Determination Of Platinum Group Elements Research Articles

Determination of low concentrations of platinum group elements in geological samples by ID-ICP-MS

Accurate and precise determination of platinum group elements (PGEs) at ppb concentrations in geological samples is important but problematic. This paper reports an improved analytical method for the determination of Pt, Pd, Ru, Ir and Rh at sub-ppb levels by isotope dilution-inductively coupled plasma mass spectrometry (ID-ICP-MS). Prior to experimentation, all reagents were carfully purified: HBO3, HCl and SnCl2 by Te coprecipitation and HNO3 and HF by subboiling distillation. HF, HNO3 and HCl were used to decompose 10 gram sample. The fluoride residue from the acid digestion is minimized by using H3BO3 for complexation, thus mini-fusion of sodium peroxide can be performed in corundum crucibles instead of bulk Na2O2 fusion to lower blank level. The solution of acid digestion and Na2O2 fusion are combined and PGEs are then pre-concentrated by Te coprecipitation. Cu, Ni, Zr and Hf are removed using cation exchange resin and P507 extraction chromatography resin combined in the same column to minimize their interference. Pt, Pd, Ru and Ir are determined using ID-ICP-MS, whereas the mono-isotopic element, Rh, is determined by external calibration using highly enriched 194Pt as the internal standard. The enriched 194Pt spike behaves similar to Rh during the Te precipitation procedure and acts as an ideal internal standard. The determination limits for PGE range from 0.01–0.19 ng g−1. The results obtained using this new method for the CCRMP (CANMET, Ottawa, Canada) certified reference materials WGB-1 (gabbro), TDB-1 (diabase) and UMT-1 (ultramafic ore tailings), show good agreement with the reported values, but have discrepancies compared with the certified values when the concentration of Ru, Rh and Ir below 0.5 ng g−1.

On the determination of platinum group elements in environmental materials by inductively coupled plasma mass spectrometry and microwave digestion

The interferences from Cd, Cu, Hf, Pb, Sr, Zn, Zr and Y on the inductively coupled plasma quadrupole mass spectrometry (ICP-MS) determination of Pt, Pd, Rh, Ru and Ir in geological (Pt-ore SARM-7, abundance range for platinum metals 0.07–3.74 μg/g) and environmental samples (sediment JSd-2 abundance range for Pt and Pd 0.0167–0.021 μg/g; road dust and plant sample) are evaluated using model solutions, real samples and comparison to inductively coupled plasma atomic emission spectrometry (ICP-AES) results. Pt, Rh, Ru and Ir can be determined usually after introduction of corrections for the interference in all investigated materials though in sediments the direct determination of Pt might be a problem depending on the actual Hf concentrations. The direct determination of Pd (after microwave-assisted acid digestion) is possible in ores using all investigated isotopes ( 105 Pd , 106 Pd , 108 Pd ), in plants using 108 Pd and correction for the interferences of Zr, Mo and Cd, and not possible in sediments and road dust. Therefore, we developed a procedure for isolation of Pd using its diethyl-dithio-carabamate (DDTC) complex. The detection limits for Pt, Pd and Ir are 0.015 ng/g, and for Ru and Rh 0.03 ng/g.

Ion chromatography with inductively coupled plasma mass spectrometry, a powerful analytical tool for complex matrices: Estimation of Pt and Pd in environmental samples

A new method for palladium and platinum direct determination in environmental samples is proposed by coupling ion chromatography with quadrupole inductively coupled plasma MS. In order to optimise Pd and Pt separation and to minimise interference from matrix in real samples, several anionic and cationic stationary phases have been compared at different mobile phase compositions. In particular, the effect of acidity and of the addition of oxalic acid to the eluent on separation and detection performance has been studied, and the anion-exchange column AG11 turned out to be more suitable. After chromatographic and mass spectrometer parameter optimisation, several potential interferences and the main quality parameters of the method, according to the Eurachem-CITAC recommendations, were evaluated: the detection limit for Pt was 5 ng l −1 while the value for Pd was 230 ng l −1. The method was successfully employed in the determination of platinum group elements in urban road dust and atmospheric particulates and the complete absence of matrix spectral interferences was demonstrated.

