Performance of electrodeposited noble metals as permanent modifiers for the determination of cadmium in the presence of mineral acids by electrothermal atomic absorption spectrometry

The analytical performance of electrodeposited noble metals (Pd, Rh or Pd+Rh) on the graphite surface for cadmium determination in the presence of inorganic acids was evaluated and discussed. The study was carried out for 16% HNO₃, 28% HCl and a mixture of both acids (aqua regia). It was demonstrated that all electrodeposited modifiers stabilized cadmium up to 800°C in the presence of HNO₃ and aqua regia. When only HCl was present in the solution the thermal stability of cadmium was less pronounced, the maximum pyrolysis temperature that could be applied was 500°C. The long-term study for Cd determination shows that permanent performance of electrodeposited modifiers is not influenced by mineral acids, moreover, the tube lifetime was doubled, compared with a non-modified tube, when Pd+Rh were electrodeposited onto the graphite surface.     

Development and application of new iondashexchange techniques for the separation of the platinum group and other siderophile elements from geological samples

Two new aniondashexchange techniques have been developed for the separation of the platinum group elements Ru, Pd, Ir, Pt and the siderophile metals Re, Ag, Zn and Cd from geological samples following a NiS fire assay digestion procedure. Both methods are simple and permit the isolation of these elements in sufficient purity for quantitative analysis by isotope dilutiondashinductively coupled plasma mass spectrometry (ID-ICPMS) at yields of 75-95%. The high affinity of the considered elements to anion exchange resins allows the use of small (1.25 ml) columns even for the processing of 5-10 g sized silicate rock samples. Following fire assay digestion and dissolution of the NiS buttons in aqua regia, the samples are loaded onto the resin bed as solutions in 1 M HCl. After elution of the bulk sample matrix with dilute HCl and HNO(3), Zn and Cd are stripped from the column using 0.8 M HNO(3). Small amounts of bromine water are added to the dilute mineral acids for the stabilization of strongly retained Ir(IV). Following this, the iondashexchange techniques permit the sequential elution of Ag, Re and the PGE using 11 M HCl, 8 M HNO(3) and 13.5 M HNO(3). The iondashexchange methods have been applied to separation of Ru, Pd, Re, Ir and Pt from the geological reference material SU-la prior to concentration measurements by ID-ICPMS. Our analytical results are in good agreement with previously published data for this sample and display an external reproducibility (based upon repeat dissolutions) of approximately 2-10% for the elements considered in this study.     

Determination of platinum and ruthenium in Pt and Pt-Ru catalysts with carbon support by direct and derivative spectrophotometry

Platinum and ruthenium in carbon supported Pt and Pt-Ru catalysts were determined by direct and derivative spectrophotometric methods. Complexes of platinum and ruthenium with SnCl(3)(-) ligands (tin(II) chloride in HCl) were used to determine both metals in solutions obtained after digestion of the samples of the catalysts. Platinum in the Pt/C catalyst can be determined in solutions obtained by digestion of the samples in aqua regia. Derivative spectrophotometry was used to determine both metals in the presence of each other in solutions obtained after digestion of samples of the Pt-Ru/C catalyst in the mixture of HCl+HNO(3) (6:1). The first derivative at 377 nm (;zero-crossing' point of ruthenium) and the second-derivative values at 495 nm (;zero-crossing' point of platinum) were used to estimate the concentration of platinum and ruthenium, respectively.     

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.     

Bestimmung der Edelmetalle Au, Pd, Pt, Rh und Ir in Gesteinen und Erzen mit der elektrothermalen Atomabsorptions-Spektrometrie

Zusammenfassung Nach einem Druckaufschluß bei 170°C von 5 g Gesteinsprobe mit HF und aqua regia werden die Edelmetalle Au, Pd, Pt, Rh und Ir durch selektive Adsorption auf den Ionenaustauscher SARAFION NMRR von der restlichen Matrix abgetrennt. Im Thioharnstoffeluat können die Edelmetalle mit der elektrothermalen AtomabsorptionsSpektrometrie quantitativ bestimmt werden. Die Methode wurde durch Analyse von internationalen Gesteinsstandards und Meteoriten geprüft.

