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A combination of analytical methods (including CHNS-O elemental analysis, X-ray diffraction, 1H and 13C NMR spectroscopy, MALDI-TOF and ICP mass spectrometry) was used to determine the elemental composition and average molecular and structural parameters of asphaltenes isolated from a heavy oil sample from the Ashalchinskoye field and vacuum residue samples from two different Russian oil refineries. The study identified differences in the nano-aggregate size of asphaltenes in heavy oil and vacuum residues, and evaluated the effects of the composition and molecular structure of asphaltenes on the composition and properties of the heavy petroleum feedstock samples.

Sulfur is present in crude oil and petroleum products in the form of various compounds: mercaptans, hydrogen sulfide, sulfides, disulfides, thiophene derivatives, high-molecular-mass heterocyclic compounds, etc. The content of elemental sulfur in petroleum feedstock is low (up to 0.1%). Sulfur negatively affects the service and transportation properties of oil; therefore, the content of sulfur compounds in petroleum products and commercial oil is strictly limited. Numerous methods are used today for removing sulfur compounds from petroleum feedstock, such as hydrotreating, bio- and oxidative desulfurization, extraction, including supercritical fluid extraction, adsorption, alkylation, etc. This review deals with the use of extraction methods for treating petroleum feedstock to remove various sulfur-containing compounds. Particular attention is paid to papers dealing with the use of cheap and available polar organic solvents and inorganic chemicals for removing sulfur and its compounds both from model solutions and from crude oils and petroleum fractions. Also, search for new “green” solvents such as ionic liquids and eutectic mixtures, allowing removal of sulfur compounds from crude oil, shows promise. As a rule, complete removal of sulfur-containing compounds from oil samples by extraction requires a multistep extraction process.

This article demonstrates possible separation of Pd(II), Pt(IV), and Rh(III) ions from chloride solutions by solvent extraction in rotating coiled columns (RCC). The most common reagents used for extraction of platinum metals were selected as extractants: trioctylamine (TOA), methyltrialkylammonium chloride (MTAA), tributyl phosphate (TBP), and relatively new reagent—N,N,N',N'-tetra-n-octyldiglycolamide (TODGA). The completeness of extraction of platinum metals from individual and mixed hydrochloric acid and chloride solutions has been analyzed as a function of the essence and concentration of extractant, acidity of the analyzed solutions, and other factors. Optimum conditions of quantitative extraction of the metals from model hydrochloric acid and chloride solutions into the extractant phase have been determined, including subsequent selective separation at the re-extraction stage. A flowchart has been proposed for multistage extraction of Pd(II), Pt(IV), and Rh(III) using 0.05 M MTAA solution in toluene as a stationary phase in RCC. The flowchart includes extraction of Pd(II) and Pt(IV) ions from the solution (0.1 M HCl + 30 g/L Cl–) into the organic phase upon simultaneous separation of Rh(III) remaining in the aqueous phase and consecutive re-extraction of Pd(II) and Pt(IV) from the organic phase using 0.01 M solution of thiourea in 0.1 M HCl and 1 M solution of thiourea in 0.5 M HCl, respectively. The flowchart has been verified for separation of platinum metals in the production process of preset composition. The degree of metal extraction after processing by 0.05 M solution of MTAA in in toluene and consecutive re-extraction by solutions of thiourea is 99.5% for rhodium(III), 99.9% for palladium(II), and 97.4% for platinum(IV). The extracted aqueous phases of rhodium and platinum after output from the column did not contain impurities of other platinum metals. In the aqueous fraction of palladium, the platinum content was 0.5%.

The characterization of the feedstock is an important analytical task in the modeling and development of processes for upgrading of petroleum residues. This work presents the results of fractionati...

Transmission electron microscopy (TEM) was used to study the structure of particles of CO2-asphaltenes precipitated from a goudron vacuum residue sample in the gas anti-solvent (GAS) process using heptane, toluene, and their mixture (heptol) as diluents. It was shown that CO2-asphaltenes, despite lower aromaticity and polarity compared to C7-asphaltenes, have a similar irregular layered internal structure, as well as a close distribution of the aromatic layers and similar distance between the layers in the packed crystallites.. The type of the diluent used affects not only the yield and composition of the precipitated CO2-asphaltenes, but also the degree of order and the size of layers of aromatic fragments of the molecules forming their structure. In this respect, toluene as a diluent ensures the formation of CO2 asphaltenes that are comparable to C7-asphaltene particles in their molecular structure and structural parameters.

