Pentanol, adsorption

The observed disaepancies in experimental results is most likely caused by the ions of the supporting electrolyte. For example, fluoride ions do not adsorb on the mercury electrode but adsorb on the silver electrode. The adsorption on the latter metal strongly depends on the face orientation.The sequence of AG° values forn-hexanol adsorption from Na2S04 and KCIO4 solutions is AC° [Ag(lll)] > AG° [Ag(lOO)] (see Table 3). However, the sequence of AG°s of n-pentanol adsorption from KF solution is just the opposite [Ag(l 10)] > AG° [Ag(l ll)]. The... 

Wahlund applied ion-pair principles using alkyl-bonded silica as the support for pentanol as liquid stationary phase [4]. Tetrabutylammonium was used as counter-ion in the mobile aqueous phase for the separation of anionic compounds such as barbiturates, carboxylates, sulfonamides and sulfonates [4, 50). Hydrophobic amines were separated as ion-pairs with inorganic anions, with long-chain ammonium ions added to the mobile phase to improve peak symmetry [23]. The content of penlanol in the mobile phase had a decisive influence on the retention. The value found for approached that calculated (eqn. 8) when the mobile phase was saturated with pentanol. At lower concentrations of pentanol, adsorption onto the hydrophobic support had a strong influence on kj.. [51]. 

Therefore some indirect methods have been worked out to determine the value of ff=0.154,259 In particular (1) salting out of organic compounds from a surface-inactive electrolyte solution, (2) F"" for 1-pentanol or other organic compounds with a high attractive interaction constant a, and (3) dependence of the capacitance minimum on thiourea concentration. It should be noted that indirect estimates based on TU adsorption give... 

Studies in surface-inactive electrolyte solutions with various organic compounds (cyclohexanol, 1-pentanol, 2-butanol, camphor, tetra-buthyl ammonium ion, TBN+) show that the adsorption-desorption peak shifts to more negative potentials in the order (0001) < (1010) < (1120) this was explained by the increasing negative value of Eff=0 in the same direction.259 629-635... 

Figure 26. Plot of the Gibbs energy of adsorption of organic substances at a = 0 vs. the interfacial parameter, AX. (1) 1-Hexanol, (2) 1-pentanol, and (3) acetonitrile. From Ref. 32, updated. Additional points (1) Au(l 11),910 Bi(l 11),152 and (2) Ga916...

Other data support the above picture. Hexanol adsorbs very weakly on Ag(l 10), more weakly than expected, and in any case less than on the (100) face.440 Such a poor adsorption on (110) faces has been explained in terms of steric hindrance caused by the superficial rails of atoms. Consistently, adsorption on the (110) face of Cu is vanishing small.587 Predictions based on a linear regression analysis of the data for pentanol (nine metals) give a value of-12 kJ mol 1 for Cu(l 10) and about -16 kJ mol 1 for Au(110). No data are available for polycrystalline Au, but Au(l 11) is placed in the correct position in the adsorption of hexanol.910 Thus, these data confirm the hydrophilicity sequence Hg < Au < Ag and the crystal face sequence for fee metals (111) < (100) < (110). 

TFe data of Popov et alm for Ag contradict the above sequence. They found that pentanol adsorbed more strongly on Ag(100) than on Ag(l 11). Similarly, Cd(0001) adsorbs less strongly than pc-Cd.661 The data for Sb and Bi are to some extent contradictory since the trend is broadly correct but with scatter, which is attributed to the crystal face specificity of space-charge effects.153 For instance, adsorption of cyclohexanol on Bi conforms to the sequence (011) > (101) > (211) > (001) >(111), while the capacitance at a - Ovaries in the sequence (001) > (011) > (211) > (101) > (111). Thus only the faces (001), (211), and (111) are in the expected order. Surprisingly, the Cd data of Lust etal. show similarities with those of Naneva etal.,212 although capacitances disagree. Thus the order of cyclohexanol adsorbability is (1010) > (0001) while the capacitance varies in the order (1010) > (1120) > (0001), i.e., the other way round. In these cases one might wonder whether the G(M-B) term is really independent of face. 

The most spectacular peak profiles, which suggest self-associative interactions, were obtained for 5-phenyl-1-pentanol on the Whatman No. 1 and No. 3 chromatographic papers (see Figure 2.15 and Figure 2.16). Very similar band profiles can be obtained using the mass-transfer model (Eqnation 2.21), coupled with the Fowler-Guggenheim isotherm of adsorption (Equation 2.4), or with the multilayer isotherm (Equation 2.7). 

