Determination of platinum and palladium in environmental samples by graphite furnace atomic absorption spectrometry after separation on dithizone sorbent

A graphite furnace atomic absorption method of platinum and palladium determination after their separation from environmental samples has been presented. The samples were digested by aqua regia and the analyte elements were separated on the dithizone sorbent. The procedure of sorbent preparation was described and their properties were established. Two various procedures of elution by thiourea and concentrated nitric acid were described and discussed. The low limit of detection was established as 1 ng g⁻¹ for platinum and 0.2 ng g⁻¹ for palladium.There was also investigated the behaviour of platinum and palladium introduced into the soil in various chemical forms.     

Spectrophotometric Determination of Palladium with Methylthymol Blue

A new, sensitive spectrophotometric method for the determination of palladium(II) with methylthymol blue has been developed. The palladium methylthymol blue complex has an absorption maximum at 530 nm. The colour reaction has a sensitivity of 0.005 µg of palladium/cm² and obeys Beer's Law over the range 0.4 to 3.24 ppm of palladium. The effects of concentration of perchloric acid, reagent, heating, stability of colour and diverse ions have been investigated. The ratio of metal: ligand in the complex is 1:1 and the formation constant was calculated to be 1.18×10⁴.     

Atomic absorption spectrometric determination of molybdenum in lubricating oils with use of emulsions

Samples (0.1 g) containing molybdenum disulphide are digested with aqua regia or with a (1 + 1) hydrofluoric/nitric acid mixture, without complete destruction of the matrix, and the molybdenum is determined in an air/acetylene flame, after emulsification with a non-ionic surfactant (Nemol K-39). The detection limit is ca. 30 μg Mo g^?1, and the r.s.d. is 2.9% for 6 analyses of a sample containing 6.5 mg Mo g^?1.     

Determination of platinum, palladium and silver in geological materials and their concentrates by fire assay and emission spectrography

A method is described for the determination of platinum down to 10 ng, palladium to 5 ng and silver to 10 pg in 50 or 100 g of sample. Fire-assay techniques are used to preconcentrate these metals into a bead which is first treated with nitric acid to dissolve palladium and silver and then with aqua regia to dissolve platinum. Both solutions are diluted and adjusted to pH 4, then analysed by optical emission spectrography of the residue from a measured volume evaporated on a pair of flat-top graphite electrodes. This method requires much less sample handling than most published methods for these elements.     

Determination of bismuth,cadmium and lead in soil extracts by atomic absorption spectrometry with loop sample introduction

Bismuth, cadmium and lead in soil extracts with aqua regia, 2 M nitric acid, 2.5% acetic acid or ammonium acetate solution from top-soils at different locations in Turkey, were determined by atomic absorption spectrometry with loop sample introduction. Detection limits were 0.8, 0.025 and 0.5 μl^?1 for bismuth, cadmium and lead, respectively, after concentration with ammonium pyrrolidinedithiocarbamate. Use of a silica tube for atom trapping improved the detection limits.     

Electrochemical behavior and electrowinning of palladium in nitric acid media

In this study, the electrochemical behavior of Pd(II) in nitric acid media was investigated using various electrochemical techniques. By analyzing the cyclic voltammogram of Pd(II) recorded at Pt electrode, a series of electrochemical reactions associated with palladium were recognized, indicating that Pd(II) undergoes a single step two-electrons irreversible process. Electroreduction reaction of Pd(II) and auto-catalytic reactions of nitrous acid are supposed to play a leading role in low and high concentrations of nitric acid, respectively. Stirring could facilitate the reduction of Pd(II) in relatively low nitric acid concentration (? 3 mol/L). The value of charge transfer coefficient was determined to be 0.18 for the measurements at 298 K. The diffusion coefficient of Pd(II) increased from 1.89 × 10^?8 cm²/s at 288 K to 4.23 × 10^?8 cm²/s at 318 K, and the activation energy was calculated to be 21.5 kJ/mol. In electrowinning experiments, SEM images of palladium obtained by electrolysis reveal the dendrite growth in all cases, which is uniform all over the entire surface of Pt electrode. The recovery ratios of Pd at different nitric acid concentrations are high, and the faradic efficiency of electrolysis decreases with increasing the nitric acid concentration. When stirring was introduced during electrolysis, the electrodeposition rate of Pd increased substantially.     

