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The capabilities of countercurrent chromatography (CCC) in the elemental analysis of samples with different chemical and phase compositions are demonstrated. The combination of the characteristic features of extraction chromatography and multistage extraction with separation and preconcentration processes performed in a closed system (a Teflon coiled column) opens up prospects for applying this method to the analysis of a wide range of materials from high-purity substances to oil and rocks. The use of CCC at the stage of sample preparation makes it possible to decrease the detection limits of impurity elements in high-purity materials to a pg/g level, i.e., by two or three orders of magnitude, as compared with those in the direct determination by inductively coupled plasma mass spectrometry. In the analysis of oil samples, CCC allows one to determine their complete trace element composition (including platinum group, rare, and rare earth elements) due to the concentration of trace elements in a small volume of a stationary aqueous phase retained in the column.

For the first time, widespread aqueous biphasic polymer-salt extraction system was applied for selective separation of Pd(II) and Pt(IV) from chloride technological solutions by countercurrent chromatography using a rotating coiled column (an analog of centrifugal extractor). The principle novelty of the proposed approach is the possibility of multistage extraction process and the needlessness to add any specific reagents for targeted metal binding. The results showed that the use of poly(ethylene glycol)-1500 (PEG-1500) as a stationary phase allows 96–100% of both Pd(II) and Pt(IV) to be recovered from chloride solutions containing copper and nickel. To obtain individual solutions of targeted metals it is enough to change the composition of the salt-rich phase for stripping stage, in particular the salt concentration and pH value. The final purity of the targeted metal fractions obtained after their extraction from model technological solutions is ≥ 99.9%. The components of the aqueous biphasic system are recyclable, non-toxic, available, and widespread in laboratory and technology practice. A scheme of the multistage separation of platinum metals using a rotating coiled column is proposed.

A novel approach of rare earth elements (REE) determination in crude oil is suggested. Special application of countercurrent chromatography (CCC) is used as a sample pretreatment tool. An oil sample is continuously pumped through the rotating coil column (RCC) as a mobile phase, while an aqueous phase (nitric acid solution) is retained as a stationary phase. Two phases are kept well mixed and agitated, but there is no emulsion at the interface under the chosen conditions. Special features of CCC give an opportunity to vary the volume of oil samples to be analyzed from 10 mL to 1 L or more. Trace metals are preconcentrated into 10 mL of stationary phase (acidic solutions) pumped out of the column so that analysis can be easily determined with inductively coupled plasma mass spectrometry (ICP-MS) without additional sample preparation procedures. Optimal concentration of nitric acid in the stationary phase for preconcentration of REE from oil by CCC has been investigated. The combination of CCC with ICP-MS gives the possibility to develop a rapid, reliable, and accurate method of trace metal including rare earth elements (REE) determination in crude oils and oil products. Such method could be an alternative for unexpanded and expensive neutron-activation analysis (NAA).

The possibility of changing the composition of the stationary phase inside a rotating coiled column (RCC) in the course of a chromatographic process was discussed. The creation of a reagent concentration gradient in the stationary phase retained in a RCC significantly improves the efficiency of the separation of platinum-group elements by countercurrent chromatography. To separate palladium(II) and rhodium(III), a two-phase system containing methyltrialkylammonium chloride (MTAA) in toluene-hydrochloric acid was used.

The separation of U, Pu, and Am recovered from MOX fuel with the adduct of HNO3 with N,N′-dimethyl-N,N′-dioctylhexylethoxymalonamide by countercurrent chromatography (CCC) was studied. Solutions of N,N′-dimethyl-N,N′-dibutyldodecylethoxymalonamide in dodecane were used as stationary phase. The separation of U, Pu, and Am was carried in both isocratic and stepwise elution modes. The better separation of actinides and their higher radionuclidic purity are reached with stepwise elution. The first eluate fraction contained only Am (100%). The second eluate fraction contained U (100%) and Pu (0.7%). The third eluate fraction contained 99.3% of Pu.

The article deals with the use of countercurrent chromatography (CCC), support-free partition chromatography, for separation of U and Pu from the organic extract obtained directly by the dissolution of MOX fuel in supercritical CO2 containing the complex TBP · nHNO3. White spirit solutions with various TBP concentrations were used as a stationary phase. The effects of the compositions of the stationary and mobile phases on the U/Pu partition efficiency are studied. The CCC method allows the separation of U and Pu under conditions of a TBP concentration gradient in the stationary phase and also of an HNO3 concentration gradient in the mobile phase. Chromatographic separation first gives the Pu fraction containing 98.9% of Pu and 0.07% of U, and then the U fraction (99.93% of U and 1.1% of Pu). The separation time is 50 min.

