Peak, asymmetrical

Furthermore, in the example given, the peaks were considered to be truly Gaussian in shape. Asymmetric peaks can distort the position or the peak maximum of the envelope to an even greater extent. In general, the retention time of a composite peak should never be assumed to have a specific relationship with those of the unresolved pair. 

Volume overload results from too large a volume of sample being placed on the column, and this effect will be discussed later. It will be seen that volume overload does not, in itself, produce asymmetric peaks unless accompanied by mass overload, but it does broaden the peak. Mass overload, however, frequently results in a nonlinear adsorption isotherm. However, the isotherm is quite different from the Langmuir isotherm and is caused by an entirely different phenomenon. 

Sometimes it is not possible to improve the resolution of a complex mixture beyond a certain level and, under these circumstances, the use of some de-convolution technique may be the only solution. The algorithms in the software must contain certain tentative assumptions in order to analyze the peak envelope. Firstly, a particular mathematical function must be assumed that describes the peaks. The function used is usually Gaussian and, in most cases, no account is taken of the possibility of asymmetric peaks. Furthermore it is also assumed that all the peaks can be described by the same function (i.e. the efficiency of all the peaks are the same) which, as has already been discussed, is also not generally true. Nevertheless, providing the composite peak is not too complex, de-convolution can be reasonably successful. 

The splitting of the asymmetric peak is ascribed to a Jahn-Teller splitting of the excited state which latter involves the open e configuration e ... 

This presents a problem since it is difficult to estimate the area of the peak. One cannot simply extend the baseline as in Case I. A much better solution is that shown in Case II, wherein the two very asymmetrical peaks, i.e.- the initial and final parts of the overall thermal reaction taking place, are delineated. This problem has not been satisfactorily answered as yet and represents a challenge to anyone using DCS methods to characterize a solid state reaction. 

For an approximate determination of the sample composition it is often sufficient to measure the peak height of the core level. In general, however, core level structures are asymmetric peaks above a finite background and sometimes accompanied by satellite structures. These structures originate from the many-body character of the emission process. Therefore a peak integration including satellites and asymmetric tails is much more reliable. Due to the above difficulties quantitative analysis of XPS data should be taken as accurate to only within about 5-10%. 

The relatively poor resolution of the XPS systems has lead to an extensive use of deconvolution techniques in order to prove the presence of shifted core levels of low intensity in the presence of unshifted levels (thin oxide layers on metal substrates). Deconvolution techniques should be used only in those cases where the presence of multi components is shown up by a shoulder in the intensity distribution. Interpretation of asymmetric peaks in terms of chemical shifts can be misleading in some cases because the asymmetry may change due to a change of the electron population at the Fermi level as was demonstrated for the metallic oxide Ir02 [23, 24],... 

Asymmetrical Peaks are rarely found in WAXS from polymers, but they are ubiquitous in the MAXS of liquid crystalline polymers. For asymmetrical peaks in isotropic patterns it is best to determine the peak position from the maximum of the peak, if peak asymmetry is a result of linear or planar disorder. Linear disorder means that the crystals are more or less one-dimensional (a tower of unit cells). Planar disorder means that the crystallites are made from only very few layers of unit cells (cf. Guinier [6] Chap. 7). 

Microfibrillar structure in isotropic materials makes asymmetrical peaks, because microfibrils are materials with linear disorder. Steep is the increase from small scattering angle. The peak shape can be quantitatively analyzed (S tribeck [106]) yielding extra information on the lateral extension of the microfibrils. 

Asymmetrical peaks with a steep decrease towards high scattering angle are typical for data recorded by a slit-focus (Kratky camera). An isotropic and infinitely sharp peak at s0, (J(s) = 8(s — so)), measured by means of an ideal slit becomes... 

Due to the possible change in retention time and peak profile that may take place during day-to-day operation, it is necessary to measure peak characteristics every day to verify the status of the method validation. A blank sample should be evaluated for an analysis run, where the resolution is determined. For asymmetric peaks, the Gaussian equation cannot be used, so the modified equation, using an exponentially modified Gaussian (EMG) method has been proposed [21]. 

The peak is cut from the original chart paper or from a photocopy and weighed on an analytical balance. This method is fairly precise and particularly useful for asymmetrical peaks but is subject to errors arising from variation in thickness and moisture content of the paper. 

The CV shows an asymmetrical peak-shaped current wave or wave couple. The current output increases upon increasing the potential scan rate and it is the potential scan rate that contributes dominantly to the peak shape of the... 

The cyclic voitammogram for Pt (111) in 5 M sulfuric acid is shown in Fig. 2-21. Compared with that in 0.5 M sulfuric acid (Fig. 2-15), the anodic part of the two split hydrogen adsorption-desorption areas was compressed in the cathodic direction and became two sharp peaks while the cathodic part did not change its shape very much. The asymmetric peak at 700 mV shifted cathodicly and became more symmetric and sharp. The oxidation of platinum shifted about 100 mV in the anodic direction. All these changes could be attributed to the increase in specific adsorption of anions or the decrease of the activity of water as well as the pH change. 

However, further milling for 10 and 20 h does not measurably shift the peak maximum to progressively lower temperatures (Fig. 2.29b). Second, a smooth and symmetrical DSC peak of the as-received powder transforms after milling into an asymmetrical peak having a pronounced low-temperature shoulder (Fig. 2.29a,b). The appearance of this shoulder on a DSC pattern can be assigned to the decomposition of mostly y-MgH being formed. 

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