Peak width, factors influencing

The EMR spectra of the ferrofluid demonstrate a broad line with peak-to-peak width depending on concentration and temperature (Figure 1). The increasing of line width with concentration increasing and temperature decreasing occurs due to dipole-dipole interaction and local ME influence. In diluted suspension at room temperature where dipole-dipole interaction can be neglected the peak-to-peak width is equal to 680 G. It is typical for resonance of microparticles with a broad size distribution of the particles [11-13]. Center of this line at room temperature locates in the ME near 3400 G (g-factor = 2.25). With temperature decreasing the center shifts to lower MFs. 

When the crystallites within a sample are smaller than lOOnm (0.1 p,m) the X-ray reflections are broadened. Diffraction theory indicates that the diffraction peaks should be extremely thin, just a few seconds of a degree. However, all diffraction peaks have a measurable width, as illustrated in Figure 23. This width arises from the divergence of the incident beam and the width of the X-ray source. These factors are termed instrumental broadening and depend upon the instrument used. There is another factor that influences the peak width known as domain size. Even highly ordered crystals are thought to consist of small domains that are... 

The separation is influenced by thermodynamic and kinetic factors. The retention times are dependent on a thermodynamic control while the reduction in the peak widths are dependent on kinetic factors. 

In the following discussion, we will examine the factors that influence peak width and peak shape of a single peak in preparative chromatography. There are three distinct factors, which for the purpose of simplification we will treat separately. 

Before we discuss the influence of pH, additives, and temperature in more detail, we need to understand another important factor for optimization of peak resolution. Peak resolution is affected by the difference in retention time between peaks and the peak shape. We have discussed the intrinsic effect of band dispersion in chromatography, which leads to a symmetrical broadening of peaks. This peak width is described in a standardized way by the plate number. In practical LC, however, perfectly symmetric peaks are rather the exception, and it is an important criterion of method optimization to remove root causes for peak distortion. Every increase in peak asymmetry negatively affects resolution (under otherwise constant conditions). It must be emphasized in this context that Eq. 2.1 in Section 2.2.1 is only valid for Gaussian peaks with perfect symmetry, while any peak distortion will lead to smaller effective resolution. There are cases where the... 

The plate theory does not consider the effects of the carrier gas flow rate and the rate of mass transfer on the peak width, so that it says nothing about the factors which influence the equivalent height of a theoretical plate. According to plate theory, H decreases continuously with increase of flow rate, as distinct from experimental results which reveal a minimum at a certain flow rate. 

Example The influence of relative slit width on peak shape and resolution is demonstrated on the second isotopic peak of toluene molecular ion, m/z 94 (Fig. 4.25). With the entrance slit at 50 pm and the exit slit at 500 pm the peak is flat-topped (left), because a narrow beam from the entrance sweeps over the wide open detector slit keeping the intensity constant as the scan proceeds until the beam passes over the other edge of the slit. Closing the exit slit to 100 pm increases resolution to 2000 without affecting the peak height (middle), but reduces the peak area by a factor of 4 in accordance with an increase in resolution by the same factor. Further reduction of the exit slit width to 30 pm improves... 

Since petroleum wax is a mixture of hydrocarbons with different molecular weights, its transitions occur over a temperature range. This range is one factor that influences the width, expressed in °C, of the DSC peaks. The highest temperature transition is a first-order transition. If, for a series of waxes, there is supporting evidence that the highest temperature transition of each wax is the major first-order transition, its relative width should correlate with the relative... 

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