A simple procedure for the determination of platinum group elements and rhenium (Ru, Rh, Pd, Re, Os, Ir and Pt) using ID-ICP-MS with an inexpensive on-line matrix separation in geological and environmental materials

A simple and highly selective analytical procedure is presented here for the concentration determination of Ru, Rh, Pd, Re, Os, Ir and Pt via isotope dilution, which is suitable for the investigation of geological and environmental materials. Sample preparation consists of a sample digestion step in a high pressure asher (HPA-S) with concentrated HNO3 and HCl and drying down of the sample solution after the Os concentration was determined via sparging OsO4 into an ICP-MS. After drying and redissolution of the remaining solution the other PGEs are separated on-line from their matrix in a simple cation-exchange column that is coupled to a quadrupole ICP-MS. Through this technique it is possible to monitor in every sample the isotopes of the analytes as well as of those elements that cause isobaric interferences or that potentially cause interferences through molecular species. Concentrations of the two or more isotopic elements can be calculated through isotope ratios, whereas Rh is calculated via the peak area. Data for ultramafic reference materials UB-N and GP13 with concentrations lower than 8 ng g−1 show excellent reproducibilities (n = 9) for Re, Pd and Pt (2.5–3.9% RSD) and Pt, Ru, Rh, Os and Ir (4.5–7% RSD). It can be demonstrated that a large portion of the higher standard deviations is caused by sample heterogeneity. Road dust (BCR-723) was included to demonstrate the strength of this procedure for the determination of environmental samples. Reproducibilities (n = 5) for Re, Pt and Os were between 1.2 and 2.3% RSD, 5.2% RSD for Pd and 11% RSD for Rh. Data for Ru and Ir are presented for the first time.

Determination of platinum-group elements and gold in silicates by gamma activation autoradiography and instrumental gamma activation analysis

The potential of the gamma activation determination of platinum-group elements and gold both by instrumental gamma activation analysis (bulk analysis) and by monitoring their distribution using autoradiography (local analysis) is studied. It is shown that platinum-group elements and gold can be determined by direct gamma-ray spectrometry in silicate samples with a detection limit of 10–3–10–5%. In contact gamma activation autoradiography, the detection limit for these elements is about 10 ng with a spatial resolution of 10–20 μm.

Determination of Platinum‐Group Elements and Forty Two Other Elements in Two Candidate Danish Cretaceous‐Tertiary Boundary Clay Reference Materials by INAA, ENAA and RNAA

Ruthenium, rhodium, palladium, osmium, iridium and platinum (PGEs) and forty two other elements in two candidate geological Cretaceous‐Tertiary boundary clay reference materials taken from the Fish Clay, Stevns Klint, Denmark, were determined by a combination of neutron activation analysis (NAA) consisting of instrumental, epithermal and radiochemical NAA with or without nickel sulfide fire assay preconcentration. The accuracy of the experimental values was assessed by the comparative analysis of the certified reference materials.

NAA of Platinum Group Elements and Gold in Reference Materials: A Comparison of Two Methods

Two methods have been developed for the determination of platinum group elements (PGEs) and gold in four geological reference materials: one using radiochemical neutron activation analysis and the other using nickel sulphide fire assay, followed by instrumental neutron activation analysis. The results from ten multiplicate measurements have been discussed in terms of precision and accuracy. The average precision for both methods is about 5%. Comparing the reported data with existing values in the literature, the accuracy of the proposed methods is good agreement in most cases. Detection limits in the range 0.001–0.015 ng have been derived for both methods under the operational conditions.

