L. N. Moskvin

Flow injection analysis with the chromatomembrane—a new device for gaseous/liquid and liquid/liquid extraction

A new device makes extraction procedures work continuously by realizing chromatographic principles in flow-injection analysis. The method allows independent mass transfer between two phases within a chromatomembrane cell. In spite of the small size of the cell-volume (about 3 cm(3)) the relevant contacting area is extended to 2 m(2). A mixing of phases is simply prevented, and an additional step of phase separation is no longer necessary. A chromatomembrane is generated from porous hydrophobic material (PTFE) with two types of pores, namely, macropores and micropores. Whenever two phases flow within the cell the aqueous one exclusively fills the large pores because of the capillary pressure produced by polar liquids in micropores. On the other hand these micropores remain available only for the extraction agent, e.g. non-polar liquids or gases. The mass exchange is significantly increased compared with conventional techniques. The wide field of practical applications can be seen from several results obtained from trace determinations in liquid and gaseous phases.

Stepwise injection spectrophotometric determination of epinephrine

Simple, rapid and fully automated methods for the manual and automated spectrophotometric determination of epinephrine have been developed by using schemes of stepwise injection (SWIA) and sequential injection analysis (SIA) implemented in the same manifold. The determination is based on the formation of reduced form of 18-molybdodiphosphate heteropoly anion by its reaction with epinephrine. Using of the reaction vessel in the general SWIA configuration instead of a holding and reaction coil in the SIA manifold provides several essential advantages, including higher sensitivity and lower reagent consumption. The linear dependence of the analytical signal on the epinephrine concentration was preserved over the range of 1.5-30, 3.0-30, and 1.5-25μmolL(-1) by using of SWIA, SIA and spectrophotometric analysis, respectively. The relative standard deviation for the SWIA determination of 10μmolL(-1) epinephrine was 1.8% (n=10).

Separation and determination of traces of ammonia in air by means of chromatomembrane cells

Chromatomembrane cells are new devices for gaseous/liquid and liquid/liquid extractions consisting of porous hydrophobic material (PTFE) with two types of pores, i.e., micropores and macropores. Their application benefits from established procedures of preconcentration and continuous extraction being used at the present to automate sample preparation in analytical chemistry. A method is reported to separate traces of ammonia from air by means of a chromatomembrane cell with subsequent potentiometric determination. The measuring system responds proportionally to both gas phase concentration of ammonia and preconcentration time.

Chromatomembrane method for the continuous separation of substances

A novel chromatomembrane method for the continuous separation of substances was developed. Mass exchange in liquid-liquid and liquid-gas systems proceeds according to chromatographic principles. Capillary effects in porous hydrophobic membranes with two preferential pore types are utilized to realize independent transport of phases in arbitrary directions. The macropores form channels for the polar liquid phase. The non-polar liquid or gas phase passes through the micropores, which are inaccessible to the polar phase because of capillary pressure. The possibilities of the method are demonstrated by schemes of continuous separation with preset extraction coefficients, schemes of application of the method in flow-injection analysis and results obtained in chromatomembrane blood oxygenation.

Determination of Trace Elements in Biological Fluids

Main approaches to the trace element analysis of biological fluids and problems appearing in this case are considered. The specific character of these approaches is illustrated by the examples of the analysis of real samples for various trace elements. The advantage of methods for the direct determination of trace elements in these samples is demonstrated.

Photometric determination of anionic surfactants with a flow-injection analyzer that includes a chromatomembrane cell for sample preconcentration by liquid-liquid solvent extraction.

Chromatomembrane cells proved to be applicable to flow-injection analysis whenever computer-operated manifolds for liquid-liquid or liquid-gas extraction procedures were required. Proceeding in accordance with the Methylene Blue method the determination of anionic surfactants was studied by applying the chromatomembrane cell for preconcentration and extraction of the ion-pair complex being formed. Spectrophotometric detection at 650 nm was made possible by using a flowthrough cell within a range of 0.02-5.0 mg dodecylsulfate per liter of water. The absorbance was found to respond proportionally to the product of preconcentration time and surfactant concentration, its slope factor being calculated with +/- 3% standard deviation. A mechanism for the preconcentration cycle inside the cell is suggested.

Determination of antipyrine in saliva using the dispersive liquid-liquid microextraction based on a stepwise injection system.

A fully automated stepwise injection spectrophotometric method for determination of antipyrine in saliva (agent for non-invasive assessment of the activity of the drug metabolizing system in hepatocytes) has been developed. The method is based on the antipyrine derivatization by nitrite-ion dispersive liquid-liquid microextraction (DLLME) of formed 4-nitrosoantipyrine with subsequent UV-vis spectrophotometric detection. Under optimal experimental conditions (0.5 М sulfuric acid, 6×10(-3) М sodium nitrite, time 6 min) the absorbance of the colored extract at the 345 nm obeys Beer׳s law in the range of 3-200 μM of antipyrine in saliva. The LOD, calculated from a blank test, based on 3σ, found to be 1 μM. The relative standard deviation for the determination of 50 μM antipyrine was 4.5% (n=10). The proposed method was successfully applied to the determination of antipyrine in saliva and the analytical results agreed fairly well with the results obtained by reference HPLC method.

Continuous chromatomembrane headspace analysis

Abstract A novel version of headspace analysis is substantiated by theory and experiment. The version assumes chromatomembrane extraction of the analyte components into a gas phase. The boundary conditions for the process of chromatomembrane gas extraction are established. Two modes are suggested for analysis with continuous extraction of analyte substances: the mode of ultimate equilibrium saturation and that of total isolation. The advantages of the method in the determination of traces of volatile substances are obvious from its comparison with traditional techniques based on stripping or membrane diffusion.

Absorption, concentration and determination of trace amounts of air pollutants by flow injection method coupled with a chromatomembrane cell system: application to nitrogen dioxide determination

The concentration distribution of an analyte in a chromatomembrane cell (CMC) was examined by using various air samples of different air pollutant (NO(2)) concentrations and volumes, and the results obtained could be explained by a proposed principle of the concentration distribution of the analyte in the CMC. This principle was for the first time proved experimentally in the present study. On-line preconcentration and continuous determination of the air pollutant (NO(2)) in air samples were realized by coupling a three-hole CMC with a flow injection analysis (FIA) system, where a triethanolamine (TEA) aqueous solution (2 g l(-1)) was used as an absorbing solution for NO(2) in the air samples. A calibration method with standard nitrite aqueous solutions was developed for the determination of NO(2) in the air samples. Concentrations of NO(2) in indoor air and its diluted air samples were determined by the proposed CMC/FIA method. The volume of air sample necessary for the measurement was decreased to only 5 ml. The measuring time for one sample was about 5-6 min even when a 20 ml air sample was used.

Extraction-chromatographic preconcentration with chromatomembrane separation of extract from aqueous phase for luminescence determination of oil products and phenols in natural water by flow injection analysis.

The new method of preconcentration by extraction for flow injection analysis (FIA) with luminescence and photometric detection is proposed. Preconcentration is carried out on extraction-chromatographic column, extract is eluted by extragent with the following separation of extract from aqueous phase in chromatomembrane cell. Possibilities of the proposed method are illustrated in the examples of FIA with luminescence determination of oil products and phenols in natural water.