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.     

Platinum-group element concentrations in BCR-723: a quantitative review of published analyses

BCR-723 is the only environmental certified reference material for platinum-group elements (PGEs) Pt, Pd and Rh. It has been an integral component of quality control/quality assurance procedures in environmental laboratories measuring PGEs, since 2001. Here, we present an extensive quantitative review of the published PGEs measured in BCR-723, since its introduction. A statistical examination of concentrations, measurement precision and accuracy for 25 studies is presented. Measurement typically starts with an aqua regia digestion, followed by some form of pre-concentration or separation procedure, and quantitation by ICP-MS. Use of a sample mass below the recommended value of 100 mg has been shown to produce biased results for acid-based digestions or with laser ablation. Platinum is the most precisely and accurately measured PGE in BCR-723, followed by Rh, and finally by Pd. Literature precision data for all autocatalyst PGEs did not differ significantly (α = 0.05) from those obtained by the original laboratories used to certify BCR-723. Measurement accuracies for the literature tabulated PGE data did not differ significantly from zero, indicating an overall lack of directional bias. These results should be encouraging to the analytical community, but further advancements, especially for Pd quantification are required.     

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     

Influence of sample pre-treatment on the determination of trace silver and cadmium in geological and environmental samples by quadrupole inductively coupled plasma mass spectrometry

The suitability of three different digestion procedures has been evaluated with regard to the quantitative determination of trace amounts of silver and cadmium in geological and environmental samples. Procedure A: extraction with aqua regia in an open vessel system; Procedure B: extraction with aqua regia in a closed pressurized vessel system; Procedure C: digestion with HF + HNO₃ in a closed pressurized vessel system. It was found that procedure A represented an effective way of extracting analytes from different types of geological samples while the effect of extracting interfering metals is low. Because it is interference-free, poses a low risk of contamination and is time-saving, sample treatment procedure A was preferred. For this digestion procedure, a series of Chinese geological reference materials was determined by ICP-MS, the results of which were found to be in reasonable agreement with the certified values.     

Electrodeposition Sample Introduction for Ultra Trace Determinations of Platinum Group Elements (Pt,Pd, Rh,Ru) in Road Dust by Electrothermal Atomic Absorption Spectrometry

A novel method for the determination of the platinum group elements (PGEs: Pt, Pd, Rh, Ru) in environmental samples by electrothermal atomic absorption spectrometry (ET-AAS) was developed. Sample preparation involved complete microwave-assisted acid digestion of the matrix with HNO₃-HF-HClO₃/HClO₄mixtures in a high-pressure Teflon bomb. Traces of PGEs were deposited on the inner wall of a graphite tube in a flow-through cell of 1 ml volume. A flow system for this preconcentration was constructed. For the electrodeposition, a three-electrode arrangement was used. The geometry of the cell, flow rate during electrodeposition, deposition potential and electrolyte composition were optimized. After the deposition step, the graphite tube was placed into the graphite furnace and an atomization program applied. Detection limits (LOD, 3σ_{total procedure blank}, peak area) of 3.6, 0.5, 0.3 and 5.9 ng were obtained for Pt, Pd, Rh and Ru, respectively, reflecting preconcentration factors of 416, 503, 423 and 46, respectively. The detection limits were restricted by variations in the blank. Precision of replicate determination was typically 21% RSD at a concentration 25-fold above the LOD for a 100-mg sample mass. Reasonable agreement was found between results for CW7 road tunnel dust literature and for CRM NIES No. 8 Vehicle Exhaust Particulates. Calibration was achieved via the method of standard additions.     

Investigation of the solubilization of car-emitted Pt,Pd and Rh in street dust and spiked soil samples

A sequential extraction procedure (three-step), proposed by the Standards, Measurements and Testing Programme (formerly BCR) of the European Union, was applied to street dust and spiked soil samples for the determination of PGEs. Analyses were carried out using inductively coupled plasma-mass spectrometry (ICP-MS). The results indicate that up to 5% from Pt, 70% from Pd and 14% from Rh are in mobile forms in street dust. The results for the soil samples spiked with crushed catalytic converter are significantly lower indicating that PGEs are oxidised more efficiently in natural conditions. Additionally Pt and Pd bound to humic acids were investigated.     