Countercurrent chromatography (CCC) works with a liquid stationary phase. It is proposed to create a concentration gradient in the stationary phase during the chromatographic run. The gradient concentration is initiated putting a known volume of neat stationary phase at the head of the CCC column and a known volume of dithizone (a test die) concentrated stationary phase at the end of the CCC column. Water‐organic solvent biphasic liquid systems were tested. The aqueous phase is the mobile phase. Hexane, decane, chloroform, methylisobutyl ketone, tetrachloromethane, or ethyl acetate were used as the dithizone containing stationary phase. It was found that the concentration gradient created inside the column is dependent on the operational hydrodynamic parameters and physicochemical properties of two‐phase liquid systems used. The water‐organic solvent liquid systems were divided into two types: 1. “Nimble” (easily mixed) systems that readily form concentration gradients, which can be completely le...

The capability of dynamic phase mixing in a two-phase liquid system in a rotating coiled column, which is used to separate substances in liquid countercurrent chromatography, was studied. The effects of the hydrodynamic conditions of the chromatographic process and the physicochemical properties of the two-phase liquid systems now in use on the efficiency of phase mixing in a rotating coiled column were found. A new approach to creating a concentration gradient in the stationary phase was proposed. The following three modes of mixing stationary-phase regions within a column were found: the formation of a stable reagent concentration gradient within the rotating coiled column, the slow mixing of zones, and the complete mixing of zones.

The separation of Am(III) and Cm(III) by countercurrent chromatography (CCC) was achieved using the liquid phase systems "diamide–hydrogenated tetrapropylene (TPH)–HNO3" following the optimisation of: (i) the compositions of the mobile (HNO3 concentration) and the stationary (nature of the diamide and its concentration in TPH) phases, (ii) column length and (iii) operating parameters of the CCC (flow rate of the mobile phase and rotation speed of the coil column). The following diamide extractants have been studied: (i) N,N´-dimethyl-N,N´-dibutyltetradecylmalonamide (DMDBTDMA), (ii) N,N´-dimethyl-N,N´-dioctylhexyl-ethoxymalonamide (DMDOHEMA) and (iii) N,N´-dimethyl-N,N´-dibutyldodecylethoxymalonamide (DMDBDDEMA). It is shown that these diamides can be used for the separation of Am(III) and Cm(III) by CCC. Increasing the column length leads to an increase of the stationary phase retention on the column while improving the Am/Cm separation. Increasing the speed of rotation of the centrifuge from 660 to 950 rpm also results in increasing the stationary phase retention but does not influence the resolution of the Am/Cm separation. Decreasing the flow rate of the mobile phase from 1.0 to 0.5 mL/min leads to a better resolution of Am and Cm separation. The best Am/Cm separation was achieved with systems based on DMDBDDEMA and DMDOHEMA in TPH using a two-layer coil column and an isocratic elution mode. The application of CCC makes it possible to separate the elements within 100 min: the Cm fraction contains 99.5% of Cm(III) and 0.6% of Am(III) inventories and the Am fraction contains 99.4% of Am(III) and 0.5% of Cm(III).

The effect of hydrodynamic parameters and the specific features of instrument design on the efficiency of substance separation in countercurrent liquid chromatography (CCC) was studied using a constant retention factor of the stationary phase in the column. The study was conducted with the separation of benzyl alcohol and p-cresol in a two-phase liquid system heptane–ethyl acetate–methanol–water (1.4 : 0.6 : 1 : 1) in as an example. It was shown that the peak resolution is improved with an increase in the rotational speed of the column and a decrease in the flow rate of the mobile phase. The best peak separation was attained using columns for which the ratio of the column rotation radius to the radius of column revolution was 0.615. It was shown that countercurrent chromatography allows the separation of substances with low partition constants (K < 1) in dilute solutions. The volume of the test sample may be up to 15% of the total volume of the chromatography column.