Determination of platinum group elements and gold in geological samples with ICP-MS using a sodium peroxide fusion and tellurium co-precipitation

A reliable and rapid method with inductively coupled plasma mass spectrometry is developed for the determination of Ru, Rh, Pd, Ir, Pt and Au in geological samples. After fusion of the sample with sodium peroxide, the digested solution is dried to convert silica to an insoluble form to discard SiO2. The platinum group elements are pre-concentrated and separated from a large amount of matrix elements by Te co-precipitation. The detection limit of this method is 1–9 pg g−1 when 10 g of sample are weighed and 10 mL is the final volume used. Results obtained for the reference materials, WGB1,SARM7 and GBW07288-GBW07294, are in agreement with the certified values.

Trace Element Microanalysis in Iron Meteorites by Laser Ablation ICPMS

A laser ablation microanalysis system has been developed that can analyze trace elements with a sensitivity in the ppb range, using a CETAC LSX-200 laser ablation system with a Finnigan Element. This capability has been applied to a set of iron meteorites to demonstrate the laser microprobe's analytical capability for the determination of platinum group elements (PGEs) with a spatial resolution of ∼20 μm, comparable to that of dynamic secondary ion mass spectrometry (SIMS). The laser is shown to provide an accurate means of solid sampling for magnetic sector inductively coupled plasma mass spectrometry (ICPMS), allowing the determination of bulk metal composition, chemical zoning within the sample, and depth profiling. Recovery of the chemical zoning in taenite lamellae was achieved for Ru, Rh, and Pd, which was not previously possible using SIMS. The methods presented here show that magnetic sector ICPMS can be successfully coupled to a laser ablation system, providing the advantages of higher sensitivity of the sector instrument, low background count rates (<0.1 counts/s), and flat-topped spectral peaks, while minimizing tradeoff against the speed of data acquisition required to handle the transient signals from the laser ablation system.

Determination of platinum group elements by inductively coupled plasma-mass spectrometry combined with nickel sulfide fire assay and tellurium coprecipitation

A method was developed for the determination of trace platinum group elements (PGEs) by nickel sulfide fire assay inductively coupled plasma-mass spectrometry (ICP-MS). With isotope dilution, the improved technique gives precise Os content data. Through the purification of the reagent nickel oxide, reagent blank was greatly reduced. Results obtained for the standard reference materials (SRM) GPt-1-GPt-7(GBW 07288-07294, China), DZ Σ-2 (GBW 07102, China) and Guilin Cu–Ni Ore are in good agreement with the recommended values for platinum group elements. The detection limits ranged from 0.01 to 0.39 ng/g. The relative standard deviations for Ru, Rh, Pd and Ir were less than 5%, for Os less than 1%, and Pt less than 8% for SRM GPt-6.

Study of interfering nuclear reactions in determination of platinum group elements by neutron activation analysis

Eighteen interfering nuclear reactions that likely occur in neutron activation analysis of platinum group elements are studied. Their degrees are calculated by the basic principle of activation analysis. The calculation results indicate that most of the nuclear interferences become significant only if the interfering elements exist in major amount and the elements of interest in trace amount. However, the second-order interference to platinum analysis from gold and the fission interference to analysis of ruthenium and palladium from uranium cannot be neglected even if the gold and uranium exist as trace constituents in samples.

Determination of platinum group elements and gold in geological materials using an ultraviolet laser ablation high-resolution inductively coupled plasma mass spectrometric technique

In this work, a UV laser system coupled to high-resolution ICP-MS was used in the determination of platinum group elements (PGE) and gold in nickel sulfide buttons prepared by the fire assay technique. A Nd:YAG laser operating at 266 nm quadrupled frequency was used. The laser operating parameters were established by studying signal intensity and the precision for different energy beams and frequencies. TheF-test was used to evaluate the homogeneity of the buttons, demonstrating that for most elements the distribution is homogeneous. The analyses were performed on three different sites in three replicates of the materials. The detection limits obtained (3σ) were in a range from 0.2 for Os (and Ir) to 7 ng g–1 for Pt. The accuracy of the results was better than 16.7% for most elements. The effects of isobaric interference on the 103Rh signal (206Pb2+ and 40Ar63Cu+) were evaluated by analysing NiS buttons doped with lead and copper. For Au, Pt and Pd, the standard deviations obtained were higher than expected and are related to a non-homogeneous distribution of these elements in the buttons. The concentrations of the elements in the geological reference materials UMT-1 and WPR-1 were obtained by external calibration curves.

