8-Hydroxyquinoline chelates, extraction

Burns et al. [106] used electrothermal AAS to determine inorganic and butyltin in seawater. The butyltin is extracted into toluene and the inorganic tin extracted as its Sn(IV) 8-hydroxyquinoline chelate into chloroform. The detection limit was 0.7 ng of tin. 

Chelating extractants such as beta-diketones, tropolones, hydroxyoximes, and 8-hydroxyquinolines (Figure 2.1), have been used extensively for the extraction of actinide ions from moderate to weakly acidic solutions (15-17). Beta-diketones such as acetylacetone (acac), HTTA, benzoyl trifluoroacetone (BTFA), and dibenzoyl-methane (HDBM) have been commonly used for the separation of actinide ions. The extraction mechanism involved formation of the enol form of the beta-diketone prior to complexation and extraction of the metal ion (Figure 2.2). 

Low concentrations of aluminum and beryllium can be determined by chelating with 8-hydroxyquinoline and extracting the chelates into MIBK and aspirating into a N20-acetylene flame. 

Hydroxyquinoline (oxine) (formula 4.42) reacts in ammoniacal media with cerium ions to give a sparingly soluble chelate, extractable into CHCI3. The brown-red colour of the extract is used for determining cerium. 

Chelating extractants may be used for ionic salts. Examples include beta diketones such as thenoyltrifiuoroacetone (TTA), acetylacetone, benzoylacetone, and dibenzoylmethane 8-hydroxyquinoline (oxine) oximes such as dimethyl-glyoxime nitrosophenyl compounds and nitrosohydroxylamines such as N-nitrosophenyl hydroxylamine (cupferron) and diphenylthiocarbazone (dithizone). 

The extraction of metal ions depends on the chelating ability of 8-hydroxyquinoline. Modification of the stmcture can improve its properties, eg, higher solubility in organic solvents (91). The extraction of nickel, cobalt, copper, and zinc from acid sulfates has been accompHshed using 8-hydroxyquinohne in an immiscible solvent (92). In the presence of oximes, halo-substituted 8-hydroxyquinolines have been used to recover copper and zinc from aqueous solutions (93). Dilute solutions of heavy metals such as mercury, ca dmium, copper, lead, and zinc can be purified using quinoline-8-carboxyhc acid adsorbed on various substrates (94). 

Elimination of a cofactor needed for luminescence. The chelators EDTA and EGTA efficiently quench the luminescence of Ca2+-activated systems such as aequorin, obelin and mnemiopsin. The luminescence systems that require ferrous ions, such as extracts of the polychaete Chaetopterus, can be inhibited by 8-hydroxyquinoline and... 

Owing to inadequate detection limits by direct analysis, various workers examined preconcentration procedures, including dithiocarbamate preconcentration [447,732-734], ion exchange preconcentration [735-737], chelation solvent extraction [736], coprecipitation [738], and preconcentration in silica-immobilised 8-hydroxyquinoline [129]. 

An extractive spectrophotometric procedure based on the complexation of reduced Iron(II) with 5-Chloro-7-iodo-8-hydroxyquinoline (CIHQ) for the estimation of micro amounts of vitamin C. The resulting brown colored complex was extracted into chloroform to give a reddish brown extract which shows an absorption band at 485 nm. This chelate was formed immediately and the apparent molar absorptivity and Sandell s sensitivity for vitamin C was found to be 8.5 x 105 dm3 mol"1 cm 1 and 2.072xl0 4g cm 2. Linear relationship between absorbance and concentration of ascorbic acid is observed up to 0.8 pg ml"1. Interference studies of different substances including sugars, vitamins and amino acids, metal ions and organic acids were carried out. The utility of the method was tested by analysing some of the marketed products of vitamin C... 

Ashbrook, A. W. Commercial chelating solvent extraction reagents, II. w-Al-kenyl-8-hydroxyquinoline Purification and properties, Metallurgy Division, Mines Branch, Dept. Energy, Mines and Resources, Canada Report EMA 73-34 1973. 

Extraction of transition metals from low grade ores. Factor (c) (formation of a chargeless chelate complex) can be illustrated by considering the formation of complexes between 8-hydroxyquinoline (HQ) and a mixture of metal ions, say, M2+ = Fe2+, Co2+, Ni2+, and Cu2+. This is in fact the order of increasing stability constants of the complexes MQ2 (equilibrium constants /J2 for Eq. 17.14) log 2 = 15.0, 17.2, 18.7, and 23.4, respectively, in dilute solution at 20 °C. This commonly encountered sequence for complex formation by the divalent Fe, Co, Ni and Cu ions is known as the Irving-Williams order (cf. the susceptibility of Ni2+ and Cu2+ to complexing by NTA3-, noted in Sections 14.4 and 16.5). 

