Column evaluation hydrophobicity

A dependency on the type of ligand, its density, the eluent used and temperature is found when evaluating hydrophobicities of stationary phases. This property can be assessed by the retention factor of a hydrophobic solute or by the ratio of the retention factors of two non-polar solutes. The latter is called selectivity for example, when the components differ only in one methyl group, the term methylene selectivity coefficient is applied. Hence, hydrophobic properties describe the polarity of a column and its selectivity towards solutes with only small differences in polarity. This becomes rather important when endcapped stationary phases are compared (Section 3.2.3.1) as some new types of adsorbents allow separation with 100% water as eluent. 

The silanophilic character of 16 reversed-phase high-performance liquid chromatographic columns was evaluated with dimethyl diphenycyclam, a cyclic tetraza macrocycle [101]. The method is rapid, does not require the removal of packing material, and uses a water-miscible solvent. The results demonstrate two points first, cyclic tetraza macrocycles offer substantial benefits over currently used silanophilic agents second, the method can easily differentiate the performance of various columns in terms of their relative hydrophobic and silanophilic contributions to absolute retention. 

A wide variety of substituted boronates are available commercially. For phenyl supports, use a phenyl or biphenyl (napthalene) derivative. For nonphenyl supports, evaluate both weakly and strongly hydrophobic alkyl derivatives (straight chain or branched). Raise sample pH to at least 8 and add the boronate derivative of choice to a concentration of at least 1 mM. The sample need not be buffer-exchanged prior to injection. Column buffers should be at least pH 8. 

Isolation-Fractionation Scheme. Figure 1 illustrates the isolation-fractionation scheme devised and evaluated in this study. Step 1 The test solution was first acidified to pH 2 and passed through the XAD-8 column by gravity flow at a rate of 15 bed volumes/h. The last portion of the test solution remaining in the column was displaced from the resin by 1 bed volume of 0.01 N HC1 rinse, which was combined with the original test solution. Step 2 The hydrophobic acid fraction was desorbed with 0.25 bed volumes of 0.1 N NaOH followed by 1.5 bed volumes of OFW. Step 3 The test solution effluent from the XAD-8 (pH 2) was adjusted to pH 10 with 1 N NaOH and recycled through the XAD-8 column at a flow rate of 15 bed volumes/h. Following the sample, 2.5 bed volumes of OFW were used to rinse the XAD-8 column. The rinse was com-... 

Szepesy, L. and Rippel, G. 1992. Comparison and evaluation of H1C columns of different hydrophobicity. Chromatographia 34 391-397. 

Thus, surfactant enhanced subsurface remediation is a mature technology for remediating hydrophilic NAPL, as displayed at the field level. These successful field demonstrations provide encouragement for further evaluation of hydrophobic oils with a similar goal of field deployment. To this end, the current research evaluated laboratory batch and column studies for surfactant enhanced remediation of hydrophobic oil contamination, including phase behavior studies, column studies, and evaluating separation... 

Liquid-liquid extraction of hydrophobic oil-laden surfactant solution was evaluated using counter-flow, porous hollow fiber membranes. Our liquid-liquid extraction experiments were conducted using Liqui-Cel Extra-Flow 2.5x8 Membrane Contactor purchased from Celgard LLC (Charlotte, NC). The dimensions of the column are 6.3 cm diameter and 20.3 cm. length with... 

The objective of this portion of the research was to experimentally evaluate surfactant effects on the liquid-liquid separation of hydrophobic oils from a surfactant system. For pump-and-treat subsurface remediation in the absence of surfactant, contaminated ground water would be pumped from the subsurface and through a liquid-liquid extraction column where the contaminant partitions from the aqueous phase into an extraction solvent phase. In the absence of surfactant, the driving force for partitioning is a function of the contaminant hydrophobicity. In the presence of surfactants, the contaminant is subject to competitive partitioning (i.e., into the micelles and into the extracting oil). 

