Separation of trace amounts of palladium (II) with crown ether from hydrochloric acid and potassium thiocyanate media

A new method for the separation of trace amounts of palladium from hydrochloric acid and potassium thiocyanate media has been established based on the formation of an ion-pair complex of palladium thiocyanate anion Pd(SCN)₄ ^2– and the cationic potassium complex of dicyclohexyl-18-crown-6 (DC18C6) in chloroform. The effect of various factors (solvent, crown ether, potassium thiocyanate, hydrochloric acid, reagent concentration, shaking time, phase volume ratio, composition of the extracted species, foreign ions, etc.) on the extraction and back-extraction of palladium has been investigated. The method can be combined with subsequent FAAS determination of palladium. The procedure was applied to determine palladium traces in chloroplatinic acid and rhodium chloride.     

Use of dicyclohexano-18-crown-6 to separate traces of silver(I) from potassium thiocyanate in hydrochloric acid media,and determination of the silver by atomic absorption spectrometry

Solvent extraction with 0.05 mol L(-1) dicyclohexano-18-crown-6 (DC18C6) in 1,2-dichloroethane, coupled with flame atomic absorption spectrometry (AAS), has been investigated as a new method for separation of trace amounts of silver(I) from 0.05 mol L(-1) potassium thiocyanate in 1.0 mol L(-1) hydrochloric acid media and quantification of the amount of silver present. The method is based on the formation of an extractable ion-association product, [DC18C6.K](+)[Ag(SCN)(2)](-), with a metal-to-crown ether ratio of 1:1 (as derived from slope analysis data). Stripping of the extracted silver(I) in the 1,2-dichloroethane phase was achieved within 5 min by use of 3.0 mol L(-1) potassium thiocyanate. Reducing the concentration of acid in the sample solution to 0.1 mol L(-1) improved the preconcentration factor severalfold. Excellent tolerance of the proposed method to the presence of foreign ions in solution with silver(I) was demonstrated. A detection limit of 13 ng mL(-1) was derived from the mean value of the blank plus three times its standard deviation. The method was used to determine traces of silver(I) after separation from gold(III), platinum(IV), and palladium(II) matrices on the basis of extractability differences with 18-membered crown ethers under specified conditions. The efficiency of the adopted ion-association mechanism for silver(I) extraction was apparent from the average recovery of 96% for spiked standards by use of the back-washing technique. The proposed extraction procedure was applied to the determination of traces of silver(I) in a selection of chemical reagents.     

Anwendung von ionenaustauschverfahren zur bestimmung von spurenelementen in natürlichen wässern—VI: Zink

A method is described for the separation of ppM levels of zinc in natural waters and final determination by atomic absorption. The sample is acidified, filtered, treated with potassium thiocyanate, and passed through Dowex 1 × 8 (thiocyanate form). The anionic zinc thiocyanate complex is sorbed and separated from most of the accompanying elements. The column is washed with an aqueous-organic hydrochloric acid solution and with 1M hydrochloric acid, and the zinc is then eluted with 0.15M hydrobromic acid and determined directly in the eluate by atomic-absorption. The method was used for determining zinc in some Austrian waters, zinc contents in the range 18–685 ppM being found.     

Determination of uranium in natural waters after anion-exchange separation

A method is described for the determination of uranium by fluorimetry and spectrophotometry in samples of natural non-saline waters. After acidification with hydrochloric acid, the water sample is filtered and, following the addition of ascorbic acid and potassium thiocyanate, passed through a column of the strongly basic anion-exchange resin Dowex 1-X8 (thiocyanate form). On this exchanger uranium is adsorbed as an anionic thiocyanate complex. After removal of iron and other coadsorbed elements by washing first with a mixture consisting of 50 vol.% tetrahydrofuran, 40 vol.% methyl glycol and 10 vol.% 6 M hydrochloric acid, and then with pure aqueous 6 M hydrochloric acid, the uranium is eluted with 1 M hydrochloric acid. In the eluate, uranium is determined fluorimetrically or by means of the spectrophotometric arsenazo III method. The procedure was used for the routine determination of uranium in water samples collected in Austria.     

Mechanism of extraction of the palladium(ii) thiocyanate complex by polyether foam

The mechanism of sorption of the palladium(II) thiocyanate complex by polyether-type Polyurethane foam has been investigated. At low thiocyanate concentration, palladium is most likely extracted as Pd(SCN)(2). The results obtained in the presence of enough thiocyanate for formation of the Pd(SCN)(4)(2-) complex are in disagreement with several possible mechanisms for sorption of the anionic metal complex by the foam, such as adsorption, solvent extraction, ligand addition or exchange, and weak or strong base anion-exchange. The extraction of Pd(SCN)(4)(2-) at high pH increased in the order Li(+)< Na(+) < Cs(+)< Rb(+) < K(+)< NH(4)(+) which is in good relation with the "cation-chelation" mechanism. This mechanism was also found predominant in the extraction of Pd(SCN)(4)(2-) complex from hydrochloric acid solutions.     