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Determination of the precious metals Au, Pd, Pt, Rh and Ir in rocks and ores by electrothermal atomic absorption-spectrometry

Summary After pressure digestion at 170°C of 5 g rock samples with HF and aqua regia the precious metals Au, Pd, Pt, Rh and Ir are separated from the rest matrix with selective adsorption on SARAFION NMRR ion exchange resin. The precious metals can be determinated in the thiourea eluate by electrothermal atomic absorption spectrometry. The reliability of the procedure was confirmed by analysing rock standards and meteoritic material.

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Die Untersuchungen wurden durch Mittel der Deutschen Forschungsgemeinschaft

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Die Untersuchungen wurden durch Mittel der Deutschen Forschungsgemeinschaft     

Binary modifiers for the determination of zinc in pure copper and nickel-based alloy by longitudinal Zeeman electrothermal atomic absorption spectrometry

The determination of zinc in pure copper and nickel-based alloy was successfully accomplished with a longitudinal Zeeman-effect correction and end-capped transversely heated graphite atomizer. Since aqua regia (an acid mixture of nitric acid and hydrochloric acid, 1:3, v/v) was used as the dissolving reagent, volatile ZnCl₂ was formed. Consequently, less Zn was found in the sample. EDTA could improve the atomic absorption profiles. Binary modifiers, EDTA + Pd(NO₃)₂ and EDTA + Mg(NO₃)₂, were effective for eliminating the chloride interference and the spectral interference from Cu I 213.853 nm. The experimental results obtained with and without the modifiers were compared. Increase of 200 °C in the pyrolysis temperature resulted from the addition of binary modifiers for both pure copper and nickel-based alloys. For pure copper, the atomization temperature increased from 1400 to 1600 °C whereas the atomization temperature increased from 1100 to 1600 °C for nickel-based alloys. The analytical performance of the proposed method was evaluated. Zinc contents in the pure copper and nickel-based alloy standards determined with both binary modifiers agreed closely with the certified values. The recovery ranged from 93 ± 2 to 104 ± 6% at 95% confidence level. The detection limits obtained by the binary modifiers of EDTA + Pd(NO₃)₂ and EDTA + Mg(NO₃)₂ were 0.77 and 0.31 pg, respectively.     

Comparison of chemical modifiers for selenium determination in soil aqua regia extracts by ZETAAS

The effect of various chemical modifiers 0.5 g l⁻¹ Pd, 1% (w/v) Ni, 0.5 g l⁻¹ Pd + 1% (w/v) Ni and 1.0 g l⁻¹ Pd on the measurement of selenium in soil aqua regia extracts, by ZETAAS, is described. Two Certified Reference Materials (CRMs) RTC-CRM 023-050 and RTC-CRM 025-050 were used for this study. Pyrolysis and atomization curves were obtained for each chemical modifier and their optimal values were assessed. By using standard addition as calibration method, accurate results were obtained for all the chemical modifiers studied. The precision was similar for both CRMs, with a maximum value of 7.5% R.S.D. The limits of detection and quantification for selenium in the soil extracts (n = 10) were 3.0 and 6.0 μg l⁻¹, respectively. The characteristic mass of selenium is assessed as 10 pg. The use of aqua regia as extractant gave quantitative results for selenium in the CRMs assayed.     

