The use of flow splitters between the two dimensions in on-line comprehensive two dimensional liquid chromatography (LC×LC) has not received very much attention in comparison to their use in GC×GC where they are quite common. In principle, splitting the flow after the first dimension column and performing on-line LC×LC on this constant fraction of the first dimension effluent should allow the two dimensions to be optimized almost independently. When there is no flow splitting any change in the first dimension flow rate has an immediate impact on the second dimension. With a flow splitter one could for example double the flow rate into the first dimension column and do a 1:1 flow split without changing the sample loop size or the sampler’s collection time. Of course, the sensitivity would be diminished but this can be partially compensated by use of a larger injection; this will likely only amount to a small price to pay for this increased resolving power and system flexibility. Among other benefits, we found a 2-fold increase in the corrected 2D peak capacity and the number of observed peaks for a 15 min analysis time by using a post first dimension flow splitter. At a fixed analysis time this improvement results primarily from an increase in the gradient time resulting from the reduced system re-equilibration time and to a smaller extent it is due to the increased peak capacity achieved by full optimization of the first dimension.
Recent results of research work on colour‐difference evaluation are reviewed in reports of two CIE Technical Committees; however, a global solution of the problem is still lacking. Therefore, guidelines for planning new research work are included in those reports. Here, these guidelines are explained and extended to stimulate new studies in a coordinated way, which could improve modeling of colour‐difference evaluations for industrial applications.
In four of the jive CIE color regions, the correlation of perceptibility of color differences and colorimetric measures is studied for painted samples at threshold. Sample pairs resulting in three-dimensional color diperences ranging from zero to just clearly perceptible were used. The variability of color-difference ellipsoids is shown for single observers and for observer groups. Randomisation of mean results by a Monte-Carlo method produces deviation ellipsoids that describe shells of uncertainty inherent in the data. Interobserver and inter-group variability turns out to be widely covered by random noise, but the variances leave some stability of ellipsoid shapes. Color-digerenee formulas should be able to predict color differences within the shells of uncertainty.
Following the CIE guidelines for coordinated research on color‐difference evaluation, a set of painted color samples was produced near the green reference color. Visual experiments were carried out by two different methods, absolute threshold and pair comparison. Perceptibility ellipsoids at and near threshold were determined for different mathematical models and for different groupings of observers. The main findings are: insensitivity to the method of optimization, inhomogeneity of the total set of answers but homogeneity within ranked observer groups, and change of volume but similarity of shape of the ellipsoids for extreme groups. Comparisons with other visual studies are discussed.
Experiments on thresholds of perceptible color‐difference at CIE color centers have been extended for the parametric effects of the lightness of an achromatic surround and of a separating gap between a pair of painted specimens. Components of perceived color‐difference (hue, chroma, lightness) approximately could be assigned to geometric elements of threshold ellipsoids and used for component analysis. A study of ellipsoid and city‐block modelling revealed ellipsoid to be slightly better. An increase of total threshold by changed lightness of the achromatic surround was found only in the case of the dark CIE Blue, but in every case a gap increased threshold the darker the CIE color center. The results can be used for a correction in color‐difference evaluation.
Introduction of a sample into the separation column (microchip channel) in capillary zone electrophoresis (microchip electrophoresis) will cause a disturbance in the originally uniform composition of the background electrolyte. The disturbance, a system zone, can move in some electrolyte systems along the separation channel and, on reaching the position of the detector, cause a system peak. As shown by the linear theory of electromigration based on linearized continuity equations formulated in matrix form, the mobility of the system zone--the system eigenmobility--can be obtained as the eigenvalue of the matrix. Progress in the theory of electromigration allows us to predict the existence and mobilities of the system zones, even in very complex electrolyte systems consisting of several multivalent weak electrolytes, or in micellar systems (systems with SDS micelles) used for protein sizing in microchips. The theory is implemented in PeakMaster software, which is available as freeware (www.natur.cuni.cz/gas). The linearized theory also predicts background electrolytes having no stationary injection zone (water zone, water gap, water dip, EO zone) or unstable electrolyte systems exhibiting oscillations and creating periodic structures. The oscillating systems have complex system eigenmobilities (eigenvalues of the matrix are complex). This paper reviews the theoretical background of the system peaks (system eigenpeaks) and gives practical hints for their prediction and for preparing background electrolytes not perturbed by the occurrence of system peaks and by excessive peak broadening.
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