A mathematical model was developed which describes the behavior of various liquid systems in a rotating coiled column used in countercurrent chromatography. The conditions of retaining the liquid stationary phase were described in detail for hydrophilic (slowly settling) systems. Various forces that act on liquids in the column were considered. Equations were derived for the steady-state retention process. Mathematical expressions were obtained which make it possible to estimate the stationary-phase volume retained in a column with consideration for the physicochemical properties of the liquid system in use, the speed of column rotation, and the main design parameters of the planet centrifuge. This volume directly affects the column capacity and separation efficiency, and it is crucial for choosing liquid systems and experimental conditions.

The effects of physicochemical properties of two-phase liquid systems (interfacial tension and differences in density and viscosity) on the retention of the stationary phase in the column were examined. These effects mainly determine the separation parameters of compounds. Extractant/decane–aqueous phase systems were used; their physicochemical properties changed both as a result of adding an extractant (di-(2-ethylhexyl) phosphoric acid, trioctylamine, or tributyl phosphate) to the organic solvent and because of a change in the composition of the aqueous phase. Aqueous ammonium sulfate of varying concentration was used as a mobile phase. It was shown that interfacial tension substantially affects the behavior of the systems under consideration. An increase in the ammonium sulfate concentration only slightly affects the retention factor of the stationary phase in the column. With a proper choice of the stationary phase, countercurrent chromatography can be used for the extraction of components from salt solutions of various concentrations.

The potentialities of rotating coiled columns in countercurrent chromatography (CCC) and centrifugal field-flow fractionation (CFFF) are demonstrated. A rotating coiled column is a fluoroplastic or steel coil wound around a rigid cylindrical drum, which revolves about its axis and, at the same time, revolves around the central axis of the device called planet centrifuge. The stationary (liquid, solid, or heterogeneous) phase is retained in the column because of the centrifugal force field, and the mobile liquid phase is continuously pumped through the column. The methods for recovery, separation, and preconcentration of various trace elements in geological samples and high-purity substances with the use of two-phase liquid systems (CCC) are developed. Procedures are proposed for the continuous sequential extraction of various element species from soil and for the recovery of polycyclic aromatic hydrocarbons from sewage sludge with the use of natural suspensions or solid particulates as stationary phases. It is also shown that rotating coiled columns can be used in a new field, microparticle fractionation by CFFF.

A method has been developed for the separation of the entire group of rare-earth elements from high-purity calcium chloride by countercurrent chromatography, and subsequent determination of the elements by ICP-MS. A solution of diphenyl[dibutylcarbamoylmethyl]phosphine oxide in chloroform (0.5 mol L(-1)) has been chosen as reagent for the extraction and preconcentration of trace rare-earth elements from aqueous 5% CaCl2 solution, 3 mol L(-1) in HNO3 and 0.1 mol L(-1) in HClO4. The analytes are back-extracted into a small volume of water and the aqueous eluate is subjected to ICP-MS measurements. The performance characteristics of the procedure developed have been checked by use of the standard addition technique and a real CaCl2 sample (Merck product) has been analyzed. The results obtained demonstrate the applicability of countercurrent chromatography to the determination of ultratrace elements.

The effect of physicochemical properties of two-phase liquid systems (interfacial tension and differences in the densities and viscosities of the two phases) on the retention of the stationary phase in a rotating coil column was studied, taking as examples complex liquid systems containing an organic solvent (n-decane, n-hexane, chloroform, carbon tetrachloride and methylisobutylketone), an extracting reagent (di-2-ethylhexylphosphoric acid, tri-n-butyl phosphate, trioctyl amine), water, and a mineral salt (ammonium sulfate). Extracting reagent additions to the organic solvent and salt additions in the aqueous phase lead to changes in physicochemical properties of the liquid system and affect, strongly, the stationary organic phase retention. The influence of the rotational speed on the stationary phase retention for different systems was also investigated. Some recommendations for the selection of proper systems for CCC separations are formulated.

The present work is an attempt to correlate the composition and some physico-chemical properties of two-phase systems with the stationary phase retention in a coil planet centrifuge of J-type. Complex liquid systems containing an organic solvent (n-decane or chloroform), an extracting reagent (di-2-ethylhexylphosphoric acid, D2EHPA), water and a mineral salt (ammonium sulphate) are considered.

A hypothesis of the mechanism of the retention of one (stationary) phase of a two-phase liquid system in a rotating coil column has been proposed. The balance of forces of different nature acting on the stationary phase retained in the coil column has been considered. The basic equation of the retention process stationarity has been derived. Theoretical dependencies of retention factor on rotational speed for hydrophobic systems and experimental data are in good agreement.

