Organic phase samples back-extracted with

The liquid-liquid extraction feed solutions were prepared by dilution of the neodymium nitrate stock solution with distilled water and nitric acid. These then were contacted with equal volumes of 1M HDEHP in separatory funnels, agitated for. 5 hr by a mechanical shaker, allowed to separate for. 5 hr, shaken another. 5 hr, then allowed to settle for 12 hr before the phases were separated carefully. A volumetric sample of the organic phase was back-extracted four times with an equal volume of 6M HN03. This solution was evaporated to dryness in order to remove the excess acid and then diluted to an appropriate concentration. The pH of this solution was adjusted to 3.0 to eliminate any hydrolysis effects... 

Szathmary and Luhmann [50] described a sensitive and automated gas chromatographic method for the determination of miconazole in plasma samples. Plasma was mixed with internal standard l-[2,4-dichloro-2-(2,3,4-trichlorobenzyloxy) phenethyl]imidazole and 0.1 M sodium hydroxide and extracted with heptane-isoamyl alcohol (197 3) and the drug was back-extracted with 0.05 M sulfuric acid. The aqueous phase was adjusted to pH 10 and extracted with an identical organic phase, which was evaporated to dryness. The residue was dissolved in isopropanol and subjected to gas chromatography on a column (12 m x 0.2 mm) of OV-1 (0.1 pm) at 265 °C, with nitrogen phosphorous detection. Recovery of miconazole was 85% and the calibration graph was rectilinear for 0.25 250 ng/mL. 

Klinkhammer [432] has described a method for determining manganese in a seawater matrix at concentrations ranging from about 30 to 5500 ng/1. The samples are extracted with 4 nmol/1 8-hydroxyquinoline in chloroform, and the manganese in the organic phase is then back-extracted into 3 M nitric acid. The manganese concentrations are determined by graphite furnace atomic absorption spectrophotometry. The blank of the method is about 3.0 ng/1, and the precision from duplicate analyses is 9% (1 SD). 

Tseng et al. [69] determined 60cobalt in seawater by successive extractions with tris(pyrrolidine dithiocarbamate) bismuth (III) and ammonium pyrrolidine dithiocarbamate and back-extraction with bismuth (III). Filtered seawater adjusted to pH 1.0-1.5 was extracted with chloroform and 0.01 M tris(pyrrolidine dithiocarbamate) bismuth (III) to remove certain metallic contaminants. The aqueous residue was adjusted to pH 4.5 and re-extracted with chloroform and 2% ammonium pyrrolidine thiocarbamate, to remove cobalt. Back-extraction with bismuth (III) solution removed further trace elements. The organic phase was dried under infrared and counted in a ger-manium/lithium detector coupled to a 4096 channel pulse height analyser. Indicated recovery was 96%, and the analysis time excluding counting was 50-min per sample. 

The simplest principle for analyte trapping was described in Section 13.2.1.1. In order to perform enrichment of an acidic compound, the pH of the acceptor is held enough alkaline, so the main fraction of the acidic analyte becomes charged and thus nonextractable in the acceptor. This is analogous with the principle of back extraction in LLE, where an organic extract of an acidified sample is extracted with a second aqueous phase, in order to isolate acidic compounds. 

Nickel An equal amount of 10% sodium citrate solution was added to the sample. The acidity of the samples was then adjusted to pH > 7.5 by addition of NH3. Thereafter, 2 ml 1% dimethyl-glyoxime (DMG) was added to the solution. The nickel-DMG complex was extracted into pure chloroform. The extraction was repeated with fresh chloroform to improve the yield. The combined organic phases were then washed with 0.5 M NH3 to remove impurities. Nickel was then back-extracted into 0.5 ml HNO3. The back-extraction was repeated once to improve the yield. The HNO3 solution was then used for IGP-MS and liquid scintillation measurements, y-spectrometry showed no contamination that could disturb the LSC measurements. The overall yield of this standard procedure is >99%. 

A typical extraction manifold is shown in Figure 13.2. The sample is introduced by aspiration or injection into an aqueous carrier that is segmented with an organic solvent and is then transported into a mixing coil where extraction takes place. Phase separation occurs in a membrane phase separator where the organic phase permeates through the Teflon membrane. A portion of one of the phases is led through a flow cell and an on-line detector is used to monitor the analyte content. The back-extraction mode in which the analyte is returned to a suitable aqueous phase is also sometimes used. The fundamentals of liquid liquid extraction for FIA [169,172] and applications of the technique [174 179] have been discussed. Preconcentration factors achieved in FIA (usually 2-5) are considerably smaller than in batch extraction, so FI extraction is used more commonly for the removal of matrix interferences. 

The uranium is separated, after dissolving the sample as described for lead, by extraction with tributyl phosphate (TBP) from 4M nitric acid. After the organic phase is scrubbed with 4M nitric acid, the uranium is back-extracted into distilled water and evaporated to dryness. The uranium is loaded on a rhenium filament for analysis by dissolving the purified sample in a small volume of 0.05M nitric acid. 

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