Organic compounds Peak shape

A typical IR spectrum such as that of hexane m Eigure 13 31 appears as a series of absorption peaks of varying shape and intensity Almost all organic compounds exhibit a peak or group of peaks near 3000 cm due to carbon-hydrogen stretching The peaks at 1460 1380 and 725 cm are due to various bending vibrations... 

Gaussian curves (normal distribution functions) can sometimes be used to describe the shape of the overall envelope of the many vibrationally induced subbands that make up one electronic absorption band, e.g., for the absorption spectrum of the copper-containing blue protein of Pseudomonas (Fig. 23-8) Gaussian bands are appropriate. They permit resolution of the spectrum into components representing individual electronic transitions. Each transition is described by a peak position, height (molar extinction coefficient), and width (as measured at the halfheight, in cm-1). However, most absorption bands of organic compounds are not symmetric but are skewed... 

Mobile phases are usually binary or ternary mixtures of solvents. Selectivity is affected mostly by mobile phase composition rather than strength, and peak shape and retention are both influenced by the addition of organic modifiers.101 Some compounds naturally have 77-donor or 77-acceptor groups and can be resolved directly. In many cases, however, introduction of 77-donating groups by derivatization steps is necessary. Figure 2.20 shows the proposed three-point interaction of 3-aminobenzo[a]pyrene, a polycyclic aromatic hydrocarbon (PAH), with a Pirkle-type stationary phase.111 Two possible interactions are illustrated, showing the best orientations for maximum interaction. 

Small organic (e.g., formic and acetic) acids are effective volatile IPRs. They impact the retention behaviors of pH-sensitive compounds, changing their charge status and providing pairing anions that may easily interact with protonated solutes. Many chromatographic separations benefit in terms of retention, resolution, and peak shape under acidic conditions due to suppression of silanol activity. Furthermore, the acidity of these IPRs facilitates the formation of the protonated molecular ion [M + H] measured by mass spectrometry in the usual positive ion mode. 

In most of the methods reported, the mobile phase contained organic solvents such as acetonitrile and methanol with buffers of various pH values. This resulted in improved peak shapes, reduced tailing, and good separation for analysis of ezetimibe in combination with other compounds. It should also be noted that the percentage of acetonitrile in... 

The result of all three of the chemical modification schemes described here is to eliminate or drastically reduce EOF. In some cases, the EOF can be reversed by the attachment of a positively charged group, such as R — NH3, to the surface. Whether the EOF is diminished, eliminated, or reversed, separation is improved because electrophoretic mobility differences are enhanced. The replacement of silanols by various organic moieties also has beneficial effects with respect to the separation of basic compounds. An example of the difference in peak shapes seen for bare and modified capillaries is shown in Fig. 1. In some cases. 

For basic compounds, 0.1% acid should be mixed with the organic component, whereas water or neutral buffer should be used for neutral or acidic species. The previously discussed buffers can be used as the aqueous component to improve peak shape and resolutions by providing greater control of pH. 

DST methods are particularly competitive for organic compounds, which are more resistant to the traditional approaches and whose structural models can be easily guessed. At present, the complexity of crystal structures solved by direct-space methods is essentially limited by the number of DOFs that can be handled by the global optimization algorithms within a reasonable amount of time. In prospect, improvement of both search algorithms and computer power may overcome this limitation. The major pitfalls for the use of DST are (a) they are time consuming (b) they are dependent on the existence of reliable prior structural information. Partially incorrect models may compromise the success of the procedure independent of the computer time spent (c) they are sensitive to the accuracy of the peak profile parameterization through peak-shape and peak-width functions. ... 

Recently, organic sulfonic acids have been suggested as normal-phase and SFC additives to improve peak shapes for basic analytes [125]. These strongly acidic additives proved particularly beneficial for the separation of a broad variety of amines on a CHIRALPAK AD CSP under normal-phase conditions. The addition of ethanesulfonic and methanesulfonic acid allowed successful separation of a selection of amines which had failed to resolve wifh less acidic additives.The enantiomer separation of a basic drug compound employing ethanesulfonic acids and trifluoroacetic acid is shown in Fig. 7.8. 

Actually some chemical activities as refineries are not so variable on the point of view of wastewater quality because of the large quantities of primary matter and products (Fig. 2). Near units, the UV spectrum shape often shows peaks due to the presence of additives used in the process, acting as revelatory of the organic pollution load [3], Without these compounds and considering that saturated organic compounds do not absorb, it would be difficult to use the UV signal for wastewater quality control. However, a nonparametric measurement (NPM) based on comparison of the UV absorption spectra can be used for the characterisation of wastewater quality variability [4], Obviously, as far as wastewater... 

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