Countercurrent chromatography has been employed for the purification of solid chemical reagents, such as (NH(4))(2)SO(4), NH(4)HSO(4), NH(4)F and NH(4)Cl from a number of most common metal impurities (Fe, Al, Zn, Cu, Co, Cd, Ni, Cr, Ca, Mg, K) in order to gain high-purity reagents. After evaporation these can be used for fusion decomposition purposes in trace analysis of various refractory materials (e.g. high tech ceramics). N,N-hexamethylenedithiocarbamic acid, 8-hydroxyquinoline, dibenzo-18-crown-6 and dicyclohexano-18-crown-6 were used as extracting reagents.

This paper directly links up with Part I [ Spectrochim. Acta 48B , 1365 (1993)] which treats the first application of countercurrent chromatography (CCC) for pre-separation of rare earth elements (REE) in rocks. The rapid and reliable separation and pre-concentration of “light” REE and Y can be achieved using a system of 0.5 mol/l di-2-ethylhexylphosphoric acid (D2EHPA) in n -decane-hydrochloric acid of different concentrations and a planetary centrifuge as a CCC device. However, Tm, Yb and Lu are partially retained in the stationary phase. Comparative data is presented on three other two-phase liquid systems containing trioctylphosphine oxide (TOPO); D2EHPA and TOPO mixtures and diphenyl(dibutylcarbamoylmethylphosphine)oxide (Ph 2 -Bu 2 ) as extractants in terms of their ability for whole REE group complete isolation from the rock constituents. The partial losses of “light” REE (La and Ce) occurred in the system of 0.1 mol/l solution of TOPO in isobutylmethylketone (IBMK) (stationary phase)-1 mol/l NH 4 NO 3 -6 mol/l HCl aqueous solutions (mobile phase). Complete isolution of the entire REE group can be reached in two systems: 0.3 mol/l D2EHPA + 0.02 ml/l TOPO in the solvents mixture (3:1) of n -decane + IBMK, respectively (stationary phase)-1 mol/l NH 4 NO 3 -6 mol/l HCl aqueous solution (mobile phase), and 1.0 mol/l Ph 2 -Bu 2 solution in chloroform (stationary phase)-3 mol/l HNO 3 aqueous solution (mobile phase). The D2EHPA + TOPO mixture is recommended as more economic and accessible.

The influence of kinetic properties of several extraction systems on the separation of some elements by countercurrent chromatography (CCC) has been studied. The chromatographic behaviour of Eu(III), Fe(III), Ta(V), Nb(V), Hf(IV), Zr(IV) has been investigated in two kinetically different extraction systems on the basis of di-2-ethylhexylphosphoric acid (D2EHPA) and tetraphenylmethylenediphosphine dioxide (DTPMDP). It has been shown that the values of mass transfer coefficients determine the type of elution (isocratic or step), which is necessary for the element separation. The data on batch extraction (mass transfer coefficients and partition coefficients) and parameters of chromatographic peaks (half-widths) can be interrelated by the expression proposed.

In countercurrent chromatography (CCC) both stationary and mobile liquids undergo intense mixing in the variable force field of a coil planet centrifuge and the separation process, like the separation in conventional solvent extraction column, is influenced by longitudinal mixing in the phases and mass transfer between them. This paper describes how the residence time distribution (or the elution profile) of a solute in CCC devices and the interpretation of experimental peaks, can be described by a recently developed cell model of longitudinal mixing. The model considers a CCC column as a cascade of perfectly mixed equal-size cells, the number of which is determined by the rates of longitudinal mixing in the stationary and mobile phases. Experiments were carried out to demonstrate the validation of the model and the possibility of predicting the partitioning behaviour of the solutes. The methods for estimating model parameters are discussed. Longitudinal mixing rates in stationary and mobile phases have been experimentally determined and experimental elution profiles are compared with simulated peaks. It is shown that using the cell model the peak shape for a solute with a given distribution constant can be predicted from experimental data on other solutes.

Partition countercurrent chromatography can be used for the concentration and separation of elements of similar properties in aqueous solution — extradant systems. The angle of wetting of the column wall with the components of a two-phase liquid system has a considerable effect on the retention of the stationary phase. The method was used for the separation of orthophosphate and pyrophosphate (extradant — solution of dinonyltin dichloride in methylisobutylketone), cesium and strontium (solution of cobalt dicarbollide in nitrobenzene) and rare earth elements (di-2-ethyhexylphosphoric acid in decane).