Advances in Chromatography

Volume 9

J. Calvin Giddings

• Publisher: CRC Press
• Year: 2021
• Print ISBN: 9780824712419
• eBook ISBN: 9781000447705
• Edition: 1
• Topic: Physical Sciences
• Subtopic: Science Research & Methodology

This book provides up-to-date information on a wide range of developments in the general and gas chromatographic methods and applications. It presents timely, cutting-edge reviews in the fields of bio-, analytical, organic, polymer, and pharmaceutical chemistry.

GENERAL CHROMATOGRAPHY

Reversed-Phase Extraction Chromatography in Inorganic Chemistry

E. CERRAI AND G. GHERSINI
CENTRO INFORMAZIONI STUDI ESPERIENZE, MILAN, ITALY^†

1. I. Introduction
2. II. General
   1. A. Theoretical Background
   2. B. Experimental Features
   3. C. General Remarks
3. III. Basic Extractants as Stationary Phases
   1. A. Paper and Thin-Layer Chromatography
   2. B. Column Chromatography
4. IV. Acidic Extractants as Stationary Phases
   1. A. Paper and Thin-Layer Chromatography
   2. B. Column Chromatography
   3. C. Retention Mechanism
5. V. Neutral Organophosphorus Extractants as Stationary Phases
   1. A. Paper and Thin-Layer Chromatography
   2. B. Column Chromatography
6. VI. Miscellaneous Extractants as Stationary Phases
7. VII. Conclusions
8. References

I. Introduction

A chromatographic process is defined as occurring under "reversed-phase" conditions whenever the support, either a paper strip or a bed of particles in a column, holds the organic phase as the stationary phase, while the aqueous (or inorganic) phase is the mobile one (eluent).

The wide applications of the reversed-phase technique in organic chemistry are well-known. This technique early entered the field of inorganic separations. The stationary phases mainly consisted of chelating compounds whose properties toward metallic cations were being extensively exploited for analytical applications. Results obtained were not completely satisfactory. From 1947 on, ion-exchange resins gained a great popularity and thereafter almost all inorganic chromatographic separations were achieved by means of them. Meanwhile, however, liquid-liquid extraction rapidly achieved popularity as a separation technique in inorganic chemistry. Purposely synthesized compounds, suitably selective, proved to be the most promising means of dealing with complicated problems in nuclear technology, e.g., extraction of uranium from minerals and fuel reprocessing. Winchester first thought of coupling the favorable features of these new extractants with a chromatographic process, and by the end of 1958 he reported the use of di (2-ethylhexyl) orthophosphoric acid immobilized on alumina to separate a number of rare earths. Soon thereafter, in February 1959, an article appeared by Siekierski and Kotlińska, in which zirconium was separated from niobium with a column of silica gel supporting tributylphosphate. Results appeared satisfactory and very promising. From that time on this technique has become very popular. In addition to columns, paper and thin-layer techniques were adopted. Many separations, previously unsuccessful, were now easily obtained, and several hundred papers have now been published in this field {1-269). A number of reviews have also appeared which are more or less extensive in coverage {270-285).

† Full address: CISE, C.P. 3986, 20100 Milan, Italy.

"Reversed-phase partition chromatographers are to be commended for having established so many valuable metal separations schemes on the basis of liquid-liquid extraction data." The statement comes from a well-known liquid-liquid extraction investigator (281)! He will forgive us if we recall that a number of basic data have actually been obtained by chromatographers themselves.

In the very first works, the new technique was called "reversed-phase chromatography," or alternately "reversed-phase partition chromatography." After Hulet introduced the term "extraction chromatography," which better pictures the intimate connection between such technique and liquid-liquid extraction, the three above mentioned terms have been used indifferently by various authors. In the title of this review, we talk about "reversed-phase extraction chromatography," We believe this term better defines the subject to be dealt with. We are not going to consider either reversed-phase chromatographic systems in which partially water soluble chelating agents, e.g., dithizone, oxine, thenoyltrifluoroacetone, are the stationary phases, or "extraction chromatography" systems where the extractant is the mobile phase. Nevertheless, a question still exists about the definition of "extractant." One may begin at the very recently synthesized complicated bifunctional neutral organophosphorous compounds, and gradually arrive at "trivial" ethylether and water immiscible light alcohols or ketones, whence the step to the untreated organophilic support is easy. A short-cut is necessary; although it may be objectionable, ketones as stationary phases will be included, while alcohols and ethers will not.

II. General

A. Theoretical Background

Theory yields correlations between measurable extraction chromatographic quantities and liquid-liquid extraction parameters relevant to the particular system considered (extractant, aqueous phase, and element involved). An extension can be made of mathematical treatments applied to ion exchange columns and to traditional partition chromatography [see, e.g., the works of Beaukenkamp et al (286), Glueckauf (287), Martin and Synge {288), Hrapia and Leibnitz (289)].

In liquid-liquid extraction, the ratio between the actual concentrations (e.g., moles per volume unit) of a given element in the two phases at equilibrium, is defined as the extraction coefficient. When the ratio of organic to inorganic phase concentration is chosen, the s...

Table of contents

• Cover
• Half Title
• Advisory Board
• Title Page
• Copyright Page
• Preface
• Contributors to Volume 9
• Contents
• Contents of Other Volumes
• GENERAL CHROMATOGRAPHY
• GAS CHROMATOGRAPHY
• Author Index
• Subject Index