Flow injection methods solvent extraction

K. Kina, K. Shiraishi, N. Ishibashi, Ultramicro solvent extraction and fluorimetry based on the flow-injection method, Talanta 25 (1978) 295. 

S. Motomizu, M. Oshima, N. Yoneda, T. Iwachido, Spectrophotometric determination of calcium with dicyclohexano-24-crown-8 and propyl orange by solvent-extraction flow-injection method, Anal. Sci. 6 (1990) 215. 

Stikai, T., Solvent extraction-speetrophotometric determination of berberine and benzetho-nium in drugs with tetrabromophenolphthalein ethyl ester by batchwise and flow injection methods, Ana/y. , 1991,116,187-190. 

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 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. 

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. 

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. 

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

Method abbreviations SX, solvent extraction CV, cyclic voltammetry Fi, flow injection Pot., potentiometry. 

See alsa Chemometrics and Statistics Multivariate Calibration Techniques. Color Measurement. Extraction Solvent Extraction Principles. Flow Injection Analysis Detection Techniques. Food and Nutritional Analysis Water and Minerals. Kinetic Methods Principles and Instrumentation Catalytic Techniques. Optical Spectroscopy Detection Devices. Spectrophotometry Overview Derivative Techniques Biochemical Applications Pharmaceutical Applications. Spot Tests. Water Analysis Overview. 

In Figure 7.53 a flow-injection interface for fluorometric monitoring of focused microwave-assisted Soxhlet extraction is represented [195]. This assembly allows real-time online monitoring of the PAHs extracted from solid samples in each Soxhlet cycle and provides qualitative and semi-quantitative information from natural and spiked samples. The method has been applied to a certified reference material (CRM 524, BCR, industrial soil/organics) for quality assurance/validation. The proposed technique is as efficient as conventional Soxhlet to extract PAHs from soils but with a drastic reduction of both extraction time and organic solvent disposal. 

The solvent technique for concentrating surfactants is not discussed here. See Ref. [40] for details. Morales-Munoz et al. discuss a screening method for LAS in sediments. It is based on water Soxhlet extraction assisted by focused microwaves. The extractor is coupled with an online preconcentrator/derivatization/detection manifold through a flow injection interface [107]. 

For systems in which high levels of solvents, for example acetone, are present, methyl green is reported to be superior to methylene blue (38). The color formed by methyl green is stable for 2-3 hr, while the methylene blue color should be read within 30 min (13). A method based on formation of the fe/5(phenanthroline)-Cu(II)-surfactant complex is reported to be faster than the methylene blue method and more sensitive by a factor of two (39). l-(4-Nitrobenzyl)-4-(4-diethylaminophenylazo)pyridinium bromide is said to be a much more sensitive reagent than methylene blue (40). For automated analysis by the flow injection technique, use of l-methyl-4-(4-diethylaminophenylazo)pyridinium ion, together with chloroform extraction, was found to give the best results (41). 

An isocratic HPLC method for screening plasma samples for sixteen different non-steroidal anti-inflammatory drugs (including etodolac) has been developed [29]. The extraction efficiency from plasma was 98%. Plasma samples (100-500 pL) were spiked with internal standard (benzoyl-4-phenyl)-2-butyric acid and 1 M HC1 and were extracted with diethyl ether. The organic phase was separated, evaporated, the dry residue reconstituted in mobile phase (acetonitrile-0.3% acetic acid-tetrahydrofuran, in a 36 63.1 0,9 v/v ratio), and injected on a reverse-phase ODS 300 x 3.9 mm i.d. column heated to 40°C. A flow rate of 1 mL/min was used, and UV detection at 254 nm was used for quantitation. The retention time of etodolac was 30.0 minutes. The assay was found to be linear over the range of 0.2 to 100 pg/mL, with a limit of detection of 0.1 pg/mL. The coefficients of variation for precision and reproducibility were 2.9% and 6.0%, respectively. Less than 1% variability for intra-day, and less than 5% for inter-day, in retention times was obtained. The effect of various factors, such as, different organic solvents for extraction, pH of mobile phase, proportion of acetonitrile and THF in mobile phase, column temperature, and different detection wavelengths on the extraction and separation of analytes was studied. 

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