Optimal Parameters in High Speed Liquid Chromatography (HPLC)

Abstract

Dedicated to Professor Geza Schay on the occasion of his 81st birthdayAfter a decade, the first storm of development in high performance liquid chromatography seems to be abating. Providing the stationary phase and eluent are optimized, most routine analytical and semi-preparative separation problems require columns having betweeil 1000 and 10000 theoretical plates. Commercial apparatus and columns completely satisfy these requirements. For many separation problems the efficiency of the columns on offer is greater than required. Since optimal (not maximal) separation is required with shorter analysis times, the column inlet pressure is increased in order to increase the eluent velocity, while at the same time reducing the column efficiency. The same result can be obtained by using shorter columns and lower pressures. Since inlet pressures of more than 100 bar are seldom required in routine analysis, the term "high pressure liquid chromatography" is a misnomer.-It is probable that difficult separation problems, where several I00000 theoretical plates are required, will be studied in the next phase of development. It can be shown using nomograms that such problems can be solved within acceptable time limits using inlet pressures of less than 500 bar. Further possible directions of development are indicated.

Perspectives on Recent Advances in the Speed of High-Performance Liquid Chromatography

“…The answer to the second question is that one should always work at the velocity corresponding to the minimum in the van Deemter curve, thus h min will be given by eq 1, but one must then operate at values of the length, particle size and velocity given by eqs 2-4 6, 10, 52 . Failure to recognize this requirement invalidates any subsequent analysis involving the value of h specified by eq 1.…”

The 1000 bar and 24 hour limits of one-dimensional HPLC – graphical representations

“…It is a fact that any column performs best if it is run at its optimum flow velocity, i.e., at the lowest point of its van Deemter curve, resulting in the maximum possible number of theoretical plates [3][4][5]. If this condition is fulfilled the inevitable pressure limit will define the optimum length of a column which is packed with an optimum-diameter particular stationary phase.…”

“…The plots published in 1982 by István Halász and Gerhard Görlitz [3] did not attract much attention, probably because the paper is written in German. The authors described the underlying mathematics in detail, so it is not outlined here again.…”

“…Re-drawn and slightly modified after Ref. [3] lower viscosities). With 1000 bar and again a breakthrough time of 10,000 s or 2.8 h a theoretical plate number of 640,000 is obtained.…”

“…reversed Re-drawn and slightly modified after Ref. [3] phases) and ε = 0.82 for underivatized silica (normal phases). Other numeric parameters, for example the van Deemter constants or the viscosities, were also taken from the Halász-Görlitz paper.…”