Traces,extractive separation

Conventional UV/VIS spectrophotometer (manual measurements from strip-chart recorder traces and calculations on the basis of fitted polynomials the extraction/separation step remains). 

A logical approach which serves to minimise such uncertainties is the use of a number of distinctly different analytical methods for the determination of each analyte wherein none of the methods would be expected to suffer identical interferences. In this manner, any correspondence observed between the results of different methods implies that a reliable estimate of the true value for the analyte concentration in the sample has been obtained. To this end Sturgeon et al. [21] carried out the analysis of coastal seawater for the above elements using isotope dilution spark source mass spectrometry. GFA-AS, and ICP-ES following trace metal separation-preconcentration (using ion exchange and chelation-solvent extraction), and direct analysis by GFA-AS. These workers discuss analytical advantages inherent in such an approach. 

Solvent extraction by tributyl phosphate (TBP) (13, 96), dithizone (20, 71, 72), cupferron (89), thenoyl trifluoroacetone (TTA) (55), diiso-propyl ketone (26), mesityl oxide (92), tri-n-benzylamine and methyl di-n-octylamine (99), diisopropyl and diisobutyl carbinol (100) have all found some application on the trace scale. Acetylaeetone and methyl isobutyl ketone extract milligram amounts of polonium almost quantitatively from hydrochloric acid, but the stable polonium-organic compounds which are formed make it difficult to recover the polonium in a useful form from solutions in these ketones (7). Ion exchange (22, 115, 119) and paper chromatography (44, 87) have also been used for trace scale separations of polonium, but the effects of the intense alpha-radiation on organic com-... 

Figure 1. Tracings of separation of total capsaicinoids of capsicum extracts and reference pure compounds by paper chromatography Spot (1) red capsicum Spot (2) natural capsaicinoids pure Spot (3) green capsicum fresh and Spot (4) synthetic capsaicin (C) color (F) fat, and (Cv), capsaicinoids/capsaicin ((27) and...

The selective extraction of a radioactive nuclide as a nonpolar compound or complex from an aqueous solution by an immiscible organic solvent Is frequently the most satisfactory method for making a fast radiochemical separation In either macro or trace concentrations. Separations by solvent extraction are simple, convenient, clean, and rapid. They usually require apparatus as uncomplicated as a separatory funnel and may readily be adapted to remote handling procedures. 

When combined with solid-phase extraction, flow injection in flame AAS also enables on-line trace matrix separations to be performed. Here the matrix can be complexed and the complexes kept on the solid phase while trace elements pass on towards the atomizer. For the case of the trace analysis of Zr(>2, after dissolution it was thus possible to keep up to 4 pg of Zr as a TTA (thenoyltrifluoroacetone) complex on the column, while impurities such as Fe were eluted and determined with a high efficiency [133]. This opens up a new line of research on the use of on-line trace-matrix separations for any type of complex samples. 

To minimize the loss of materials, selective extractions were conducted in the centrifuge tubes in which the solids were originally stored. The volumes of the extracting solutions were proportioned to the weight of solids in the tube. Between each successive extraction, separation was affected by centrifugation (Sorvall Model RC2-B) at 10,000 rpm for 30 minutes. The supernatant was removed with a pipet and analyzed for trace elements. The concentrations of these elements in the extracts were determined by flameless atomic absorption spectrophotometry as described for the dissolved trace element analyses (15). The total concentration of a solid phase-associated trace element is the sum of the four extraction concentrations and does not include the residual (14) or crystalline (11) solid fraction. 

Extraction is equally useful in the preconcentration and separation of small amounts of elements, and in the separation of macrocomponents from traces. Extraction methods generally require less time than precipitation methods. The former give also purer separation of elements owing to the small area of phase contact. Co-extraction occurring in some cases [11] has not been widely used in extraction separations. 

Dithizone (H2DZ, diphenylthiocarbazone, 3-mercapto-l,5-diphenylformazane) is one of the foremost organic spectrophotometric reagents [83-85]. It provides the basis of sensitive methods for the determination of Pb, Zn, Cd, Ag, Pd, Hg, Cu, Bi, and other metals. It has often been used in the extractive separation of traces of metals before their determination. 

In designing multistage extraction systems for extractive separations by TBP, or by other extractants that can change appreciably in noncomplexed concentration as a result of extraction, it is necessary to perform analyses similar to Eq. (4.1 S) through Eq. (4.24) for each of the extractable species present in other than trace quantities to determine the distribution coefficients for each of the species in each of the contacting stages [G6, H2, L3]. Such design procedures are illustrated in Sec. 6.6 for the separation of hafnium from zirconium by TBP extraction from a nitric acid solution. 