Extraction of sulfur compounds from oil and petroleum products is a high priority task associated with tightening of the criteria of fuel quality control, negative impact of sulfur on the processing and storage of crude oil, environmental safety, as well as widespread use of organosulfur substances in different industries. The selectivity of several organic and inorganic extractants (methanol, N,N-dimethylformamide, acetonitrile, 15% NaOH, PEG 4000, PEG 200, diethylene glycol, monoethanolamine, dimethylacetamide, n -methylpyrrolidone) in relation to thiophene, dibenzothiophene, thiophenol, dodecanethiol and metilsulfide was studied for model solutions of organic sulfur compounds in n -heptane and n -octane. Extraction was carried out under static conditions. Sulfur content in the initial sample and in the sample after extraction was determined using an x-ray fluorescence analyzer SPECTROSCAN S. Chromatographic analysis of the samples was performed on an Agilent gas chromatograph with a mass-selective quadrupole detector. The selectivity of the studied extractants in relation to the studied groups of sulfur compounds was assessed through recovering (%) of a particular sulfur compound. It is shown that acetonitrile, N,N-dimethylformamide, dimethylacetamide and n -methylpyrrolidone are the most effective extractants for thiophene extraction. Methanol, N,N-dimethylformamide, acetonitrile, PEG200, diethylene glycol, monoethanolamine, dimethylacetamide and n -methylpyrrolidone are capable of extracting a wide range of organosulfur compounds from model solutions. Aqueous solutions of PEG 200 and PEG 4000 provide extraction less than 11% of organosulfur compounds, whereas 15% NaOH solution and a mixture of 50% NaOH:ethanol (1:2) are selective extractants for aliphatic mercaptans and provide up to 99% extraction of thiophenol and dodecanthiol, respectively. It was found that n -methylpyrrolidone, dimethylacetamide and N,N-dimethylformamide have the highest extraction capacity among the studied extractants. A series of studies gives ground to propose a possible extraction scheme for recovery of mercaptans from a mixture of organosulfur compounds.

A study was carried out on the precipitation of heavy fractions and the isolation of asphaltenes from a petroleum sample using supercritical carbon dioxide (SC-CO2) as the antisolvent. The experiments were carried out in a laboratory supercritical fluid extraction device using a GAS (gas antisolvent) procedure at from 50 to 140°C and pressure from 10 to 30 MPa. We determined the effects of temperature and pressure as well as of the addition of a hydrocarbon diluent on the yields of the isolated fractions. The elemental and microelement composition was determined as well as the structural properties of the components isolated in the SC-CO2 medium at various temperatures. An increase in temperature at pressures above 20 MPa as well as the addition of small amounts of toluene to the starting petroleum sample gave greater isolation selectivity, greater concentration of asphaltenes in the precipitated fractions, and drier solid particles. In contrast to C7-asphaltenes, CO2-asphaltenes have lower aromaticity, polarity, and metal content. The proposed analytical method permits the isolation of asphaltenes in only a few hours, does not require large volumes of organic solvents, and yields asphaltenes in amounts sufficient for subsequent detailed study of their composition and properties.

We demonstrate that the method based on supercritical fluid extraction (SFE) using supercritical carbon dioxide (SC-CO2) as a basis of a solvent can be used, in principle, to fractionate a sample of heavy oil into narrow fractions. Studies are conducted using heavy oil of the Ashalchinskoye field as an example. The composition and yield of the fractions extracted from heavy oil depend on the concentration of the organic modifier (toluene) added to SC-CO2. Supercritical fluid extraction was carried out in a semiperiodic mode at 50°C and a pressure of 100 bar with a gradual increase in the concentration of toluene from 0 to 40 wt %. This resulted in nine fractions extracted with a total extract yield of 83.4 wt %. The use of SFE can significantly decrease the amount of the residue after the fractionation of heavy oil. The composition and properties of narrow fractions extracted from heavy oil are determined. The distribution of group hydrocarbon components, metals, sulfur, and Conradson carbon residue (CCR) between the extract fractions and the residue is found.

