were performed on columns packed with a solid support coated with a nonvolatile liquid phase. Packed columns are not frequently used today as they have been replaced by capillary columns where the hquid phase is immobilized on the internal surface of the capillary. As there are numerous liquid phases available, it is now possible to obtain commercial columns that will separate not only the methyl esters but also the underivatized fatty acids. This advancement obviates the need for derivatization and the associated problems. A typical chromatogram of free fatty acids is displayed in Figure 3. Individual isomers of CLA are now available to aid in the identification of isomers in the chromatogram. Gas chromatography can provide quantitative information on the degree of conjugation, positional, and geometric isomer distribution when suitable standards are available. 

Driven by the concentration gradient, solutes naturally diffuse when contained in a fluid. Thus, a discrete solute band will diffuse in a gas or liquid, and because the diffusion process is random, it will produce a concentration curve that is Gaussian in form. This diffusion effect occurs in the mobile phase of both packed GC and liquid chromatography (LC) columns. The longer the solute band remains in the column, the greater will... 

Both packed columns and open tubular columns are used in supercritical fluid chromatography. Packed columns can provide more theoretical plates and can handle larger sample volumes than open tubular columns. Because of the low viscosity of supercritical media, columns can be much longer than those used in liquid chromatography, and column lengths of 10 to 20 m with inside diameters of 50 or 100 p,m are common. For difficult separations, columns 60 m in length or longer have... 

Majors, R. E. 1977. Recent advances in high performance liquid chromatography packings and columns, J. Chromatog. Sci., 15 334-351. 

The term H is usually determined for the last eluting compound. For a well-packed high-performance liquid chromatography (HPLC) column of 5-/xm particles H should be about 2 to 3 times the particle diameter. Values of 0.01 to 0.03 mm are typical. 

Liquid chromatography, or column chromatography, is perhaps the most often used chromatographic method. As in Tswett s original experiments, a mixture of organic compounds is dissolved in a suitable solvent and adsorbed onto a stationary phase such as alumina (Al Oy) or silica gel (hydrated SiOy) packed into a glass column. More solvent is then passed down the column, find different compounds are eluted at different times. 

From the 1980s, the chromatographic broadening technique has been substituted in the literature by inverse gas chromatography (IGC). The two main IGC methods for the measurement of diffusion coefficients in liquids are packed column IGCP and capillary column IGCP ... 

D Orazio, G., Rocco, A., and Fanali, S. 2012. Fast-liquid chromatography using columns of different internal diameters packed with suh-2 Il/4m sihca particles. J. Chromatogr. A 1228 213-220. 

Future development is likely to include improvements in column liquid-liquid chromatography—new column packing materials and new detection systems. Stationary phases consisting of specific groups covalently bound to inert matrices are being developed in many laboratories for use in liquid-liquid as well as gas-liquid chromatography. Such phases might be made for use in bile acid analysis. 

Unger, K.. K., Adsorbents in column liquid chromatography. Packings and Stationaty Phases in Chromatographic Techniques (K.. K. Unger, ed.), Marcel Dekker, New York, 1990, pp. 331-470. 

The dimensions of columns used in gas-solid chromatography are very similar to those of gas-liquid chromatography. Packing materials (silica, alumina, carbon blacks, zeolites, porous polymers) in proper mesh size are available commercially to fill the columns. GSC columns give lower plate numbers than GLC columns but possess very high selectivities for some typical applications. Prepacked GLC and GSC columns can be purchased commercially and are ready to be installed in the GC instrument. 

In liquid-liquid chromatography the stationary phase is a liquid film coated on a packing material consisting of 3-10 pm porous silica particles. The stationary phase may be partially soluble in the mobile phase, causing it to bleed from the column... 

Kovat s retention index (p. 575) liquid-solid adsorption chromatography (p. 590) longitudinal diffusion (p. 560) loop injector (p. 584) mass spectrum (p. 571) mass transfer (p. 561) micellar electrokinetic capillary chromatography (p. 606) micelle (p. 606) mobile phase (p. 546) normal-phase chromatography (p. 580) on-column injection (p. 568) open tubular column (p. 564) packed column (p. 564) peak capacity (p. 554)... 

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