Flow injection-solvent extraction

J.L. Manzoori, A. Miyazaki, Indirect inductively coupled plasma atomic emission determination of fluoride in water samples by flow injection solvent extraction. Anal. Chem. 62 (1990) 2457-2460. 

A. Alonso, M.J. Almendral, M.J. Porras, Y. Curto, C.G. Maria, Flow-injection solvent extraction with and without phase separation. Fluorimetric determination of aluminium in water, Anal. Chim. Acta 447 (2001) 211. 

Alonso A, Almendral MJ, Porras MJ, Curto Y. Flow-injection solvent extraction without phase separation fluorimetric determination of thiamine by the thiochrome method. J Pharm Biomed Anal 2006 42 171-7. 

Preparative strategies have been a key factor in the development of new procedures for radionuclide determination by ICP-MS. Momoshima et al. [80] used ferric hydroxide coprecipitation to scavenge Tc from seawater after technetium had been reduced to its tetravalent oxidation state. Solvent extraction and ion exchange decrease the interferences caused by spectral overlap and the sample matrix. Hollenbach et al. [81] determined Tc, and in soil by using a combination of flow injection and extraction... 

Membrane separation coupled on-line to a flow-injection system was employed for the monitoring of propazine and terbutryn in natural water. A microporous hydro-phobic membrane was utilized in which the analytes were extracted from the aqueous medium into an organic solvent that was carried to the flow cell of a photodiode-array spectrophotometer. The LCDs were 4-5 qg so the technique could potentially be used for screening purposes. Samples with positive detection would require further analysis. 

Determination of trace levels of tributyltin residues in sediments can be accomplished by solvent extraction, dilution and FIA (flow injection analysis) into the ionspray of a tandem mass spectrometer, using the 179/291 m/z pair LOD 0.2 p-g Sn/g103. 

In the past decade, several novel solvent-based microextraction techniques have been developed and applied to environmental and biological analysis. Notable approaches are single-drop microextraction,147 small volume extraction in levitated drops,148 flow injection extraction,149 150 and microporous membrane- or supported liquid membrane-based two- or three-phase microextraction.125 151-153 The two- and three-phase microextraction techniques utilizing supported liquid membranes deposited in the pores of hollow fiber membranes are the most explored for analytes of wide ranging polarities in biomatrices. This discussion will be limited to these protocols. 

In this technique, which was developed in the 1970s, microlitre volumes of liquid sample are injected, at intervals, into a continuously flowing carrier stream which is not air-segmented. Various reagent streams are introduced as required and controlled mixing of reagents and sample occurs. The fact that flow injection analysis does not involve air-segmented streams makes it possible to include such separation steps as solvent extraction and gas diffusion. 

Alternatively, direct methods (syringe infusion, flow injection) can be used as a preliminary step in determining the optimal MS detector conditions for particular molecules. This is especially useful when the MS is attached to a liquid chromatograph, in which the fluid entering the MS will vary with gradient elutions (varied solvent and salt compositions) or with sample types (varied sample matrices, extraction solvents, included salts, etc.), which can affect the predominant ion type and sensitivity, or produce other matrix effects such as ion suppression or extraneous signals. 

Solvent Extraction in Continuous Flow Injection Analysis... 

Solvent extraction can be automated in continuous-flow analysis. For both conventional AutoAnalyzer and flow-injection techniques, analytical methods have been devised incorporating a solvent extraction step. In these methods, a peristaltic pump dehvers the hquid streams, and these are mixed in a mixing coil, often filled with glass ballotini the phases are subsequently separated in a simple separator which allows the aqueous and organic phases to stratify. One or both of these phases can then be resampled into the analyser manifold for further reaction and/or measurement. The sample-to-extractant ratio can be varied within the limits normally applying to such operations, but the maximum concentration factor consistent with good operation is normally about 3 1. 

