Hydroxyquinoline Extraction Procedures

Various methods have evolved based on the complexation of monomeric aluminium species with 8-hydroxyquinoline (oxine) and the rapid extraction of the formed Al(oxinate)3 complex into organic solvents, e.g. chloroform [162], toluene [163] or methyl isobutyl ketone (MIBK) [164] detection of the aluminium content was accomplished by electrothermal atomic absorption spectrometry. 

The so-called Driscoll methods are all based around ion-exchange separation of the monomeric inorganic aluminium from the monomeric organic aluminium. The column packing is Amberlite IR-120 cation exchange resin [159]. In essence, the Driscoll method directly measures three operationally defined fractions  

The first published methods used a colorimetric 8-hydroxy-7-iodoquinoline 

From the data available, there is no consensus as to the precise experimental conditions to be used. This is especially true where the analytical separation is concerned. The resin in the column has to be conditioned with a solution of NaCl having the same ionic strength and pH as the water samples to be analysed and this is one of the main drawbacks of the method because the solution of NaCl has to be passed through the column until the pH of the effluent does not change by more than 0.2 pH units. A full Driscoll/PCV speciation procedure including all the modifications has been published elsewhere [168]. 

Some authors claim that detection limits (DLs) of 5 mgL are easily obtainable [167] using the batch PCV detection method. However, it has been reported that daily DLs range between 5 and 10 mg L and that personnel who are highly acquainted with the method were needed to achieve DLs down to 10 mg L [168]. This poses a problem when the non-labile or monomeric organic fraction of aluminium to be measured is very small. Errors for Alni can become high, and, because the Driscoll method is a subtraction method, the uncertainty of the calculated Ali fraction (Alim—Alni) can become unacceptable. To increase the precision, sample throughput and practicality of the Driscoll method, several flow injection analysis (FIA) systems have been designed both for the PCV method [169,170] and for detection with a fluorimetric determination of the 8-hydroxyquinoline-5-sulfonic acid (8-HQS) aluminium complex in a micellar medium (cetyltri-methylammonium bromide, CTAB) [168,171]. 

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Ke and Regier [71] have described a direct potentiometric determination of fluoride in seawater after extraction with 8-hydroxyquinoline. This procedure was applied to samples of seawater, fluoridated tap-water, well-water, and effluent from a phosphate reduction plant. Interfering metals, e.g., calcium, magnesium, iron, and aluminium were removed by extraction into a solution of 8-hydroxyquinoline in 2-butoxyethanol-chloroform after addition of glycine-sodium hydroxide buffer solution (pH 10.5 to 10.8). A buffer solution (sodium nitrate-l,2-diamino-cyclohexane-N,N,N. AT-tetra-acetic acid-acetic acid pH 5.5) was then added to adjust the total ionic strength and the fluoride ions were determined by means of a solid membrane fluoride-selective electrode (Orion, model 94-09). Results were in close agreement with and more reproducible than those obtained after distillation [72]. Omission of the extraction led to lower results. Four determinations can be made in one hour. 

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]. 

Among the most important indirect methods of analysis which employ redox reactions are the bromination procedures for the determination of aromatic amines, phenols, and other compounds which undergo stoichiometric bromine substitution or addition. Bromine may be liberated quantitatively by the acidification of a bromate-bromide solution mixed with the sample. The excess, unreacted bromine can then be determined by reaction with iodide ions to liberate iodine, followed by titration of the iodine with sodium thiosulphate. An interesting extension of the bromination method employs 8-hydroxyquinoline (oxine) to effect a separation of a metal by solvent extraction or precipitation. The metal-oxine complex can then be determined by bromine substitution. 

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... 

Procedure (extraction). Transfer 2.5 g air-dry soil, 2 mm mesh size, into a 250 ml polypropylene screw-cap centrifuge bottle/tube and add 100 ml acetic acid - 8-hydroxyquinoline reagent. Cap the tube and shake overnight (17 h) on a reciprocating shaker, at approximately 275 strokes of 25 mm length per minute at a constant temperature (20°C). Centrifuge for 15 min at 2800 rpm and remove an aliquot for the determination of acid extractable inorganic phosphorus (a). 

Procedure (determination of inorganic phosphate (a) in the acetic acid extract). The 8-hydroxyquinoline forms a precipitate in acidic ammonium molybdate solution, which will interfere unless the aliquot is <5 ml. It should therefore be removed by ignition as follows. Transfer 10 ml acetic acid extract to a 45-ml silica basin, add 0.5 ml 1 M magnesium acetate and evaporate to dryness on a water-bath. (Note do not use magnesium nitrate, which reacts adversely on heating with 8-hydroxyquinoline.)... 

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. 

In analytical procedures with two immiscible aqueous phases, the traditional organic solvents used in LLE can be replaced by nontoxic, nonflammable and nonvolatile solvents [154,155,197], The feasibility of implementing aqueous biphasic extraction in flow analysis was recently demonstrated by the fluorimetric determination of lead by reaction with 8-hydroxyquinoline-5-sulfonic acid [198]. The flow system was rugged and the interface formed between the different aqueous plugs acted as an extraction (enrichment) and reaction interface. This innovation is environmentally friendly as it relies on the utilisation of two immiscible phases that are intrinsically aqueous. 

After irradiation and cooling, samples are dissolved in acid and carrier added. Separation of manganese can be made by precipitation as tetraphenylarsonium permanganate (Cotzias et al.. 1966) or manganese dioxide (Miyata et al., 1983) by extraction at pH 8 into chloroform with 8-hydroxyquinoline (Versieck et al.. 1973) or with diethylammonium diethyidithiocarbamate (Damsgaard et al., 1973) by separation with anion exchange resin (Miyata et al., 1973) and after removal of alkali metal salts on a hydrated antimony pentoxide (HAP) column (Miyata et al., 1973). Addition of another manganese isotope ( Mn) can be used to check recoveries of separation procedures. 

The lUPAC (International Union for Pure and Applied Chemistry) reference method for the determination of nickel in serum and urine [43], for example, recommends an acid digestion followed by extraction with APDC-MIBK prior to ETAAS determination. Similar procedures were described for molybdenum in blood plasma which was extracted as the 8-hydroxyquinoline complex prior to its determination by ETAAS [44] and for vanadium in serum and urine [45]. There is no question, however, that these procedures require skilled operators. As multistage manual procedures they also bear the risk of analyte loss and/or contamination, so that the final result may not always reflect the analyte concentration in the original sample. 

The determination of molybdenum in soils and biological material used to be carried out mainly colorimetrically with rhodanide/isoamyl alcohol 8-hydroxyquinoline/CHCl3 methylisoamyIke-tone ammonium-pyrrolidine-dithiocarbamate/methylamylketone and with toluol-3.4-dithiol and different extracting agents (toluol, CHCI3, CCI4, n-butylacetate) [46]. The photometric methods must often be connected with accumulation procedures. 

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