Overlap of peaks

For reasonable quantitative accuracy, peak maxima must be at least 4cr apart. If so, then Rs = 1.0, which corresponds approximately to a 3% overlap of peak areas. A value of Rs = 1.5 (for 6cr) represents essentially complete resolution with only 0.2% overlap of peak areas. These criteria pertain to roughly equal solute concentrations. 

Because of the limited energy resolution in EDX spectra an overlap of peaks can often occur, depending on the composition of the material to be analyzed. The situation is much improved in WDXS, for which the energy resolution is approximately 10 eV and better. This is demonstrated in Fig. 4.25, in which the WDX and EDX spectra recorded from BaTi03 are compared. Here, WDXS enables easy resolution of the Ba-La and Ti-Ka lines this is impossible by EDXS. In addition, for WDXS the... 

Spectra for a series of Cu-Ni alloys have been obtained (91) and these are reproduced in Fig. 11. Because of overlapping of peaks from the component metals, separate indications of each element are only obtained from the 925 eV Cu peak and the 718 eV Ni peak. The results have only qualitative significance because the quoted nickel concentrations are bulk values. Nevertheless, they do suggest that for these particular samples of Cu-Ni alloys, the surface composition varies smoothly from pure copper to pure nickel. Auger spectroscopy has subsequently shown that the surface composition of the (110) face of a 55% Cu-Ni crystal was identical with the bulk composition (95a). Ono et al. (95b) have used the technique to study cleaning procedures argon ion bombardment caused nickel enrichment of... 

When searching for leaks of 3He and 4He mixture, a great care must be used in interpreting the reading of an LD even if the leak of only one of the two gasses is in reality present (e.g. 3He), due to the overlapping of peaks, the LD apparently reveals the presence of the other one (4He). The apparent flux of 4He is usually about 10% of the real flux of 3He. 

Platinum-195-NMR spectroscopy is a useful means to prove isomerization of the HH and HT isomers of Pt(2.0+)2. Both 1H- and 13C-NMR spectroscopies may also be used to examine isomerization (59, 67) however, quite often these are not useful enough because of the overlap of peaks for both isomers and difficulty in assignment. The large... 

The retention time of aziridine and the insertion product [10] are different when each of them is injected separately. However, their peaks are not separated when the mixture is injected. Therefore, peak B is considered as the overlap of peaks due to aziridine and the insertion product. The structure of the product corresponding to peak E could not be determined since its yield was very low as is shown by the low intensity of the peak in Figure 7. 

The overlapping of peaks must be taken into account while using this approach and this is not a trivial task. 

Concentrate peaks 1 and 3 by solvent evaporation until a convenient volume is obtained for injection onto a CP-HPLC column. Separate peaks 1 and 3 individually using two different CP-HPLC runs to avoid overlap of peaks. Elute using 97 3 hexane/2-propanol while monitoring with UV at 232 to 234 nm. 

The arrangement of trans isoprene-units is observed more in detail from the 13C-NMR signal splitting of C-l methylene carbon [94, 97], as shown in Figure 11.19. The mushroom rubber shows two peaks due to the trans isoprene-unit in dimethylallyl-trans and trans-trans linkages similar to those of the two-trans polyprenol. On the other hand, the rubbers from Goldenrod and Sunflower exhibit three peaks similar to the overlap of peaks of two-trans and three-trans polyprenols. This suggests the presence... 

Two-Dimensional Experiments A full NMR analysis of a carbohydrate, in which each lH and 13C peak in the spectrum is assigned to a particular position in the molecule, requires the use of two-dimensional (2D) NMR. In a 2D spectrum, there are two chemical shift scales (horizontal and vertical) and a spot appears in the graph at the intersection of two chemical shifts when two nuclei ( H or 13C) in the molecule are close to each other in the structure. For example, one type of 2D spectrum called an HSQC spectrum presents the chemical shift scale on the horizontal (v) axis and the 13 C chemical shift scale on the vertical (y) axis. If proton Ha is directly bonded to carbon Ca, there will be a spot at the intersection of the H chemical shift of Ha (horizontal axis) and the 13 C chemical shift of Ca (vertical axis). Because the peaks are spread out into two dimensions, the chances of overlap of peaks are much less and we can count up the number of anomeric and... 

