Organic modifier effect column

Robustness testing is performed to examine the effect of operational parameters on the analysis results. Typical parameters to evaluate are mobile phase pH, mobile phase flow rate, percentage of organic modifier, and column temperature. To examine the effect of variation in pH when the mobile phase pH is, say, 5.5, analyses are carried out at, for example, pH 5.3 and 5.7. If no significant change in... 

Note that the interfacing of LC techniques with MS puts significant constraints on the solvents that can be used i.e., they must be volatile, with a low salt concentration, for MS compatibility. Narrow-bore columns, which use much smaller amounts of salt and organic modifier, appear to have potential for facilitating IEC-MS applications.40 Despite the excellent sensitivity of MS detection for most elements, however, there are cases where matrix effects can interfere. In this situation, combination of IEC with atomic emission spectrometry (AES) or atomic absorption spectrometry (AAS) may be preferable, and can also provide better precision.21 32 4142 Other types of... 

Fig. 25. Effect of percentage of acetonitrile (A) and methanol (B) on electroosmotic mobility in a packed column. (Reprinted with permission from [56]. Copyright 1997 Elsevier). Conditions capillary column 100 pm i. d., total length 33.5 cm, active length 25 cm packed with 3 pm CEC Hypersil C18, mobile phase organic modifier-water+4% 25 mmol/1 TRIS pH = 8, voltage 30 kV, temperature 20 °C, marker thiourea... 

Figure 4.5 Effect of organic modifier on peptide retention. Synthetic octapeptides of the structure described in Figure 4.1 were separated by gradient elution on an octyl column using aqueous-organic systems containing a constant TFA concentration of 0.1%. (Reproduced from D. Guo, C.T. Mant, A.K. Taneja, J.M.R. Parker, and R.S. Hodges, J. Chro-matogr., 359 499 [1986]. With permission from Elsevier Science.)...

Figure 4.7 Effect of high organic modifier concentration on peptide retention. Data obtained using an octadecyl column and 20 mM ammonium acetate acetonitrile mobile phases. (Reproduced from C.T. Wehr and L. Correia, LC at Work LC-121, Varian. With permission from Varian Associates.)...

Secondly, the pH can have an effect on the selectivity. In pharmaceutical analysis, mainly compounds with either basic or acidic properties have to be analyzed. Since the pH influences the dissociation and charge of these substances, it will affect their retention behavior. Changing the organic modifier does not lead to major selectivity differences, but it can enhance the differences induced by pH and/or stationary phase changes. Also, the column... 

Fractionation of proteins according to size utilizing cross-linked dextran or polyacrylamide gel columns was first demonstrated by Porath and Flodin 63 in 1959. This technique has become the most widely accepted method for separation and molecular weight determination of hydrophilic and some hydrophobic macromolecules using aqueous buffers with or without organic modifier. While this technique might not be unique in its ability to resolve and separate proteins, it is one additional simple and effective tool in the chemist s armamentarium. The theories behind size-exclusion HPLC and size-exclusion chromatography at low pressure are identical and are described in several publications. 31 34 36 39 44 64 65 ... 

The remainder of the modified parfait column consisted of an MSC-1 cation-exchange and an A-162 anion-exchange bed. The elution conditions for these beds were modified to minimize contamination of eluates and to selectively desorb organic anions and cations. With the modified protocol, 20 model compounds (Table I), selected by the U.S. Environmental Protection Agency (USEPA) Health Effects Research Laboratory (HERL), were used to evaluate the recovery efficiency of the method. Recoveries were determined in the presence of 2 ppm of a humic acid supplied by HERL. 

In sub-FC, a detailed study of the influence of mobile phase additives on the chiral resolution of isoxazoline-based Ilb/IIIb receptor antagonists was carried out by Blackwell [145] on Chiralcel OD-H CSPs. The different mobile phase additives used were acetic acid, trifluoroacetic acid, formic acid, water, triethylamine, triethanolamine, n-hexylamine, trimethyl phosphate, and tri-w-butyl phosphate. In general, n-hexylamine and tri-/ -butyl phosphate mobile phase additives resulted in better resolution. The chiral separation of four 1,3-dioxolane derivatives on an amylose-based column has been described [151]. The effects of mobile phase composition, temperature, and pressure have been investigated. The nature of the modifier is the main parameter it has the highest impact on chiral resolution and is more important than the polarity of the mobile phase. Therefore, the organic modifier that gave the best enantiomeric separation was different for each compound. 

More elaborate means have been described for removing the acetone by distillation with relatively little isopropyl alcohol. These include various columns such as a Vigreux13 or a modified Widmer column.10 They are to be recommended when the aldehyde or ketone boils Within 50° of isopropyl alcohol, but are unnecessary under other circumstances. A reflux condenser maintained at constant temperature by boiling methanol has been suggested.6 More convenient than this is the simple but effective partial condenser designed by Hahn.49 An easily constructed modification is illustrated in Fig. 3 (adapted from Organic Syntheses).60 The partial condenser is attached directly to the round-bottomed flask, and ethanol is placed in the inner condensing tube. The... 

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