Chromatography isocratic

The practices of isocratic and gradient sorptive chromatography are very different. Isocratic chromatography tends to be very sensitive to the details of mobile phase preparation, temperature, pump speed, and sample composition. Gradient chromatography is usually more tolerant of small variations in these factors but may be extremely sensitive to column history, equilibration time, and gradient preparation. 

The theoretical parameters of isocratic chromatography are often described using the plate model. One can imagine the analyte to be distributed... 

The retention behaviour of oligomers in RPLC/-NPLC-APCI-MS (35 to 1500 Da) has been described [637]. In isocratic chromatography only a limited number n of oligomers can be separated, as the retention usually increases excessively at high n, so that gradient elution is necessary for successful separation of samples with broader molar mass distribution. RPLC-APCI-UV/QITMS was used for the analysis of accelerators (CBS, MBT, MBTS, BT) extracted... 

Isocitric acid, in citric acid cycle, 6 633 Isocontour surfaces, discrete, 10 340 Isocorrosion diagrams, 23 784 Isocratic chromatography, 3 827 Isocrotonic acid, physical properties,... 

From both theory and experimental evidence, raising the temperature by 10°C decreases the retention time by about 20% in isocratic chromatography and decreases the backpressure by 10% to 20% because of a reduction in the viscosity of the mobile phase. This can help to overcome the instrument limitations associated with running shorter columns packed with smaller particles, i.e., the pressure limitations of current HPLC systems. However, since the majority of reversed-phase columns available are silica-based, operating at temperatures above... 

Romanyshyn, L. Tiller, P. R. Alvaro, R. Pereira, A. Hop, C. E. Ultra-fast gradient vs fast isocratic chromatography in bioanalytical quantification by liquid chromatography/ tandem mass spectrometry. Rapid Commun Mass Spectrom 2001, 15, 313-319. 

Figure 12.16 Scheme of purification solution integrating isocratic chromatography coupled with eluent recycling. 

Figure 12.2 SFE windowing, (a) Apparatus (b-d) isocratic chromatography (b) fraction 1 (c) fraction 2 (d) fraction 3 AN = acetonitrile.

Using these techniques, we were able to increase concentration by 500x, while decreasing run time from the gradient to the isocratic chromatography by 12x. This is the type of simplification that can allow the full power of the HPLC to come into play. 

Eigure 17-17. Theoretical plates versus retention factor for series of parabens separated by isocratic chromatography. Extra-column effects result in decreased efficiency for early-eluting components (low values of k). 

Gradient elution in RPC, NPC or lEC systems can be optimised using principally the same strategies as in isocratic chromatography, which are briefly described in Section 1.4.7. Simultaneous optimisation of gradient time (steepness), initial concentration and — if necessary — gradient shape can use Eqs. (1.32)-(1.37) for predictive calculations of the retention and of the resolution of the individual pairs of sample compounds from the isocratic data acquired in a few mobile phases of different composition or in a few initial gradient-elution runs. 

Snyder s thorough model [1-5] of gradient elution provides an extremely convenient means to achieve the objectives outlined above. The model uses the general resolution equation for isocratic chromatography in terms adapted to gradient elution. This equation defines resolution between two closely resolved analytes in gradient RP-HPLC as a function of mean column efficiency N, mean selectivity a, and the effective retention factor Aavc experienced by the compounds during the elution process j 1-3,5). 

Romanyshyn, L. Tiller, PR. Alvaro, P. Pereira,A. Cornells,E.C.A. Ultra-fast Gradient vs. Fast Isocratic Chromatography in Bioanalytical Quantification by Liquid Chromatography/Tandem Mass Spectrometry, Rapid Commun. Mass Spectrom. 15, 313-319 (2001). 

Experiment 26. Analysis of barbiturates by reverse phase isocratic chromatography... 

Isocratic chromatography chromatographic separations, e.g. HPLC, using the same mobile phase solvent composition throughout the analysis. 

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