M. A. Statkus

X-ray fluorescence determination of As, Bi, Co, Cu, Fe, Ni, Pb, Se, V and Zn in natural water and soil extracts after preconcentration of their pyrrolidinedithiocarbamates on cellulose filters

A simple method for the elements preconcentration on thin-layer paraffin-treated cellulose filters was proposed. It was found that pyrrolydinedithiocarbamates of As(III), Bi, Cd, Co, Cu, Fe(III), Ni, Pb, Se(IV), V(V) and Zn obtained after mixing of sample (3-5 ml min(-1)) and reagent (0.7-1.0 ml min(-1)) streams were quantitatively recovered from 100 ml sample. The sample acidity was adjusted to pH 4.8-5.2 for preconcentration of Cd, Co, Cu, Fe(III), Ni, Pb, V(V) and Zn, and to 2 M HCl for preconcentration of As, Bi and Se. The optimum reagent concentration was found to be 0.1%. The elements were determined on the filters by X-ray fluorescence spectrometry. The detection limits achieved were 0.1-4.0 mug of element on the filter. Relative standard deviation (R.S.D.) was not higher than 0.08 while determining 5-50 mug of elements on filter. Accuracy and precision of the technique proposed were evaluated by the analysis of spiked natural samples.

On-line coupling of sorption preconcentration to liquid-chromatographic methods of analysis

Methods of analysis combining the on-line sorption preconcentration of analytes with their subsequent separation and determination by high-performance liquid chromatography are considered. Approaches to the selection of sorbents, the sizes of preconcentration columns, and the sorption and desorption conditions are discussed along with the corresponding instrumentation. Many examples of the determination of organic compounds of different polarity and organic and inorganic ions are presented.

Determination of rare earth elements in rock samples by inductively coupled plasma mass-spectrometry after sorption preconcentration using Pol-DETATA sorbent.

Sorption preconcentration of rare earth elements prior to introduction in inductively coupled plasma mass spectrometry is developed. For the first time Pol-DETATA sorbent was used for REEs preconcentration after digestion of wide classes of rock samples. The developed technique is based on lithium metaborate fusion, preconcentration on Pol-DETATA sorbent, elution with nitric acid and flow-injection sample introduction to the ICP-MS spectrometer. The efficiency of REEs extraction from the resulting solutions in the presence of high amounts of iron is examined. 5-sulfosalicylic acid was used as a masking reagent. Flow-injection introduction of 50 μL of eluate obtained after desorption was used to avoid corrosion of the parts of the ICP-MS instrument due to high acidity of the eluate. The accuracy of the developed technique is checked by the analysis of the certified reference materials of rock samples. The REEs recoveries within 85-100% interval were attained for most REEs in tested reference materials.

X-ray Fluorescence Determination of Heavy Metals in Solutions after the Preconcentration of Their Pyrrolidinedithiocarbamate Complexes on Cellulose Filters

Conditions of the quantitative extraction of Co, Cu, Fe(III), Ni, Pb, V(IV), and Zn from solutions on cellulose filters in the form of pyrrolidinedithiocarbamates obtained in flow were found. The elements were determined on filters by X-ray fluorescence spectrometry. The detection limits were 0.1, 1.2, 0.4, 0.2, 0.2, 0.4, and 0.3 μg on the filter, respectively. The relative standard deviation of the results of the determination was no higher than 8% for the amounts of elements on the filter of 5–50 μg. The accuracy of the determination of elements by the proposed sorption–X-ray fluorescence method in river and sea water and in soil extract was verified by the added–found method.

Determination of phenols by liquid chromatography after online adsorption preconcentration on the Strata-X adsorbent

An online adsorption-high-performance liquid chromatography (HPLC) method was developed for the determination of phenols (11 priority water pollutants) in waters, using polystyrene chemically modified with N-vinyl-2-pyrrolidone (Strata-X). The detection limits for phenols obtained using a preconcentration from 10 mL of water and calculated by different means vary from 0.3 to 2 μg/L. The accuracy of the determination of phenols in tap and river water samples was verified by the standard addition method.

