Packed particle size

Another example of the use of a C8 column for the separation of some benzodiazepines is shown in figure 8. The column used was 25 cm long, 4.6 mm in diameter packed with silica based, C8 reverse phase packing particle size 5 p. The mobile phase consisted of 26.5% v/v of methanol, 16.5%v/v acetonitrile and 57.05v/v of 0.1M ammonium acetate adjusted to a pH of 6.0 with glacial acetic acid and the flow-rate was 2 ml/min. The approximate column efficiency available at the optimum velocity would be about 15,000 theoretical plates. The retention time of the last peak is about 12 minutes giving a retention volume of 24 ml. 

Mode Manufacturer Name Packing Particle size Note... 

U. S. Sieves are identified by either micrometer (micron) designations or arbitrary numbers. Thus, a material referred to as 60/80 means particles which will pass a 60 mesh screen but not an 80 mesh screen. You may also see this written as -60+80 mesh. Particle size is much better expressed in micrometers (microns), therefore 60/80 mesh would correspond to 250-177 micrometers (micron) particle size range. Table 2.5 shows the conversion of column packing particle sizes. The table shows the relation... 

As we discussed above, efficiency and selectivity are complementary descriptors dependent on the different sets of chromatographic parameters. Efficiency is more dependent on the quality of the column packing, particle size, flow rate, and instrumental optimization, while selectivity is more dependent on the stationary phase properties and the nature of the analytes themselves. However, efficiency is sometimes affected by nonideal interactions of the analyte with the stationary phase (i.e., peak tailing). 

Other factors not covered by equation (17-23) are packing particle size and column temperature. These factors are also discussed below. These changes are discussed in more detail with examples in the resolution section. Keep in mind that these optimization approaches can be simulated in DryLab or similar software packages and should be used during the method optimization process. 

Ammonium perchlorate of various fineness is used to give a better packing. Particle size distribution is of great importance to density, rheological properties of the viscous mass, mechanical properties and burning of the propellant. Rheological properties obviously depend on polymer binder which is of course the combustible ingredient in propellants. 

Column manufacturers have developed a wide range of column bore size, length, and column packing particle size to accommodate the increased demand for smaller and more efficient columns. The column bore size will dictate the appropriate flow rate and can be tailored to meet the analyst s needs. Table 2 lists the general column bore size (inner diameter, or i.d.) and appropriate flow rates. 

The equation, though complex, shows the importance of particle size, mobile phase flow rate and diffusion coefficients and indicates that the deleterious effects on H and thus the column performance can be minimised by reducing the packing particle size, the stationary phase thickness and the solvent viscosity (thus decreasing Dyi and D ). The latter can be achieved by using elevated column temperatures. 

Of practical interest for micropumps, we also study the effect of the chaimel wall and packing particles on the overall electroosmotic flow rate in a microcapillary. Flow rate versus applied external electric field, for different packing particle sizes and the zeta potential ratio w/Cp> is plotted in Fig. 5. It is noted that the flow rate increases linearly with increasing applied voltage. For larger packing particles, the flow rate is... 

Particle size is one of the most important parameters acting on efficiency. The smaller the LC packing particle size, the higher is the efficiency [5]. The plate height, H, of a well-packed column can be as low as twice the particle diameter. A 10 pm plate height (100,000 plate/m) should be obtained when 5 pm particles are used to pack a column. 

Unfortunately the particle size affects quadratically the column permeability. When the packing particle size is divided by two, the column driving pressure must be four times higher in order to obtain the same flow-rate. Often, very small particle size is associated with short columns in order to reduce the working pressure. 

Berger " and LeseUier and Tchapla ). The reported applications include stationary-phase columns obtained from many different commercial manufacturers, covering almost the complete range of packing particle size and pore size. 

Evaluation of HA molar mass ehanges was performed with Shimadzu apparatus using a packed HEMA-BIO 1,000 colunm of dimensions 7.8 mm x 250 mm, the packing particle size was 10 pm. The mobile phase 100 mM phosphate buffer (pH 7.0) containing 0.15M NaCl was pumped by the LC-IOAD device at a flow rate of 0.5 ml/min. For catibration of the SEC system used reference HAs (M = 90.2-1380 kDa) with broader molar mass distributions (M /M = 1.60-1.88) were apphed. The samples of the volume of 20 pi with the polymer concentrations 1 mg/ml or lower were injected by a 7725i-type Rheodyne valve. The SEC analyses performance was monitored online by UV (SPD-IOAV, set at 206 run) and refractive index (RID-10) detectors. 

The theory summarized in this chapter and elsewhere [l-3a,18] has enabled the development of computer programs that allow so-called computer simulation. In this approach, two to four experimental gradient runs are first carried out for the reversed-phase or ion-exchange separation of a biological macromolecular sample. After the results of these initial experimental runs are entered into the computer, separation times of analytes can be predicted based on initial and final %B, gradient time and shape, column dimensions, flow rate, column-packing particle size, and temperature [42-47]. 

Limits of detection for absorbance detectors (325 nm) with conventional (5 qm particle size) C18 columns and methanol water mobile phases are typically 0.35 pmol (0.1 ng) at a 5 1 signal noise ratio. Even low serum retinol concentrations as found in vitamin A deficiency (0.35 to 0.7 iM, i.e., 10 to 20 Ag/dL) require sample volumes of only 1 pL Nonetheless, fiuorescence detection can give even lower limits of detection (0.07 pmol, 20 pg in tear fluid (111) 5-pL sample sizes have been used for routine plasma assays (112). Electrochemical detection has also been used for simultaneous analysis of retinol and tocopherol (113,114). Microbore columns and smaller packing particle sizes could give improved limits of detection (115,116) but require low-dispersion fittings and detector cells. The requirements for plasma retinol quantitation are not so stringent that use of these techniques has become popular. 

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