Mobile phase temperature

Today, the use of CHIRBASE as a tool in aiding the chemist in the identification of appropriate CSPs has produced impressive and valuable results. Although recent developments diminish the need for domain expertise, today the user must possess a certain level of knowledge of analytical chemistry and chiral chromatography. Nevertheless, further refinements will notably reduce this required level of expertise. Part of this effort will include the design of an expert system which will provide rule sets for each CSP in a given sample search context. The expert system will also be able to query the user about the specific requisites for each sample (scale, solubility, etc.) and generate rules which will indicate a ranked list of CSPs as well their most suitable experimental conditions (mobile phase, temperature, pH, etc.). 

This expresses tR as a function of the fundamental column parameters t0 and k tR can vary between t0 (for k = 0) and any larger value (for k > 0). Since to varies inversely with solvent velocity u, so does tR. For a given column, mobile phase, temperature, and sample component X, k is normally constant for sufficiently small samples. Thus, tR is defined for a given compound X by the chromatographic system, and tR can be used to identify a compound tentatively by comparison with a tR value of a known compound. 

C. Operative Conditions (Mobile Phases, Temperatures, Flows, Run Time)... 

Normal 1. Column temperature fluctuation. (Even small changes cause cyclic baseline rise and fall. Most often affects refractive index and conductivity detectors. UV detectors at high sensitivity or in indirect photometric mode.) 1. Control column and mobile phase temperature, use heat exchanger before detector. 

Figure 10.3. Examples of chromatograms. (a) The separation of 20 essential amino acids (in derivatized form) by RPLC using 1 mm inside diameter by 150 mm long microbore column packed with 4 ft m silica support (with C18 CBP) particles and a water/ acetonitrile mobile phase gradient. (6) The fractionation of gasoline using SFC with C02 mobile phase (temperature and pressure programmed) in 0.25 mm x 50 cm packed column with 5 fim polymeric support particles. (Courtesy of Frank J. Yang.)...

For a given column type, mobile phase, temperature, and detection system, both N and R are constant and / depends only on the H/v ratio. We have looked at H versus v curves before (Figures 12.2 and 12.4) we note here that H/v is simply the slope of the straight line on such a plot connecting the origin with the point (the specific H and v values) represent-... 

Failure to check the matrix effect by analyzing samples at various degrees of dilution Lack of control of mobile phase temperature in ion-pair chromatography Inadequate control of mobile phase pH Failure to control retention times of interfering compounds... 

System suitability parameters with their respective acceptance criteria should be a requirement for any method. This will provide an added level of confidence that the correct mobile phase, temperature, flow rate, and column were used and will ensure the system performance (pump and detector). This usually includes (at a minimum) a requirement for injection precision, sensitivity, standard accuracy (if for an assay method), and retention time of the target analyte. Sometimes, a resolution requirement is added for a critical pair, along with criteria for efficiency and tailing factor (especially if a known impurity elutes on the tail of the target analyte). This is added to ensure that the column performance is adequate to achieve the desired separation. 

L. Spearman, R. M. Smith, and S. Dube, Monitoring effective column temperature by using shape selectivity and hydrophobicity and the effects of the mobile phase temperature, 7. Chromatogr. A 1060 (2004), 147-151. 

It should be noted that Eqs. (1.7) and (1.8) are valid only if the migration velocity of a sample zone is constant during the elution, which means that the plate number can be determined only from isocratic chromatograms obtained at a constant composition of the mobile phase, temperature and flow rate. Plate number values evaluated from a gradient-elution chromatogram are subject to gross errors and have no real meaning. 

Another scale-up issue which may appear esoteric is the question of the wall temperature versus the mobile-phase temperature. By increasing the wall temperature several degrees above the mobile-phase temperature by using a jacketed column, it is... 

Another issue regarding temperature, is the temperature of the wall relative to the mobile phase. It has been suggested for processes which require plates that the wall be heated several degrees above the mobile-phase temperature to flatten the velocity profile, see Section 7.5.3 on scale-up. Regarding this issue, it is possible to collect experimental data or model the unit operation to ascertain the significance of the parameter to the performance of the unit operation. 

The binding interactions between the solute and protein usually involves stereospedfic and nonstereospecific mechanisms. These mechanisms make the type V CSPs sensitive to the composition of the mobile phase, temperature, flow rate, and pH. These parameters can be adjusted to improve the chromatography and stereoselectivity of specific solutes on the AGP CSP (88,89), OVM CSP (90,91), BSA CSP (92,93), and HSA CSP (94). 

Factors effecting the peak separation include column volume, particle porosity, pore size distribution and solute conformation. Column dispersion is influenced by column length, particle size and the mobile phase temperature, viscosity and flow rate. 

C higher than room temperature, the mobile phase (temperature of the mobile phase is supposed to be the same as room temperature in this case) will expand about 1% from when it entered the columns, resulting in an increase in the real flow rate in the column due to the expansion of the mobile phase and the decrease in the retention volume. The magnitude of the retention-volume dependence on the solvent expansion is evaluated to be about one-half of the total change in the retention volume. The residual contribution to the change in retention volume is assumed to be that due to gel-solute interactions such as adsorption. 

Factors which affect selectivity, mobile phase, temperature and nature of solute can be shown by the following selective coefficient equation ... 

MD-HPLC for natural products requires thoughtful selection of orthogonal and complementary separation modes, of the order of their utilization and independent optimization with respect to the chromatographic goals (speed, resolution, capacity, and recovery). Furthermore, besides the mobile phase composition of the employed chromatographic modes, the elution mode (isocratic, step, or gradient elution), flow rates, and mobile phase temperatures need to be considered. 

Although it is possible to reduce the analyte s diffusion coefficient by either increasing the mobile phase viscosity or reducing the mobile phase temperature (which also tends to increase the mobile phase viscosity), this has proven to be a generally ineffective and impractical means for a wide variety of reasons and is rarely done in either HPLC or GC. (In fact the mobile phase or carrier gas is often heated in HPLC and nearly always in GC.)... 

Mobile phase Temperature (°C) Pressure (atm) Density (g/ml) Diffusivity (cm /s) Viscosity (cP)... 

Water, which is always present, albeit sometimes just in traces, is adsorbed on the silica surface, and an aqueous layer is formed. The thickness of this layer, which can vary depending on flow, nature of the mobile phase, temperature etc., has a profound influence on the characteristics of polar stationary phases. If the original heptane in our case was wet , say a water content of 100 ppm, and the freshly prepared heptane is dry, with only 20 ppm water, this difference can have an enormous impact on the separation. 

Often, the column contamination is accompanied with an increase in backpressure. This indicates the accumulation of either a precipitate or a polymeric compound on the top of the column. The rise in backpressure can cause an increase in mobile-phase temperature due to frictional heating, which, in turn, leads to a decrease in retention. A column contamination severe enough to cause a rise in backpressure also often leads to a significant peak distortion. 

The separation factor (Figure 2.4) is dependent on a number of factors, such as the nature of the stationary phase, the mobile phase, temperature, and the compounds of interest. 

The effect of the mobile phase temperature on the recovery and purification speed of the desired product was also studied. Raising the temperature of the mobile phase from 25°C to 55°C increased the loading capacity of the sample. However, the resolution decreased with the over-... 

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