Note

The selectivity of cellulose gels for simple salts

Modification of a silica surface by calcium ions was studied by high-performance liquid chromatography. After treatment at pH 7.0 and 9.0 with calcium hydroxide, the calcium-modified silicas were subjected to physical and chemical analysis. From calcium measurement with a flame atomic absorption spectrometer, the extent of calcium adsorption was determined as 650 ppm on calcium-modified silica at pH 7.0 and 4800 ppm on calcium-modified silica at pH 9.0. The amount of calcium on the original silica was 58 ppm. The separation factor (α) for N-methylaniline versus N,N-dimethylaniline was measured to be 5.1 on calcium-modified silica at pH 9.0, but could not measured on calcium-modified silica at pH 7.0 or the original silica, using methanol-n-hexane (1:99, v/v) as the eluent. By comparison of calcium and amino-modified silica, the separation factors were measured under the same HPLC conditions and was found to be 9.0 on amino-modified silica. The results show that calcium-modified silicas are able to separate some basic model compounds as well as amino-modified silica.

Various concentrations of sodium and potassium chloride were eluted with sodium or potassium phosphate buffer (0.025 M, pH 7.0) in various sample—buffer combinations from a Sephadex G-15 column. A more acidic buffer (pH 6.0) or a more concentrated buffer (0.125 M) were also used as the eluent. By observing the elution behaviour of all ions in the eluate, it was found that the cation from the sample accompanied by phosphate ion from the eluent was eluted in earlier fractions, and the chloride ion from the sample accompanied by the eluent's cation was eluted in later fractions in all homocationic and heterocationic sample–eluent combinations employed. The mechanism assumed was that chloride ion from the sample was eluted slowly and the phosphate ion from the eluent rapidly, resulting in the occurrence of cation-exchange reactions between the sample and the eluent.

This chapter provides an introduction to exclusion chromatography used extensively for separating and characterizing organic polymers and biomolecules. The utility of this technique in the investigations of inorganic compounds is also demonstrated. The chapter also deals with the applications of exclusion chromatography to the separation of inorganic polymers and to the investigations of metal-ligand binding. When pure water is used for the elution of a given salt on a neutral gel col­umn, the cation and anion which constitute the sample salt must elute together with each other owing to the requirement of electroneutrality of solution. Because the distribution coefficient obtained in such a system is that for the sample salt, it depends on both the nature of the cationic constituent and that of the anionic one. The presence of a background electrolyte in the eluent allows the sample ion to move independently of the counterion which is the constituent of the sample salt injected. However, the elution behavior of sample ion is not independent of the nature of the counterion in the eluent.

The behaviour of electrolytes in chromatography on hydroxyethyl methacrylate gels in aqueous media is considered. Experiments were carried out at different temperatures and the influence of different electrolytes in the mobile phase on the elution volumes of salts and on the chromatographic behaviour of water and heavy water was studied. The exclusions of most of the ions studied from the gel pores depended mainly on the type of anions, on the temperature during separation and on the composition of the mobile phase. The results are discussed on the basis of the microheterogeneity of electrolyte solutions and the structural properties of water near the surface of amphiphilic hydroxyethyl methacrylate gels.

Citrate, sulphate, oxalate, chromate, carbonate, fluoride, acetate, formate, iodate, bicarbonate, bromate, chloride, nitrite, chlorate, bromide, nitrate, iodide, perchlorate and thiocyanate (each with sodium as counter-ion) were applied to a column of Sephadex G-15, and elution was carried out with sodium chloride solution. The elution behaviour of the anions could be followed by examining the concentration distribution of the background electrolyte (sodium chloride) by argentimetry; the elution order of the anions was in accord with the lyotropic series. The elution mechanism and the possibility of quantitative separation of the anions by gel chromatography are discussed.