Surface and subsurface examination of graphite tubes after electrodeposition of noble metals for electrothermal atomic absorption spectrometry

The modification phenomena of noble metals (Pd, Ir, Rh) electrodeposited onto the inner surface of pyrolytic graphite (PG) coated furnaces were investigated mainly by electron microprobe analysis with energy dispersive X-ray emission detection. The conditions of electrodeposition were optimized in order to achieve the best analytical performance of atomic absorption measurements. Investigations concerning the distribution of noble metals on the tube surface and in-depth were performed at different stages of the tube history. It was found that the noble metals used for the modification do not form a compact layer on the surface but penetrate into the pyrolytic graphite structure already at the deposition step. When two metals were deposited together, both penetrated into the graphite structure. The degree of penetration of the pyrolytic graphite at high temperature differs for various metals. It was also demonstrated that electrodeposited noble metals remain in sub-surface domains of the graphite for hundreds of atomization cycles, which means that they can be used as permanent modifiers.     

Electrolytic hydride generation electrothermal atomic absorption spectrometry – in situ trapping of As on different pre-conditioned end-heated graphite tubes

An automated analytical system for the determination of As combining an electrolytic hydride generator and a graphite furnace atomic absorption spectrometer has been developed. To investigate the trapping efficiency of permanent modifiers, the end-heated graphite tubes have been impregnated with Ir and mixed Pd/Ir pre-reduced modifiers, respectively, or pre-coated with Ir by electron beam evaporation under high vacuum. Furthermore, the influence of the modifier mass on the shape of the absorption signal has been studied and the performance of the modifier has been discussed. Using the pre-coated graphite tube the calculated detection limit (3s criteria ) for As was 3 pg and 15 ng/L (200 μL sample volume, two preconcentration steps) for the absolute mass and the concentration, respectively. The long-term stability of the permanent modifiers and their physical and or chemical changes during the lifetime of the tube have been observed.     

Preconcentration of platinum group metals on modified silicagel and their determination by inductively coupled plasma atomic emission spectrometry and inductively coupled plasma mass spectrometry in airborne particulates

Modified silicagel (C18) was studied for separation and preconcentration of platinum group metals (Ru, Rh, Pd, Os, Ir and Pt) as ion associates of their chlorocomplexes with cation of onium salt N(1-carbaethoxypentadecyl)-trimethyl ammonium bromide. Sample containing HCl and the onium salt was pumped through the column. After elution with ethanol the eluate was evaporated in the presence of HCl. Resulting aqueous solutions were analysed with inductively coupled plasma atomic emission spectrometry (ICP-AES) and inductively coupled plasma mass spectrometry (ICP-MS). Recovery values of 1-20 mug Pt and Pd from 50 ml of synthetic pure solution were 100+/-3 and 100+/-1%, respectively, however, they diminished with increasing sample volume and in the presence of the real sample matrix or nitrate ions. Samples of engine soot (NIES No. 8), decomposed by low pressure oxygen high-frequency plasma, and airborne particulates from dust filters of meteorological stations, leached with HNO(3) and H(2)O(2), were analysed. A reasonable agreement was found between ICP-MS and ICP-AES results for airborne dust samples and the values comparable with those in literature were determined in NIES No. 8.     

Selective extraction of platinum,iridium, and palladium with macrocyclic endo-receptors from hydrochloric acid solutions

Extraction of Pt, Ir, Pd by the macrocyclic polyethers dibenzo-18-crown-6 (DB18C6) and cis-syncis-dicyclohexyl-18-crown-6 (DCH18C6, isomer A) in organic solvents (chloroform, dichloroethane) from 3–10 M aqueous HCl was studied. It was found that DCH18C6 in dichloroethane excellently extracted Pt, Ir, and Pd in the presence of KSCN. Re-extraction of Pt, Ir, and Pd from the organic phase can be fulfilled by 1 M HNO₃. Thus, the macrocyclic polyethers are effective reagents for isolation of Pt, Ir, and Pd from HCl solutions.     