Extraction and Separation. After cooling, the product mixture was an amorphous solid. The product mixture and the reaction vessel were ground and placed in a 250-mL Soxhlet thimble. The mixture could not be easily broken up, removed from the vessel, and extracted separately thus, a small reaction vessel was sacrificed for each reaction to ensure that all product PAHs were collected. The material was exhaustively extracted in a Soxhlet apparatus with 500 mL of dichloromethane. The solution fluoresced an intense green when UV light was shown on it with a handheld light (Ultraviolet Products). This method was used to monitor the extent of extraction. The extraction typically lasted 75 h, and one Soxhlet cycle occurred every 10 min. After the dichloromethane extraction, the Soxhlet thimbles were immersed in 1,2,4-trichlorobenzene at 175 °C for 1 day to ensure that all the PAHs were removed. Synchronous scanning spectrofluorometry showed only traces of PAHs that were already seen in the dichloromethane extract. 

The vapors rising from the extractive distillation section consisting of non-aromatic components still contain small quantities of solvent. These solvent traces are separated in the raffinate section located above the extractive distillation section. The purified non-aromatics are withdrawn as overhead product. 

Electrothermal Atomic Absorption Spectrometric Determination of Trace Metals in Sea Water with On-line Sorbent Extraction Separation and Preconcentration [10,16]... 

The capability of HSCCC was also studied for enrichment and determination of metal ions at trace levels. Separation of selected divalent metal ions was performed using a small coiled column. A hexane solution of EHPA was employed as the stationary phase. Loaded divalent metal ions such as Ni, Co, Cu, and Zn were chromatographicaUy eluted in the order of increasing extractability by passing a mobile phase buffered at a desired pH. Each metal ion showed good linearity between concentrations and chromatographic peak areas of absorbance, as detected by postcolumn reaction with 4-(2-pyridylazo)resorcinol (PAR). Metal ions enriched in the stationary phase from a sample solution were separated into individual metal ions. A trace quantity of Zn in natural mineral water was determined by enrichment separation through an HSCCC column. 

Organic extracts separated from aqueous phases usually contain traces of water. Even washing with saturated salt solution (see Salting Out above) cannot... 

Figure 10.133 Trace analysis of anions in a wafer extract. Separator column lonPac ASM column dimensions 250mm X2 mm i.d. eluent 6.75mmol/L NaOH + 9mmol/L H3BO3 after 3.5 min to 30mmol/L NaOH+40mmol/L H3BO3 flow rate 0.75 mL/min detection ...

Fig. 9-73. Trace analysis of anions in a wafer extract. - Separator column lonPac AS14 (2-mm) eluant 6.75 mmol/L NaOH + 9 mmol/L H3BO3 after 3.5 min to 30 mmol/L NaOH + 40 mmol/L H3BO3 flow rate 0.75 mL/min detection suppressed conductivity injection volume 1 mL solute concentrations 1.5 pg/L each of fluoride (1). acetate (2), and formate (3), 11 pg/L chloride (4), unknown component (5), carbonate (6), 2.3 pg/L nitrate (7), and 10pg/L sulfate (8).

Gerritsma, D. A., Robertson, A., McNulty, J. Capretta, A. (2004). Heck reactions of aryl halides in phosphonium salt ionic liquids library screening and applications. Tetrahedron Letters, 45,41, 7629-7631, ISSN 0040-4039 Giiell, R., Antico, E., Salvado, V. Fontas, C. (2008). Efficient hollow fiber supported liquid membrane system for the removal and preconcentration of Cr(VI) at trace levels. Separation and Purification Technology, 62,2,389-393, ISSN 1383-5866 Guibal, E., Vincent, T. Jouannin, C. (2009). Immobilization of extractants in biopolymer capsules for the synthesis of new resins a focus on the encapsulation of tetraalkyl phosphonium ionic liquids. Journal of Materials Chemistry, 19, 45, 8515-8527, ISSN 0959-9428... 

A certain amount of hydrolysis of the original acetamide to acid and ammonia always occurs, and the final amine always contains traces of ammonia. This is separated by extracting the mixed anhydrous hydrochlorides with absolute ethanol, which dissolves the amine hydrochloride but not the ammonium chloride filtration of the hot ethanolic extract removes the ammonium chloride, whilst the amine hydrochloride crystallises readily from the filtrate on cooling. 

Place the distillate in a separating-funnel and extract the benzonitrile twice, using about 30 ml. of ether for each extraction. Return the united ethereal extracts to the funnel and shake with 10% sodium hydroxide solution to eliminate traces of phenol formed by decomposition of the benzenediazonium chloride. Then run off the lower aqueous layer, and shake the ethereal solution with about an equal volume of dilute sulphuric acid to remove traces of foul-smelling phenyl isocyanide (CaHjNC) which are always present. Finally separate the sulphuric acid as completely as possible, and shake the ether with water to ensure absence of acid. Run off the water and dry the benzonitrile solution over granular calcium chloride for about 20 minutes. 

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