Packed in HPLC

Silica-bound catalyst Packed in HPLC column ... 

Chloramphenicol (CL) in serum Diethylamino-ethyl methacrylate (DEAEM) Competitive displacement of CL-methyl red dye conjugate from CL-imprinted polymer packed in HPLC column 3 ug/ml Levi et al., 1997... 

Just as the interiors of micelles in water provide a hydrophobic environment to solubilize chlorobiphenyls and then photodegrade them by reductive dechlorination, so do octadecyl-functionalized silica gel [89], normally used as reverse phase packing in HPLC and for solid-phase extraction, and the hquid-semisohd polydimethylsiloxane [-OSi(CH3)2 -] [90,91], also used for solid-phase extraction. In both media, reductive dechlorination is the primary photochemical pathway. 

Bonded-phase packings In HPLC, a support medium to which a liquid stationary phase is chemically bonded. 

Kirkland, J.J. The use of porous silica-based column packings in HPLC method development. Curr. Issues HPLC Technol. (LC-GC Suppl.). 1997, 546-555. 

Porous silicas employed as packings in HPLC are amorphous i.e., they do not possess a long-range order of their bulk structure. Most information on the bulk and surface structure of silica and its bonded derivatives can be drawn from Si and C solid-state NMR spectroscopy [7],... 

Berek, D and Novak, I., Silica gel and carbon column packings in HPLC, Chromato-graphia, 582-590 (1990). 

Capillary Electrochromatography Another approach to separating neutral species is capillary electrochromatography (CEC). In this technique the capillary tubing is packed with 1.5-3-pm silica particles coated with a bonded, nonpolar stationary phase. Neutral species separate based on their ability to partition between the stationary phase and the buffer solution (which, due to electroosmotic flow, is the mobile phase). Separations are similar to the analogous HPLC separation, but without the need for high-pressure pumps, furthermore, efficiency in CEC is better than in HPLC, with shorter analysis times. 

The hydrophilic surface characteristics and the chemical nature of the polymer backbone in Toyopearl HW resins are the same as for packings in TSK-GEL PW HPLC columns. Consequently, Toyopearl HW packings are ideal scaleup resins for analytical separation methods developed with TSK-GEL HPLC columns. Eigure 4.44 shows a protein mixture first analyzed on TSK-GEL G3000 SWxl and TSK-GEL G3000 PWxl columns, then purified with the same mobile-phase conditions in a preparative Toyopearl HW-55 column. The elution profile and resolution remained similar from the analytical separation on the TSK-GEL G3000 PWxl column to the process-scale Toyopearl column. Scaleup from TSK-GEL PW columns can be direct and more predictable with Toyopearl HW resins. 

In HPLC, the mobile phase is a liquid delivered under high pressure (up to 400 bar (4 x 10 Pa)) to ensure a constant flow rate, and thus reproducible chromatography, while the stationary phase is packed into a column capable of withstanding the high pressures which are necessary. 

Typically, flow rates in HPLC are around 1 mlmin , while the vacuum requirements of the mass spectrometer preclude liquid delivery of more than around 15 p.lmin at the probe end. To achieve compatibility therefore requires either the splitting of the flow from a conventional column or the use of some form of HPLC, such as a packed microcolumn, which provides directly compatible flow rates. Whichever of these solutions is employed, the amount of analyte reaching the mass spectrometer, and thus the overall sensitivity of the analysis... 

Microbore and packed capillary HPLC column technology has not yet met the requirements for breakthrough of new technologies [554]. On commercial instruments in general efficiency and detectability with microbore columns are lower than with normal-bore columns. Microbore and capillary HPLC suffer from... 

Detector selectivity is much more important in LC than in GC since, in general, separations must be performed with a much smaller number of theoretical plates, and for complex mixtures both column separation and detector discrimination may be equally significant in obtaining an acceptable result. Sensitivity is important for trace analysis and for compatibility with the small sizes and miniaturised detector volumes associated with microcolumns in LC. The introduction of small bore packed columns in HPLC with reduced peak volume places an even greater strain on LC detector design. It is generally desirable to have a nondestructive detector this allows coupling several detectors in series (dual... 

Manufactured hplc columns have about 50 000 plates m 1 if packed with 5 fim particles and about 25 000 plates m-1 if packed with 10 particles, so that from a 12.5 cm column with a 5 fim packing we would expect a plate number of about 6500, corresponding to a plate height of 0.02 mm. Whether or not these high efficiencies are required depends on the sort of work you are doing a great deal of routine work in hplc is done at efficiencies far lower than this. 

Column inlet pressures in hplc can be as much as 200 times atmospheric pressure, and hplc columns are packed using much larger pressures (up to 700 times atmospheric). The SI unit of pressure is the Pascal (1 Pa = 1 Nm-2) normal atmospheric pressure is about 105 Pa. Because it is convenient to express pressure using reasonably small numbers, experimental workers and instrument manufacturers report pressures in bar, or pounds per square inch (psi), or sometimes in kg cm-2. The bar is defined by 1 bar = 105 Pa, so that 1 bar corresponds roughly to normal atmospheric pressure. You will need to be able to convert between these units. 

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