Induced peak

The silanol induced peak tailing is also a function of the pH of the mobile phase. It is much less pronounced at acidic pH than at neutral pH. Therefore many of the older HPLC methods use acidified mobile phases. However, pH is an important and very valuable tool in methods development. The selectivity of a separation of ionizable compounds is best adjusted by a manipulation of the pH value. The retention factor of the non-ionized form of an analyte is often by a factor of 30 larger than the one of the ionized form, and it can be adjusted to any value in between by careful control of the mobile phase pH. This control must include a good buffering capacity of the buffer to avoid random fluctuations of retention times. 

Fraction collection from analytical systems When collecting fractions, whether manually or automatically, be sure that the leads from the detector to the fraction collector are narrow-bore metal tubing rather than plastic as the latter may induce peak broadening and potential loss of material. 

The procedure is to extract by deconvolution from the measured emission probabilities the surface density of occupied states for energies between the Fermi level and about 10 eV below that, and to predict the relative atomic positions from that information about the electronic structure of the surface for example, adsorbate-induced peaks will occur, that depend on the adsorbate and its position, as in UPS. This technique is primarily sensitive to the outermost atoms of the surface, in particular adsorbates, since the emitted electrons originate from those regions only. The difficulties in deconvoluting and interpreting the density-of-states information have limited the use of INS. 

FIG. 8.4 Determination of the microenvironment of a molecule (a) a portion of the ultraviolet spectrum of benzene in (1) heptane, (2) water, and (3) 0.4 M sodium dodecyl sulfate and (b) ratio of the intensity of the solvent-induced peak to that of the major peak for benzene versus the index of solvent polarity. The relative dielectric constant is also shown versus the index of polarity. (Redrawn, with permission, from P. Mukerjee, J. R. Cardinal, and N. R. Desai, In Micellization, Solubilization and Microemulsions, Vols. 1 and 2 (K. L. Mittal, Ed.), Plenum, New York, 1976.)... 

One of the best studied sensor material is YAG doped with Sm3+, whose most intense luminescence feature is a doublet at 16 186.5 cm-1 and 16 231.5 cm-1 (Yi and Y2 lines). This doublet has been studied at room temperature up to a maximum pressure of 180 GPa (Bi etal., 1990 Yusaetal., 1994 Liu and Vohra, 1994) and it was found that the pressure-induced peak shift is comparable to the Ri shift of ruby. At the same time, the temperature-induced shift is almost two orders of magnitude smaller than the observed shift for the Ri peak. In fact, measurements at elevated temperatures up to 900 °C and 10 GPa (Hess and Exarhos, 1989 Hess and Schiferl, 1990) as well as studies at temperatures above 400 °C up to 25 GPa, indicated that the pressure could be determined from the Sm3+ luminescence without any temperature correction in this range (Hess and Schiferl, 1992). 

Fig. 5.19 Tracings of DSC thermograms of DPPS alone and in presence of MDR modifiers at a lipid-drug ratio of 1 0.05 (drug concentration of the ionized form). The small peaks on the left of the main phase transition peaks represent the drug-induced peaks, Tinj. A control B trifluperazine ...

The Si-H bonds add further features to the density of states distribution. The Si-H bonding electrons are more localized than the Si-Si states and lead to sharper features in the density of states. One set of calculations, shown in Fig. 3.4, finds a large hydrogen-induced peak... 

System peaks arise when one or several components of the mobile phase are adsorbed on the stationary phase, and because their concentrations are such that their adsorption isotherms are not linear. Injection of the sample in the multicomponent mobile phase perturbs the equilibrium of the strong solvent(s) or other additives of the mobile phase, which is nonlinear. As a result of this perturbation, more peaks may be recorded than there are components in the injected sample. For example, the injection of a sample of the pure weak solvent may generate as many peaks as there are additives in the mobile phase, if these additives are all adsorbed by the stationary phase. These extra peaks have received a variety of names in the early literature. They have been called system peaks, pseudopeaks, ghost peaks, eigen peaks, vacancy peaks, induced peaks, etc. We call them system peaks. Note that not all system peaks are recorded this depends on the type of detector used. Also, system peaks may be positive or negative, depending on the experimental conditions. 

