Band width volume dependence

The volume dependence of the d band width is expected from a simple approximation within resonant scattering theory (Heine (1967)) to behave as... 

The volume expansion accompanying hydrogen uptake In metals and alloys has recently been calculated55 using a semi-empirical model which relates the heat of formation, AH, of a metal hydride to the difference of the Fermi energy, Fp and the center, Fg, of the s band of the host metal.56 The remarkable constancy of AV was shown to be in agreement with the model and due mainly to the volume dependence of the width, W, of the electronic bands.55... 

The main contributions are the sample volume and the profile of the injected band characterized by both the injection volume and the injection time 16, 20, 27, 5). We want to calculate the maximum permissible sample size which causes a relative increase in the zone width by a factor 6, hence a decrease in the efficiency by 0. The sensitivity depends little on the column length at constant plate number if the maximum sample size is used in all cases. 

A rule of thumb is that the injection volume can be as high as 30% of the volume of a peak that elutes from the column when using a small injection (e.g., 10 juL) and there should be no significant broadening of the peak with this larger injection. To understand this rule of thumb, one must consider the contributions to band broadening. At injection, the sample volume will be diluted to a volume that is mainly dependent upon the efficiency of the column. The final peak width, Wpeak, observed in the detector is a result of the volume of the sample injected and of the spreading from the column, the detector, and the extra column effects. 

It is obvious from Fig. 1 that the chromatographic separation of components in a mixture is dependent on two factors the difference in retention times of two adjacent peaks, or more precisely, the difference between peak maxima and the peak widths. It was shown in the preceding discussion that the retention of a solute is a thermodynamic process controlled by the distribution coefficient and the stationary-phase volume. The peak width, or band broadening, on the other hand, is a function of the kinetics of the system. 

The largest elution volume in size-exclusion chromatography is the total mobile-phase volume in the column the sum of the pore volume and the interstitial volume, thus the separation space is constrained. Therefore, how good a separation can be obtained depends strongly on the width of the individual band, namely, on the plate count. System plate count is very important in SEC. 

Blockage of column frits or channeling in a column bed will cause a loss of resolution. Any packing void will be a source of dead volume and thus of band spreading this can be checked by carefully removing the front frit from the eolumn. A void is indicative of the imminent end of the column s usefulness, especially in SEC, which is inherently dependent on peak widths and column efficiency. 

---