Mobility diameter definition

H is the plate height (cm) u is linear velocity (cm/s) dp is particle diameter, and >ni is the diffusion coefficient of analyte (cm /s). By combining the relationships between retention time, U, and retention factor, k tt = to(l + k), the definition of dead time, to, to = L u where L is the length of the column, and H = LIN where N is chromatographic efficiency with Equations 9.2 and 9.3, a relationship (Equation 9.4) for retention time, tt, in terms of diffusion coefficient, efficiency, particle size, and reduced variables (h and v) and retention factor results. Equation 9.4 illustrates that mobile phases with large diffusion coefficients are preferred if short retention times are desired. 

Karlsson and Novotny [12] introduced the concept of nanoliquid chromatography in 1988. The authors reported that the separation efficiency of slurry packed liquid chromatography microcolumns (44 xm, id) was very high. Since then, many advance have been reported in this modality of chromatography and it has been used as a complementary and/or competitive separation method to conventional chromatography. Unfortunately, to date no correct and specific definition of this technique has been proposed, probably due to the use of varied column sizes (10 to 140 xm). Some definitions of nanoliquid chromatography are found in the literature based on column diameter and mobile... 

Example 12.2 Determine the mobility of a 10-(j.m-diameter unit-density sphere when it carries 100 unit charges. Remember, E = 1 statvolt/cm is included in the definition of Zp. 

In gas chromatography the analyte partitioning between mobile gas phase and stationary liquid phase is a real retention mechanism also, phase parameters, such as volume, thickness, internal diameter, and so on, are well known and easily determined. In liquid chromatography, however, the correct definition of the mobile-phase volume has been a subject of continuous debate in the last 30 years [13-16]. The assumption that the retardation factor, i /, which is a quantitative ratio, could be considered as the fraction of time that components spend in the mobile phase is not obvious either. 

Nanoscale liquid chromatography (nano-LC) using RP separation materials is the default choice for LC-MS of peptides from proteome digests. Nano-LC has excellent sensitivity using 50-100 pm diameter columns and 200-300 nL/min flow rates (166). An all-inclusive definition for nano-LC is an LC that separates nanoliter amounts of sample, with nanoliter amounts of mobile phase, and yields detection limits in the range of nanograms per milliliter (167). 

The basic assumption in any chromatographic theory is that retention is determined by the thermodynamic factors. In such a way, mobile and stationary phases are interpreted as true thermodynamic phases with volumes Vm and Vs, respectively, so that retention volume depends on the partition (distribution) equilibrium coefficient A" of the solute in these two phases Vr = Vm +KVs-By definition, all enthalpic and entropic interactions between the macromolecules and the chromatographic surface occur in the stationary phase. If the size of macromolecules in solution is comparable with the internal diameter of pores, the entire pore volume represents the stationary phase. Vs = Vp, yet the mobile phase is formed by the interstitial volume only, Vm = Vq. This is not always the case for... 

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