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We have investigated which of the different existing peak variance read-out methods (including the effect of a deconvolution pre-treatment method) are most suited to eliminate the system contribution from the total observed band broadening observed in LC systems. Emphasis is put on the most demanding case, i.e., the measurement of non-retained component peaks, which typically are very narrow and tailed. The problem with such peaks is that the method that is generally considered to be the only mathematically correct method (i.e., the method of moments) leads to peak variance values that are so strongly dominated by the tail of the peak that they become highly exaggerated and practically meaningless (i.e., they are dominated by the peak width at 10 or 12σt, which corresponds to resolutions and peak purities that are so high they are never pursued in practice). Interestingly, filtering away the extra-column contribution from the entire peak shape using peak deconvolution (wherein not only the second order moment is corrected but also all other moments) produces corrected 4σt- and half height peak widths that are physically meaningful, i.e., the corrected values allow to make sufficiently accurate predictions of how the peak width at 4σt and at half height changes when the column length changes. This result now allows to navigate away from the classical method of moments to define the column plate height, and resort to plate heights based on the practically much more relevant 4σt- and 5σt-widths, provided theses are corrected via peak deconvolution., (Copyright © 2016 Elsevier B.V. All rights reserved.)

Due to the developing insights in the theory of chromatography, column manufacturers of any kind (industrial, academic) nowadays have a broad array of experimental column testing tools at their disposal. The present tutorial aims at helping the novice in the field getting an overview of these tools and provides a fixed procedure to carry out the subsequent steps in the column quality analysis (guided via an Excel template file). After some brief introduction about the main equations, the reader is taken step by step through the theories underlying the measurement methods for the different column and performance parameters. In the final section, the reader is taken through the different items in the Excel template., (Copyright © 2015 Elsevier B.V. All rights reserved.)

The study of radial and axial temperature profiles always has been an area interest both in liquid chromatography (LC) and supercritical fluid chromatography (SFC). Whereas in LC always an increase in temperature is observed due to the dominance of viscous heating, in SFC, especially for low modifier content, a decrease in temperature is found due to the much larger decompression cooling. However, for higher modifier content and higher operating pressure, the temperature effects become a trade-off between viscous heating and decompression cooling, since in SFC the latter is a strong function of operating pressure and mobile phase composition. At a temperature of 40°C and for neat CO2, the effect of decompression cooling and viscous heating cancel each other out at a pressure 450bar. This pressure decreases almost linearly with volume fraction of methanol to 150bar at 25vol%. As a result, both cooling and heating effects can be observed when operating at high back pressure, large column pressure drops or high modifier content. For example at a back pressure of 150bar and a column pressure drop of 270bar decompression cooling is observed throughout the column. However at 300bar back pressure and the same pressure drop, the mobile phase heats up in the first part of the column due to viscous heating and then cools in the second part due to decompression cooling. When coupling columns (2.1mm×150mm, 1.8μm fully porous particles) at very high operating pressure (e.g. 750bar for 8vol%), the situation is even more complex. E.g. at a back pressure of 150bar and using 8vol% methanol, viscous heating is only observed in the first column whereas only decompression cooling in the second. Further increasing the inlet pressure up to 1050bar resulted in no excessive temperature differences along the column. This implies that the inlet pressure of SFC instrumentation could be expanded above 600bar without additional band broadening caused by excessive radial temperature differences., (Copyright © 2014 Elsevier B.V. All rights reserved.)

This study reports on the possible advantages of switching from constant flow (cF) based gradient elution separations to constant pressure (cP) based ones in Supercritical fluid chromatography (SFC) by means of mathematical models. All the important parameters (e.g. viscosity) were fitted as a function of pressure and mol% methanol in CO2. It is shown that when switching towards a cP approach in SFC, a time gain of 34% at the end of a 0 to 50% methanol in CO2 gradient is expected. Actual analysis time gains depend on the point at which it is evaluated (e.g. up to 41% after the equilibration step). Due to the dependence of retention on density, cF- and cP-mode do not yield the same selectivity even if the same volumetric-based gradient program is used. Because the components experience a higher average pressure in the cP-mode, the apparent retention factor is slightly lower., (Copyright © 2013 Elsevier B.V. All rights reserved.)