Fractionation of fish oil fatty acid methyl esters by means of argentation and reversed-phase high-performance liquid chromatography, and its utility in total fatty acid analysis

The utility of reversed-phase and argentation high-performance liquid chromatography (HPLC) as pre-fractionation methods in fatty acid analysis is discussed. Both HPLC modes were applied to cod liver oil fatty acid methyl esters. Apart from positional isomers, the fractions obtained by reversed-phase HPLC were analysed by gas-liquid chromatography and appear to be free of the usually occurring “critical pairs”. The mechanism of retention of the fatty acid methyl esters on low-loaded silver nitrate-impregnated silicas is discussed. It is shown that argentation HPLC is a rapid semi-preparative pre-fractionation method for highly unsaturated fatty esters with 3–6 double bonds

Heat-induced structural changes in the lichrosorb RP-18—water high-performance liquid chromatographic system and their impact on the thermodynamic adsorption data of benzene, nitrobenzene and phenol

Capacity ratio (K) data of benzene, nitrobenzene and phenol have been measured on liChrosorb RP-18 with water as the eluent at temperatures between 5 and 85°C. The influence of temperature on the structure of the RP-18 layer is discussed. Partial molar free energies, entropies, enthalpies and heat capacities of adsorption have been computed as a function of temperature by fitting Taylor's series expansions to the ln k data. These thermodynamic data appear to depend on (alterations of) the structure of the RP-18 layer. The effects of cavity formation and of hydrophobic hydration of benzene in water, and of the solute polarity on the strength of the adsorption, are discussed. It is shown that enthalpy/entropy compensation effects play an important, although not readily predictable, rôle in solute adsorption

Heat-induced structural changes in the lichrosorb RP-18—water high-performance liquid chromatographic system and their impact on the thermodynamic adsorption data of benzene, nitrobenzene and phenol

Capacity ratio (K) data of benzene, nitrobenzene and phenol have been measured on liChrosorb RP-18 with water as the eluent at temperatures between 5 and 85°C. The influence of temperature on the structure of the RP-18 layer is discussed. Partial molar free energies, entropies, enthalpies and heat capacities of adsorption have been computed as a function of temperature by fitting Taylor's series expansions to the ln k data. These thermodynamic data appear to depend on (alterations of) the structure of the RP-18 layer. The effects of cavity formation and of hydrophobic hydration of benzene in water, and of the solute polarity on the strength of the adsorption, are discussed. It is shown that enthalpy/entropy compensation effects play an important, although not readily predictable, rôle in solute adsorption

Activity coefficients, interfacial tensions and retention in reversed-phase liquid chormatography on LiChrosorb RP-18 with methanol-water mixtures

Literature data on activity coefficients of various solutes in water, of some tetraalkyl compounds in methanol-water mixture and of water in organic solvents have been correlated with the product of the molecular surface area of the solute and the solute-solvent interfacial tension at ambient temperature. The conditions for which this relationship holds are examined. The retentions of apolar solutes have been measured on LiChrosorb RP-18 using methanol-water mixtures as eluents at 25°C. The results are discussed in terms of a monolayer adsorption model (according to Locke-Everett) and in terms of the adsorption model based on the solvophobic interaction theory. The important role of solute activity coefficients in the eluent on solute retention is shown quantitatively. The affinity of the adsorbent towards solutes is shown to be a result of apolar interactions in the RP-18 phase and of polar interactions in the interfacial layer of adsorbed methanol. The influence of both contributions is illustrated

Selectivity of nucleosil 10 NH2 as an adsorbent in high-performance

Net retention volumes per gram of Nucleosil 10 NH2 have been measured for a large number of mono- and disubstituted benzene derivatives and of polycyclic aromatic hydrocarbons, using n-hexane, dichloromethane and a mixture of both as eluents at 25°. The retention data are interpreted in terms of the semi-empirical adsorption model, developed by Snyder for bare adsorbents, using octadecylsilylsilica as a reference adsorbent. The effects of the bound monomers on adsorbent deactivation, solute and eluent localization, change of the charge distribution in the solute molecule and adsorption mode of the solute are evaluated and discussed in terms of donor-acceptor interaction (including hydrogen bonding)

Adsorptive properties of N-2-cyanoethyl-N-methylaminosilica in high-performance liquid chromatography

Net retention volumes per gram of N-2-cyanoethyl-N-methylaminosilica have been measured for a large number of mono- and disubstituted benzenes, some mono-substituted (cyclo)hexanes and a number of unsubstituted polycyclic aromatic hydrocarbons, using n-hexane, methylene chloride and a mixture of both solvents as eluent at 25° and 43.5°. The retention data are interpreted in terms of the semi-empirical adsorption model, developed by Snyder for bare adsorbents. The effects of adsorbent deactivation (due to the amination and the adsorption of the cyano group to the silica), temperature, solute and eluent localization, change of charge distribution in the solute molecule by substituents and mode of adsorption of the solute on retention are discussed

Determination of traces of inorganic anions by means of high-performance liquid chromatography on zipaxsax columns

Zipax-SAX pellicular beads are used as the anion-exchanger material ; a high-pressure packing technique is described. A Zipax-SAX column (200 × 4.5 mm) is used in a separation system with eluent suppression and conductivity detection as in ion-chromatography. Good separation of chloride, nitrite, bromide, nitrate and sulfate is obtained with 1.4 × 10-3 M succinate or adipate eluents at pH 7. A complete separation takes about 6 min at a flow rate of 3 ml min-1. Detection limits of 2 μg l-1 chloride, 4 μg l-1 nitrate and 10 μg l-1 sulfate can be reached if 2 ml of sample is preconcentrated