On the statistical independence of various column contributions to band broadening. Part 2: The non-equilibrium contribution predicted by a slow, statistically independent relaxation of concentrations

✍ Scribed by Nilsson, Olle

• Publisher: John Wiley and Sons
• Year: 1982
• Tongue: English
• Weight: 519 KB
• Volume: 5
• Category: Article
• ISSN: 0935-6304
• DOI: 10.1002/jhrc.1240050307

✦ Synopsis

The mass balance changes of Said's so-called "stage" model, based on the movement of the mobile phase with mean velocity ! (=L/i,), are synchronized by introduction of the relaxation timeof Giddings, t, = 1 /(km+ k,) where kmand ksare thegeneral overall mass rate constants for sample transfer to and from the stationary phase, respectively. This makes the "stage" length equal to the true theoretical plate height, AL, related to the classical HETP contribution due to non-equilibrium, H(al, according to the "discontinuousdL" relation Here k = (ims -I,,,) / im is the central moment-based capacity ratio, L the column length, and o&) the second moment contribution from the non-equilibrium only. Correct application of the relaxation-time model to chromatography requires that the real sample concentration in the stationary phase at a given position and time, is in a continuousequilibrium with the real sample concentration in the mobile phase, C,,l+~~,z,t at that time displaced down the column by a distance This leads to the classical HETP contribution obtained from various other continuous models, which implies that AL is a good estimation of the true theoretical plate height.