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.

Fuel development for solvent deasphalting (SDA), by means of which it is possible to obtain high yields of deasphalted oil (DAO) with acceptable quality for subsequent refining in catalytic cracking processes and hydrocracking in particular, is nowadays becoming increasingly important. In this paper, an experimental study of the SDA of tar (vacuum residue) with n-pentane at various extraction temperatures and pressures was undertaken, and this made it possible to determine the effect of the phase state of the solvent on the yield, composition, and properties of the separation products,. It was shown that transfer of pentane from the liquid phase state to the region of a subcritical and then supercritical fluid (SCF) increases the solubility of the tar components and the yield of the DAO for fixed values of the solvent density. Despite some decrease in the quality of the DAO in the case of supercritical extraction at temperatures close to the critical temperature of the solvent (220°C), the phase state of the pentane has little effect on the metal content of the products, the carbon residue content of the DAO, and the softening point of the asphalt for the given yields.

Highly dispersed materials Fe3O4@TEOS and Fe3O4@PVP for asphaltenes extraction from organic media have been synthesized via modifications of nanosized magnetite with tetraethoxysilane and N-polyvinylpyrrolidone. Using model compounds simulating the main functional groups of asphaltenes and some natural asphaltenes isolated from crude oil, the sorption capacity was estimated for Fe3O4@TEOS. It was found that the extraction degree of asphaltenes from a toluene solution at 45 °C reached 65–70%, and the sorption capacity was 28 mg g–1.

The development and use of instrumental methods for the determination of a wide range of trace elements in oil is considered. Special attention is paid to methods of the direct introduction of samples into spectrometers. It is shown that preliminary sample preparation is in certain cases necessary for the determination of trace elements in oil. The main methods of sample preparation of oils, including methods of extraction of a series of trace elements from crude oil (extraction, membrane, sorption, etc.), are described.

Possibilities of demetallization of heavy petroleum feedstocks (HPF) using supercritical fluid extraction (SFE) have been studied. Experiments with various solvent mixtures were carried out in a semibatch extractor and in dynamic mode to assess the effect of modifier type and concentration as well as extraction time on the yield of extract and content of vanadium, nickel and iron in produced phases (extract and residual phase). Vacuum residue was used as the feedstock and supercritical carbon dioxide (scCO2) was used as the primary solvent for extraction. Methanol, ethanol, acetonitrile, acetone, ethyl acetate, n-heptane, toluene and o-xylene were added to scCO2 as modifiers to form the solvent mixtures. Extraction temperatures and pressures were maintained at 50 °C and 30 МPa to achieve a high density of scCO2. It has been found that methanol and o-xylene containing mixtures provide the highest metal content in the extract while ethyl acetate, n-heptane and toluene provide the lowest. Higher extract yield and the degree of metal concentration in residue were obtained with increasing both toluene concentration in scCO2 and the time of dynamic extraction. The demetallization efficiency is estimated to be at a level above 95wt % at the yields of extract (demetallized oil) up to 60wt % using toluene as a modifier.

A comprehensive approach to the determination of the elemental composition of oils (including those with a viscosity of 5000 mm2/s) is proposed. It ensures the determination of the most elements present in oils using two versions of sample preparation, autoclave decomposition of oil samples and extraction preconcentration of elements from oil into an aqueous solution on rotating coiled columns (RCCs). The application of RCCs in the elemental analysis of oil ensures the preconcentration of a number of trace elements from oil (including rare-earth elements) and the determination of their concentrations at a level of ng/kg. The preconcentration factor of trace elements from oil using an RCC depends on the volume of oil sample pumped through a constant volume of the stationary phase (acid solution) retained in the column and on the speciation of elements in the oil.