The solvent evaporates and the sample is then re-dissolved in another solvent as the belt moves into a new section of the manifold. This technique is particularly suitable where there is a need to change the solvent matrix to ensure compatibility with the measurement stage, as in liquid chromatography. The application of solvent extraction in flow-injection applications has been described by Karlberg and Thelander [3]. 

As nowadays wine making has factory dimensions, the need for a rapid method is important, so a flow injection techniqne for liqnid-solid extraction coupled to an HPLC was developed [368]. The target analytes were extracted from wine in a continuous way by means of a minicolumn packed with C18, the elntion was carried ont by means of acid water (pH 2) and acetonirile, then the solvent was evaporated by nitrogen stream on-line to a HPLC injector. Malvidin-3-glucoside, cyaniding-3-glncosyde, and peonidin-3-glncoside antocyanins were determined in a more rapid, accurate, and sensitive way than with the traditional methods. 

LC-NMR can be operated in two different modes on-flow and stopped-flow. In the onflow mode, LC-NMR spectra are acquired continuously during the separation. The data are processed as a two-dimensional (2D) NMR experiment. The main drawback is the inherent low sensitivity. The detection limit with a 60 p.1 cell in a 500 MHz instrument for a compound with a molecular weight around 400 amu is 20 pig. Thus, on-flow LC-NMR runs are mainly restricted to the direct measurement of the main constituents of a crude extract and this is often under overloaded HPLC conditions. Typically, 1 to 5 mg of crude plant extract will have to be injected on-column.In the stopped-flow mode, the flow of solvent after HPLC separation is stopped for a certain length of time when the required peak reaches the NMR flow cell. This makes it possible to acquire a large number of transients for a given LC peak and improves the detection limit. In this mode, various 2D correlation experiments (COSY, NOESY, HSQC, HMBC) are possible. 

The assay was performed with a HPLC-system consisting of a Spectra-Physics (Spectra Physics, San Jose, CA 95134, USA) model SP8700 solvent delivery system used at a flow rate of l.Oml.min", a Kratos (Kratos Analytical Instruments, Ramsey, NJ 07446, USA) model 757 UV-detector, wavelength 260 nm, range 0.005 aufs, rise-time 1 second. Injections of extracts into a Zymark (Zymark Corporation Inc., Hopkinton, MA 01748, USA) Z 310 HPLC-injection station, equipped with an electrically controlled Rheodyne valve and a 20 pi sample loop, were performed by a Zymate II robot system. The Zymark Z 310 Analytical Instrument Interface was used to control the HPLC-injection station. 

S. Ch. Nielsen, S. Sturup, H. Spliid and E. H. Hansen, Selective flow injection analysis of ultra-trace amounts of Cr(VI), preconcentration of it by solvent extraction and determination by electrothermal atomic absorption spectrometry (ETAAS), Talanta, 49(5), 1999, 1027-1044. 

Solvent Extraction Using a Polymer as Solvent with an Amperometric Flow-Injection Detector... 

Solvent extraction offers unique advantages among separation techniques. A system based on extraction into a polymer [poly(vinyl chloride)] as solvent was examined here because of possible advantages in speedy simplicity, sample size, solvent handlingy etc.f especially when coupled with flow injection and an amperometric detector. Solutes examined included salicylic acid and 8-hydroxy quinoline. The apparatus typically consisted of 0.8-mm i.d. X 170-cm coiled tubing that could be connected directly to the injection loop of a flow-injection amperometric detector system containing a nickel oxide electrode. 

Liquid extraction FOR THE SEPARATION and enrichment of organic compounds in aqueous samples has been used successfully. Automated solvent extraction with flow-injection analysis has been reported (I). 

