Number of peaks

The absolute measurement of areas is not usually usefiil, because tlie sensitivity of the spectrometer depends on factors such as temperature, pulse length, amplifier settings and the exact tuning of the coil used to detect resonance. Peak intensities are also less usefiil, because linewidths vary, and because the resonance from a given chemical type of atom will often be split into a pattern called a multiplet. However, the relative overall areas of the peaks or multiplets still obey the simple rule given above, if appropriate conditions are met. Most samples have several chemically distinct types of (for example) hydrogen atoms within the molecules under study, so that a simple inspection of the number of peaks/multiplets and of their relative areas can help to identify the molecules, even in cases where no usefid infonnation is available from shifts or couplings. 

Al Ihe beginning of Ihis seclion we noted lhal an NMR speclrum provides slruc lural mformalion based on chemical shift Ihe number of peaks Iheir relative areas and Ihe mulhphcily or splitting of Ihe peaks We have discussed Ihe lirsl Ihree of Ihese fea lures of H NMR speclroscopy Lei s now torn our attention to peak splitting to see whal kind of information il offers... 

The number of peaks into which the signal for a particular proton is split is called Its multiplicity For simple cases the rule that allows us to predict splitting m H NMR spectroscopy is... 

In the simplest cases the number of peaks into which a signal is split is equal to n + 1 where n is the number of protons to which the proton in question is coupled Protons that have the same chemical shift do not split each other s signal... 

Monomer (Section 6 21) The simplest stable molecule from which a particular polymer may be prepared Monosaccharide (Section 25 1) A carbohydrate that cannot be hydrolyzed further to yield a simpler carbohydrate Monosubstituted alkene (Section 5 6) An alkene of the type RCH=CH2 in which there is only one carbon directly bonded to the carbons of the double bond Multiplicity (Section 13 7) The number of peaks into which a signal IS split in nuclear magnetic resonance spectroscopy Signals are described as singlets doublets triplets and so on according to the number of peaks into which they are split... 

It is equivalent, when an ftk spectrometer is used, to re-apodization of the data. Curve fitting is a method of modeling a real absorption band on the assumption that it consists of a series of overlapped peaks having a specific lineshape. Typically the user specifies the number of peaks to attempt to resolve and the type of lineshape. The program then varies the positions, sizes, and widths of the peaks to minimize the difference between the model and the spectmm. The largest difficulty is in knowing the correct number of peaks to resolve. Derivative spectra are often useful in determining the correct number (18,53,54). 

Thus, the number of peaks in the spectrum corresponds to the number of occupied energy levels in the atoms whose BEs are lower than the X-ray energy hv, the position of the peaks direcdy measures the BEs of the electrons in the orbitals and identifies the atom concerned the intensities of the peaks depend on the number of atoms present and on the a values for the orbital concerned. All these statements depend on the idea that electrons behave independently of each other. This is only an approximation. When the approximation breaks down, additional features can be created in the spectrum, owing to the involvement of some of the passive electrons (those not being photoejected). 

The peak capacity of a column has been defined as the number of peaks that can be fitted into a chromatogram between the dead point and the last peak, with each peak being separated from its neighbor by 4a. The last peak of chromatogram is rather a... 

Thus, assuming that the number of peaks that can be fitted into the chromatogram between the dead time and the time for the complete elution of the last peak is (r), then... 

After metallization of the plasma-modified polyimide, there were a number of peaks in the TOF-SIMS spectra that confirmed the existence of Cu-N bonds as required by the proposed reaction mechanism (see Fig. 28). The most significant... 

At the beginning of this section we noted that an NMR spectrum provides structural infoiination based on chemical shift, the number of peaks, their relative areas, and the multiplicity, or splitting, of the peaks. We have discussed the first three of these features of H NMR spectroscopy. Let s now turn our attention to peak splitting to see what kind of infonnation it offers. 

Multiplicity (Section 13.7) The number of peaks into which a signal is split in nuclear magnetic resonance spectroscopy. Signals are described as singlets, doublets, triplets, and so on, according to the number of peaks into which they are split. 

In oxidized Rieske proteins, a larger number of peaks are observed that have been attributed to vibrations of the iron-sulfur core this is indicative of the reduced symmetry of the iron-sulfur core in Rieske proteins since ungerade vibrations are Raman-inactive in the centro-symmetric (in first approximation) [2Fe-2S]-Cys4 core (point group D2h or Cih) while the corresponding modes are Raman-active in C2 symmetry. The characteristic peak of the SL mode of proteins con-... 

N is the number of data points M is the number of peaks Peakloc(j) is the location of the peak Intensity(j) = lntegral(j)/(pi linewidth)... 

A 3D spectrum of a three-spin subsystem in which all the nuclei are coupled to one another, such as C(H/i)(Hb)-C(Hc), will lead to 27 peaks, comprising six cross-peaks, 12 cross-diagonal peaks (six at o) — o>2 and the other six at 0)2 = (O3), six back-transfer peaks, and three diagonal peaks. However, in the case of a linear three-spin network (e.g., CH -CHg-CHc), the number of peaks will depend on whether two equal (e.g., COSY-COSY or NOESY-NOESY) or unequal (e.g., COSY-NOESY) mixing processes are... 

Ag(l 11) that was emersed from 1 mM NaOH + 0.5 mM NaF at specified potentials. The data were deconvoluted into a number of peaks. Above —0.8 V vs. Hg/HgO, the data indicate the presence of a nnmber of adsorbed oxygen species. They coupled the XPS with thermal desorption in an effort to identify the species. The peaks at 529.6eV and 531.6eV conld be assigned to adsorbed oxygen and OH species, respectively. 

The fluorescence excitation spectrum of a Q-CdS sample, with several maxima in the absorption spectrum, also has a number of peaks. However, the maxima in the two spectra do not always occur at the same wavelengths This effect is not surprising, as excitation at different wavelengths leads to the excitation of particles of different sizes which do not have the me fluorescence intensity at the wavelength where the fluorescence is recorded. 

Another approach to defining the separation capacity of a column is by its peak capacity (the number of peaks than can be resolved at any specific resolution, usually R, i, in a given separation time). For SEC the pe2dc capacity, PCgc, is given approximately by... 

The separating power of a column can Ise expressed as its peak capacity defined as the number of peaks that can be resolved, at any specified resolution level, in a given separation time. For the general case it can be calculated using equation (1.49)... 

Therefore, a 4a separation (R = 1), in which peak retention times differ by four times the width at half-height, corresponds to a 2% area overlap between peaks.1 The maximum number of peaks that could be separated in a given time period assuming a given value of R, is defined as the peak capacity.1 The peak capacity must be greater — usually much greater — than the number of components in the mixture for a separation to succeed. The resolution of two compounds can also be written in terms of the number of plates of a column, N, the selectivity, a, and the capacity factors, k, and k j, as12... 

The IMS response for a compound is strongly dependent on temperature, pressure, analyte concen-tration/vapour pressure, and proton affinity (or elec-tron/reagent affinity). Pressure mainly affects the drift time, and spectral profiles are governed by concentration and ionisation properties of the analyte. Complex interactions among analytes in a mixture can yield an ambiguous number of peaks (less, equal to, or greater than the number of analytes) with unpredictable relative intensities. IMS is vulnerable to either matrix or sample complexity. 

A typical MALDI spectrum of a bacterial sample has a number of peaks that vary greatly in intensity superimposed on a relatively noisy baseline. This can be problematic for many peak detection routines. Therefore methods that eliminate the need for peak detection also eliminate problems associated with poor peak detection performance. Full-spectrum identification algorithms use the (usually smoothed) spectral data without first performing peak detection. 

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