To the article “Structural Features of Particles of Goudron CO2 Asphaltenes Precipitated with Various Organic Diluents,” by R. N. Magomedov, A. V. Pripakhailo, D. I Panyukova, L. S. Foteeva, and T.A. Maryutina, Vol. 56, No.3, pp. 325-332, July, 2020

Solvent deasphalting of vacuum residue using carbon dioxide-toluene mixture was studied to assess the effect of the process parameters and mixture composition on the yield and composition of deasphalted oil (DAO) produced. An insignificant effect of the toluene content in the mixture on the DAO yield was found at a concentration above 30 wt.%, which was attributed to effective anti-solvent properties of carbon dioxide. At relatively low-pressure region, an increase in temperature and the transition of the mixture to the supercritical state led to a rapid decrease in the solvent density and the DAO yield. At the same time, at pressures providing a mixture density in the region above ∼0.6 g/mL, an increase in temperature above the mixture critical value was accompanied by increasing the DAO yield, even despite a noticeable decrease in the solvent density. However, conducting the extraction at temperatures near and beyond the mixture critical temperature reduces the separation selectivity at close the extraction yields due to increased solubility of metal-containing polar compounds. A proposed mixture in the single-phase liquid state can provide high DAO quality with metal and CCR removal efficiency of more than 90 and 80 wt.%, respectively.

The effect of magnetic field on the composition and physicochemical properties of oil and petroleum products is described. Experimental data are presented, illustrating that the structure of heavy oil residues (HORs) of different origin can be changed upon exposure to a magnetic field. The effect of exposure time and power of magnetic field on changes in the composition of HOR solutions in various solvents (toluene, n-hexane, dichloromethane, and isopentane) is studied. The use of magnetic field at the stage of sample preparation of solutions is proposed in the identification of heavy oil residues and the elucidation of their origin based on gas chromatography with a mass-selective detector (GC–MS).

Comparative assessment of the prospects of development of heavy petroleum feedstock (HPF) upgrading technologies in terms of the possibility of removal and recovery of metals contained in the feedstock is presented. It has been shown that HPF demetallization with different efficiencies can be achieved as a result of destructive thermal conversion of the feedstock and nondestructive mass transfer processes. Solvent deasphalting is characterized by simplicity of engineering design and operating flexibility and makes it possible to remove both asphaltenes and metals, whose deposition leads to irreversible deactivation of oil refining catalysts. Promising lines in demetallization by destructive feedstock conversion are associated with processes that provide the highest degree of HPF conversion and the lowest yield of the unconverted residue, in which the feedstock metals are concentrated. In this regard, the development and implementation of petroleum residue upgrading technologies based on the slurry hydrocracking, fluid coking or flexicoking, and supercritical fluid extraction processes creates real prerequisites for the organization of high-conversion comprehensive processing of heavy oils with the isolation of a metal concentrate.

This is an Open Access Article. It is published by International Union of Pure and Applied Chemistry (IUPAC) under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International Licence (CC BY-NC-ND). Full details of this licence are available at: http://creativecommons.org/licenses/by-nc-nd/4.0/

A method is proposed for the sample preparation of oil-contaminated soils based on the dynamic extraction of petroleum products in a microcolumn of special design. By an example of the analysis of GSO (State Standard Sample) 8673-2005 of an oil-contaminated soil and model soil samples, a comparative evaluation of the efficiency of dynamic and batch (shaking in a shaker) extraction for the sample preparation of oil-polluted soils is carried out. The concentration of petroleum products in the extracts was determined by IR spectrometry. It was shown that the recovery of petroleum products into carbon tetrachloride in extraction in a microcolumn is, on the average, 50% higher than that in mixing the sample and reagent in a shaker. The rapid and efficient extraction of petroleum products in a microcolumn is possible because of dynamic extraction occurring at a constant renewal of the reagent.

A method is proposed for the sample preparation of heavy oil residues characterized by viscosity of more than 700 mm2/sec at 100°C to study their elemental composition. It is shown that a wide range of elements can be determined in heavy oil residues by inductively coupled plasma atomic emission spectrometry (IC-AES) when the sample dissolved in an organic solvent is injected into the instrument. The optimal parameters for the determination of metals in heavy oil residues by ICP-AES are selected, including an organic solvent and the method of sample dilution. The results of elemental analysis of heavy residues of oils from Chernigovskoe, Shpakovskoe, and Samarskoe deposits are compared. The developed method for determining metals in heavy oil residues significantly reduces the analysis time and does not require complex sample preparation.

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).