Determination of Cd, Cu, Pb and Zn in environmental samples: microwave-assisted total digestion versus aqua regia and nitric acid extraction

We validated the determination of the content of Cd, Cu, Pb and Zn using two digestion protocols: a microwave-assisted total digestion and an aqua regia extraction procedure based on the International Organization for Standardisation (ISO) 11466 method. Our goal in validating these two protocols, along with a nitric acid digestion, is to propose a rapid, cheap and easily automated digestion method for monitoring heavy metal content in environmental samples. We applied the digestion protocols to samples with a wide range of organic matter such as sediments, soils, sludges and plant material.For samples with a low carbonate or organic matter contents, such as sediments and agricultural soils, aqua regia digestion in an aluminium block was revealed to be an optimum estimator for the total metal content. For samples with a high organic matter content, such as organic horizons of forest floor layers, plant material and organic soils, nitric acid digestion could substitute microwave (MW)-hydrofluoric acid (HF) digestion. Except in a few samples with high organic matter or low heavy metal content, the RSD values obtained after the application of the proposed digestion procedures were lower than 5%. Based on the obtained results, a decision flow chart for choosing the fit-for-purpose digestion procedure is suggested.     

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.     

The role of different soil sample digestion methods on trace elements analysis: a comparison of ICP-MS and INAA measurement results

The measurement of trace-element concentration in soil, sediment and waste, is generally a combination of a digestion procedure for dissolution of elements and a subsequent measurement of the dissolved elements. “Partial” and “total” digestion methods can be used in environmental monitoring activities. To compare measurement results obtained by different methods, it is crucial to determine and to maintain control of the bias of the results obtained by these methods. In this paper, ICP-MS results obtained after matrix digestion with modified aqua regia (HCl+HNO₃+H₂O₂) method and two “total” digestion methods (microwave aqua regia+HF and HNO₃+HF) are compared with those obtained by instrumental neutron activation analysis, a non-destructive analytical method for the determination of the total mass concentrations of inorganic components in environmental matrices. The comparison was carried out on eight agricultural soil samples collected in one test area and measured by k₀-INAA and ICP-MS to determine As, Co, Cr, Sb and Zn mass concentration. The bias of results for As, Cd, Co, Cr, Cu, Ni, Pb, Sb and Zn of the three digestion methods were assessed using selected measurement standards. This paper highlights that the digestion procedure is an integral part of the measurement and can affect the measurement result in environmental analysis.     

Comparison of wet microwave digestion methods of plant materials for the determination of metals by flame atomic absorption spectrometry

Microwave closed-system wet digestion procedures for plant samples were examined. Each procedure was tested with samples of tobacco and cabbage, and included digestion by the use of different acids composition, almost complete evaporation of the digest, and then dissolution of the residue in 1% nitric acid. Three microwave digestion programs that varied power, duration, and temperature were used. Closed-vessel reactions followed open-vessel reaction-delay time. Using flame atomic absorption spectrometry on the digests, four or five elements were determined to evaluate effectiveness, precision and accuracy of analytes extraction into solution. After a preliminary study of tobacco digests, the four most effective procedures were chosen, and detailed investigations were carried out on both tobacco and cabbage reference materials. Although all four of the final procedures were accurate, the most precise procedure, with the lowest errors of determination, was using reverse ‘aqua regia’ for tobacco and ‘aqua regia’ for cabbage.     

Determination of Platinum-Group Elements (PGE) from catalytic converters in soil by means of docimasy and INAA

The nickelsulfide fire assay (docimasy) for the enrichment of platinum-group elements (PGEs) has been modified for the use with small samples and combined with instrumental neutron-activation analysis (INAA). This procedure has been applied to the determination of PGEs exhausted from catalytic converters and deposited in soil near the Wiesbadener Kreuz (highway A3, Frankfurt-Köln). Our results show a considerable enhancement of the Pt (up to 330 ng/g), Pd (6.6 ng/g) and Rh (7.5 ng/g) contents close to the highway.     