A simulated moving bed system has been proposed for the production of p-cresol from mixtures of cresol isomers even derived from coal tar [52]. Neuzil et al. give details of the development of the adsorbent and desorbent system reviewing balancing mass transfer issues with selechvity [53]. The desorbent for the cresol system is 1-pentanol. For these Hquid adsorptive systems where highly polar molecules are adsorbed and desorbed with polar desorbents, the tolerance of the system for trace polar contaminants is higher because the feed and desorbent can more easily exchange with them on the surface of the zeolites. 

Alcohols Richer and Lipkowski [268, 269] have performed extensive studies on adsorption of tert-pentanol... 

Some conclusions pertaining to adsorption of 1-pentanol riboflavin and thioctic acid on Au electrode have been drawn from differential capacity-potential curves [274]. It has been found, for instance, that adsorption of these compounds obeys the Langmuir isotherm. Moreover, the free energies of adsorption have been determined. 

Plots of surface tension versus concentration for n-pentanol [49], LiCl (based on Ref. [50]), and SDS in an aqueous medium at room temperature are shown in Fig. 3.7. The three curves are typical for three different types of adsorption. The SDS adsorption isotherm is typical for amphiphilic substances. In many cases, above a certain critical concentration defined aggregates called micelles are formed (see Section 12.1). This concentration is called the critical micellar concentration (CMC). In the case of SDS at 25°C this is at 8.9 mM. Above the CMC the surface tension does not change significantly any further because any added substance goes into micelles not to the liquid-gas interface. 

The adsorption isotherm for pentanol is typical for lyophobic substances, i.e., substances which do not like to stay in solution, and for weakly amphiphilic substances. They become enriched in the interface and decrease the surface tension. If water is the solvent, most organic substances show such a behaviour. The LiCl adsorption isotherm is characteristic for lyophilic substances. Most ions in water show such behaviour. 

Determinations of the adsorption isotherms for a number of organic solvent-water systems in contact with hydrocarbonaceous stationary phases have shown that a layer of solvent molecules forms on the bonded-phase surface and that the extent of the layer increases with the concentration of the solvent in the mobile phase. For example, methanol shows a Langmuir-type isotherm when distributed between water and Partisil ODS (56). This effect can be exploited to enhance the resolution and the recoveries of hydrophobic peptides by the use of low concentrations, i.e., <5% v/v, of medium-chain alkyl alcohols such as tm-butanol or tert-pentanol or other polar, but nonionic solvents added to aquo-methanol or acetonitrile eluents. It also highlights the cautionary requirement that adequate equilibration of a reversed-phase system is mandatory if reproducible chromatography is to be obtained with surface-active components in the mobile phase. 

After partial hydrolysis the starches lose a major part of their flavour binding properties. Examples of partially hydrolyzed starch products are dextrins (acid or enzymatic hydrolysis) and maltodextrins (generally enzymatically hydrolized). Acetaldehyde, ethanol, decanal and limonene only bind weakly to dextrins (presumably by adsorption) [22[, while ethylacetate is not adsorbed at all [1[. In the same way, alcohols (such as ethanol, propanol, butanol, pentanol and hexanol) and menthol are only weakly adsorbed on maltodextrins [11, 23]. 

In fact, a pure barrier regime of adsorption is not frequently observed. It is expected that the barrier becomes more important for substances of low surface activity and high concentration in the solution. Such adsorption regime was observed with propanol, pentanol, 1,6-hexanoic acid, etc. see Reference 85 for details. 

Taking into account their usefulness as adsorbants, clay minerals can be successfully hydrophobized with cationic surfactants [2]. Such hydrophobized matrices can be used for the interlayer adsorption of many organic species such as 1-pentanol. 

We draw attention to two aspects of these curves. At 5Vo pentanol the interfacial tension already reaches very low values (<0.05 mN/m), and at 20% pentanol the curve seems to dip under the y = 0 level. Furthermore, in the lower parts of the curves the points nearly follow a straight line, indicating, according to the Gibbs adsorption equation, Eq. (1), that the adsorption is constant ( saturation adsorption ). 

