Retention Of Carboxylic Acids Research Articles

The Application of the Nanofiltration Membrane NF270 for Separation of Fermentation Broths.

The potential for nanofiltration (NF) in removing both relatively low molecular weight (MW) organic species and charged solutes from complex media is noteworthy. The main aim of the current work was to improve understanding of the separation mechanisms of fermentation broths components in the NF process. For this purpose, the experimental investigations were performed using the commercial polyamide NF270 membrane. The feed solution was ultrafiltered 1,3-propanediol (1,3-PD) broths. The separation results were analyzed and discussed in light of the detailed characteristics of both the membrane and the broth components. It has been noted that the membrane ensured the complete 1,3-PD permeability and significant rejection of some feed components. A thorough analysis showed that the retention of carboxylic acids was based on both the Donnan effect and sieve mechanism, according to the following order: succinic acid > lactic acid > acetic acid > formic acid. Indeed, acids retention increased with increasing charged acids ions valency, Stokes radius (rS) as well as MW, and decreasing diffusion coefficient (D). In turn, for ions, the following orders retention was determined: SO42− = PO43− > Cl− and Ca2+ > Na+ > NH4+ ~ K+. It indicated that the ions retention increased with increasing ions charge density, hydrated radius (rH), and hydration energy (Eh). It showed that the separation of the ions was based on the Donnan exclusion, sieving effect, and dielectric exclusion.

The influence of a carbon layer deposited on a zirconia surface on the retention of polar analytes in an organic rich mobile phase

Hydrophilic interaction liquid chromatography (HILIC) represents a modern MS-friendly approach to the analysis of polar compounds. To date especially silica-based HILIC stationary phases are utilized. Recently the papers concerning retention of polar analytes on unmodified titania and zirconia as well as a polybutadiene modified zirconia stationary phase under HILIC conditions have been published. In this work the investigation of a highly hydrophobic carbon-coated zirconia column under HILIC conditions was reported. The influence of buffer concentration, buffer type, pH and temperature on the elution and chromatographic efficiency were studied. The processes participating on the retention of polar compounds showed a multimodal character. The retention was governed rather by surface adsorption than phase partition in high ACN mobile phases. The ligand exchange remained an important retention force although the access of the analytes to the active surface was significantly hindered by the carbon coating. Besides ligand exchange and hydrophilic interactions also the hydrophobic carbon layer was involved in the retention of carboxylic acids and especially xanthines in the organic rich mobile phase.

Effects of stationary phase cross-linking and ion-exchange capacity on the retention of carboxylic acids in ion-exclusion chromatography using sulfonated resins.

Ion-exclusion chromatography (IEC) has been widely used in the separation of carboxylic acids, finding applications in the analysis of food and beverages, pharmaceuticals, biological samples, and acid rain samples.' The retention mechanism of carboxylic acids in ion-exclusion chromatography has also been investigated in many studies, and the factors which affect retention can be divided into three categories: analyte effects, mobile phase effects, and stationary phase effects. In IEC, the chromatographic system can be considered to consist of three phases: the mobile phase which comprises the eluent passing through the interstitial volume of the column, the stationary phase which comprises the occluded liquid trapped within the pores of the resin and the resin phase which is the solid resin network and functionalized groups.' In this mode of chromatography, the analytes being separated have the same charge as the functional group on the resin; that is, anions are separated on cation-exchange columns and cations are separated on anion-exchangec columns.

Waste water treatment using reverse osmosis: real osmotic pressure and chemical functionality as influencing parameters on the retention of carboxylic acids in multi-component systems

The influence of chemical functionality in carboxylic acids and osmotic pressure of multi-component solutions on the retention in the reverse osmosis process are discussed. Therefore formic-, acetic-, propionic-, glycolic-, acrylic- and methoxyacetic acid ( target substances) were combined with one or two other carboxylic acids ( active substances), chosen out of a pool of 16. All investigations were carried out with an aromatic polyamide membrane and the operating conditions were kept constant. Although the combination of all effects is extremely complex, the experiments showed that the influence on the retention of a substance equate as an outcome of molecular mass, acidity, functionality and spatial requirement. The influence of functionality in the active substances could be further divided into an additional carboxylic group, double bond and aromaticity. The calculation of the osmotic pressure demonstrated that there was no observable difference between the real and ideal one when the solution contained the same number of components. Therefore it can be concluded that in this study the osmotic pressure has no influence on the retention of the target substance.

Elution behaviour of aliphatic carboxylic acids on a strong cation-exchange resin column

The retention behaviour of aliphatic mono- and dicarboxylic acids on a strong cation-exchange resin column in the alkali metal and ammonium ion forms has been studied by ion chromatography. Carboxylic acids eluted in order of the carbon number. Small acids, such as formic, oxalic and malonic acids, were excluded from the column by the ionic exclusion effect, whereas the larger carboxylic acids were strongly retained owing to hydrophobic interactions. The retention of carboxylic acids was controlled through the combination of several interaction forces such as Donnan potential, size exclusion and hydrophobic interactions. The elution volumes of carboxylic acids on resins in various ionic forms decreased in the order K + > Cs + > NH + > Na + > Li + > H + resin forms.

Tributyl Phosphate as Stationary Phase in Reversed Phase Liquid Chromatographic Separations of Hydrophilic Carboxylic Acids, Amino Acids and Dipeptides

Abstract Tributyl phosphate (TBP) has been used as stationary liquid phase in reversed phase liquid column chromatography with aqueous buffers or aqueous buffers + methanol as the mobile phase. Hydrophobic microparticulate (5 μm) alkyl-derivatized silica was used as support. The stability of the columns is very high as is their separating efficiency. The strong hydrogen accepting properties of TBP makes retention possible of highly polar solutes containing hydrogen donating groups. Retention of carboxylic acids is obtained by the distribution of the uncharged form into TBP and it is regulated by the pH of the mobile phase. No influence from the support on the retention of carboxylic acids has been seen. Benzoic, phenylacetic, mandelic, indole-3-acetic and glucuronic acid derivatives, amino acids and dipeptides have been chromatographed and the influence of structural effects on the separation factors is discussed.