Bands chromatographic

The width of a solute s chromatographic band measured at the baseline (w). 

Nonideal asymmetrical chromatographic bands showing (a) fronting and (b) tailing. Also depicted are the corresponding sorption isotherms showing the relationship between the concentration of solute in the stationary phase as a function of its concentration in the mobile phase. 

To determine how the height of a theoretical plate can be decreased, it is necessary to understand the experimental factors contributing to the broadening of a solute s chromatographic band. Several theoretical treatments of band broadening have been proposed. We will consider one approach in which the height of a theoretical plate is determined by four contributions multiple paths, longitudinal diffusion, mass transfer in the stationary phase, and mass transfer in the mobile phase. 

Adsorption-Desorption Kinetics and Chromatographic Band Broadening... 

FIGURE 2.1 The linear isotherm of adsorption and the corresponding Gaussian distribution of the analyte s concentration in the chromatographic band. 

FIGURE 2.4 Three types of concentration profiles encountered among the thin-layer chromatographic bands (a) symmetrical (Gaussian) without tailing, (b) skewed with front tailing, and (c) skewed with back tailing [14],... 

Use of densitometric detection provides an insight into the concentration profiles of chromatographic bands, thus furnishing an indispensable prerequisite, needed for proper assessment of the retention mechanisms in the preparative adsorption TLC. Figure 2.4 shows three types of the band eoncentration profiles. The Gaussian peak (a) in this figure represents the linear isotherm of adsorption of a given species, peak... 

Mixed lateral interactions can occur in the case of the following pairs of molecules A. .. B, AB. .. A, AB. .. B, and ABj. .. ABj. Their appearance is even more importunate than that of the self-associative lateral interactions. With the self-asso-ciative lateral interactions alone, tailing of chromatographic bands lowers separative performance of a given chromatographic system, whereas with the mixed lateral... 

Circular (or symmetrically ellipsoidal) chromatographic band shape... 

It regards the center of a chromatographic band as the point at which the local concentration of the analyte is the highest. 

It also regards the center of the chromatographic band as the center of gravity of the mass distribution of the analyte in the band. 

The numerical value of the Rp coefficient for a given chromatographic band can be determined for the maximum value of the concentration profile of the band (which actually is the point at which local concentration of the analyte is the highest). The Rp eoeffident determined according to this definition can be denoted as Rp mmy... 

Alternatively, the numerical value of the Rp coefficient can be determined from the center of gravity of the distribntion of analyte mass in the band. With nonsymmetrical chromatographic bands, this valne cannot be identical with that obtained from the maximnm of the analyte s concentration profile. The Rp coefficient determined in this manner can be denoted as Rp y... 

Yau, W. W., Characterizing skewed chromatographic band broadening, Anal. Chem., 49, 395, 1977. 

As the contaminated fluid in the simulation passes into the aquifer, the Hg++ ions sorb to the ferric surface tightly enough to exclude the other metals. Once the Hg++ is exhausted from the fluid, the Pb++ begins to sorb, and the Zn++ sorbs where the Pb++ is depleted, leaving each metal bound within its own chromatographic band. Where Hg++ in the migrating fluid passes from the first to second band, it displaces Pb++,... 

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