RESUMO
Chromatomembrane process represents a universal approach to the separation of compounds in liquid-gas and liquid-liquid phases systems. However, the broad application of chromatomembrane separation methods in chemical analysis is restricted by the absence of serially produced chromatomembrane flow cells and the difficulties of their laboratory production. The present work addresses the preparation of chromatomembrane flow cell by using 3D printing. Fused deposition modeling and stereolithography were modes for the production of the flow cell using acrylonitrile-butadiene-styrene and polyacrylate-based Anycubic UV resins respectively. The separation and analytical performance of the 3D-printed flow cell were compared with a polyimide unit fabricated by a milling machine, the trial addressing the determination of phenol in the air. The method is based on chromatomembrane absorption of the analytes in 95 µL of the aqueous phase positioned in the cell. Reversed-phase HPLC with fluorimetric detection was applied for the determination of the absorbed analytes. The detection limit of phenols (phenol and m-cresol) in the air was 0.9 µg/m3 by absorption preconcentration time of 10 min. The volumetric flow rate of the analyzed air through the chromatomembrane cell using an electrodriven aspirator was 0.1 L/min.
RESUMO
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.
RESUMO
With the intention of combining partition chromatography and membrane techniques, we succeeded in developing the chromatomembrane cell which has proved to be reliable as an extraction and preconcentration manifold in flow injection analysis. With this technique, two immiscible phases can be induced to flow independently through a block of biporous (macro and micro) PTFE in order to promote analyte exchange. Consequently, the application of chromatomembrane cells in environmental analysis resolves all problems of sample pretreatment simply and effectively whenever a preconcentration step by gas/liquid or liquid/liquid solvent extraction is included. The link-up with analyzers (AAS, UV-Vis photometry, GC, IC, HPLC, voltammetry, ion selective electrodes, etc.) makes possible computer aided automization for environmental monitoring.
RESUMO
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.
RESUMO
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.
RESUMO
The possibilities of the new chromatomembrane method in the removal of oxygen dissolved in water are studied. The scheme of the water deoxygenation process is determined. The new reagent-free method allows production of water with oxygen content at the level of a few ppb.
RESUMO
Chromatomembrane cells (CMC) operate as unique manifolds for extraction and preconcentration procedures in computer controlled flow-injection-analysis (FIA). By coupling to an ion chromatograph and to a conductometer, respectively, instrumentation is obtained that allows the pretreatment and the detection of ozone- and ammonia-containing samples after absorption of the gaseous constituents of air inside a chromatomembrane cell. The analysis of air even in the presence of liquid aerosols is discussed.
Assuntos
Poluição do Ar , Amônia/análise , Ozônio/análise , Automação , Condutividade Elétrica , Filtros Microporos , ReologiaRESUMO
The economical use of modern analytical instrumentation requires an online-coupling of efficiently working flow-systems which automate both sampling and sample pretreatment. Whenever extraction and preconcentration procedures are necessary the application of chromatomembrane cells proved to be very worthwhile. On this occasion the analyte exchange takes place inside a block of biporous PTFE wherein the two immiscible phases come into contact with each other. A special enclosure enables water and the extracting nitrogen to flow independently through that block. In case of gaseous extractants the behavior of the biporous PTFE and its mechanical parameter have to be investigated precisely in order to overcome the special problems of trace analysis in gases. The gas-chromatographic detection of volatile organic compounds (VOC's) requires a discussion on the effects of gas-sorption and the kinetics of equilibration which should be taken into consideration for using the chromatomembrane cell as an extractor from waste water. The investigation realizes at least that a quick pretreatment is made possible and, however, sample sizes decrease remarkably in comparison with competing methods as head space analysis or purge and trap technique. The application of chromatomembrane cells permits reasonable accuracies with a limit of detection on the ng/l level.