Extraction and determination of biologically active components of St. John’s wort and its pharmaceutical preparations

A procedure is developed for the determination of biologically active substances (BAS) of common St. John’s wort (Hypericum perforatum L.) by HPLC using two columns, Luna C18, 100 Å (for the determination of phenolcarboxylic acids and flavonoids), and Onyx Monolithic C18 (for the determination of phloroglucinols and naphthodianthrones), in the gradient elution mode with diode array detection. The detection limits for analytes are 0.05–0.20 μg/mL. To optimize the conditions, we studied the extraction of biologically active substances from St. John’s wort by a water–ethanol solution at different temperatures and pressures and under the effect of microwave radiation and ultrasound. The maximum amounts of substances were extracted in a dynamic mode under heat and pressure. The procedure was applied to the St. John’s wort samples of different brands and some pharmaceutical products based on it. The components of extracts were identified by retention times, UV spectra, and mass spectra. It was shown that the content of biologically active substances in pharmaceutical samples of St. John’s wort depends on the herb habitat. It was shown that hyperforin decomposed in pharmaceutical formulations based on St. John’s wort during storage.

Sorbents with non-covalently immobilized β-diketones for preconcentration of rare earth elements

A comparison of the efficiency of sorbents obtained by different methods of non-covalent immobilization of β-diketones on some low-polar matrices with respect to extraction of rare earth elements (REEs) was carried out. It was shown that sorbents containing reagent amounts of 1-8mmol/g can be obtained by sorption of reagents on low-polar matrices from aqueous and aqueous-organic solutions, and the value for the maximum capacity of the sorbent correlates with the specific surface of the matrix. Similar sorbents were also prepared by impregnating the matrix with reagent. It was found out that, under the chosen conditions, sorbents modified by extracting reagent from the aqueous solutions are more stable and extract lanthanum with higher distribution coefficients than those obtained by impregnation. We have found conditions for quantitative extraction of REEs from seawater in the proposed preconcentration systems (pH 4.0, minicolumn dimensions 2×10mm, v=4ml/min). It was shown that all REE may be quantitatively recovered in both ways: on modified sorbents and as complexes with reagents on unmodified matrices. We have proposed a sorbent for lanthanum preconcentration from large volumes of water samples (500ml). The sorbent is stable in dynamic conditions and is based on hyper cross-linked polystyrene modified with 1-phenyl-3-methyl-4-benzoylpyrazol-5-one (PMBP). Desorption could be carried out with 1-2M HNO3. REEs were determined by ICP-MS, LODs achieved were in ng/l range.

Methods for the extraction of biologically active substances from medicinal plants based on an example of St. John’s wort components

The efficiency of extraction of biologically active substances from common St. John’s wort (Hypericum perforatum L.) under varied conditions was compared in order to optimize a sample preparation procedure. The extraction with water and water–alcohol solutions under static conditions and with stirring was examined; the effect of ultrasonic treatment and extraction with water and water–alcohol mixtures under dynamic conditions at elevated temperature and pressure and the extraction with supercritical carbon dioxide were studied. It was established that, in the extraction of biologically active substances from plant materials, the chemical affinity of an extractant the extracted component is of primary importance; an increase in the pressure under dynamic conditions is the second factor in importance, which increases the efficiency of extraction.

Different Approaches to Solid-Phase Extraction of Lanthanum with Low-Polar Sorbents: Comparison of Dynamic Coating, Impregnation and On-Line Mixing

Three different approaches to preconcentration of metal ions using low-polar sorbents were compared: dynamic coating of the sorbent surface with hydrophobic chelating reagent; impregnation of the sorbent with a solution of the reagent in a suitable volatile organic solvent; and on-line merging of sample and reagent streams prior to solid-phase extraction of metal-reagent complexes. Lanthanum was used as a model analyte; 1-phenyl-3-methyl-4-benzoylpyrazol-5-one (PMBP) as a reagent for preconcentration. It was found out that the most effective approach for the analyte recovery from a large sample volume is the use of a dynamically coated sorbent with high specific surface.

On-line solid-phase extraction and HPLC determination of phthalic acid monoesters including desorption with subcritical water

The possibility of on-line solid-phase extraction and HPLC determination of phthalic acid monoesters is demonstrated. The combined procedure includes solid-phase extraction of phthalates from 10 mL of water on a Hypercarb porous graphitic carbon sorbent, desorption with subcritical water at 150°C, focusing of the analytes at the initial part of the HPLC column, and separation with a water–acetonitrile mixture.