Extraction of iridium (IV) from hydrochloric acid media with crown ether in chloroform, and its determination by ICP-AES

A new method for the quantitative extraction and determination of trace amounts of iridium from hydrochloric acid media has been established based on the formation of an ion-association complex of iridium hexachloro anion IrCl6(2-) with dicyclohexyl-18-crown-6 (DC18C6) oxonium cation in chloroform, then determination by inductively coupled plasma atomic emission spectrometry (ICP-AES). The effect of various factors (solvent, acid concentration, crown ether, reagent concentration, shaking time, composition of the extracted species, foreign ions, etc.) on the extraction and back-extraction of iridium has been investigated. The procedure was used to determine traces of iridium in palladium chloride and rhodium chloride.     

Extraction of iridium(IV) from hydrochloric acid media with crown ether in chloroform, and its determination by ICP–AES

A new method for the quantitative extraction and determination of trace amounts of iridium from hydrochloric acid media has been established based on the formation of an ion-association complex of iridium hexachloro anion IrCl₆ ^2– with dicyclohexyl-18-crown-6 (DC18C6) oxonium cation in chloroform, then determination by inductively coupled plasma atomic emission spectrometry (ICP–AES). The effect of various factors (solvent, acid concentration, crown ether, reagent concentration, shaking time, composition of the extracted species, foreign ions, etc.) on the extraction and back-extraction of iridium has been investigated. The procedure was used to determine traces of iridium in palladium chloride and rhodium chloride.     

Extraction-spectrophotometric determination of niobium with dibenzo-18-crown-6 and thiocyanate

A method is described for the direct spectrophotometric determination of micro-amounts of niobium by extraction into a benzene solution of dibenzo-18-crown-6 (L) from 3M hydrochloric acid containing potassium thiocyanate. The molar absorptivity of the extracted complex is 3.85 +/- 0.03 x 10(4) 1.mole(-1).cm(-1) (relative standard deviation 0.8%). Co-ordinatively unsaturated complexes of the type [NbO(SCN)(3)](2)L and NbO(SCN)(3)L are extracted, along with ion-pairs, especially when small amounts of L are used for extraction. The ion-pair complex [NbOCl(2)(SCN)(3)][(LK)(2)] seems to be the main species formed in the organic phase.     

双(正-辛基硫醚)乙烷对钯的萃取及其机理的研究

本文研究了双(正-辛基硫醚)乙烷[C₈H₁₇S(CH₂)₂SC₈H₁₇]对钯的萃取;讨论了盐酸浓度、稀释剂对萃取钯的影响;并且通过等克分子系列法、饱和法、Asmus法、固态络合物的化学分析及核磁共振谱,红外光谱的研究,确定了萃合物的组成和结构。     

Mesostructured tin oxide as sensitive material for C(2)H(5)OH sensor

A solvent extraction, separation, preconcentration method and recovery of tantalum is reported. Tantalum is extracted with dibenzo-18-crown-6 (DB18C6) in dichloromethane in presence of niobium from 4 M hydrochloric acid. The transport of tantalum(V) ions through a supported liquid membrane containing DB18C6 has been studied. The influence of molarity of acid, carrier concentration, temperature and kinetics of transport is discussed. Tantalum-DB18C6 extract was directly inserted in the plasma for ICP-AES measurement which enhances the sensitivity to 20-folds with the detection limit 1 ng. The mixed compelxes of tantalum-DB18C6 with methyl violet and thiocyanate have also been studied. Tantalum was recovered from tin scrap and determined in standard and sea water samples.     

Sorption of palladium(II) on stannous ferrocyanide

A fine-crystalline stannous ferrocyanide (SCF) has been prepared by adding tin(II) chloride to potassium hexacyanoferrate(II) solution. The material was characterized by chemical analysis, thermogravimetry, X-ray diffraction and infrared spectra. The solubility of SCF, kinetics and sorption mechanism of palladium in hydrochloric acid solutions were investigated. The palladium exchange capacity of 2.20 mM/g dry weight have been found.     

Determination of trace thiocyanate in body fluids by a kinetic fluorimetric method

A simple and very sensitive kinetic fluorimetric method is reported for the determination of trace amount of thiocyanate. The proposed method is based on the inhibition effect of thiocyanate on oxidation of rhodamine 6G by potassium bromate in sulfuric acid solution. The detection limit for thiocyanate is 1.63 x 10(-6) mmol/l. The linear range of the determination is 4.82 x 10(-6)-4.13 x 10(-5) mmol/l. This method has been used to determine trace thiocyanate in urine and saliva of smokers and non-smokers. The results obtained are satisfactory.     

Catalytic determination of ultratrace amounts of ruthenium with oscillopolarographic detection

The oscillopolarographic behaviour of Methyl Red in sodium hydroxide medium has been studied, and the results show that the wave at -0.79 V is an irreversible two-electron adsorption wave. A very sensitive and selective catalytic reaction-oscillopolarographic method for the determination of Ru down to 3 ng/l. is described, based on the Ru(III)-catalysed redox reaction of Methyl Red and potassium periodate in hydrochloric acid medium. Potassium thiocyanate is used to quench the reaction and the oscillopolarography is then performed with sodium hydroxide as the supporting electrolyte. The influence of 41 foreign ions has been examined. Ruthenium in ore samples has been determined by the method, with satisfactory results.     