Figure 1 Interfacial tension y as a function of the surfactant concentration Cs (in g/g) between aqueous solutions of sodium dodecyl sulfate (SDS) containing 0.3 M NaCl and solutions of 0-20 wt Ki u-pentanol in cyclohexane. Without pentanol the cmc is found at about 0.0004 M SDS, and above the cmc, y = 2.42 mN/m. Pentanol decreases the cmc and the interfacial tension above the cmc until, at 5% pentanol, y above the cmc becomes as low as 0.036 mN/m. The area per molecule of SDS at saturation adsorption increases from 0.52 nm in the absence of pentanol to about 0.9 nm at 20% pentanol. Obviously the pentanol, which is adsorbed to the extent of two to three molecules per molecule of SDS, drives some of the SDS out of the interface. The experiments were carried out at 25 C...

Water-.soluble alcohols present a slightly po.sitive function, i.e.. their addition increases the hydrophilidiy of the surfaciantfalcoho amphiphile. but very liiilc indeed. As a consequence isopropanol effect in the correlation is negative, i.e, the same as decreasing salinity, 5CC-Butanol and /en-pentanol have practically no tormulation effect since their functions are essentially nil whatever the concentration. These arc the alcohols that are the more interface-seeking ones, and their miiin effect is to dilute the surfactant adsorption density without changing the formulation. 

Stability depends upon so many things that it is easy to alter its value. However, in most eases the general phenomenology versus formulation and eomposition is valid. The presenee of aleohol, partieularly an intermediate-solubility alcohol, such as rec-butanol or ter-pentanol, or a mixture of propanol and butanol, tends to reduce the interfacial adsorption of the surfactant, thus reducing all associated effects, in particular the repulsion that eontributes to stabilization. It is worth noting that the use of mixed surfae-tant systems, which is often advised in emulsion making manuals, can be detrimental in some eases in which a selective partitioning of surfactant species takes plaee (191, 192), and little surfactant is left at the interfaee. 

The adsorption pseudocapacitance is dominated by the term ddjdE and hence a plot of Cq versus-S gives information about the coverage directly. Figure 1.15 shows a set of Cs-E plots for a pentanol solution at a mercury electrode. The peaks are due to adsorption/desorption processes, so, for example, from the 0.1 M solution, the alcohol adsorbs in the potential range between —0.1 V and —1.1 V. 

Hinze was the first to investigate the capabilities of micellar bile salt mobile phases [11, 12]. He found that a significant amount ( 5% v/v) of a long chain n-alcohol (pentanol, hexanol or heptanol) was useful to minimize the bile salt adsorption on the C18 stationary plmse. A wide range of solutes could be separated by these phases, PAHs, quinones, steroids, indoles, polar and lipophilic vitamins. These phases were also able to resolve optically big enantiomers such as binaphthyl derivatives [12]. Such compounds are... 

Ion pairing agents in liquid-liquid systems in reversed-phase mode have included dihydrogenphos-phate for separation of tricyclic amines, octyl sulfate for catecholamines, and tetrabutylammonium for aromatic carboxylates and anions of sulfonamides, to exemplify some of the comparatively few applications. Liquid stationary phases coated on the alkyl-bonded phase include 1-pentanol, butyronitrile, and tributylphosphate. In normal-phase liquid-liquid ion pair chromatography aqueous perchlorate solution has been coated on to silica particles for ion pair separation of catecholamines and related compovmds and tetrabutylammonium ion at neutral pH for carboxylates and anions of sulfonamides. The organic mobile phase often contained dichloromethane and butanol. In the normal-phase mode on silica alternative separation systems have been described with aqueous perchloric acid in methanol added to dichloromethane as mobile phase for separation of amines such as drug substances. This is not an extensively utilized, but quite useful, kind of separation, which has been named ion pair adsorption chromatography. 

Ionic compounds added to the micellar system for pH or ionic strength adjustment increase usually the surfactant adsorption. Organic solvents, in contrast, decrease the amount of adsorbed surfactant. The alkyl chains of propanol and longer -alcohols form on the stationary phase a monolayer similar to that of adsorbed surfactant molecules, with the hydroxyl group oriented toward the aqueous phase. Alcohol and surfactant molecules compete for adsorption sites. For ionic surfactants, the desorbing ability depends on the organic solvent polarity (methanol adsorbed surfactant molecules decreases linearly with the organic solvent concentration. 

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