Boris Ya. Spivakov

Countercurrent chromatography in analytical chemistry (IUPAC Technical Report)

Countercurrent chromatography (CCC) is a generic term covering all forms of liquid-liquid chromatography that use a support-free liquid stationary phase held in place by a simple centrifugal or complex centrifugal force field. Biphasic liquid systems are used with one liquid phase being the stationary phase and the other being the mobile phase. Although initiated almost 30 years ago, CCC lacked reliable columns. This is changing now, and the newly designed centrifuges appearing on the market make excellent CCC columns. This review focuses on the advantages of a liquid stationary phase and addresses the chromatographic theory of CCC. The main difference with classical liquid chromatography (LC) is the variable volume of the stationary phase. There are mainly two different ways to obtain a liquid stationary phase using centrifugal forces, the hydrostatic way and the hydrodynamic way. These two kinds of CCC columns are described and compared. The reported applications of CCC in analytical chemistry and comparison with other separation and enrichment methods show that the technique can be successfully used in the analysis of plants and other natural products, for the separation of biochemicals and pharmaceuticals, for the separation of alkaloids from medical herbs, in food analysis, etc. On the basis of the studies of the last two decades, recommendations are also given for the application of CCC in trace inorganic analysis and in radioanalytical chemistry.

Fractionation and characterization of nano- and microparticles in liquid media.

Submicron and micron particles present in liquid environmental, biological, and technological samples differ in their dimensions, shape, mass, chemical composition, and charge. Their properties cannot be reliably studied unless the particles are fractionated. Synthetic particles applied as components of analytical systems may also need preliminary fractionation and investigation. The review is focused on the methods for fractionation and characterization of nanoparticles and microparticles in liquid media, the most representative examples of their application, and the trends in developing novel approaches to the separation and investigation of particles. Among the separation techniques, the main attention is devoted to membrane filtration, field-flow fractionation, chromatographic, and capillary electrokinetic methods. Microfluidic systems employing the above-mentioned and other separation principles and providing a basis for the fabrication of lab-on-chip devices are also examined. Laser light scattering methods and other physical techniques for the characterization of particles are considered. Special attention is given to “hyphenated” techniques which enable the separation and characterization of particles to be performed in online modes.

Size separation of silica nanospheres by means of capillary zone electrophoresis

The electrophoretic mobility of silica nanospheres was shown to be a function of separation conditions such as pH and phosphate concentration of a carrier electrolyte. The separation selectivity can be controlled by the separation conditions and optimised depending on the sample composition. The effects of pH and phosphate concentration of buffer solutions on the nanosphere electrophoretic mobility are explained using the Overbeek-Booth electrokinetic theory taking into account both electrophoretic retardation and the relaxation effect.

Investigation of iron oxide nanoparticles by capillary zone electrophoresis

The electrophoretic behavior of gamma-Fe(2)O(3) nanoparticles was studied in aqueous solutions of Na(2)SO(4)-NaOH (pH 10.8) and of Na(2)SO(4)-Na(3)cit (pH 7.1) as running electrolytes. Two electrophoretic zones (smooth and with spikes) due to colloidal and suspended particles of approximately the same size range were formed during the runs. The suspension stability and size distribution were shown to depend on the composition of electrolyte used for dispersing the solids. The effects of electric field strength, injection time, injection pressure as well as sodium citrate concentration were studied and particle electrophoretic mobilities were calculated. Electron micrographs of particles studied were obtained. Preparation of reference samples based on the colloidal gamma-Fe(2)O(3) has been discussed.

A hyphenated flow-through analytical system for the study of the mobility and fractionation of trace and major elements in environmental solid samples.

A flow-through hyphenated analytical method has been tested that enables not only the accelerated and efficient fractionation of trace elements (TE) species in environmental solids to be achieved but allows real-time studies on the leaching process to be made. Rotating coiled columns (RCC), earlier used mainly in countercurrent chromatography, have been successfully applied to the dynamic fractionation of heavy metals in soil, sediment, and sludge samples. A ground solid sample (about 0.5 g) was retained in a PTFE rotating column as the stationary phase whereas different aqueous eluents, chosen according to recent data on the selectivity of leachants, were continuously pumped through. Elements were determined in the effluent on-line by inductively coupled plasma atomic emission spectrometry (ICP-AES). Since the flow rates used in the RCC are in good agreement with those needed for cross-flow nebulization in the ICP-AES spectrometer, both devices were coupled directly without any additional interface systems. Simultaneous investigation of the elution profiles of trace and major elements has made it possible to study the elements association in separated fractions and hence to prove the efficacy of extractants and their selectivity toward targeted mineralogical phases of samples. The close association of heavy metals with Mn oxides in the sediment and sludge samples was confirmed. The time-resolved dissolution of different organic complexes of metals was observed for the sediment sample. It was found that in sediment and sludge samples the dynamics of iron release under the action of Tamms reagent is somewhat different from that of aluminium. In addition, the proposed method can also be applied to develop effective leaching schemes and in the analysis of environmental solids for risk assessment of their contaminants addressed to water quality and bioavailability.

Separation of unmodified polystyrene nanosphere standards by capillary zone electrophoresis.

