Column matching factor

Every reversed phase available on the marked has its own measurable set of characteristic parameters H, A, B, C, and S. They can be quantified, listed and compared.These parameters help to identify similar or very different columns compared to a given one. The distance Fs between two phases is calculated by the column matching factor ... 

When two columns are compared a fitting factor is obtained, which is a direct measure of how well the columns match. For any method, the most similar and also the most dissimilar column to the chosen column can easily be identified, as can be seen in the figure 4.17. For the sake of completeness, a further database, based on the work of Tanaka, Euerby, and Peterson, is mentioned (ACD Labs Column Selection Database) ... 

After a successful separahon, one should use a completely different column-eluent combinahon and inject 1-2 pL, exploiting the possibilities of the DAD. Orthogonal separahons yield more security than match factors, etc., of the DAD after a one-dimensional separahon. 

It is appropriate at this time to discuss some of the limitations associated with LC-NMR. It is more accurate to say the limitations of the NMR spectrometer in an LC-NMR instrument. As compared to MS, NMR is an extremely insensitive technique in terms of mass sensitivity. This is the key feature that limits NMR in its ability to analyze very small quantities of material. The key limiting factor in obtaining NMR data is the amount of material that one is able to elute into an active volume of an NMR flow-probe. The quantity of material transferred from the LC to the NMR flow-cell is dependant on several features. The first being the amount of material one is able to load on an LC column and retain the resolution needed to achieve the desired separation. The second is the volume of the peak of interest. The peak volume of your analyte must be reasonably matched to the volume of the flow-cell. An example would be a separation flowing at lml/min with the peak of interest that elutes for 30 s. This corresponds to a peak volume of 500 pi, which clearly exceeds the volume of the typical flow-cell. This is the crux of the problem in LC-NMR. There is a balance that must be struck between the amount of compound needed to detect a signal in an... 

The basis and various parameters for the economic analysis are given in Table II. The overall column efficiency used was obtained from a plot of efficiency vs. the product of relative volatility and liquid viscosity (9), corrected to match predicted (10) data for the propane-propylene system. The value from the plot (9) was increased by a factor required to make the efficiency of the propane-propylene binary distillation equal to 100%. Costs were calculated by the Venture Analysis method (II), because this method yields the appropriate weighting factors for the fixed and operating costs in order to calculate the total costs. Results are expressed as annual costs, before taxes. The important process variables are discussed below. 

For online applications, an alternative to the above procedure is to tune the extraction factors periodically to match plant data and laboratory analysis. The factors determined in this manner can be used to predict the column product compositions between parameter updates. The predictions should take into account the effect on the extraction factors of measured flow rates Q and E. 

In order to calculate the retention factor k oi a compound or the selectivity coefficient between two compounds, the distances migrated along the plate are compared, for matching, with the migration times read on the chromatogram. Assuming that the ratio of the migration velocities m/mq is the same on the plate as on the column (which is really only an approximation), then and k can be linked ... 

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