Preconcentration and matrix separation of precious metals in geological and related materials using metalfix-chelamine resin prior to inductively coupled plasma mass spectrometry

A method for determining Au, Pt, Pd, Ir and Rh in ores and silicates and Fe-formation rocks is described. Sample decomposition was carried out with aqua regia and HF, followed by fusion of any insoluble residue with Na₂2O₂ in a glassycarbon crucible. The precious metals were separated, in 1.2 mol dm⁻³ HCl media, from the matrix elements by ion-exchange, using a mini-column with tetraethylenepentamine (metalfix-chelamine) resin. The resin was destroyed with HNO₃ and H₂O₂ in a high-pressure vessel assisted by microwave heating, and the precious elements were determined by flow-injection inductively coupled plasma mass spectrometry. The sample treatment, optimization of analytical variables and measurable concentration levels are discussed. The limits of quantification (10 sd_{n − 1}) calculated from a procedural blank sample solution were 4.0, 2.0, 1.5, 0.8 and 0.5 ng g⁻¹ for Au, Pt, Pd, Ir and Rh, respectively. The accuracy of the proposed method was tested by determining these elements in SARM 7 platinum-ore reference material. For all the analytes, the relative standard deviation of the combined dissolution, separation and determination methods was below 3.5% (n = 6).     

Determination of thallium in sediments of the River Elbe using isotope dilution mass spectrometry with thermal ionization.

By using isotope dilution mass spectrometry with thermal ionization, TI concentrations were determined in sediments from six sampling positions of the River Elbe in the area of the former GDR (Bad Schandau, Dresden, Barby, Magdeburg, Werben/Havel and Cumlosen). For comparison, two samples from the River Rhine near Emmerich taken in 1978 and 1990 and the Community Bureau of Reference (BCR) certified reference material (CRM) 320 River Sediment were also analysed. Thallium concentrations after complete decomposition by high-pressure digestion (HNO3 + HF) and aqua regia [HCI-HNO3 (3 + 1)] ranged from 537 micrograms kg-1 in the BCR CRM 320 to 5192 micrograms kg-1 in the River Rhine sediment (1978) near Emmerich. The reproducibility of the method ranged from 0.06 to 4.7%. Only 49-94% of the total amount of TI was found after extraction with 1 mol dm-3 HNO3 and 43-86% after extraction with aqua regia. Sediments from Dresden, Barby, Werben/Havel and Cumlosen were found to have virtually identical TI concentrations as the River Rhine sediment sampled in 1990. In comparison with the extremely high Hg and As concentrations found in the River Elbe in an earlier study, the TI concentrations were not as high as expected.     

Comparison of open digestion methods and selection of internal standards for the determination of Rh,Pd and Pt in plant samples by ICP-MS

An analytical procedure for the reliable determination of Pd, Pt and Rh in plant samples by inductively coupled plasma-mass spectrometry (ICP-MS) was developed. An ultrasonic nebulizer (USN) was used for sample introduction to improve sensitivity. Under various synthetic plant sample matrix compositions, it was established experimentally that moderate amounts (0.2–2%) of dissolved solids decreased the analyte signals significantly. Internal standardisation with In (for Pd and Rh) and Ir (for Pt) proved to be essential for obtaining correct results. Five open digestion approaches, used for converting solid plant samples to aqueous solution, were also tested for the purpose, namely dry-ashing, dry-ashing followed by HF attack, wet digestion with H₂O₂–HNO₃, wet digestion followed by HF attack and aqua regia digestion. Recovery tests in two spiked plant materials showed that only wet digestions must be used. With these ways, all PGEs could be reliably quantified by USN-ICP-MS without applying a separation or preconcentration step with a good precision (below 10% RSD). The aqua regia procedure was applied to the determination of PGEs in various plant matrices collected along a highway. Results showed that mosses were probably the best choice of samples to monitor the bioaccumulation of PGEs in time.     

