Retention of acids

Hill, A. P., Roses, M., Retention of ionisable compounds on HPLC. 8. Influence of mobile phase pH change on the chromatographic retention of acids and bases during gradient elution, Anal. Chem. 2001, 73, 4937-4945. 

Fig. 1.95. Retention of acid in percent of the initial concentration (0.05 M) as the function of dextran concentration. Three retained acids ...

FIGURE 14.6 Retention of acidic analytes with respect to mobile phase pH. The inflection point of the curve corresponds to the pKa of the acidic analyte. 

In acidic eluents (Figure 3.9C and D), the retention of acidic compounds becomes stronger and that of basic compounds becomes weaker. In this system, uric acid (h) is not suitable as a void volume marker due to its longer retention time. In neutral and basic eluents, an ionized acid can be used as the marker because no other compounds are eluted more rapidly. Fructose (c) is a very... 

The retention of acids in reversed-phase liquid chromatography can be predicted by Equation 4.1. The same equation can be applied to predict the... 

Buffers are commonly used to control the pH of the mobile phase, which greatly affects the retention of acidic or basic analytes. Table 1 summarizes the common buffers for HPLC and their respective pK and UV... 

The PS-DVB sorbents can be more retentive than the bonded silica sorbents. Polymeric sorbents have been shown to be capable of retaining chemicals in their ionized form even at neutral pH. Pichon et al. [88] reported SPE recovery of selected acidic herbicides using a styrene-divinylbenzene sorbent so retentive that no adjustment of the pH of the solution was necessary to achieve retention from water samples at pH 7. At pH 7 the analytes were ionized and thereby retained in their ionic form. To effect retention of acidic compounds in their nonionized form using bonded silica sorbents, it is necessary to lower the pH of the sample to approximately 2. Analysis at neutral pH can be preferable to reduced pH because at lower pHs undesirable matrix contaminants, such as humic substances in environmental samples, can be coextracted and coeluted with the analytes of interest and subsequently may interfere with chromatographic analyses. 

Hung, C.T. and Taylor, R.B. Mechanism of retention of acidic solutes by octadecyl silica using quaternary ammonium pairing ions as ion exchangers. J. Chmmatogr. 1980, 202,... 

Espinosa, S., Bosch, E., and Roses, M. Retention of ionizable compounds on HPLC 5 pH scales and the retention of acids and bases with acetonittile-water mobile phases. Anal Chem. 2000, 72, 5193-5200. 

Variations in the selectivity are sometimes observed with the change in the type of organic modifier due to the specifics of the analyte-solvent interactions (solvation) and the specific adsorption behavior of the organic modifier. In the following example the effect of type and concentration of methanol and acetonitrile modifiers on the retention of acidic, basic, and neutral analytes is discussed. 

Since membrane distillation exhibits high abihty of concentration of aqueous solutions with high retention of acids, salts, and other low-volatile compounds, it can be used for concentration of different radioactive waste streams with high volume reduction and high retention factors [97-99]. 

Graphitized carbon black (GCB) has been reported to be a highly effective sorbent for sample clean-up but also removes structurally planar analytes, limiting its applications. Addition of HOAc to the extraction solvent may help to improve recovery of analytes, but it also inhibits the retention of acidic matrix compounds. Several papers have reported the use of Cl8 for dSPE in veterinary residue analysis. " The use of PSA, NH2, and silica has also been reported. While dSPE does not provide the same degree of clean-up as SPE, it does provide good recovery and reproducibility, coupled with practical and cost advantages. ... 

Si-OH groups are also focal points of attack for water and other reagents in the mobile phase, causing dissolution of underlying silica with gradual deterioration in column performance and eventual reduction in column lifetime (5,6). The pH of the silica surface also varies from acidic, neutral, to basic, and is believed to influence the preparation and properties of bonded phases (7). The inclusion of traces of transition metals in silica matrix can further influence the retention of acids, bases or neutral compounds that can undergo complexation reactions (1). Thus the selectivity and retention characteristics of bonded phase columns also depend on the quality of silica used for the bonding reactions. 

T. Hanai, R. Miyazaki, A. Koseki and T. Kinoshita, Computational chemical analysis of the retention of acidic drugs on a pentyl-bonded silica gel in reversed-phase liquid chromatography,/. Chramatagr. Set, 2004, 42, 354-360. 

T. Hanai and H. Homma, Chromatography in silica retention of acidic drugs on a guanidino ion-exchanger,/. Liq. Chromatogr. Relat Technal, 2007, 30, 1723-1731. 

Figure 2.7 RP Retention of acids and bases as a function of the mobile phase pH. Reproduced from Snyder et al. [3] with permission of John Wiley Sons.

Alkalosis an increase in the pH of body fluids. It is corrected by excretion of bicarbonate and retention of acid. There 2 types ... 

The suppression of acid loss can be a more challenging problem for improving the durability of HT-PEMFC MEA. The acid loss is caused by evaporation, compression pressure of stack, diffusion from MEA to flow field, and volume change caused by hydration of acid which can occur when exposed to highly humid environment. The retention of acid within the catalyst layer can be improved by adding materials that can either absorb acid [40] or form... 

In any case, pickling should be avoided, because efiicient rinsing of the interior of a tank is always very difficult the retention of acidic or alkaline pickling chemicals may lead to severe corrosion in recesses. Furthermore, the water should be replaced regularly, for instance every month. In most cases, this will be sufficient for stopping (or slowing down) pitting corrosion. 

Significant softening or creeping of rock under closvu e after contact with acid, resulting in poor retention of acid-etched fractures... 

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