Identified possible substances to be indican, kynurenic acid, tryptophan, and 5-hydroxy-3-indoleacetic acid Sera and hemodialysate was filtered used reversed-phase HPLC with fluorescence detection, cochromatography, and arylsulfatase-induced peak shift... 

In polyvalent liquid elements, the existence of an electronically induced peak or shoulder at the high K-value side of the first peak close to 2kF is quite common [5.54] and has successfully been ascribed to preferred positions of the ions at medium-range distances [5.8,11], The matching of the ionic positions with... 

Structural effects on the DOS have been shown. There is an MDOS close to f due to the electronic induced peak at Kp(. as well as an MDOS well below F due to the peak at Kp. The latter could only be shown for liquid elements. The depth of the MDOS at F is proportional to the structural weight S(2kF). 

Although this approach works in principle with uniformly 15N-labeled protein, it is more favorable in combination with selective amino acid labeling. First, in the absence of a spin-labeled inhibitor, the specific amino acid resonances are identified when compared to the spectra recorded from uniformly labeled kinases. The number of peaks is reduced and therefore more manageable if the spin-labeled inhibitor is added in a second step. Especially in regions with aggravated signal overlap, the selective labeling technique clearly separates the peaks and, therefore, enables the quantification of the induced peak attenuation. 

Fig. 4.22 Photoemission spectra taken in normal emission with hv = 16.85 eV for a smooth Gd film being pre-exposed to 1 L hydrogen as a function of CO dosage. With increasing offer the hydrogen induced peak at a binding energy of 4 eV completely disappears whereas around 2 eV a broad structure shows increasing intensity. Reprinted with permission from [3]. Copyright (1999) by the American Physical Society...

To explain the potential-induced peak fading and consequently the compaction to the TT-state (Section 4.3.1.2.1.) two further processes are invoked ... 

In addition to a sample peak, some anomalous peaks often appear in chromatograms. when multicomponent eluent is used [ref. 71, 72]. Such an induced peak can be observed when polyelectrolyte is chromatographed using a simple electrolyte solution as eluent the first peak corresponds to polyelectrolyte and the second to an induced peak which has the elution volume exactly the same as that of the eluent salt [ref. 33, 45-48, 73-76]. This effect of polyelectrolytes in exclusion chromatography has been explained in terms of Donnan salt exclusion established on the gel [ref. 33, 45-48, 73-76] a polyelectrolyte is barred from the gel interior and thus promote the diffusion of the penetrable eluent coion into the inner volume of the gel, the gel matrix acting as a semipermeable membrane. The eluent coion thus excluded from the polyelectrolyte zone produces an induced peak. It has been reported that the area of the induced peak allows to calculate the Donnan salt exclusion parameter [ref. 33, 74] or the osmotic coefficient [ref. 46-48, 76] of the polyelectrolyte. 

Similar induced peaks also appear in the chromatogram obtained by the elution of inorganic ions with a salt eluent [ref. 12, 16, 23, 26, 33, 55, 77]. For instance, when magnesium chloride is eluted on Sephadex G-15 with sodium chloride solution, the elution curve obtained by argentometry shows two peaks, one peak... 

The area of the induced salt peak depends on the charge and the concentration of the sample ion. Kadokura et al. [ref. 33] have recently attempted to evaluate quantitatively the area of the induced peak on the basis of the Donnan equilibrium. They assumed that chloride, sulphate and naphthalene-1,3,6-trisu1phonate anions used as sample ions are excluded by Sephadex G-10 gel, but not the eluent anion (nitrate ion) and the common cation (sodium ion), and demonstrated that the amount of the eluent colons (in moles) excluded from the sample zone, can be related to the total amount of sample ions injected (in moles), Q, by the following equation... 

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