Development of an analytical method for monitoring worker populations exposed to platinum-group elements

The increasing industrial use of platinum-group elements (PGEs), namely Ir, Pd, Pt and Rh, and related allergies such as rhinitis, conjunctivitis, asthma, urticaria and contact dermatitis, have led to a growing need to monitor selected populations of exposed workers. In this study, the levels of PGEs were measured in indoor airborne particulate matter and in biological samples taken from employees of a plant where car catalytic converters are produced and precious metals are recovered from spent carbon catalysts. The development of an analytical procedure based on quadrupole inductively coupled plasma mass spectrometry (Q-ICP-MS) for the analysis of PGEs in airborne particulate matter and on sector field inductively coupled plasma mass spectrometry (SF-ICP-MS) for the analysis of PGEs in blood, serum, urine and hair is described. For airborne particulate matter deposited on filters, the limits of detection (LoDs) were found to be 0.006 ng m⁻³, 0.020 ng m⁻³, 0.018 ng m⁻³ and 0.006 ng m⁻³ for Ir, Pd, Pt and Rh, respectively. Repeatability of measurements ranged from 1.8 to 8.5%, while recovery was in the range from 92 to 102%. For biological samples LoDs in blood, serum, urine and hair ranged from (in ng l⁻¹) 0.2–0.6 for Ir, 5–10 for Pd, 1–3 for Pt and 2–3 for Rh. For all biological materials, the repeatability varied from 1.1 to 12% for the four elements. Recovery data for the determination of PGEs in biological matrices were found to range from 84.0 to 107.8%. The method was applied to the determination of either total or respirable airborne PGEs collected from five different work areas in the plant. The difference between areas with high and low exposure correlates closely with metal levels in hair, blood and urine. The correlation coefficients between Pt in airborne particulate matter and Pt in biological materials was 0.994, 0.991 and 0.970 for blood, hair and urine, respectively.     

Determination of Platinum-Group Elements (PGE) from catalytic converters in soil by means of docimasy and INAA

The nickelsulfide fire assay (docimasy) for the enrichment of platinum-group elements (PGEs) has been modified for the use with small samples and combined with instrumental neutron-activation analysis (INAA). This procedure has been applied to the determination of PGEs exhausted from catalytic converters and deposited in soil near the Wiesbadener Kreuz (highway A3, Frankfurt-Köln). Our results show a considerable enhancement of the Pt (up to 330 ng/g), Pd (6.6 ng/g) and Rh (7.5 ng/g) contents close to the highway.     

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).     

Analytical Determination and Bio-Monitoring of Platinum Group Elements in Roadside Grass Using Microwave Assisted Digestion and Electrothermal Atomic Absorption Spectrometry

The analytical conditions that enable the determination of traffic related platinum group elements (PGEs) in roadside grass using microwave digestion and electrothermal atomic absorption spectrometry were evaluated as an alternative to the biomonitoring of traffic related PGEs and Pb levels in urban areas. To optimize the analytical conditions and account for matrix effects that could import error in the analysis, method optimization was based on matrix simulation through analyte recovery from spiked unpolluted samples against a matrix blank. A mixture of nitric and hydrofluoric acid under progressively increasing microwave irradiation was optimized to afford the quantitative extraction of platinum group elements from plant matrix. Due to the low levels of platinum group elements in real samples, preconcentration was accomplished using sample evaporation followed by dissolution in dilute nitric acid prior to deliverance to the atomic detector. Quantitation limits below 1 ng g^?1 for Pd and Rh and lower than 2 ng g^?1 for Pt, were accomplished, enabling the monitoring of platinum group elements bioaccumulation in roadside grass with satisfactory recoveries, as determined from the analysis of spiked samples. The results from method application in an annual monitoring survey of PGEs and Pb levels in urban flora and other roadside media are presented and discussed.     

