Fractional peak overlap

Simplex Optimization Criteria. For chromatographic optimization, it is necessary to assign each chromatogram a numerical value, based on its quality, which can be used as a response for the simplex algorithm. Chromatographic response functions (CRFs), used for this purpose, have been the topics of many books and articles, and there are a wide variety of such CRFs available (33,34). The criteria employed by CRFs are typically functions of peak-valley ratio, fractional peak overlap, separation factor, or resolution. After an extensive (but not exhaustive) survey, we... 

Fig. 1 Graphical interpretation of the selected elementary criteria (a) resolution, R (b) the peak-to-valley ratio, P (c) the fractional peak overlap, FO.

If a emitters are separated and collected by fraction collection, the preparation of very thin counting sources in a consistent matrix is required to obtain high-energy resolution. These are placed in close proximity to a diode detector, typically in vacuum. Nevertheless, a energy peak overlap can still occur for various combinations of radionuclides if they are not chemically separated, for example, M1AmPPu and 237Np/234U. 

Lower 170 jjlM CbS-Aiug showing a HOMO-LUMO gap. It can be seen that the as-prepared solution contains a residual fraction of AU38 that smears out the charging response in E regions where QDL peaks overlap. The electrode potential was scanned negative to positive.10 (Reprinted with permission from B. M. Quinn et al., J. Am. Chem. Soc. 2003, 125, 6644—6645. Copyright 2003 American Chemical Society.)... 

When collecting fractions from chromatographic separations in which peaks overlap, a judgment has to be made between quality and quantity that is, taking a cut at A (Fig. 14) will result in recovery of the mam compound that IS purer than that obtained if the cut were taken at B, but will mean a lower recovery. 

If the aim is to extract only some material of high purity, it is more sensible to sacrifice some of the compound of interest and take a cut that contains little or none of the peak overlap. If, on the other hand, the emphasis is on isolating the maximum yield, a broader cut should be taken with a view to subsequent purification steps to remove minor contaminants. Additionally, of course, it is often prudent to collect material in a number of fractions so that a majority of compound will be contained in a fairly pure form, and only a small proportion will need to be fiirther purified. (All of these estimations are based on the assumption that both compounds give the same detector response per unit of concentration.)... 

Peak overlap is an important cause of erroneous quantitation. The reason becomes clear when looking at Figure 19.6. If the integrator divides the two peaks by a vertical drop some fractions of their areas become a part of the wrong peak. Similarly, area partition is not accurate if the division is done by a tangent instead of a vertical line (this method is often used for small rider ... 

In these equations (see Fig. 8.15), hj is the height of the valley between two adjacent peaks, h2 the interpolated height between the maxima of two adjacent peaks measured at the abscissa of the valley, W is the total area of a given peak, and w j the area of this peak overlapped by other peaks. The overlapped fractions extends the global function of resolution to all individual peaks in the chromatogram, n-1 should thus be substituted for n ineq. 8.42. 

The low-molecular part of the gamma-fraction could not be evaluated because of the interfering salt peak. After separation into the alkali-soluble and alkali-insoluble fraction an overlapping of the molecular weight fractions was detected showing that parts of the same molecular wei t are both acid soluble and insoluble. 

In the case of citrus essential oils, LC pre-fractionation can be used to obtain more homogeneous chemical classes of compounds for analysis by GC without any problems of overlapping peaks. 

Figure 14.19 Typical GC chromatogram of the separated di-aromatics fraction of a middle distillate sample Peak identification is as follows 1, naphthalene 2, 2-methylnaphthalene 3, 1-methylnaphthalene 4, biphenyl 5, C2-naphthalenes 6, C3-naphthalenes 7, C4-naph-thalenes 8, C5+-naphthalenes 9, benzothiophene 10, methylbenzothiophenes 11, C2-ben-zotliiopIrenes. Note the clean baseline between naphthalene and the methylnaphthalenes, which means that no overlap with the previous (mono-aromatics) fraction has occuned.

An increasing intensity of the diffraction peaks of hematite is observed when comparing the dried and calcined catalyst as shown in Fig. 2(a), indicating that hematite forms at M er temperatures. No obvious diffraction peaks to lithium such as lithium iron oxide (LiFcsOg) could probably be ascribed to the small fraction of lithium or overlapped peaks betwem hematite and lithium iron oxide. The diffraction peak intensity of magnetite in tested catalysts increases significantly. 

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