The low level of aluminium in some samples may require concentration by chelation—solvent extraction prior to introduction into the flame. A procedure described for wines [36] involves digestion with HN03—H2S04, extraction with 8-hydroxyquinoline in MIBK and determination with a nitrous oxide—acetylene flame. Aluminium has also been extracted with 2,4-pentanedione [185], EAAS has been applied to measuring aluminium in beer [186]. Gorsuch [139] proposes wet oxidation to be preferred and mentions that adverse comments reported in respect of sample destruction have usually applied to dry ashing. 

The widespread occurrence of iron ores, coupled with the relative ease of extraction of the metal, has led to its extensive use as a constructional material with the result that the analysis of steels by both classic wet and instrumental methods has been pursued with vigour over many years.3 Iron complexes are themselves widely used as the basis of convenient analytical methods for the detection and estimation of iron down to parts per million. Familiar tests for iron(III) in aqueous solution include the formation of Prussian blue as a result of reaction with [Fe(CN)6]4, and the formation of the intensely red-coloured [Fe(H20)5SCN]2+ on reaction with thiocyanate ion.4 Iron(II) forms particularly stable red tris chelates with a,a -diimines such as 1,10-phenanthroline or 2,2 -bipyridine that have been used extensively in spectrophotometric determinations of iron and in the estimation of various anions.5 In gravimetric estimations, iron(III) can be precipitated as the insoluble 8-hydroxyquinoline or a-nitroso-jS-naphthol complex which is then ignited to Fe203.6 In many situations the levels of free [Fe(H20)6]3+ may be controlled through complex formation by addition of edta. 

Formation of complexes with ratio M L = 1 3 is observed for the 8-hydroxyquinoline and its derivatives [44]. Americium and plutonium solid compounds were obtained in the form of complexes [Am(Ox)3], [Pu(Ox)3], [Am(DCOx)3], [Am(MCOx)3]. Chelates with halogenated 8-hydroxyquinoline are better extractable from the solution than complexes with 8-hydroxyquinoline. Plutonium (111) easily oxidizes in the presence of 8-... 

Other extraction agents such as dithizone, diethyl dithiocarbamates, and 8-hydroxy-quinoline (oxine) are also useful as chelating agents and extract several metals including transition metals, alkali and alkaline metals. The dithizone can extract up to 20 elements and these complexes behave the same and there is no additional advantage of using one over the other. The compound 8-hydroxyquinoline will form stable complexes with Al, Ca, Sr and Mg at pH 8.0 these metals form unstable complexes with APDC. At carefully controlled pH the oxidation states of metals may also separated, e.g. Fe[II] and Fe[III], The stmcture of 8-hydroxyquinoline is ... 

Several useful extractive separations with 8-hydroxyquinoline have been developed. In addition, numerous chelating agents that behave in a similar way are described in the literamre." As a consequence, pH-controlled extractions provide a powerful method of separating metallic ions. 

A large group of the methods is based on difunctional organic reagents that with metal ions form inner chelates, soluble in non-polar solvents. Such reagents are generally used in the extraction-spectrophotometric methods involving, e.g., dithizone, dithiocarbamates, 8-hydroxyquinoline, l-nitroso-2-naphthol, dioximes and PAN [l-(2-pyridylazo)-2-naphthol]. 

Between pH 4.5 and 10, 8-hydroxyquinoline (oxine) forms the chelate AKCgHeON), which is sparingly soluble in water but dissolves readily in CHCI3. The yellow extract of aluminium oxinate is the basis for the determination method [2,14]. Carbon tetrachloride and trichloroethylene are also used as extraction solvents. The absorption maximum of the chloroform extract is at 390 nm (e= 7.310, a = 0.27). The absorption of oxine in CHCI3 increases rapidly below 390 nm. 

Small amounts of Mo are extracted from many metals as the chelates, formed with BPHA [15,16], 8-hydroxyquinoline [17], and HDEHP [18,19]. Also, Mo has been separated from tungsten oxide by extraction with DDTC [20]. 

Tungsten has been extracted as the chelate with 8-hydroxyquinoline and its derivatives [21]. The possibilities of the extractive separations of W [22] and both Mo and W [23] have been discussed in detail. 

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