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.

Inductively coupled plasma mass spectrometry for the determination of platinum group elements and gold

The determination of the platinum group elements and gold by means of inductively coupled plasma mass spectrometry is reviewed. The technique has been applied to analyses of geological, biological, and botanical samples, water and airborne particulate matter. The multi-element capability of the technique and the excellent detection limits have been distinct advantages in research programs which require accurate determinations of small concentrations of precious metals.

The determination of platinum-group elements (PGE) by nickel sulfide fire-assay: Coexisting PGE-phases in the nickel sulfide button

The chemical composition of phases in buttons obtained by nickel sulfide fire-assay during the determination of platinum-group elements (PGE) has been investigated by electron microprobe analysis. Different PGE-containing phases, due to varying flux constituents and species of added PGE, have been detected. By using sodium tetraborate as flux constituent and adding PGE as chlorides, in a cryptocrystalline Ni3S2 matrix with low PGE (mainly Rh and Ru) contents, Rh- and Ru-bearing nickel sulfides ((Ni7.68–7.80Ru0.84–0.90Rh0.35–0.43)9S8) and Ir alloys ((Ir,Pt,Os)0.56–0.62(Ru,Rh)0.25–0.28Ni0.12–0.19) are found. Treatment with lithium tetraborate leads to a Ni3S2 matrix exhibiting slightly higher Rh and Ru contents, with inclusions of nickel-rhodium sulfides (Ni8Rh4S9) and platinumnickel alloys (Pt0.45Ni0.36–0.39Ru0.11–0.14Rh0.05). Finely dispersed metallic colloidals from an automobile catalyst, with platinum and rhodium as main components, have given only platinum-nickel alloys (Pt1−xNix). Considerable losses of PGE during analytical steps following the fire assay are expected when their contents in sulfidic phases, which are more likely to be dissolved, are high.

The determination of platinum group elements (PGE) in target rocks and fall-back material of the Nördlinger Ries impact crater, Germany

The nature of the impactor for the Nördlinger Ries has, so far, remained elusive. Suggestions have been made for a chondritic or an aubritic proctile but all studies had difficulties to establish beyond doubt the meteoritic parental material. The majority of the Ries samples so far analyzed derived from the present surface, which may have lead to some bias. Therefore, we analyzed fifty-five drill core samples from the research borehole Nördlingen 1973 to characterize the indigenous Ir concentrations of the target rocks and to search for any enrichments of Pt group elements in the suevite and the so-called Graded Unit. We found that ultramafic rocks in the crystalline basement at a depth of 826 m—far below the current crater bottom—contain up to 0.5 ng/g Ir, the highest concentrations ever measured in the target rocks. These rocks comprise about 8% of the crystalline basement, and thus, form a substantial indigenous source of Pt group elements. Taking this into account, one has to consider Ir concentrations of up to about 0.060 ng/g as indigenous, although the median concentration is 0.013 ng/g, close to earlier estimates. Our results show that there is no indication of unequivocal extraterrestrial contamination in the cored materials of the crater ejecta. It is surprising that this also holds for the current crater bottom and the Graded Unit, which have previously been suspected to contain meteoritic contamination. It seems that a chondritic projectile can be ruled out, but a clear geochemical association of any of the known meteorite types with the Ries bolide is not possible.

