Peaks tailing

In practice, the calculation of peak skew for highly tailing peaks is rendered difficult by basehne errors in the calculation of third moments. The peak asymmetry factor, A, = b/a, at 10 percent of peak height (see Fig. 16-32) is thus frequently used. An approximate relationship between peak skew and A, for taihng peaks, based on data in Yau et al. is Peak skew= [0.51 -t- 0.19/(A, — 1)] . Values of A, < 1.25... 

Tailing peaks or longer than expected elution volumes are sometimes caused by low solubility of the protein in the mobile phase. Using a trial-and-error process, select the proper pFf and ionic strength to address this problem. Detergents such as sodium dodecyl sulfate (SDS) are sometimes helpful but, because they change the conformation of many proteins and are difficult to remove from the column should be used only if other methods fail. 

Tailing peaks The column is deteriorating (often caused... 

The column needs to be reconditioned after about 12h of use or whenever the RPA 202248 peak has shifted to a retention time greater than about 6 min. To recondition, the column should be flushed with 100% acetonitrile for 15 min and then stored in that solvent for about 8 h before re-use. Storing columns in mobile phase will result in an extremely long retention time and a tailing peak for RPA 202248. Just before use the columns will have to be conditioned with the mobile phase for 5-30 min or until the RPA 202248 peak is fully separated from the isoxaflutole peak. 

For all degrees of peak overlap it is well established that peak height is a more accurate measure of sample size than peak area for symmetrical peaks (277,279). For either method the error increases for disproportionate peak sizes. For tailed peaks errors in either peak height or area can assume large proportions using perpendicular drop method (279,281). In general, the most... 

Overloading effects seem even more complex at intermediate pH because silan-ols are now partially ionized and involved in the retention of bases. As mentioned previously, the overload of now-ionized silanols could at least be part of the cause of tailing peaks, even when very small amounts of ionized base are used [18,24]. However, it has been observed that as solute mass increases in experiments at pH 7, column efficiency may improve from an initially low value to a maximum, afterward declining in the usual way [33]. This observation could be due to the blocking or saffiration of ionized silanols by a portion of the sample, such that the rest interacts mainly by hydrophobic processes, resulting in better efficiency. At higher pH still, the solute should not be ionized if appreciably above its p a and therefore should... 

What is the reason for the overwhelming acceptance of stationary phases based on high-purity silicas in the pharmaceutical industry The answer is simple superior peak shapes for analytes with basic functional groups, which has been a problem with older phases. The older, low-purity silicas contain metal ions buried in the matrix of the silica. These contaminants acidify the surface silanols, and the consequence is a strong and non-uniform interaction with basic analytes. This in turn results in tailing peaks, which is an impediment for accurate peak integration and peak resolution. Of course, adding appropriate additives, such as amine modifiers, to the mobile phase can solve these difficulties. But this is an unnecessary and undesired complication in methods development. Therefore, silicas that are free from this complication are much preferred. 

Suppression of tailing peaks, especially for samples containing basic compounds... 

The origin of tailing peaks of basic compounds in reversed-phase chromatography has been an issue in the chromatographic literature for many years. Erom the foregoing discussion, it follows... 

In the specific case of the tailed sapphyrin carboxylates 5 and 6, for which evidence of self-assembly was noted in the solid state (vide supra), H NMR spectroscopic studies carried out in 4-methanol, d-chloroform, and mixtures of the two solvents showed strong line broadening, and upfield shifts of the methylene tail peaks. Such findings are, of course, fully consistent with the proposed dimerization. Further, dilution experiments performed over a concentration range of 50 to 5 mM in these solvents showed little change in the spectra, indicating that the dimeric form prevails under these conditions, even in highly polar solvents. In the case of 6, the actual dimeric stoichiometry was confirmed by vapor pressure osmometry (VPO) measurements carried out in 1,2-dichloroethane. 

Coreduction of Au and Pt ions by refluxing alcohol in the presence of PVP gives the colloidal dispersions of Au-core/Pt-shell structured bimetallic nanoparticles, as mentioned before. The formation of this bimetallic nanoparticles was traced by in situ UV-Vis spectra (68). The spectral change is shown in Figure 9.1.15, in which the peaks ascertained to be the metal ions disappear at first, and then the broad tailing peaks due to the colloidal dispersions appear. More precisely speaking, the tetrachloroauric(III) acid (at —320 nm) is reduced first, followed by reduction of hexachloroplatinic(IV) acid (at —265 nm). This order of reduction is consistent with the standard redox potential of the two metal ions. After the reduction of two... 

Tertiary amines can also be selectively derivatized with citric acid on acetic acid anhydride, a mixture that is mixed with the eluent after chromatography and then heated to 393 K to develop a violet-red color (237). Absorbance is measure at 550 nm but some compounds can show strongly tailing peaks. 

Free Fatty Acids. In our gas chromatographic analyses of brandy extracts prepared for fatty acid ester measurements, free fatty acids also emerged as broad tailing peaks at the end of the programmed temperature run. Free fatty acids have been identified as components of various... 

When the starting point is reached the dial reads a number proportional to the area. On some planimeters the number is proportional to area via a settable scale factor. On other instruments the factor must be determined by measuring a known area. The major advantage of the technique is the ability to handle distorted and tailing peaks to produce a true area. The major problems are the painstaking nature of tracing the peak and the use of a tool not normally found in a laboratory. 

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