铂族元素在环境和生物样品中的积累及毒性研究进展

由汽车尾气净化器的安装使用而导致环境中的铂族元素尤其是铂、钯、铑的含量逐渐增长,铂族元素对于生活和生态环境的影响也越来越多受到关注.论述了汽车三元催化剂中铂族元素毒性、铂族元素在环境和生物样品的分布、环境样品中铂族元素的消解、测定方法以及干扰处理方法,总结了多国测定结果并对结果进行了综合评述.     

A Novel Way of Sampling Particles Containing Platinum Group Elements from Automobile Catalysts

A new sampling system was developed in order to be applied directly at the exhaust pipe of vehicles combined with an exhaust gas analyzer during the standard New European Driving Cycle (NEDC). In that way a quantitative sampling of Pt, Pd, and Rh (Platinum Group Elements, PGEs) in particle form on filters and gas monitoring could be achieved simultaneously, applying the sampling system on a variety of vehicles of different age and engine capacity. The samples were examined by SEM-EDX for morphological and qualitative analysis of the particles. By using an appropriate digestion procedure and the analytical techniques of ICP-MS and GFAAS, concentrations were found in the range of 0.35–87 ng/km for Pt, 3.3–437 ng/km for Pd, and 0.9–72 ng/km for Rh. Furthermore the investigation showed that fresh catalysts as well as engines with larger capacity emitted higher amounts of PGEs in comparison to older catalysts and smaller capacity engines. According to the results of this research the palladium emissions were dominant in comparison to the platinum ones. This way of sampling might prove advantageous in testing new technology catalysts through their PGEs emission.     

Determination of noble metals in silicate rocks, ores and metallurgical samples by simultaneous multi-element graphite furnace atomic absorption spectrometry with Zeeman background correction

A new method has been developed for rapid determination of mug/g and ng/g amounts of noble metals in silicate rocks, ores and metallurgical samples by attacking with hydrofluoric acid and aqua regia, preconcentration by ion-exchange chromatography and measuring in a simultaneous multi-element graphite furnace atomic absorption spectrometer equipped with a polarized Zeeman background correction device which eliminated interferences from any incompletely separated common elements. The method was tested for Ru, Rh, Pt, Ir, Pd, Ag and Au with three Canadian certified reference materials, and then applied to the determination of ng/g amounts of these elements in four new Canadian candidate reference materials.     

Comparative study of different digestion procedures using supplementary analytical methods for multielement-screening of more than 50 elements in sediments of the river Elbe

The suitability of four different digestion procedures, i.e. i.) an aqua regia digestion according to DIN 38 414-S7, ii.) a pressure digestion using HNO₃/HF in PTFE-vessels, iii.) a HNO₃/HF + HCl-pressure digestion in PTFE-vessels and iv.) a HNO₃/HF + HCl-pressure digestion using microwave induction, has been evaluated with regard to the quantitative determination of about 50 elements in environmental samples. Three sediments of the river Elbe and two standard reference materials (MESS-1 and NIST 1645) have been employed. The analytical results from the dissolved samples, obtained using inductively coupled plasma mass- and optical emission spectrometry as well as total reflection X-ray fluorescence spectrometry, have been compared with those obtained by instrumental neutron activation analysis. Only digestion procedures using HNO₃/HF with a subsequent evaporation to dryness and dissolution in HCl have led to appropriate results for a wide range of elements (more than 50 elements in total). Because of its low contamination risk and its time saving, the microwave digestion is preferred. For this digestion procedure the accordance among the different instrumental methods used is high (better than 15% deviation) in general. A few elements (16) could be determined quantitatively only by a single method.     

不同消解方式对土壤中锑的原子荧光法检测影响

氢化物发生-原子荧光光谱法是土壤环境中锑检测所广泛使用的方法．土壤的消解前处理分别采用王水微波消解（半消解）、混酸全消解（硝酸＋高氯酸＋氢氟酸）方式．研究结果表明王水微波消解对锑的检测效果较好,标准土壤9次测定值的相对标准偏差为3．6％,实际样品的回收率为96％-102％．而采用混酸全消解的方式测定值偏低,实际样品的回收率为78％～86％,而且精密度超过5％,这是由于在赶酸过程中样品易被蒸干而造成痕量锑元素的损失．