A. A. Voshkin

Controlled-cycle pulsed liquid-liquid chromatography. A modified version of Craig's counter-current distribution.

A new liquid-liquid chromatography technique developed from a combination of controlled-cycle operation and a pulsed-mixing technique is suggested and validated. The controlled-cycle pulsed liquid-liquid chromatography (CPLC) system operates without involving a centrifuge and consists, of a series of multistage units, and a method for imparting pulsation motion to the liquids inside the units (the pulsation cycle). This chromatography technique can be considered as an improved continuous form of Craigs counter-current distribution method, or, alternatively, as a form of droplet chromatography with the cycling mode of operation. The theoretical model has been designed to account for the effects of the basic parameters influencing the CPLC operation. The theoretical models suitability was proved by direct comparison between the experimental and model responses. The CPLC devices containing 1, 2, 4 and 5 multistage columns (each column was divided into 26 stages) have been designed, fabricated and tested; experiments were conducted to test the chromatographic behavior of organic (monocarboxylic) and mineral acids. The mass transfer rate in the stages depends on the nature of both--phase and sample systems: the highest values were achieved in experiments with acetic acid by using the octane/water biphasic system, where an equilibrium concentration distribution between stationary and mobile phases in the stages was attained. The results obtained demonstrated the potential of the new technique for preparative and industrial scale separations.

Intermittent counter-current extraction—Equilibrium cell model, scaling and an improved bobbin design

This paper describes an equilibrium cell model for intermittent counter-current extraction that is analytically solved for the first time for continuous sample injection between a pair of columns. The model is compared with practice for injections of a model mixture of compounds on a standard high-performance counter-current chromatography instrument giving good agreement for compound elution order and the times to maximum concentration for the eluted components. An improved design of end fittings for the counter-current chromatography bobbins is described which permits on-column switching of the mobile and stationary phases. This on-column switching successfully eliminates the displaced stationary phase seen in fractions when operating ICcE with standard flying leads and gives a 6% reduction in the retention time of compounds and improved resolution due to the elimination of the time delay required to pump the previous mobile phase from standard flying leads.

Analysis of cyclic liquid chromatography

A new method for the chromatographic separation of liquid mixtures is considered which is distinguished by a discrete (cyclic) supply of the mobile phase to a chromatographic apparatus. Theoretical analysis of the cyclic mode of chromatography is performed taking into account the effect of the rate of interphase mass transfer.

Support-free pulsed liquid-liquid chromatography

A simple technique of support-free liquid-liquid chromatography is suggested that operates without incorporation of a centrifuge. The pulsed chromatography apparatus consists of a stationary coiled tube and a pulsation device to produce reciprocating motion of liquid phases within each individual coil segment. This reciprocating motion generates a centrifugal force field varying in intensity and direction that leads to an improved mixing of the two liquid phases and retains the stationary phase in the coiled tubing. The intensity of the back and forth motion of liquid phases within each coil unit can be varied by varying the frequency and/or the amplitude of the pulsations generated by the pulsation device. As the magnitude of the stationary phase retention is of paramount importance for success of the technique, the retention of the stationary phase in the pulsed coil column was experimentally studied. A few experiments were conducted to test the chromatographic behavior of valeric (n-pentanoic) and caproic (n-hexanoic) acids. The results obtained demonstrate the potential of the new separation method for preparative purposes.

Extraction of monocarboxylic acids with binary extracting agents based on amines and quaternary ammonium bases

The distribution of monocarboxylic acids is reported for extraction systems with binary extracting agents, namely, amine and quaternary ammonium base (QAB) salts of organic acids with widely varied acid dissociation constants (pKa 1.5–10). Monocarboxylic acid extractability orders have been obtained for systems with binary extracting agents based on trioctylmethylammonium and trioctylammonium (TOA). The best extractability is shown by acids with long hydrocarbon radicals (butyric and caproic acids). Lactic acid is the least extractable. Extractive power orders have been obtained for QAB- and TOA-based binary extracting agents. For monocarboxylic acid extraction with QAB salts, the extractive power order correlates with the acid dissociation constants of the parent organic acids: trioctylmethylammonium p-tert-butylphenolate ≫ caprylate > dialkylphosphinate > dialkylmonothiophosphinate > dialkylphosphate > dinonylnaphthalene sulfonate > dialkyldithiophosphinate. The extractive power of the QAB-based binary extracting agents is much higher than that of the TOA salts.

Pulsed Cyclic Device for Liquid Countercurrent Chromatography

A new apparatus for the chromatographic separation of liquid mixtures is investigated. The apparatus contains a number of vertical columns connected in a serpentine shape and consisting of cells placed on top of each other. The cells in the columns are separated by perforated septa. A special dosing unit is used to provide a discrete (cyclic) mobile-phase feed [flow?] into the apparatus and a pulsed cyclic mode of phase contact in column cells. Studies on a single column and on an apparatus consisting of four columns have been performed to assess the efficiency of the pulsed cyclic device. The results of experimental investigations have confirmed the potential of the newly developed topic in the area of liquid mixture separation processes.

Study of metal extraction in high-frequency vibration mini-columns

The prospects of high-frequency vibration mini-columns for use as models for studying the extraction recovery and separation of metals are demonstrated.

A new extraction method for the preparation of zinc oxide nanoparticles in aqueous two-phase systems

An extraction method was suggested for the preparation of differently shaped nano- and micrometer- sized zinc oxide particles at the interface boundary of aqueous two-phase systems based on polyethylene glycol (polyethylene oxide) and sodium sulfate using NaOH and aqueous ammonia as precipitating agents.

Extraction of rare earth metals, uranium, and thorium from nitrate solutions by binary extractants

The interphase distribution of the salts of rare earth metals (REMs) that coexist in systems containing dialkyl phosphinate and dialkyl dithiophosphinate of quaternary ammonium base (QAB) was studied. It is shown that, in principle, binary extractants based on derivatives of phosphinic acids and QAB can be used to separate REMs from the associated metals (uranium and thorium), as well as to separate uranium and thorium. A numerical investigation of the application prospects of the binary extractants for extracting and separating REMs and uranium using liquid pseudomembranes has been performed; the prospects of developing these processes have been demonstrated.

Interphase distribution of weak acids in systems with binary extractants

General dependences of interphase distribution of weak acids in systems containing binary extractants were studied. Substantial differences in the extraction dependences of the composition of the organic and aqueous phases were shown for weak acids compared to systems that contain strong acids and binary extractants, as well as weak acids and neutral extractants. The influence of hydrogen bonding between two extracted compounds was observed when low-molecular monocarboxylic acids were extracted with agents based on quaternary ammonium bases and organic hydroxy acids.