Capacity factor reversed-phase

A useful guide when using the polarity index is that a change in its value of 2 units corresponds to an approximate tenfold change in a solute s capacity factor. Thus, if k is 22 for the reverse-phase separation of a solute when using a mobile phase of water (P = 10.2), then switching to a 60 40 water-methanol mobile phase (P = 8.2) will decrease k to approximately 2.2. Note that the capacity factor decreases because we are switching from a more polar to a less polar mobile phase in a reverse-phase separation. 

Haddad and associates report the following capacity factors for the reverse-phase separation of salicylamide (k i) and caffeine... 

This is because the increased turbulence from higher flow rates decreases the possibility for inclusion complexation, a necessary event for chiral recognition in reversed phase. Some effect has also been observed in the new polar organic mode when (capacity factor) is small (< 1). Flow rate has no effect on selectivity in the typic normal-phase system, even at flow rates up to 3 inL miir (see Fig. 2-11). 

Several theoretical models, such as the ion-pair model [342,360,361,363,380], the dyneuaic ion-exchange model [342,362,363,375] and the electrostatic model [342,369,381-386] have been proposed to describe retention in reversed-phase IPC. The electrostatic model is the most versatile and enjoys the most support but is mathematically complex euid not very intuitive. The ion-pair model emd dynamic ion-exchange model are easier to manipulate and more instructive but are restricted to a narrow range of experimental conditions for trtilch they might reasonably be applied. The ion-pair model assumes that an ion pair is formed in the mobile phase prior to the sorption of the ion-pair complex into the stationary phase. The solute capacity factor is governed by the equilibrium constants for ion-pair formation in the mobile phase, extraction of the ion-pair complex into the stationary phase, and the dissociation of th p ion-pair complex in the... 

Solvent optimization in reversed-phase liquid chromatography is commenced by selecting a binary mobile phase of the correct solvent strength to elute the seuaple with an acceptable range of capacity. factor values (1 < k <10 in general or 1 < k < 20 when a larger separation capacity is required). Transfer rules (section 4.6.1) are then used to calculate the composition of other isoeluotropic binary solvents with complementary selectivity. In practice, methanol, acetonitrile and tetrahydrofuran are chosen as the selectivity adjusting solvents blended in different... 

The isocratic reversed phase solvent system consists of water (polarity, p = 10.2), the most polar solvent in RPLC, as a primary solvent to which water-miscible organic solvents such as methanol (p = 5.1), acetonitrile (p = 5.8), or tetrahydrofuran (p = 4.0) are added. In order to optimize the speed of separation for an analyte pair, the proportions of water to nonpolar solvent are chosen such that the capacity factor of the last-eluting analyte of interest has a value of about 2.13... 

Hafkenscheid, T.L., Tomlinson, E. (1983) Correlations between alkane/water and octan-l-ol/water distribution coefficients and isocratic reversed-phase liquid chromatographic capacity factors of acids, bases and neutrals. Int l. J. Pharmaceu. 16, 225-239. 

Hamisch, M., Mockel, H.J., Schulze, G. (1983) Relationship between log Pow shake-flask values and capacity factors derived from reversed-phase HPLC for n-alkylbenzenes and some OECD reference substances. J. Chromatogr. 282, 315-332. 

Sherblom, P.M., Eganhouse, R.P. (1988) Correlations between octanol-water partition coefficients and reversed-phase high-performance liquid chromatography capacity factors. J. Chromtogr. 454, 37-50. 

Opperhuizen, A. (1987) Relationships between octan-l-ol/water partition coefficients, aqueous activity coefficients and reversed phase HPLC capacity factors of alkylbenzenes, chlorobenzenes, chloronaphthalenes and chlorobiphenyls. Toxicol. Environ. Chem. 15, 349-364. 

The separation of substituted benzene derivatives on a reversed-phase C-18 column has been examined [78]. The correlations between the logarithm of the capacity factor and several descriptors for the molecular size and shape and the physical properties of a solute were determined. The results indicated that hydrophobicity is the dominant factor to control the retention of substituted benzenes. Their retention in reversed-phase HPLC can be predicted with the help of the equations derived by multicombination of the parameters. 

Trithiolane is a stable compound at room temperature, although it will polymerize eventually and is best kept cool and sealed from the atmosphere. Separation of cisjtrans mixtures of 3,5-dialkyl-1,2,4-trithiolanes is possible on alumina. Reverse-phase HPLC has been used to separate cyclic methylene sulfides, and tellurides with retention times and capacity factors dependant in a systematic way on ring size, number and type of chalcogens and the number of heteronuclear bonds within the ring. 

Some non-steroidal anti-inflammatory drugs (NSAIDs) were found to have the following capacity factors in a particular mobile on a reverse-phase column aspirin 0.4, naproxen 3.6, ibuprofen 14.5, diclofenac 10.4, paracetamol 0.2. Given that the column had a t of 2 min determine the retention times of the NSAIDs. 

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