Extraction-based Determination

In a simple liquid-liquid extraction the solute is partitioned between two immiscible phases. In most cases one of the phases is aqueous, and the other phase is an organic solvent such as diethyl ether or chloroform. Because the phases are immiscible, they form two layers, with the denser phase on the bottom. The solute is initially present in one phase, but after extraction it is present in both phases. The efficiency of a liquid-liquid extraction is determined by the equilibrium constant for the solute s partitioning between the two phases. Extraction efficiency is also influenced by any secondary reactions involving the solute. Examples of secondary reactions include acid-base and complexation equilibria. 

For fluorescence PAH determination in tap water acid-induced cloud point extraction was used. This kind of extraction based on the phase separation into two isotropic liquid phases a concentrated phase containing most of the surfactant (surfactant-rich phase), where the solubilised solutes are exttacted, and an aqueous phase containing a surfactant concenttation closes to the critical micellar concentration. 

The procedure of simultaneous extracting-spectrophotometric determination of nitrophenols in wastewater is proposed on the example of the analysis of mixtures of mono-, di-, and trinitrophenols. The procedure consists of extraction concentrating in an acid medium, and sequential back-extractions under various pH. Such procedures give possibility for isolation o-, m-, p-nitrophenols, a-, P-, y-dinitrophenols and trinitrophenol in separate groups. Simultaneous determination is carried out by summary light-absorption of nitrophenol-ions. The error of determination concentrations on maximum contaminant level in natural waters doesn t exceed 10%. The peculiarities of application of the sequential extractions under fixed pH were studied on the example of mixture of simplest phenols (phenol, o-, m-, />-cresols). The procedure of their determination is based on the extraction to carbon tetrachloride, subsequent back-extraction and spectrophotometric measurement of interaction products with diazo-p-nitroaniline. 

Method of Rh(III) - Ru(III) separation and isolation them from rai e and nonferrous metals based on formation of different charged complexes with varied stability has been proposed. Possibility of sepai ation of Ru(III), Rh(III), Pd(II), Pt(II) by water-soluble extractants from concentrated thiocyanate solutions has been displayed. Accelerated procedures of extraction-photometric determination of Rh(III), Ru(III) in solutions and waste products, which ai e chai acterized by high selectivity, availability, usage of non-toxic extractants have been worked out. 

SOLID PHASE EXTRACTION AND DETERMINATION OF TRACE AMOUNT OF Co + BY MODIFIED ANALCIME ZEOLITE WITH A NEW SCHIFF-BASE LIGAND... 

Brombenztiazo (BBT) is known to be one of the best reagents for extraction-photometric determination of cadmium(II). The reagent also fonus complexes with Co(II), Cu(II), Fe(II), Ni(II), Zn(II). The aim of this work was to develop a solid-phase reagent on the base of BBT immobilized on silica gel for sorption-spectroscopic and visual test determination of Cadmium, and also for soi ption-atomic-adsoi ption determination of total heavy metals contents in natural waters. 

Famoxadone, IN-JS940, and IN-KZ007 residues are measured in soil (p-g kg ), sediment (p-gkg ), and water (pgL ). Quantification is based on analyte response in calibration standards and sample extract analyses determined as pg mL Calibration standard runs are analyzed before and after every 1 samples in each analytical set. Analyte quantification is based on (1) linear regression analysis of (y-axis) analyte concentration (lagmL Q and (x-axis) analyte peak area response or (2) the average response factor determined from the appropriate calibration standards. The SLOPE and INTERCEPT functions of Microsoft Excel are used to determine slope and intercept. The AVERAGE and STDEV functions of Microsoft Excel are used to determine average response factors and standard deviations. 

Isaeva [181] described a phosphomolybdate method for the determination of phosphate in turbid seawater. Molybdenum titration methods are subject to extensive interferences and are not considered to be reliable when compared with more recently developed methods based on solvent extraction [182-187], such as solvent-extraction spectrophotometric determination of phosphate using molybdate and malachite green [188]. In this method the ion pair formed between malachite green and phosphomolybdate is extracted from the seawater sample with an organic solvent. This extraction achieves a useful 20-fold increase in the concentration of the phosphate in the extract. The detection limit is about 0.1 ig/l, standard deviation 0.05 ng-1 (4.3 xg/l in tap water), and relative standard deviation 1.1%. Most cations and anions found in non-saline waters do not interfere, but arsenic (V) causes large positive errors. 

Statham [448] has optimised a procedure based on chelation with ammonium dithiocarbamate and diethylammonium diethyldithiocarbamate for the preconcentration and separation of dissolved manganese from seawater prior to determination by graphite furnace atomic absorption spectrometry. Freon TF was chosen as solvent because it appears to be much less toxic than other commonly used chlorinated solvents, it is virtually odourless, has a very low solubility in seawater, gives a rapid and complete phase separation, and is readily purified. The concentrations of analyte in the back-extracts are determined by graphite furnace atomic absorption spectrometry. This procedure concentrates the trace metals in the seawater by a factor of 67.3. 

Bjarnborg [464] has studied shipboard methods of continuous recording of in vivo chlorophyll fluorescence and extraction-based chlorophyll determinations in Swedish archipelago waters. 

Catalytic Cycle. Attempts to determine the reasons for the improved activity of the base on alumina reagents followed two paths. Being as solubility of base in methanol appeared to greatly effect the production of methyl benzyl ether, we compared the amount of extractable base with selectivity to ester. This concentration of base, presumably alkoxide, was determined by stirring the base in methanol, filtering, and titrating the filtrate with acid. This comparison is given as Table VII. 