From the view point of the assessment, the quality of an HPLC separation in response to changes in different system variables, such as the stationary phase particle diameter, the column configuration, the flow rate, or mobile phase composition, or alternatively, changes in a solute variable such as the molecular size, net charge, charge anisotropy, or hydrophobic cluster distribution of a protein, can be based on evaluation of the system peak capacity (PC) in the analytical modes of HPLC separations and the system productivity (Peff) parameters in terms of bioactive mass recovered throughput per unit time at a specified purity level and operational cost structure. The system peak capacity PC depends on the relative selectivity and the bandwidth, and can be defined as... 

Pore size was also found to be the main factor affecting separation selectivity of C18 columns from different manufacturers, compared to evaluate the applicability of sequence-specific retention calculator peptide retention prediction algorithms. Differences in end capping chemistry did not play a major role while the introduction of embedded polar groups to the C18 functionality enhanced the retention of peptides containing hydrophobic amino acid residues with polar groups [6]. 

The hydrophilicity of the nanoparticle surface can be evaluated by hydrophobic interaction chromatog-raphy. This technique, based on affinity chromatography, allows a very rapid discrimination between hydrophilic and hydrophobic nanoparticles. The nanoparticles are passed through a column containing a hydrophobic interaction chromatography gel. The nanoparticles that are retained by the gel and only eluted after the addition of a surfactant are considered as hydrophobic, whereas the nanoparticles that do not interact with the gel and that are directly eluted from the column are considered as hydrophilic. Apart from the hydrophobic interaction chromatography, the field flow fractionation techniques recently appeared to present interesting potential for the characterization of nanoparticles with different surface characteristics. ... 

Recent studies have made it possible to classify water-organic solvent systems in CCC for separation of organic substances on the basis of the liquid-phase density difference, the solvent polarity, and other parameters from the point of view of stationary-phase retention in a CCC column [1,3-9]. Ito [1] classified some liquid systems as hydrophobic (such as heptane-water or chloroform-water), intermediate (chloroform-acetic acid-water and n-butanol-water) and hydrophilic (such as n-butanol-acetic acid-water) according to the hydrophobicity of the nonaqueous phase. Thirteen two-phase solvent systems were evaluated for relative polarity by using Reichardt s dye to measure solvachromatic shifts and using the solubility of index compounds [6]. 

A set of 25 barbiturates was analyzed using CZE and MEKC. Buffers consisting of 90 mM borate, pH 8.4 (CZE), and 20 mM phosphate, 50 mM sodium dodecylsulfate (SDS), pH 7.5 (MEKC). The methods were evaluated for their suitability in systematic toxicological analysis (STA), especially when a combination of methods having a low correlation is used (305). A solid-phase microextraction device in combination with CE for the determination of barbiturates was described (see 306 and Sec. VII). The detection limit for 10 barbiturates was 0.1 ppm in urine, while the limit of detection was about 3 times poorer in bovine serum (306). Polyacrylamide-coated columns have been used for barbiturates and benzodiazepines. Seven kinds of barbiturates were sucessfully separated with the coated columns without further additives (307). The benzodiazepines, which are electrically neutral solutes, were separated in the presence of SDS. The CE method offered fast and efficient separations of the more hydrophobic solutes. 

Several polymers were evaluated in the form of a surface coating on glass beads packed in columns to determine their ability to retain platelets when whole human blood passes over the surface. This ability was measured as the platelet retention index p, the fraction of platelets retained on the column. Lowest values of p were found for poly(ethylene oxide), polypropylene oxide), poly(tetramethylene oxide) (in the form of polyurethanes), and polydimethylsiloxane. Highest values (around 0.8) were found for cross-linked poly(vinyl alcohol) and the copolymers of ethylenediamine with diisocyanates. Intermediate values were found for polystyrene and its copolymers with methyl acrylate, for polyacrylate, and for poly(methyl methacrylate). The results are interpreted in terms of possible hydrophobic and hydrogen bonding interactions with plasma proteins. 

Yang and Khaledi [27] applied LSER to the evaluation of the retention behavior (k and K m) of uncharged substituted aromatic compounds of diverse hydrophobicity, using C8 and diphenyl columns, and pure and hybrid mobile phases of SDS and C14TAB with 2-propanol and 1-butanol as modifiers. Zou et al. [28] made a similar study with K m and P s, and found high correlations between the retention and solvatochromic parameters of solutes. 

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