Peaks unresolved

Peak. That portion of a differential chromatogram recording the detector response or eluate concentration when a component emerges from the column. If the separation is incomplete, two or more components may appear as one peak (unresolved peak). 

Sense wide variety of compounds Sense peaks unresolved from background... 

The EDX spectrum of the nylon membrane (not shown) presents the characteristic peaks assigned to the C, O and N Ka lines, the last two as a single broad peak unresolved due to their proximity and small concentration. The presence of these chemical elements corresponds to the chemical formulation of polyamide [26]. The EDX study of supported ionic liquid membranes is based on the selection of characteristic elements of interest in each ionic liquid, for example F and P for [bmimq... 

Another serious error can occur if it is known that there are two peaks which are unresolved, and the retention time of the maximum of the envelope is taken as the mean retention time of the two isomers. This measurement can only be true if the peaks are absolutely symmetrical and the two peaks are of equal height. The effect of different,proportions of each isomer on the retention time of the composite envelope is shown in Figure 3. It is seen that the position of the peak maximum of the composite envelope is significantly different from the mean of the retention times of the individual peaks. 

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. 

The fact that we have peaks within a 2D space implies that where no peak is found represents a true detector baseline or electronic noise level. In a conventional petroleum sample, a complex unresolved mixture response causes an apparent detector baseline rise and fall throughout the GC trace. It is probably a fact that in this case the true electronic baseline is never obtained. We have instead a chemical baseline comprising small response to many overlapping components. This immediately suggests that we should have more confidence in peak area measurements in the GC X GC experiment. 

The PL spectrum and onset of the absorption spectrum of poly(2,5-dioctyloxy-para-phenylene vinylene) (DOO-PPV) are shown in Figure 7-8b. The PL spectrum exhibits several phonon replica at 1.8, 1.98, and 2.15 eV. The PL spectrum is not corrected for the system spectral response or self-absorption. These corrections would affect the relative intensities of the peaks, but not their positions. The highest energy peak is taken as the zero-phonon (0-0) transition and the two lower peaks correspond to one- and two-phonon transitions (1-0 and 2-0, respectively). The 2-0 transition is significantly broader than the 0-0 transition. This could be explained by the existence of several unresolved phonon modes which couple to electronic transitions. In this section we concentrate on films and dilute solutions of DOO-PPV, though similar measurements have been carried out on MEH-PPV [23]. Fresh DOO-PPV thin films were cast from chloroform solutions of 5% molar concentration onto quartz substrates the films were kept under constant vacuum. 

Modem data processing software includes routines that can be used to obtain accurate quantitative results from chromatograms where the components of the sample are incompletely resolved. The routines, in fact, deconvolute the individual peaks from the composite envelope and calculate the area of the individual de-convoluted peaks. Such algorithms can be used very effectively on peaks that are entrained in the tail of a major peak but are not so accurate for composite envelopes containing many unresolved peaks. 

In some data acquisition and processing systems, software is included that mathematically analyze convoluted (unresolved) peaks, identify the individual peaks that make up the composite envelope and then determine the area of the individual peaks. 

The NMR spectrum of the dry sample showed broad unresolved peaks that correspond to a typical mixture of 4-O-methyl-D-glucuronic acid, L-arabinose and D-xylose, and proteins (Oliveira et al., 2010) (Figure 5). 

There are three main reasons for this choice. Firstly, it becomes more and more difficult to obtain recordable, molecular-ion signals from un-derivatized carbohydrates as their M, increases significantly above 3000. Secondly, the mass spectrometers that have been used in all high-mass-carbofiydrate studies published at the time of writing this article are not capable of very sensitive analysis above —3800 mass units (see later). Thirdly, at masses >4000, it is usually not practicable to work at the resolution necessary for adjacent peaks to appear as separate signals in the spectrum. To do so would require that the source and collector slits be narrowed to such a degree that there would be an unacceptable loss in sensitivity. Thus, spectra acquired at mass >4000 are usually composed of unresolved clusters. 

Fig. 6.—One of the Molecular-ion Clusters Obtained from a Sample of Deuteropermethy-lated. Cyclic /3(l- 2)-Glucans (see Section VI,S). [All high-mass samples give unresolved clusters of this type if the mass spectrometer is operated at low resolution. The peak is 6 mass units wide at half height. The mass is assigned by using the mass marker, which gives marks every 4 mass units, as shown. The center of the peak corresponds to the chemical molecular weight of an [M + NKJ species.]...

Within a few exceptions, all singlet states can be correlated to an observed experimental feature. Especially, the high density of states around 11.8 and 12.7 eV is compatible with the observation of unresolved broad peaks in the 11.6-11.9 eV and 12.5-12.8 eV spectral intervals [60], Unfortunately, the lack of spectroscopic resolution makes any unambiguous one-to-one assignment impossible in these regions. 

It is important to note that expression (23) can be applied to the crystalline phase intensities only if we include, in the first integral, its own smooth diffuse background and not just the intensity belonging to the crystalline peaks. In fact, a pure crystalline sample also has a smooth background due to the incoherent inelastic scattering (i.e. Compton scattering), the TDS, disorder scattering and, very often, unresolved tails of overlapped peaks. 

GCxGC is most often applied for target analysis. Main application areas for GCxGC are to be found where unresolved peaks are the norm, i.e. for atmospheric organics (e.g. urban air), food and flavour (organoleptics), (petro)chemical and forensic analyses,... 

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