Comparative elemental analysis of the Tengiz oil and diesel fuel is performed by inductively coupled plasma mass-spectrometry with autoclave digestion, digestion, dilution with organic solvents, and also rotating coiled columns (RCCs). The advantages and drawbacks of each of the listed sample preparation techniques for the separation of microelements are discussed. In contrast to the other versions, the use of RCCs is shown to provide a unique opportunity to preconcentrating microelements from oil and petroleum products into tiny volumes of aqueous solutions (10 mL of 0.5 M HNO3). The eluate prepared can be used in the subsequent analysis by ICP MS with no extra sample preparation steps. The RCC preconcentration of elements from oil and petroleum products makes it possible to determine metals in concentrations from μg/kg to ng/kg.

A novel approach to the elemental analysis of crude and diesel oil permitted preconcentration of trace elements is presented. An oil sample is continuously pumped through the rotating coil column as a mobile phase while an aqueous nitric acid solution is retained as a stationary phase. Two phases are kept well mixed and agitated but there is no emulsion on the interface at chosen conditions. Preliminary investigation of features of stationary phase retention of two-phase liquid systems (oil/oil products-aqueous solution) in rotating coil column has been shown. 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 aqueous acidic phase which pumped out of the column for analysis can be easily determined with inductively coupled plasma mass spectrometry (ICP-MS) without additional sample preparation. Optimal concentration in the stationary phase of nitric acid for preconcentration of elements from oil by CCC has been investigated. 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. Combination of preconcentration method by CCC and highly sensitive determination method (ICP-MS) for quantitative detection of the trace elements (without any additional sample preparation) has been suggested for the first time.

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.

It is shown for the first time that rotating-coiled columns (RCC) can be used as sample preparation tools in the analysis of petropolluted soils. The use of RCC allows for the extraction of petroleum products from soils in the dynamic mode without using additional means of sample preparation. A test sample of soil is retained in an RCC as a stationary phase. Petroleum products are extracted from soil in 15–25 mL of an organic solvent (n-hexane, acetonitrile). Sample preparation lasts no more than 60 min. Examples are presented for the extraction of hydrocarbons, constituents of diesel fuel, and phthalates in the analysis of petropolluted soil samples taken from the territory of oil-extracting and oil-refining enterprises of the Krasnoyarsk region and the Khanty-Mansiisk autonomous area.

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).

This paper describes an investigation of organic phase retention and how it is affected by changing certain variables that are in the control of the user. A binary approach is taken in order to perform a quick evaluation of how key factors, like the addition of an extraction agent or a change of temperature, flow, tubing material, and bore affect stationary phase retention. Several different phase systems were studied in this way (decane–water, chloroform–water, methylisobutylketone–water, and carbon tetrachloride–water). The results show that retention is higher and more stable for larger bore tubing, and that at the analytical scale, there are threshold affects at low rotational speeds, which can create significant differences in retention behavior.

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.

The distribution and motion of liquid–liquid two-phase systems in thin tubes under conditions modeling rotation (including planetary rotation) of chromatographic columns are considered. Criteria are derived that determine the conditions for transition between various types of distribution of the liquid phases in a column using different physicochemical and rotation parameters.

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.

Environmentally significant phosphorus species in water and phosphorus fractions in sediments are briefly discussed and the methods for their determination are described. One of the most critical analytical steps is the separation of the different forms which, after conversion into orthophosphates, may be determined by a multitude of various techniques. Spectrophotometric methods are often preferred for routine analysis. Several rapid automatic methods for the separation and determination of orthophosphate, linear polyphosphates, cyclic condensed phosphates and lower oxidation state anions of phosphorus, which may exist in natural and waste waters, have been developed. They are mainly based on the use of flow-injection analysis, high-performance liquid chromatography including ion chromatography, capillary electrophoresis and a few of other techniques. These methods have been described and critically evaluated.

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 study assessed the genetic contribution to the waveform and parameters of visual event-related potentials (VERPs) in adult twins. VERPs were recorded in 21 MZ twin pairs and 20 DZ same sex twin pairs to different types of stimuli. As expected, there was a large genetic contribution to the waveform and parameters of VERPs to flash stimuli, and also to the waveform and some parameters of VERPs to semantic stimuli with polyvariant description. The waveform and parameters of VERPs to simple semantic stimuli (a word and a picture) were mainly determined by environmental factors.