Chemical tailing

Electrophoretic fraction III chemical tail peptide (1-13) Di-DNP-Lys 0.55 1.0 (Grig. NHj-termi-nal Lys)... 

Chemical Tailing, Incompatibility of Sample with Stationary and/or Mobile Phase... 

Figure 2.24 Chemical tailing of a basic analyte. Conditions sample, 2,3-xylidine, 2,3-dimethylphenol, and m-xylene column, 25 cm x 4 mm i.d. stationary phase, LiChrospher 60 RP-Select B, 5ixm mobile phase, 1.5mlmin water-methanol (35 65) UV detector, 260 nm.

You injected ionic solutes, interacting with ionic parts of the stationary phase (residual silanol groups, metal ions). The slow adsorption kinetics and especially the slow desorption results in chemical tailing. 

In an actual case, what is the cause of the tailing Is it chemical tailing or is it due to the packing quality ... 

What can be the reasons for a change in retention times 81 I use up a lot of RP columns what should I do 83 Why does my normal-phase system not work any more 85 Chemical tailing at the presence of metal ions 87 How to avoid memory effects 91... 

Therefore, one can conclude that it is not the ionic interactions per se that are responsible for the chemical tailing. However, if as a consequence of some mechanisms - in this case ionic interactions — the kinetics of the desorption of the analytes from the surface of the stationary phase is slowed down, then tailing will result. 

While most vesicles are formed from double-tail amphiphiles such as lipids, they can also be made from some single chain fatty acids [73], surfactant-cosurfactant mixtures [71], and bola (two-headed) amphiphiles [74]. In addition to the more common spherical shells, tubular vesicles have been observed in DMPC-alcohol mixtures [70]. Polymerizable lipids allow photo- or chemical polymerization that can sometimes stabilize the vesicle [65] however, the structural change in the bilayer on polymerization can cause giant vesicles to bud into smaller shells [76]. Multivesicular liposomes are collections of hundreds of bilayer enclosed water-filled compartments that are suitable for localized drug delivery [77]. The structures of these water-in-water vesicles resemble those of foams (see Section XIV-7) with the polyhedral structure persisting down to molecular dimensions as shown in Fig. XV-11. 

Another important class of materials which can be successfiilly described by mesoscopic and contimiiim models are amphiphilic systems. Amphiphilic molecules consist of two distinct entities that like different enviromnents. Lipid molecules, for instance, comprise a polar head that likes an aqueous enviromnent and one or two hydrocarbon tails that are strongly hydrophobic. Since the two entities are chemically joined together they cannot separate into macroscopically large phases. If these amphiphiles are added to a binary mixture (say, water and oil) they greatly promote the dispersion of one component into the other. At low amphiphile... 

It is easy to see that the full shape of the orbital is better represented by the sum of these two Gaussians, especially at the tail of the cur ve where chemical bonding takes place, than it is by one Gaussian. When we run an STO-2G ab initio calculation on the hydrogen atom using the GAUSSIAN stored parameters rather than supplying oirr own, the input file is... 

Most uranium ore has a low, ca 1 part in 500, uranium content. Milling involves physical and chemical processing of the ore to extract the uranium. The mill tailings, which release gaseous radon-222 [13967-62-9] Ra, half-life 3.82 d, are placed in large piles and covered to prevent a local health problem. 

Chemical Grafting. Polymer chains which are soluble in the suspending Hquid may be grafted to the particle surface to provide steric stabilization. The most common technique is the reaction of an organic silyl chloride or an organic titanate with surface hydroxyl groups in a nonaqueous solvent. For typical interparticle potentials and a particle diameter of 10 p.m, steric stabilization can be provided by a soluble polymer layer having a thickness of - 10 nm. This can be provided by a polymer tail with a molar mass of 10 kg/mol (25) (see Dispersants). 

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