The extraction was shown to be endothermic with an enthalpy of 34.3 kj/mol. The mechanism of exfracfion was proposed and partially verified by means of nuclear magnetic resonance (NMR) and FT-IR spectra. This mechanism involves interactions between the IL cation and P-O bonds of phosphate groups in the DNA molecule. The authors also suggested an extraction-based procedure for the quantitative determination of dsDNA. 

As an extraction technique, SFE proved to give comparable recoveries to those of Soxhlet extraction. In all cases, SFE dramatically shortened extraction times and minimized most environmental hazards, solvent concentration steps, and waste disposal costs. A summary of this comparison is included as Table XII and is a projected cost comparison of SFE to Soxhlet extraction, based on our experiences with the SFE system used in these studies (Isco SFE System 1200). The projected cost per extraction was determined to be 15.85(SFE) vs. 22.60(Soxhlet). 

The principle of combination of electrochemical glucose oxidase biosensor with the clean-up method for direct extraction and determination of methyl mercury has been successfully demonstrated. The extraction of methyl mercury from the organic solvent has been based on invertase enzyme inhibition. The combination of very low concentration of invertase enzyme and 10 min of incubation time allows the detection of methyl mercury at 5 ppb level. Our method permits the detection of this inhibitor below the legal limit given by the European Union with good recoveries when fish samples were measured. 

In addition to the above method, based on the use of pyrocatechol violet, Tecator also describes a flow injection analysis for determining 0.5-0.5mg/l aluminium in soil extracts based on the measurement of the chromazurol-aluminium complex at 570 nm [4,5]. 

A. Constantinos, D. Yannis, K. Constantinos, L.L. Yannis, Quantitative determination of donepezil in human plasma by liquid chromatography/tandem mass spectrometry employing an automated liquid-liquid extraction based on 96-well format plates application to a bioequivalence study, J. Chromatogr. B 848 (2007) 239-244. 

Acid hydrolysates were added to a low aroma intensity white wine (ie the base wine), and the aroma properties of these samples were assessed by sensory descriptive analysis. In addition, the glycoside isolates from the Australian vineyards were subjected to glycoside hydrolase enzyme treatment, and duo-trio difference tests were performed on these hydrolysates added to a base wine. The volatile composition of each of the hydrolysates was investigated by GC/MS, and relationships between the two sets of data were determined. Finally, the glycoside concentration of each of the juices and skin extracts was determined by the glycosyl-glucose assay. 

Cells from animal or human origin can be isolated from different tissue and used as uptake systems. Normally, the isolated cells are suspended in a buffer under O2/CO2 in the presence of the permeant and shaken well. After a certain time period, the cells are separated from the buffer and extracted to determine the amount of permeant inside the cells. Because of the low volume of the cells, the assay is based mostly on use of radiolabeled compounds (23). Cells can be isolated from different origin, and one animal can give rise to experiments with many different compounds or conditions. However, many disadvantages exist as well, like the lack of reproducibility with large variations in viability, because of the chemical or mechanical stress during isolation. This method also only allows for uptake, not transport or permeability, to be studied, but the polarity of the uptake whether a compound is taken up on the apical or basolateral side cannot be decided (22). 

Methods based on iodine titration with thiosulfate Iodide, being a weak reduc-tant, can react with an enormous variety of oxidants to liberate an equivalent quantity of I2 that can be titrated with thiosulfate. Such oxidants include peroxides, peroxy compounds, peroxydisulfate, ozone, iron(III), chromate, selenium (as Se03 ), silver(II) oxide, xenon trioxide, iodate, and bromate. Bromide can be determined by oxidizing it to bromine, followed by extraction and determination of the bromine... 

Sample preparation is important here because matrices of biological fluids are so comphcated that interfering signals are likely to appear in typical separation-based determinations. Among various sample preparation techniques, there are two major approaches combined with CE liquid-hquid extraction (LEE) and solid-phase extraction (SPE) [or solid-phase microextraction (SPME)]. 

Altliough methods involving organic solvent extraction or protein precipitation wfil estimate both free and protein-bound cortisol in tlie circulation, immunoassay-based methods that determine cortisol directly from serum have essentially replaced all extraction-based methods for routine cortisol measurements save for urine free cortisol methods. Flistorically four general methods have been used for the quantitative estimation of total blood cortisol concentrations in the clinical laboratory. These are the Porter-Silber color reaction method modified for plasma,the use of sulfuric acid-induced fluorescence, HPLC methods, or immunoassay. In general, HPLC and immunoassay are now used in both clinical laboratories and reference laboratories for the quantitative determination of cortisol in serum or urine. 

Antonis (A3, A5) has presented an automated colorimetric procedure for the determination of acyl esters in serum lipid extracts, based on his manual method (A2). The ester groups are subjected to alkaline hy-droxylaminolysis to form hydroxamic acids, which react with ferric ion to form highly colored chelates. 

Extraction and stripping of copper(I) as a neocuproine complex in a surfactant medium was used to determine Cu in steel [4], Solid-phase extraction based on the preconcentration of the complex with neocuproine on a preconditioned membrane disc containing octadecyl-bonded silica followed by extraction of Cu and elution with isopentyl alcohol was applied to the determination of copper in distilled, tap and spring waters [5]. 

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