Determination of gold in geological samples by x-ray fluorescence spectrometry after extraction with tributyl phosphate

The behaviour of gold and elements impeding its x-ray fluorescence spectrometric (XRF) determination, namely zinc, lead and arsenic, was studied during their extraction from hydrochloric acid, nitric acid, and aqua regia solutions using tributyl phosphate as a solid extractant [SE(TBP)]. Extraction of gold from pulps after aqua regia leaching was found to be the most favourable approach for the quantitative and selective recovery of gold. The gold distribution ratio, D_Au, is ca. 10⁴ ml g^?1. For extraction from hydrochloric acid solutions the D_Au value also exceeds 10⁴ in the whole range of gold concentrations studied (10^?8?10^?4 M), but it decreases substantially with increasing extraction temperature, from 5 × 10⁵ ml g^?1 at 20°C to 9 × 10³ ml g^?1 at 70°C. An anomalously high distribution ratio of lead, D_Pb ≈ 10³ ml g^?1, was observed during extraction from hydrochloric solutions in the presence of chlorine. This could be explained by the formation of the chloro complexes of lead(IV). An XRF method for the determination of gold in natural samples was developed, which includes back-extraction of gold from SE(TBP) using a hot 0.025 M thiourea solution, providing a thin sample layer for secondary XRF. For 25 g of sample material the limit of determination is 10 ng g^?1 (10^?6%). The accuracy of the technique was checked using different reference materials. The results agreed within 10%.     

Ion-exchange resins containing s-bonded dithizone and dehydrodithizone as functional groups : Part 3. Determination of Gold,Platinum and Palladium in Geological Samples by means of a Dehydrodithizone Resin and Plasma Emission Spectrometry

A procedure is described for the determination of gold, platinum and palladium in sulphide ores, concentrates and mattes. The method is based on chromatographic separation and selective elution of precious metals on small resin beds (0.7 × 2.5 cm) of the sorbent P-TD. After roasting, the samples were digested with aqua regia, and the residues fused with sodium peroxide. The acid leaching solutions obtained from both procedures were separately passed through an ion-exchange column. The metals were quantitatively retained after one loading step and eluted by a sequence of 2 M perchloric acid and 5% (w/v) thiourea solution. Preconcentrated Au, Pt and Pd were finally quantified with a d.c. plasma emission spectrometer. The effect of roasting temperature on the recovery of precious metals as well as the efficiency of the aqua regia leaching from the different materials were investigated in detail. Repeated analyses of standard reference samples proved the proposed method to be reliable.     

Spectrophotometric Determination of Thioctic Acid in its Dosage Forms through Complex Formation with Pd(II)

A simple and sensitive spectrophotometric method has been developed for the determination of thioctic acid in pharmaceutical preparations. The proposed method is based upon the formation of a complex with palladium(II) in acetate buffer of pH 4.8 with an absorption maximum at 318 nm. The absorbance obeyed Beer's law over the range of 2–20 μg mL^?1 with a minimum detection limit of 0.15 μg mL^?1 and molar absorptivity (ζ) of 7 × 10³ L mol^?1.cm^?1. The different experimental parameters affecting the development and stability of the color were carefully studied and optimized. The proposed method was successfully applied to the analysis of commercial tablets and ampoules. The results obtained were in good agreement with those obtained using a reference spectrophotometric method. A proposal of the reaction pathway is presented.     

Simultaneous spectrophotometric determination of uranium, nitric acid and nitrous acid by least-squares method in PUREX process

Multi-wavelength linear regression spectrophotometry combined with method of least squares for simultaneous determination of uranium, nitric acid and nitrous acid in PUREX (Plutonium/URanium EXtraction) process was developed. The molar absorbance matrix was calibrated with absorbance data measured in the wavelength range of 350–500 nm for a series of standard solutions by linear least-squares regression. This method used information from the absorption spectra of U(VI)–nitrous acid–nitric acid solutions to determine U(VI), nitrous acid and nitric acid. In the range of 0.95–74.1 g/L U(VI), 5 × 10^?4–2 × 10^?3 mol/L nitrous acid and 3–5 mol/L aqueous nitric acid solution, the measuring precision for determination of U(VI), nitrous acid and nitric acid was 0.46, 4.09, and 0.68 % respectively. In the solution of 30 % TBP–kerosene, the measuring precision for determination of U(VI) and nitrous acid was 0.42 and 4.2 % respectively in the range of 0.95–74.1 g/L U(VI) and 5 × 10^?4–2×10^?3 mol/L nitrous acid. The spectrophotometric method can be valuable for monitoring and controlling of both species in PUREX process operation, thanks to its simplicity, efficiency and accuracy.     

Analytical applications of 3-(2′-thiazolylazo)-2,6-diaminopyridine: Spectrophotometric determination of palladium

3-(2′-Thiazolylazo)-2,6-diaminopyridine reacts with palladium(II) in strongly perchloric acid media, to produce a blue 1:1 complex (λ_max = 665 nm, ? = 1.37 × 10⁴ liters · mol^?1 · cm^?1), which allows the spectrophotometric determination of 0.6 to 4.5 ppm of palladium. The method is applied to the determination of palladium in small samples of hydrogenation catalysts.     

