C.L. De Ligny

CORRELATIONS BETWEEN LIQUID CHROMATOGRAPHIC CAPACITY RATIO DATA ON LICHROSORB RP-18 AND PARTITION COEFFICIENTS IN THE OCTANOL-WATER SYSTEM

SUMMARY Retention data of methylbenzenes, n-alkylbenzenes, fused arenes, polyphenyls, chlorobenzenes, -anilines and -phenols and some polar monosubstituted benzenes have been measured on LiChrosorb RP-18, using methanol-water mixtures as eluents at 25’C. The important effect of solute activity coefficients in water on capacity ratio (k) data, holding for water as eluent, and on partition coefficients in the octanol-water system (PO,,_) is shown. The log k-log I’,,,,_ correlation is improved by using (1inearIy extrapolated) log X- values in water, instead of those in methanol-water mixtures. At similar log Pact_ values the log k values of the polar benzenes are slightly higher than those of the lipophilic compounds_ Consequently, two log k-log Pa,,_ regression equations are proposed. Steric and intramolecular electronic effects on the values for log P,,,,_ of halogenated anilines and phenols are described quantitatively. The results cast doubt on the reliability of Rekker’sf-method for the prediction of log PO,,_ values of highly substituted aromatic compounds_

Isoelectric points of proteins, determined by isoelectric focusing in the presence of urea and ethanol.

Abstract Isoelectric points, pIapp, in sucrose-urea-water and glycerol-ethanol-water mixtures and isoelectric points, pI, in water have been determined at 25° for some carrier ampholytes. The differences, pIapppI, are shown to account for the primary medium effect and the pH measuring cell effect on the isoelectric point. The diferences, pIapppI, for Ampholines are used to correct apparent isoelectric points of proteins. pI shifts resulting from the denaturing effect of urea and ethanol are discussed in terms of the conformation change.

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).

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.

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.

A test of Pierotti's theory for the solubility of gases in liquids, by means of literature data of solubility and entropy of solution

Pierottis theory for the solubility of gases in liquids is tested by means of a large amount of literature data on solubility and entropy of solution. The involved solutes comprise the noble gases, mercury vapour, inorganic gases and hydrocarbons up to propane. The involved solvents comprise alkanes, cycloalkanes, nitromethane, polythene, aromatics, dimethylsulfoxide and perfluoromethyl-cyclohexane. It appears, that this theory describes the solubilities satisfactory. The description of the entropies of solution is less good. The enhanced solubilities of BF3, CO2, Cl2 and C2H2 in some solvents are ascribed to electron donor—acceptor interaction. The association constants for donor—acceptor complex formation are tabulated.

Three-mode factor analysis of data on retention in normal-phase high-performance liquid chromatography

It is shown that the Snyder equation is not quite satisfactory for fitting retention data in normal-phase high-performance liquid chromatography (HPLC) on chemically bonded phases. This equation is a special case of the mathematical—statistical three-mode factor analysis model. This model, in its general form, has been used to fit two sets of literature data on the retention in normal-phase HPLC for 19 solutes on six adsorbents with two eluents, and for 39 solutes on three adsorbents with two eluents, respectively. This study represents the first application of three mode factor analysis with missing data, and also the first application of three-mode factor analysis in the field of the natural sciences. The accuracy of the fit of the observations and of the prediction of the missing data, for various numbers of extracted factors, is discussed.

Determination of arsenic(III/V) in aqueous samples by neutron activation analysis after sequential coprecipitation with dibenzyldithiocarbamate

Abstract A simple and sensitive method for distinguishing between As (III) and As (V) is presented. It is based on sequential coprecipitation with dibenzyldithiocarbamate (DBDTC) of As (III) and with a mixture of potassium iodide and thiosulphate. The precipitates are collected successively on 0.45-μm membrane filters and arsenic is determined by neutron activation of the filters and subsequent γ-spectrometry. Optimum conditions for the two steps of the sequential coprecipitation technique were determined using 74 As (III) and 74 As (V) tracers. Under the optimized conditions some other heavy metal tracers were applied to study the selectivity of the method; of these, Cd and Fe were quantitatively and Ag and Zn partly recovered. The accuracy of the method was checked by determination of the total arsenic concentration in some water reference materials by applying the second step of the coprecipitation technique. The values found were well within the certified ranges. The applicability of the method to the speciation of arsenic in a fresh water sample is demonstrated. As (III) and As (V) could be determined with relative standard deviations of 3 and 5%, respectively, and a detection limit of 0.02 μg 1 −1 . Investigation of the behaviour of some other arsenic species, e.g., monomethylarsonic acid (MMAA) and dimethylarsinic acid (DMAA), in the sequential coprecipitation technique showed that neither MMAA nor DMAA is coprecipitated in the first step; in the second step, MMAA is coprecipitated quantitatively whereas DMAA is not coprecipitated at all. This implies that MMAA interferes in the determination of As(V).

Temperature and eluent effects on the selectivity of some nitroaromatic bonded phases in high-performance liquid chromatography

Abstract Nucleosil 10 NH2 has been converted into 2,4-dinitroanilino, bis(3-nitrophenyl) sulphone and 2,4,7-trinitrofluorenimine silicas. Net retention volumes per gram of sorbent have been measured for a number of monosubstituted benzenes and unsubstituted polycyclic aromatic hydrocarbons, using n-hexane and dichloromethanehexane (35:65) as eluent at 10, 25 and 40°C. The influences of temperature and of eluent strength on the bonded phase properties are described and related to the structure of the phases. At equilibrium, net retention data can be described in terms of the adsorption model, developed by Snyder for bare adsorbents.

Isoelectric focusing as a method for the characterization of ampholytes : III. Isoelectric points of carrier ampholytes and dissociation constants of some carboxylic acids and alkyl-substituted ammonium ions in sucrose-water, glycerol-water and ethylene glycol-water mixtures

Abstract Isoelectric points at 25° and 4° of some carrier ampholytes containing different protolytic groups and dissociation constants at 25° of some carboxylic acids and alkyl-substituted ammonium ions have been determined in water and in sucrose-water, glycerol-water and ethylene glycol-water mixtures. These data were used to evaluate the errors made in the measurement of isoelectric points of ampholytes (especially proteins) by the conventional execution of density-gradient isoelectric focusing. A correction term, which serves to obtain isoelectric points of proteins in water from density-gradient isoelectric focusing experiments, is given at 25° and 4° as a function of solvent composition and apparent isoelectric point. The usefulness of this correction term was checked experimentally by performing density-gradient isoelectric focusing experiments on bovine serum albumin in the three solvent systems studied. Its isoelectric point in water at 25° was found to be 4.75 ± 0.02.