The handling and disposal problems associated with the use of liquid solvent extractors have resulted in increased attention to the separation and preconcentration of organic compounds in water by collection in synthetic polymers followed by elution with an organic solvent (2). For example, selective collection and concentration of organic bases on methylacrylic ester resin from dilute water samples have been reported (3). Such collection techniques are especially well-suited to flow-injection measurement techniques. In this study, ionizable organic analytes such as salicylic acid and 8-hydroxyquinoline (oxine) were extracted into a polymer and then back extracted by an aqueous solution. Amperometric measurement using a flow-injection technique was employed to monitor the process. 

In spite of the sensitivity of the determination, because of the low concentrations of cadmium in most environmental samples, the element is still often preconcentrated. For example, discrete nebulization flame AAS has been used to measure foliar cadmium after extraction of the APDC complex into chloroform.15 Cobalt was extracted at the same time. Many other solvent extraction procedures have been described.1 Alternatively resins such as a chelating polydithiocarbamate resin have been employed to concentrate cadmium prior to determination.16 Extractions onto solid phase materials for preconcentration may be made more convenient by automation, for example using flow injection methodology.17... 

In 1978, Karlberg and Thelander [5] described the flow injection extraction (FIE) technique, and in 1979 Murray [6] improved the microextraction, reducing the amount of solvent to 200 pL. The main disadvantage of these methods was the necessity to use complicated equipment. Jeannot and Cantwell [7] and, independently, Hee and Lee [8] introduced a simpler kind of microextraction in which a solvent drop is applied, single drop microextraction (SOME). They designed a microreactor with 8 pL of -octane in a Teflon tube (Fig. 14.3) [7]. The authors performed measurements of diffusion coefficients and the kinetics of the system, which suggested a mass transfer model. 

For the analysis of esters by RP-HPLC, it is very hard to avoid water because it will be present in the sample extraction solvent and even in the mobile phase. However, the kinetics of ester hydrolysis in solution can be studied by stopped flow injection experiments to determine compatibility with mobile phase. The same experiment must be repeated with different pH (from pH 1.2 to pH 6.8), since it is known that ester hydrolysis is pH-dependent. An example of pH-dependent ester hydrolysis is methylphenidate HCl. Methylphenidate HCl has an ester functional group, and its hydrolysis is pH-dependent. Refer to Table A15-1 for stability of methylphenidate HCl at different pHs [5]. The hydrolysis product of methylphenidate HCl is the free acid (refer to Figure A15-3) [5]. 

A stainless column packed with Lichrospher lOORP-18 was used to analyze Acanthoside-D from the solvent extraction. The composition of mobile phase in analytical HPLC was experimentally determined and it was water/acetonitrile/methanoi=80/14/6 vol.%. From the chromatogram, retention time of Acanthoside-D was found to be 12 min. Figure 1 shows the analysis of Acanthoside-D from the extraction of the trunk of Acanthopanax senticosus. The flow rate of mobile phase and injection volume were 1 nt(/min and 20pl, respectively. 

Flow injection systems can also incorporate several sample processing units, such as solvent extraction modules, dialysis modules, heating modules and others. 

Because no separation is used, only crude information about the purity of the compounds can be obtained. For example, if unreacted, synthetic starting materials (Fig. 10b) are present in a sample of a combinatorial product (Fig. 10a), these can show up in the mass spectrum of the crude product (Fig. 10c). Because the starting materials are often structurally different from the finished product, a simple extraction can be used after the synthesis to remove much of the unused reactants and obtain a cleaner mass spectrum (Fig. lOd) for a solution-phase product. Conversely, washing the resin after solid-phase synthesis or using a scavenger resin in a solution-phase synthesis can also yield improved purity by removing these excess reactants. When direct flow injection is used to characterize combinatorial libraries, it is best to avoid dimethyl sulfoxide (DMSO) as a solvent, because it interferes with reliable ionization of the analytes. 

Fang, Q., Sun, Y., and Fang, Z. Automated continuous monitoring of drug dissolution process using a flow injection online dialysis sampling, solvent extraction separation spectrophotometric system. Presenilis J. Anal. Chem. 364(4) 347—352,1999. 

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