Microwave-assisted aqua regia digestion for determining platinum,palladium, rhodium and lead in catalyst materials

This study investigated a microwave-assisted aqua regia digestion of catalyst samples prior to the determination of Pt, Pd, Rh and Pb by ICP-OES. While optimising the method, the effect of digestion temperature on the digestion efficiency was investigated. Few aqua regia digestions were also carried out using a high pressure asher, with a digestion temperature of 280 °C. In addition, XRD (X-ray diffractometry) was used to characterise digestion residue. The study showed that accurate and reliable results for Pt, Pd, Rh and Pb in a recycled monolith catalyst (NIST SRM 2557) were obtained by ICP-OES after the microwave assisted aqua regia digestion. The amounts of Pt, Pd and Rh in the prepared catalyst samples were also at the expected levels. Furthermore, the results indicated that the main part of the impurities and supporting material elements can be quantitatively extracted from the catalyst samples by using the microwave-assisted aqua regia sample pre-treatment.     

Study on stable coatings for determination of lead by flow-injection hydride generation and in situ concentration in graphite furnace atomic absorption spectrometry

Lead hydride was generated by flow-injection from 0.05 M oxalic acid sample solution by using 0.1 M HCl carrier solution and the reaction with 1.5% sodium borohydride in the presence of 2% potassium hexacyanoferrate(III) as a mild oxidizing agent. Pb was determined by in situ concentration in graphite furnace AAS. The hydride generation by flow-injection and trapping in the graphite tube coated with a highly stable trapping reagent (e.g. tungsten) allows automatic Pb determination. In a systematic investigation, the in situ concentration of Pb was studied in the temperature range 50–600° on graphite tubes coated with noble metals (Ir, Ir/Mg, Pd/Ir), and with W or Zr. The highest response was found on the Ir coatings at trapping temperatures of 200–300°, followed by the W and Zr coatings. The radiotracer ²¹⁰Pb was used to measure hydride generation (95%) and trapping efficiency (71%) on a W-coated tube. Signal stability and reproducibility was tested over 400 trapping and atomization cycles, and the better performance was found with the W and Zr coatings at a precision of 3%. Trapping temperatures above 450°C can lead to errors in absorbance values owing to an adsorptive “carry-over” effect. A characteristic mass of about 21 pg Pb for W-coated tube (283.3 nm) and a detection limit (3σ) of about 0.25 ng was obtained with a 0.5 ml sample loop. The problem with Pb hydride generation is the relatively high reagent blank (1.3 ng in 30 s trapping time) even using chemicals of the highest purity. The method has been tested by applying it to the determination of Pb in a sediment certified reference material.     

Extractability of HgS (cinnabar and metacinnabar) by hydrochloric acid

In this work we investigated the behaviour of pure HgS during extraction with dilute HCl to establish its extractability in 1 and 6 M HCl at the concentration level close to those occurring in natural sediments and soils. We found that neither cinnabar nor metacinnabar were soluble in 1 M HCl, whereas both were partially extracted by 6 M HCl. Metacinnabar precipitated in the laboratory was most prone to dissolution in 6 M HCl (up to 90%), followed by crystalline (commercial) metacinnabar (up to 70%) and cinnabar (up to 15%). Solubility of HgS in 6 M HCl was found to be dependent on its concentration, and an exponential relationship between quantity of HgS added to 20 mL of 6 M HCl (the range of 0.1-10 mg was used) and the solubility in 6 M HCl was established. For higher concentrations of HgS (10 mg in 20 mL of acid), a similarly low solubility of cinnabar was obtained as found in the literature. A study of dissolution kinetics of HgS in 6 M HCl indicated that it was a fairly slow process. Unexpected oxidation of HgS in water or 1 M HCl was found for extractions performed in Teflon vials previously used for the digestion of residual undissolved HgS by aqua regia. We presumed that the Teflon material could preserve some oxidising gases (presumably Cl(2)) developed during digestion with aqua regia which can then oxidise HgS during extraction with water or 1 M HCl. Regarding the extraction of Hg from natural sediments, we concluded that 6 M HCl could not be used to extract reactive Hg and predict bioavailability of mercury in sediments containing HgS and that experiments with model compounds should not be done at a concentration level several orders of magnitude higher than in natural samples.     

