Elution Modes

Two basic elution modes can be applied in operating column chromatography iso-cratic elution and gradient elution (Guiochon et al., 2006). In isocratic elution the 

At isocratic elution the peaks broaden and become flatter with increasing retention, and might even disappear in the baseline noise. As a rule of thumb, the retention factor k of the last eluting solute in isocratic elution should not be larger than 

This corresponds to an elution volume of less than 10 column volumes. Very strongly retained solutes may not be eluted and, hence, the column has to be washed with a strong solvent from time to time. 

Atkins, P.W. (1990) Physikalische Chemie, WUey-VCH Verlag GmbH, Weinheim. 

Bellot, J.C. and Condoret, J.S. (1993) Modelling of liquid chromatography equilibria. Process Biochem., 28, 

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A liquid chromatography-mass spectrometry (LC-MS) method that can quantitatively analyze urinar y normal and modified nucleosides in less than 30 min with a good resolution and sufficient sensitivity has been developed. Nineteen kinds of normal and modified nucleosides were determined in urine samples from 10 healthy persons and 18 breast cancer patients. Compounds were separ ated on a reverse phase Kromasil C18 column (2.1 mm I.D.) by isocratic elution mode using 20 mg/1 ammonium acetate - acetonitrile (97 3 % v/v) at 200 p.l/min. A higher sensitivity was obtained in positive atmospheric pressure chemical ionization mode APCI(-i-). 

A multisolvent system ean be adapted to aehieve the GPC elution mode. Figures 6.30 and 6.31 (page 206) show how to aehieve GPC elution by ehanging the mixing ratio of ehloroform and methanol in the analysis of Epikote 1001. 

Separation mode Development mode Elution mode... 

Normal-phase (NP) and reversed-phase (RP) liquid chromatography are simple divisions of the LC techniques based on the relative polarities of the mobile and stationary phases (Figure 4.10). Both NPLC and RPLC analysis make use of either the isocratic or gradient elution modes of separation (i.e. constant or variable composition of the mobile phase, respectively). Selection from these four available separation techniques depends on many variables but basically on the number and chemical structure of the compounds to be separated and on the scope of the analysis. 

In addition, the use of fast gradients elution mode has become the bioanalytical mainstream as a possible way to improve peak parameters (shape and symmetry) and to minimize method development time, especially for the multi-analytes methods. 

Hydroorganic Elution Mode Superimposition of RP or HILIC Mechanisms... 

Fig. 10 ACE using an etched capillary with heparin bound, (a) SLPI concentration, 10 mg/mL. ACE condition etched capillary, 75-/rm ID X 55 cm (47 cm from injection to detection window), heparin bound via silane spacer. Injection mode gravity, height 55 cm, time 15 s. Washing and elution mode pressure injection, 2 psi, 300 s. Buffer A, 25 mM sodium phosphate, pH 7.4 buffer B, buffer and 1.0 M NaCl. Detection wavelength, 220 nm. (b) ATIII concentration, 4.5 mg/mL. (c) Bovine serum albumin, 0.3 mg/mL. (From Ref. 85.)... 

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