Fractionation mode

There are two ways to operate the stop-flow mode. The by-level mode, which is based upon the defined count zone(s), operates by signaling the instalment to continue running until a radioactive peak above a designated level is detected. The instrument will then stop and count the predefined fraction (in seconds), which is defined in the count zone. A second way to operate the stop-flow mode is the by-fraction mode. The instalment will stop and count every fraction (in seconds) within the predefined count zone, regardless of whether any radioactivity is detected or not. The fraction size in the stop-flow mode and the volume of liquid scintillant used for counting can be automatically calculated by the instalment or the parameters can be defined by the user. 

By the use of different modes of liquid chromatography it is possible to separate polymers selectively with respect to hydrodynamic volume (molar mass), chemical composition or functionality. Using these techniques and combining them with each other or with a selective detector, two-dimensional information on different aspects of molecular heterogeneity can be obtained. If, for example, two different chromatographic techniques are combined in a cross-fractionation mode, information on CCD and MMD can be obtained. Literally, the term chromatographic cross-fractionation refers to any combination of chromato-... 

These two equations are plotted in Fig. 25, from which it is seen that in a perfectly mixed crystallizer the dominant-size fraction (mode) appears at l/L = 3. Saeman illustrated his analysis with data from large-scale vacuum crystallization of ammonium nitrate (M9, SI). 

This book covers some of the significant advances in hyphenated chromatographic separation methods for polymer characterization. Chromatographic separation techniques in this volume include size-exclusion chromatography, liquid chromatography, and field flow fractionation methods that are used in conjunction with information-rich detectors such as molecular size-sensitive or compositional-sensitive detectors or coupled in cross-fractionation modes. 

Within batch chromatography there exist many approaches for optimization. Basically, though, they can be classified into two approaches, which differ in their fractionation mode or cut strategy (Fig. 7.6). 

FIGURE 10.5 Analysis of two radioactive compounds using stop flow HPLC-RFD (a) nonstop mode (b) stop by fraction mode and (c) stop by level mode. Radioactivity in stop by fraction and stop by level analyses were counted for 1 min each fraction. 

FIGURE 10.11 Quantification of muraglitazar glucuronide in the incubation with UGTl A3 by off-line HPLC-LSC (four fractions per min) (top panel) and online stop-flow HPLC-RFD (operated with the stop by-fraction mode) (bottom panel). 

Fractionation Equipment. Similar to molecular weight fractionation, most of the conventional equipment for crystallization fraction is rather simple and requires significant operator time. Fully automated crystallization fractionations are possible using mc2-PREP, in both Crystaf-mode and TREF-mode (the c2 in mc2-PREP stands for these two fractionation modes). 

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