Studies on extraction of indium by tributyl phosphate from thiocyanate solutions

Indium can be quantitatively separated from a large number of elements which are usually associated with it, by extraction with 15% tributyl phosphate solution in kerosene from hydrochloric acid (pH 1)/0.5M potassium thiocyanate medium and stripping with 6M nitric acid. The equilibration takes 20 min.     

A new solvent extraction scheme for the separation of platinum,palladium, rhodium and iridium

A new scheme is proposed for the separation of platinum, palladium, rhodium and iridium in hydrochloric acid solutions, by solvent extraction. Platinum and palladium are complexed with 2-mercaptobenzothiazole and potassium iodide and simultaneously extracted into chloroform, thus separating them from rhodium and iridium. Palladium is separated from platinum by extracting its dimethylglyoxime complex into chloroform, while rhodium is separated from iridium by extracting its 2-mercaptobenzothiazole complex into chloroform after reduction with tin(II) chloride.     

Spectrophotometric determination of molybdenum with lobeline

Lobeline hydrochloride has been tested as a reagent for molybdenum(V). Molybdenum(VI) is reduced with hydrazine sulfate in hydrochloric acid solution to Mo(V) only and complexed with thiocyanate and lobeline which is extracted with chloroform. In the paper experimental conditions for the formation of the ion pair of lobeline with molybdenum thiocyanate are described and the composition of this complex is given.     

Extraction of manganese(II) with dithizone and potassium thiocyanate on foam sorbents for spectrophotometric determination in silicates

A method for selective extraction of Mn(II) with dithizone and potassium thiocyanate has been described. The method involves formation of a Mn(II)-thiocyanate-dithizone complex in a hexamine medium containing potassium thiocyanate (2.8M), dithizone (5.5-6.5 x 10(-5)M) and hydroxylamine hydrochloride (0.25%) at pH approximately 6 followed by extraction of the complex on polyurethane foam using batch squeezing mode within 1 hr. The sorbed Mn-thiocyanate-dithizone complex is eluted with acetone and made alkaline with 0.5 ml of a stabilizer solution (19 ml 2M NH(3) solution + 1 ml 5% hydroxylamine hydrochloride). The absorbance of the solution is measured at 506 nm. The adverse effect due to Pb may be obviated by separating the Pb as the sulphate during decomposition of sample and that due to iron may be removed before extraction of Mn by any suitable method. The other interfering elements (Cd, Zn, Ni, Co, Cu, etc.) are masked with KCN (6 x 10(-3)M optimum) solution. The method obeys Beer's Law from 0.1 to 2.0 mug Mn/ml. The method has been applied to various silicates, carbonates and glasses.     

Determination of antimony in ores and related materials by continuous hydride-generation atomic-absorption spectrometry after separation by xanthate extraction

A continuous hydride-generation atomic-absorption spectrometric method for determining approximately 0.02 mug/g or more of antimony in ores, concentrates, rocks, soils and sediments is described. The method involves the reduction of antimony(V) to antimony(III) by heating with hypophosphorous acid in a 4.5M hydrochloric acid-tartaric acid medium and its separation by filtration, if necessary, from any elemental arsenic, selenium and tellurium produced during the reduction step. Antimony is subsequently separated from iron, lead, zinc, tin and various other elements by a single cyclohexane extraction of its xanthate complex from approximately 4.5M hydrochloric acid/0.2M sulphuric acid in the presence of ascorbic acid as a reluctant for iron(III). After the extract is washed, if necessary, with 10% hydrochloric acid-2% thiourea solution to remove co-extracted copper, followed by 4.5M hydrochloric acid to remove residual iron and other elements, antimony(III) in the extract is oxidized to antimony(V) with bromine solution in carbon tetrachloride and stripped into dilute sulphuric acid containing tartaric acid. Following the removal of bromine by evaporation of the solution, antimony(V) is reduced to antimony(III) with potassium iodide in approximately 3M hydrochloric acid and finally determined by hydride-generation atomic-absorption spectrometry at 217.8 nm with sodium borohydride as reluctant. Interference from platinum and palladium, which are partly co-extracted as xanthates under the proposed conditions, is eliminated by complexing them with thiosemicarbazide during the iodide reduction step. Interference from gold is avoided by using a 3M hydrochloric acid medium for the hydride-generation step. Under these conditions gold forms a stable iodide complex.     

Extraction of platinum metals from hydrochloric acid medium with triphenylphosphine solution in 1,2-dichloroethane

Extraction of platinum metals with TPP in 1,2-dichloroethane from hydrochloric acid medium has been examined. At hydrochloric acid concentrations higher than 6M, palladium, platinum and osmium are extracted, whereas at low acidity only palladium is quantitatively extracted. Addition of stannous chloride as labilizing agent makes possible a group separation of platinum metals (except osmium). Possible extraction mechanisms are discussed.