New convenient dissolution of iron-rhodium alloys using hydrochloric acid containing a small amount of nitric acid without heating for an ICP-AES analysis.

A new convenient dissolution method for Fe-Rh alloys has been developed. Aqua regia has been used for the dissolution of rhodium alloy samples. However, it is difficult to dissolve high-concentration rhodium (more than 50 mass%) in aqua regia, because a rhodium-passivity on the alloys surface occurs with nitric acid. By using hydrochloric acid containing a small volume of nitric acid, Fe-Rh (24-64 mass%) alloys could be completely decomposed and dissolved under mild experimental conditions. The principal advantages of this method are simplicity and time-saving compared with other dissolution methods.     

Rapid derivative spectrophotometric method for the determination of platinum in Pt-Ru/C catalyst using iodide media.

A rapid spectrophotometric method for the determination of platinum in 20% Pt-Ru (Pt:Ru (1:1)) carbon-supported catalyst has been developed. The samples of catalyst (0.85-12.60 mg) have been digested 1) in aqua regia after preliminary separation of carbon by burning or 2) directly in aqua regia in the presence of carbon. The detection of platinum was carried out in the obtained solutions after conversion of the metal into the iodide complex. The interfering effect of ruthenium on the detection of platinum was eliminated by the use of derivative spectrophotometry. Platinum was selectively determined by numerical calculation of the 4th-order-derivative absorption spectrum of the mixture of iodide complexes of both metals.     

A quantum chemical consideration of ligand exchange in palladium(ii) aqueous and chloride complexes

The behavior of potassium tetrachloropalladate(II) in media simulating biological fluids has been studied. In aqueous solutions of NaCl, the aquation rate is higher than the rate of chloro ligand introduction into the internal coordination sphere of palladium. In HCl solutions, on the contrary, the process of palladium chloro complex formation predominates. The latter is apparently due to protonation of water molecules composing aqua complexes. By means of the ZINDO/1 method, the substitution of ligands – water molecules and hydronium ion – in planar complexes of palladium(II) by chloride ion has been investigated. All complexes containing H₂O and H₃O⁺ ligands, other than [Pd(H₂O)₄]²⁺, have intramolecular hydrogen bonds. In [Pd(H₂O)₃(H₃O)]³⁺ and trans-[Pd(H₂O)₂(H₃O)Cl]²⁺, a “non-classic” symmetric hydrogen bond O ··· H ··· O is established (ZINDO/1, RHF/STO-6G*). By the first three steps the substitution of hydronium ion in the internal sphere of palladium atom is more favorable thermodynamically, compared to water molecules. Logarithms of stepwise stability constants of palladium(II) chloride complexes correlate linearly to enthalpies (ZINDO/1, PM3) of water substitution by chloride ion.     

A fire-assay and wet chemical method for the determination of palladium, platinum, gold, and silver in ores and concentrates

A method is presented for the determination of palladium, platinum, gold and silver in ores and concentrates by a fire-assay and wet chemical technique. After parting of the lead assay button with dilute nitric acid, and separation of the solution from the residue, the palladium and platinum in the solution are precipitated by the addition of stannous chloride, with tellurium as collector. The resulting precipitate is combined with the gold residue and dissolved in aqua regia, then the solution is analysed for palladium, platinum and gold by atomic-absorption spectrophotometry (AAS). Silver is determined in the original solution by AAS before the reduction step.     

Atomic absorption spectrometric determination of mercury in soil standard reference material following microwave sample pretreatment

Several decomposition procedures and their influence on the determination of mercury by electrothermal (ET) and cold vapour (CV) atomic absorption spectrometry (AAS) have been studied. Soil samples were decomposed by microwave digestion in closed and open vessels as well as by digestion under reflux according to German standard. The use of different acids (HNO₃, HCl or aqua regia) was evaluated and compared in respect to their influence on the determination of mercury by ET AAS and CV AAS. The digestion solutions were analyzed by ET AAS with a palladium modifier and by CV AAS using SnCl₂ or NaBH₄, as reducing agents. The detection limits obtained with different procedures were also evaluated. For the soil containing 6.25 g/g of Hg the ET AAS measurements were possible. In the case of lower concentration of mercury the CV AAS determination following the microwave digestion procedure with HCl or aqua regia is recommended. The accuracy of the proposed procedure was confirmed by the determination of total mercury in SRM 2711 Montana Soil.On leave from: Institut für Analytische Chemie, Technische Universitat Wien, Getreidemarkt 9, A-1060 Wien, Austria     

Palladium(II) complexes of aliphatic amines and their oxidation by chloramine‐T in perchloric acid medium