Size separation of five unmodified polystyrene nanosphere standards with diameters between 50 and 600 nm has been achieved in phosphate buffer solutions as carrier electrolyte. The electrophoretic mobility increases with particle diameter. Optical spectra was shown to be different for particles of different size. Effects of injection time, applied voltage, pH, and phosphate concentration in carrier electrolyte on particle separation were studied. Under optimal conditions the peak efficiency ranged from 600 to 10,500 theoretical plate numbers depending on nanosphere diameter was achieved.

Speciation of metals associated with natural water components by on-line membrane fractionation combined with inductively coupled plasma atomic emission and mass spectrometries

Abstract Specially designed multistage membrane filtration devices for the size fractionation of suspended particles and solutes were tested and used for speciation studies of metals associated with natural water components. The separated fractions were adapted to analysis by plasma source atomic emission and mass spectrometry. The distribution patterns for Al, Fe, Zn, Mn, Ni, Co, as well as Na, K, Mg, Ca in samples of river waters in Saxony were studied. Alkali and alkaline earth metals are distributed evenly between the fractions whereas easily hydrolysed trace elements mainly remain in the fraction containing the largest amounts of paniculate matter. The distribution of the analytes between the different fractions is influenced by both the storage time of the solution before fractionation and the addition of acids to stabilise the aqueous samples during storage.

Suspension column for recovery and separation of substances using ultrasound-assisted retention of bead sorbents

A novel approach to sorption recovery and separation of different substances is proposed which is based on the use of suspended bead sorbents instead of conventional packed beds of such sorbents. This makes it possible to employ small-sized beads which are trapped in a low-pressure column due to ultrasound-assisted retention, without any frits to hold the sorption material. A flow system including a separation mini-column, named herein a suspension column, has been developed and tested by the studies of solid phase extraction (SPE) of trace metals from bi-distilled water and sea water using a 150-μL column with a silica-based sorbent containing iminodiacetic groups (DIAPAK IDA) and having a grain size of 6 μm. The adsorption properties of DIAPAK IDA suspension (9.5mg) were evaluated through adsorption/desorption experiments, where the effect of solution pH and eluent on the SPE of trace metals were examined by ICP-MS or ICP-AES measurements. When sample solution was adjusted to pH 8.0 and 1 mol L(-1) nitric acid was used as eluent, very good recoveries of more than 90% were obtained for a number of elements in a single-step extraction. To demonstrate the versatility of the approach proposed and to show another advantage of ultrasonic field (acceleration of sorbate/sorbent interaction), a similar system was used for heterogeneous immunoassays of some antigens in ultrasonic field using agarose sorbents modified by corresponding antibodies. It has been shown that immunoglobulins, chlamidia, and brucellos bacteria can be quantitatively adsorbed on 15-μm sorbent (15 particles in 50 μL) and directly determined in a 50-μL mini-chamber using fluorescence detection.

A new approach to the studies of submicron particle suspensions based on the effect of pressure in capillary zone electrophoresis

A new approach based on the effect of pressure in CZE is suggested for acceleration of particle migration in electrophoretic runs resulting in reduction of the analysis time. It provides conditions for studying fast processes in suspensions. The effect of pressure on the migration of silica spheres with average diameters of 100, 150, and 390 nm was studied by CZE at an applied voltage of 25 kV. The particle hydrodynamic behavior was also investigated under the same capillary dimensions and BGE composition. The total particle mobility (excluding the average flow rate) was found to increase with increasing the pressure applied and particle size. The particle migration mechanism explaining the effect of pressure on particle velocity was shown to be almost the same as in wide‐bore hydrodynamic chromatography. It is based on changing radial distribution of particle concentration along the capillary cross section depending on particle diffusivity. On the basis of this mechanism appearance of a zone of negatively charged particles in electropherograms ahead of the marker peak can be explained.

Multi-Elemental Analysis in Size Fractions of Fine-Grained Solid Residue of Ore Grinding

Abstract Suspensions of fine-grained material originated from a former uranium mine in Central Germany and deposited in a settling plant were investigated. Total concentrations in the waste material ranged from 150 mg kg−1 (Ni), 215 mg kg−1 (As), 285 mg kg−1 (U), 290 mg kg−1 (Pb) to 1230 mg kg−1 (Zn). In order to find a correlation between particle size and the concentration of selected elements (As, U, Cu, Zn, Ni, Mn, Fe and Pb) the material was separated into different particle size fractions by independent procedures: (I) subsequent step-by-step fractionation (standard cascade) and (II) on-line multistage membrane filtration (OMFD). Using ICP-AES and ICP-MS the concentration of these elements in the particles, in solution and in the material deposited on filter (after dissolution with aqua regia) were determined. The main advantage of OMFD over cascade filtration exists therein, that the clogging of the membranes by particles is diminished indicated by a significant increase of the yield of particles in the individual fractions. It was shown that the sample preparation is very important for size fractionation of fine-grained materials. Surfactants, like sodium metaphosphate, led to an increase of the concentration of several elements in the dissolved form. This could be mainly attributed to the dissolution of analytes which were bounded on the particle surfaces as shown for uranium. It was found that As and Pb are homogeneously distributed in all size fractions of the uranium processing waste. The concentration of the elements Fe, Zn, Cu and Mn varied with particle size. They showed a similar pattern in size distribution. The highest amounts of these elements were found in the particular fraction > 8 μm. High amounts of U are sorbed on the particle surface.