COMPARISON BETWEEN THE USE OF SODIUM AND LITHIUM TETRABORATEIN PLATINUM‐GROUP ELEMENT DETERMINATION BY NICKEL SULPHIDE FIRE‐ASSAY

The alternative use of lithium tetraborate and/or sodium tetraborate as flux constituents in the quantitative determination of platinum group elements (PGE) in standard reference materials SARM‐7, CHR‐Pt+ and CHR‐Bkg by graphite furnace atomic absorption spectrometry after preconcentration by nickel sulphide fire assay was reinvestigated. Results showed that lithium tetraborate has a lower recovery rate than sodium tetraborate, except for chromitites with PGE abundances in the ppm‐range. Best results for chromitites were obtained by using a mixture (1:1) of the two tetraborates. Examination of the NiS‐reguli by an electron microprobe revealed finer grain‐sizes of PGE‐phases for lithium tetraborate and coarser ones for sodium tetraborate, the finer grains being a possible reason for greater losses during analysis filtration.

Nickel sulphide fire assay ? ICPMS method for the determination of platinum group elements: a detailed study on the recovery and losses at different stages

Detailed studies for evaluating the optimum nickel sulphide button size in the estimation of platinum group elements (PGE) by inductively coupled plasma mass spectrometry (ICPMS) were carried out. PGE losses in various stages of the process have been studied. The results indicate that among the three button sizes investigated, i.e., 2.5, 5 and 8 g, the 2.5 g button was found to be adequate for the full recovery of the PGE. Losses of PGE in the fusion slag and in the pulp at the second filtration stage have been found to be negligible. Tellurium coprecipitation was found to minimize the losses during the dissolution of the nickel sulphide button.

Effects of fusion charge composition on the determination of platinum group elements using collection into a minimized nickel sulphide button

For characterizing fire assay fusion and the collection of platinum group elements (PGE) into a NiS button, two parameters referring to the charge before fusion were defined. One is the extraction ratio E, expressed as the mass ratio of the sample plus flux to the collector (Ni + S) and the other is the sulphur content in the collector S c, expressed as a percentage. Using graphite furnace atomic absorption spectrometry after fire assay into a minimized NiS button, the PGE recoveries were investigated when varying these two parameters. The experimental data show that for an acceptable recovery S c may vary in a fairly broad range, namely 30–50%. Any excess of sulphur seems to be easily removed during fusion by oxidation with atmospheric oxygen. For full recovery, an extraction ratio E ≥ 30 is admissible. However, at high extraction ratios the sample composition, particularly its sulphur content, becomes highly critical and sulphur must be taken into account when preparing the fusion charge. The precision and accuracy of the recommended procedure were tested on ten reference materials. The comparison of the results with those of SARM-7, which is used by most analysts, was favourable. There is a need for many more analysts to report their results before “usable values” can be established for other reference materials and statistical tests can be done.

Dry-chlorination inductively coupled plasma mass spectrometric method for the determination of platinum group elements in rocks

A dry-chlorination procedure has been developed for use in the determination of low concentrations of platinum group elements (PGE) and Au in rock pulps. The PGE and Au, present as native metals, natural alloys and as PGE-(or Au-) bearing sulfide group minerals, are converted by dry-chlorination into PGE (or Au) sodium salts. These salts are dissolved in weak HCl. The solutions are analysed for PGE and Au content by inductively coupled plasma mass spectrometry (ICP-MS). Tests on three reference rock pulps [diluted South African Bureau of Standards Reference Material (SARM)-7 Platinum Ore; diluted INCO S-1800; Nevada Bureau of Mines (NBM) 6a Stillwater] and one gabbro rock showed that the dry-chlorination–ICP-MS method produced results that were usually comparable to, and often better than, fire assay techniques. Reagent contamination was extremely low (Pt⩽1 ng g–1; other PGE and Au⩽0.2 ng g–1). The recoveries of PGE obtained by dry-chlorination–ICP-MS were often >90%.