Simultaneous determination of manganese and selenium in serum by electrothermal atomic absorption spectrometry

A method for determination of manganese and selenium in serum by simultaneous atomic absorption spectrometry (SIMAAS) is proposed. The samples (30 mul) were diluted (1+3) to 1.0% v/v HNO(3)+0.10% w/v Triton X-100 directly in the autosampler cups. A total of 20 mug Pd+10 mug Mg(NO(3))(2) was used as chemical modifier. The pyrolysis and atomization temperatures for the simultaneous heating program were 1200 and 2300 degrees C, respectively. The addition of an oxidant mixture (15% w/w H(2)O(2)+1.0% v/v HNO(3)) and the inclusion of a low temperature pyrolysis step (400 degrees C) attenuated the build-up of carbonaceous residues onto the integrated platform. An aliquot of 15 mul of the reference or sample solution was introduced into the graphite tube and heated at 80 degrees C; subsequently, 10 mul of oxidant mixture+10 mul of chemical modifier was introduced over that aliquot and the remaining heating program steps were executed. This strategy allowed at least 250 heating cycles for each THGA tube without analytical signal deterioration. The characteristic masses for manganese (6 pg) and selenium (46 pg) were estimated from the analytical curves. The detection limits were 6.5 pg (n=20, 3delta) for manganese and 50 pg (n=20, 3delta) for selenium. The reliability of the entire procedure was checked with the analysis of serum from Seronormtrade mark Trace Elements in Serum (Sero AS) and by addition and recovery tests (97+/-9% for manganese and 96+/-7% for selenium) using five serum samples.     

Rapid determination of antimony in steel by flameless atomic-absorption

A method for the determination of 1-30 ppm or more of Sb in steel by using flameless atomic absorption has been developed. The sample was dissolved in aqua regia and 10 mul were pipetted into the Massmann-type furnace. It was shown that interferences from HCl, HNO(3), Ni and Fe could be eliminated if oxygen was excluded and the heating rate was sufficiently high. Chromium was added to the samples and standards to compensate for its influence. Cu, Co, Mn, Ti and Sn did not interfere. An intercomparison with other laboratories showed that this method gives the same result as extraction with TOPO in MIBK. The time for a complete analysis including dissolution was 15 min.     

Multielement electrothermal atomic absorption spectrometry: A study on direct and simultaneous determination of chromium and manganese in urine

A study was carried out on the direct determination of Cr and Mn in urine using simultaneous atomic absorption spectrometry (SIMAAS). The heating program conditions, the absorbance signal profiles, the influence of different chemical modifiers, and the urine sample volume delivery into the tube were optimized to perform the calibration with aqueous solutions. Among several chemical modifiers tested, the best recovery and repeatability results were obtained for 3 microg Mg(NO3)2. On using this modifier, the pyrolysis and atomization temperatures for simultaneous determination of Cr and Mn were 1,300 degrees C and 2,500 degrees C, respectively. Urine samples were diluted (1+1) with 2.0% (v/v) HNO3 + 0.05% (w/v) Triton X-100 prepared in high purity water. A 20-microL aliquot of analytical solution and 10 microL of chemical modifier solution were delivered to the graphite tube. The characteristic masses were 7.8 pg for Cr (RSD=4.0%) and 4.6 pg for Mn (RSD=2.6%). The limits of detection were 0.08 microg L(-1) (n=20, 3s) for Cr and 0.16 microg L(-1) (n=20, 3s) for Mn. Recovery studies for 1.0 or 2.5 microg L(-1) of Cr and Mn added to different urine samples showed acceptable results for Cr (100%, RSD=14%) and Mn (88%, RSD=5.6%).