Figure 14.11 shows the l3C-NMR spectrum of 3-buten-2-one. In contrast to H-NMR, the peak for each carbon appears as a sharp singlet. Chemical shifts are measured by using the carbons of TMS as a standard. The chemical shift range is much larger in l3C-NMR than in H-NMR—peaks appear as far as 240 ppm downfield from TMS. Therefore, overlap of peaks resulting from different carbons occurs much less often than overlap of hydrogen peaks. It is usually possible to count all of the different types of carbons in a compound by examination of its l3C-NMR spectrum. 

Quinine is an optically pure derivatizing reagent that forms a diastereomeric mixture of salts whose 13c NMR spectrum would be expected to show individual peaks for the diastereomers present. A 13c NMR of the salt formed from 1 equivalent of quinine and 1 equivalent of racemic acid (V) revealed two peaks for the carbon atom 3 to the carbonyl group. The NMR (25.2 MHz) of the salt of the partially resolved acid (Figure 1) indicates that the ratio of diastereomers is approximately three to one (optical purity 75%). As is seen in the expansion, overlap of peaks precludes precise determination of enantiomeric composition, but a more powerful instrument should completely resolve the two peaks. We are currently investigating the generality of this procedure. 

Furthermore, certain prerequisites of HPDC were stated, such as the Emit of the mobile phase flow velocity, slight overlapping of peaks during fractionation, etc. 

The flame ionization detector (FID) is still widely applied for the detection and quantitation of some of the essential oil components, such as terpenoids. As usual in GC/FID, the primary criterion for the identification of peaks is the comparison of the standard retention times with the retention times of peaks in the sample s chromatogram. However, this procedure is sometimes not useful as the identification is quite difficult and overlapping of peaks makes determination not possible. 

However, this evidently improved approach in instrumentation is only available to relatively few regions of chromatographic analysis, as overlapping of peaks in the same area can be too complex for a complete resolution... 

The As-HAO system presents special difficulties for IR and XAFS spectroscopic analysis. In an XAFS spectrum, the magnitude of peaks in the Fourier transformed EXAFS spectrum is a function of several variables, two of which are atomic number (z) and distance from the central As atom. With only half as many electrons as Fe, the scattering power of Al is weak, therefore peaks representing As-Al scattering in the Fourier-transformed EXAFS are smaller and more difficult to interpret. IR and Raman spectra of As(V) sorbed on gibbsite are difficult to interpret for an entirely different reason substantial overlap of peaks representing Al(V)-0/Al-OH vibrations and As(V)-0/As(V)-OH vibrations (Myneni et al, 1998). 

Assignment of all peaks in the 13C NMR is difficult because of I3c-3lp coupling and the overlapping of peaks. 

In Eq. (13), Wi and W2 are measured at the base of each peak. For Gaussian peak distributions, these widths equal 4a, and a column resolution of 1.0 means that there is 4.6% overlap of peak 1 in peak 2 and vice versa a resolution of 1.5 means there is 0.3% overlap between the two peaks. Generally, the resolution for a given separation can be increased by lengthening the column and, thus, increasing the number of theoretical plates. Here again, the trade-off for this increased resolution is a longer retention time. 

As the rotation rate increases, the peaks shift to a greater elution angle (Fig. 1.4). The rotation rate also affects the peak width, with an increase in the rate resulting in band broadening. Overlapping of peaks in the purification of lipase has been reported by Genest et al. [50]. 

The parameter B determines the line width of the peaks in an RDF. B depends on the resolution of distances, that is, the step size used for calculating the RDF descriptor components. With decreasing B and increasing number of atoms, an RDF descriptor usually exhibits increasing overlap of peaks. Overlaps in RDF descriptors are not necessarily a disadvantage it can be a desired property for the processing of RDF descriptors with methods that rely on interpolation, such as artificial neural networks (ANNs). The relationship between B and the resolution Ar is... 

The increased resolution that is gained by the addition of another frequency dimension is not without cost. Acquiring the three-dimensional cube is equivalent to acquiring 32 to 128 two-dimensional spectra. If the two-dimensional spectra required 8 h, to obtain, the three-dimensional spectrum will require 24 to 64 h, depending on how many different slices are required and how much time is spent acquiring each slice. However, it is clear that the two-dimensional spectra cannot be analyzed owing to severe overlap of peaks, while the three-dimensional spectra can be analyzed. 

Normally you will be given two 13C-NMR spectra (Fig. 29.11). The upper spectrum, which is more complex (more lines) is called the off-resoncince decoupled spectrum and shows the 13C-LH coupling to enable you to determine which carbon signals are CH3, CH2, CH and C. Then overlapping of peaks may make the identification of different carbon atoms difficult. The... 

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