Column capacity factor

Breneman, C. M. and Rhem, M. (1997) QSPR Analysis of HPLC column capacity factors for a set of high-energy materials using electronic van der Waals surface property descriptors computed by transferable atom equivalent method. J. Comput. Chem. 18, 182-197. 

Ca detector cell capacity factor/column capacity factor for a given solute... 

This is confirmed by the results achieved by Podlaha and Torregard (6), who could not elute tristearin at ambient temperature with propionitrile on a 50-cm RP-18 column but could do it at 30°C in about 105 min (flow rate 0.5 ml/min, column capacity factor around 13). It is known that the solubility of TGs increases very rapidly with increasing temperature. 

In a series of papers, Szabo et al. (1990 a,b) used a variety of stationary phases, including octadecylsilica (ODS), cyanopropyl, ethylsilica, and immobilized humic acid, to investigate the relationship between Koc and RP-HPLC capacity factors for 11 aromatic hydrocarbons. While capacity factors generated with all the stationary phases showed significant correlations with log Koc, the authors concluded that the immobilized humic acid column capacity factors, obtained by extrapolation of retention data from binary elements to 100% water, gave the best correlation. 

Figure 11.5 Comparison between the results of the calculations of the individual band profiles of a 3 1 binary mixfure using the CXZFE method and two finite difference methods (Eqs, 10.78 and 10.80). Solid fine profile calculated with the OCFE method, with Sz = 0.050 cm, St = 0.15 s. Dotted line profile calculated with the forward-backward method (Eq. 10.78), Sz = 0.0050 cm and St = 0.33 s. Dash-dotted line profile calculated with the backward-forward method (Eq. 10.80), Sz = 0.0050 cm and St = 0.033 s. Calculation parameters column length 15 cm. Phase ratio 0.25. Mobile phase flow velocity 0.15 cm/s. Column capacity factors (Cg j = 4, fcpj = 5. Np = 3. 3 1 binary mixture. Langmuir competitive isotherms parameters = 20, fl2 = 16/ = 5 62 = 4 Input profile ...

When the mobile phase concentration of an analyte is large and the isotherm is not linear, the retention time of the pulse depends on the concentration of the component in the mobile phase. The apparent column capacity factor is proportional to the slope of the isotherm at the mobile phase concentration k = Fdq/dC, Eq. 

Capacity factor or column capacity factor, k A dimensionless retention time or volume, more generally called the retention factor (see this term). The original name is a source of ambiguity in nonlinear chromatography because it is related to the slope of the tangent to the isotherm, not to its saturation capacity. The retention factor is the product of the initial slope of the isotherm and the phase ratio. 

The actual volume of eluting solvent required is dependent on the void volume of the SPE sorbent and on the retention of the solute in the eluting solvent. A typical SPE cartridge that contains 500 mg of sorbent that is 60 pm in diameter will have a void volume of approximately 120 pL per 100 mg of sorbent (Hennion and Pichon, 1994), which is approximately 600 pLor 0.6 mL. Given that a k (the column capacity factor) of many of the solutes could be 2 to 3 in the elution solvent, the prediction of the elution volume is given by the equation below ... 

When templates are polar, the increase of the aqueous content in the mobile phase causes a marked decreasing of the column capacity factor, whereas templates of moderate or low polarity are increasingly retained and the column behaves as a true reverse phase. Such increase in retention can be attributed to a shift of the partition equilibrium towards the stationary phase (bulk of the polymer+binding sites) due to hydrophobic interactions with the template. 

Fig. 5-21 Plot of logarithm of column capacity factor versus water content in the mobile phase [98].

Gas phase non-ideality and carrier gas adsorption influence analyte retention [41, 10]. The influence of carrier gas adsorption is often more important. For example, when alkanes are eluted on Porasil C (50-100 m2/g) using carbon dioxide as carrier gas at 80 C a considerable (30-40%) decrease of column capacity factor is measured if the pressure is raised from 1.3 atm to 5.1 atm [105). It can be estimated that about 15% of the silica surface is covered with carbon dioxide at corresponding average pressure [106]. 

It is common for the test mixture used by a manufacturer to check the performance and quality of an HPLC column to be totally umelated to the assay for which the column was purchased because they are made up of quite simple compounds, which are readily available in the laboratory. When setting up a test procedure for monitoring column performance over its lifetime, the same procedure as the manufacturer should be used if possible. It is useful to note that a different result for the efficiency of a column will occur for each different test method, and it is therefore important for each HPLC laboratory to standarize on one dy. Suggested test mixtures, along with their respective test conditions, are outlined in Table 12. Commonly, two or three components are used, one with a very short retention time [typically with a k of about 0.2, where k is the column capacity factor (see Figure 19) to assess band broadening caused by... 

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