Chromatography Handbook Of Hplc - Katz Eksteen Schocnmakers Miller wiley Sons -112

Alas, discussions at contemporary conferences are not equally inspired. Maybe this is a good reason for no longer including them in conference proceedings. This is a pity, however, be-cause (outsides such as the foregoing) the use the heart of the matter, which in this case is the complexity of optimization beyond the use of the accepted optimum conditions Hmin and uexp. History has awarded both speakers in their own right.\n\n(f) Plate Height in Packed Columns Using the Golay Equation. In Sec. II.E.4, we dis-cussed all kinds of pragmatic alternative expressions for plate height in packed columns, here we continue the discussion, for there are possibilities and pregnant preferences of authors to use plate height equations, based on the foregoing Golay equation for open tubular or capillary columns and also for packed columns, both in GC and in LC.\n\nIt was Golay himself who opened the discussion in this direction by comparing his results directly with those of even Deemter. Golay concentrated on the C term, but Purnell et al. [29,30] argued that packed columns may be considered as a bundle of capillaries, the radius with which can be reasonably approximated by the particle radius of the packing. They thus adopted the Golay equation [see Eq. (55)] and used it rather successfully for characterizing and optimizing packed columns in GC. The general conclusion of Boehm and Purnell [31] was that in packed column GC the following equation is useful:\n\nH = 1.5dpDm/(um) + (3/2)f(km)(uexp2/Dm) + (2/3)(k)(um)(g2/Dm) (58a)\n\nIn LC, Scott et al. [21,31] tested a variety of variations, among which the ones in Table 3, but also the van Deemter equation in a Golay adaptation. It was observed that, notwithstanding that good fits with experimental data could be obtained with most equations, physically meaningful values for the coefficients in the A, B and C terms could be assigned to only the modified van Deemter-Golay equation in the following form (written in our notation):\n\nH = A + B(n)(um) + (C)(-1)(um) = 2Adc + 2y2yDm(1 + k0/Db)(um)\n+ [(1/24)(k0)(k) + (2/3)(k)(um)2Dg](58b)\n\nThe new symbols are k0 (a modified retention factor) and ? (a correction factor), which will be discussed in the following.\n\nHere, we retained the notation in the usual velocity (um), while in the equations naturally the interstitial velocity u0 = φ(um) occurs, where φ represents the fraction of mobile phase that actually moves in the interstitial pores between particles that have an internal porosity εi, contributing to the total bed porosity ε0 = εi + εe, so ε0 = εb/εw. As usual (um) is found from the residence time τ0 of a nonretained low molecular mass marker solute that penetrates both interstitial and intraparticle pore space: (um) = L/τ0. Both the interstitial velocity u0 and the modified retention factor k0 replacing the conventional capacity factor k, are found from the retention time τ0 of a completely excluded (from the intraparticle pores) solute, such as a high molecular mass standard compound of a nanodispersed polymer (for instance a polystyrene standard with molar mass 83,000), u0 = L/τ0 and k0 = (kr - τ0)/τ0. Note, that we now have two equivalent expressions for the retention time:\n\nτk = τ0(1 + k) = τ(1 + k0)\n\nIn this way, the packing particle as a whole, including pores filled with mobile phase (but