The formation of palladium(II) complexes with aliphatic amines and their oxidation by chloramine‐T in perchloric acid medium has been studied. The spectrophotometric studies showed the formation of 1:1 and 1:2 complexes between palladium(II) and amine in absence of HClO₄. An increase in [HClO₄] in reaction mixture suppresses the complex formation and in presence of [HClO₄] ～10^?3 mol dm^?3 only a 1:1 complex between palladium(II) and amine has been observed. The effect of Cl^? on the complex formation has also been studied. Palladium(II)‐catalyzed oxidation of these amines by chloramine‐T showed a first‐order dependence of rate with respect to each—oxidant, substrate, catalyst, and H⁺. The mechanism consistent with kinetic data for the oxidation process has been proposed in absence as well as in presence of initial [Cl^?]. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 603–612, 2002     

Monothiourea-3-nitrophthalic acid as a new reagent for spectrophotometric analyses: I. Determination of palladium(II) ions

The results of the examination of the reaction between a new reagent, MT3NF acid, and palladium(II) ions, as well as the composition of the formed complexes have been discussed. The new extraction-spectrophotometric method for the determination of palladium(II) ions by using MT3NF acid was presented. Beer's law is obeyed over the range 0.1 to 3 μg of Pd/cm³. Molar absorptivity is 2.9 × 10⁴ liter mol^?1 cm^?1 at the absorption maximum of 306 nm. The influence of different ions has been described.     

Synergistic extraction and spectrophotometric determination of palladium(II), iron(III), and tellurium(IV) at trace level by newly synthesized p-[4-(3,5-dimethylisoxazolyl)azophenylazo]calix(4)arene

A spectrophotometric method for the determination of palladium, iron and tellurium from nitric acid media after extraction of their p-[4-(3,5-dimethylisoxazolyl)azophenylazo]calix(4)arene [DMIAPAC] complexes has been developed and possible synergistic effects have been investigated. Chloroform, carbon tetrachloride, cyclohexane, 1,2-dichloroethane, toluene and xylene were used as the diluents. The maximum enhancement was obtained in the presence of 30% 1,2-dichloroethane. The trace amounts of metals were determined spectrophotometrically. Beer’s law obeyed in the concentration range of 5.0–95.0 μg, 8.0–120.0 μg and 10.0–140.0 μg/10 mL of the final solution of palladium, iron and tellurium, respectively. The molar absorptivities (l mol^?1cm^?1) and Sandell’s sensitivities (μg cm ^?1) were calculated: Pd(II) = 1.73 × 10⁴ and 0.0061; Fe(III) = 1.08 × 10⁴ and 0.0052; Te(IV) = 1.67 × 10⁴ and 0.0077. Ten replicate analyses containing 20 μg of Pd(II), 12.5 μg of Fe(III) and 32 μg of Te(IV) gave mean absorbance of 0.326, 0.242 and 0.418 with relative standard deviation of 0.36, 0.65 and 0.82% for Pd(II), Fe(III) and Te(IV), respectively. The interference of various ions was studied and optimum conditions were developed for the determination of these metals in certain alloys and synthetic mixtures.     

Development of a new microelectrolysis system for in-situ electrodeposition of ultra-traces of gold prior to measurement by ETAAS

Electrodeposition is known to be suitable for separation and preconcentration of extremely low concentrations of analyte from bulk samples and is instrumentally is very simple. In this approach a new combined system was designed for in-situ electrodeposition of ultratrace levels of gold from micro samples on to a graphite furnace prior to determination by electrothermal atomic absorption spectrometry (ETAAS). Sediment samples were digested and traces of the gold content were extracted with boiling aqua regia. To prevent the highly corrosive effect of aqua regia media, the graphite tube surface was pre-coated by electrodeposition of ppm amounts of Pd prior to sample introduction. Separation of the analyte from the matrix was achieved by electrodeposition of the analyte in situ on the Pd/C surface of the furnace tube. Vanadium was also used as a modifier to stabilize the analyte from decomposition at charring temperatures. By using the proposed microelectrolysis preconcentration technique a considerable improvement in sensitivity and detection limit was achieved compared with conventional ETAAS. Characteristic masses for ED-ETAAS techniques in both nitric acid and aqua regia were reported to be m(o)=4.1 pg, with %RSD=2.9; the calculated LOD was 0.105 ppb, and typical calibration graphs for this element in nitric acid and aqua regia for both techniques were linear up to 70 microg L(-1) with about 99% recovery. Six reference sediments samples were tested by the proposed technique and by the Conv-ETAAS method. The results were in agreement with recommended values (reported by a reference laboratory using UV-visible spectrometry), demonstrating the efficiency of extraction and preconcentration of ultratrace levels of gold.