Performance of permanent iridium modifier in the presence of corrosive matrix in graphite furnace atomic absorption spectrometry

The influence of up to 16% HNO3, 28% HCl, and the mixture of both acids in aqua regia on the analytical performance of electrodeposited modifiers (Ir or Ir+Pd) was evaluated and discussed. Cadmium was used as an example of volatile elements often determined by graphite furnace atomic absorption spectrometry (GF AAS). In the presence of HCl, the maximum pyrolysis temperature that could be applied was found to be 600 degrees C. In the presence of HNO3 and aqua regia, both modifiers stabilized cadmium up to 800 degrees C. The long-term performance of electrodeposited Ir or Ir+Pd was not influenced by mineral acids; moreover the tube lifetime was significantly prolonged compared with a non-modified tube.     

Critical evaluation of analytical performance of atomic absorption spectrometry and inductively coupled plasma mass spectrometry for mercury determination

The analytical performance of cold vapor atomic absorption spectrometry (CV AAS), graphite furnace atomic absorption spectrometry (GF AAS) and inductively coupled plasma mass spectrometry (ICP-MS) for mercury determination have been investigated with the use of two reference materials SRM 2710 Montana I Soil and BCR-144R (sewage sludge from domestic origin). The digestion conditions and their influence on determination of mercury have been studied. Samples were decomposed by microwave digestion in closed vessels with the use of HCl alone or mixture of HCl+HNO₃+HF. The digestion solutions were analyzed by CV AAS using NaBH₄ as a reducing agent, by GF AAS with Pd or mixture of Pd/Rh as modifiers and by ICP-MS with Rh as internal standard. In the case of CV AAS, results were not dependent on digestion conditions. In the case of GF AAS and ICP-MS, results depended significantly on digestion conditions; in both cases, the use of the mixture of acids as defined above suppressed the signal of mercury. Therefore, in those cases, the microwave digestion with HCl is recommended. Detection limits of 0.003, 0.01 and 0.2 μg g⁻¹ were achieved by ICP-MS, CV AAS and GF AAS, respectively.     

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.     

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.     

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.     

Comparison of Sample Digestion Procedures for the Determination of Arsenic in Bottom Sediment Using Hydride Generation AAS

Certified reference materials (JMS-2 and JMS-1 – Marine sediment, LKSD-1 Lake Sediment, and STSD-1 Stream Sediment) and bottom sediment were analysed for arsenic by hydride generation atomic absorption spectrometry (HG-AAS) after digestion by different methods (microwave digestion, digestion in aluminium block, dry digestion) and different combinations of acids (HNO₃, HCl, HClO₄, H₂SO₄). The study revealed that both wet and dry digestion can be used to digest the reference materials and bottom sediment. Exceptionally satisfactory results were produced by the application of aqua regia, HNO₃ + HCl + HClO₄, and HNO₃ + HCl mixtures. Addition of Mg(NO₃)₂ during dry digestion caused an increase in arsenic recovery in the reference materials and improved the accuracy of arsenic determination in the bottom sediments.     

Radiotracer study of the behaviour of arsenic in the graphite furnace

Summary The behaviour of As(III) and As(V) in the graphite furnace during the individual steps of the temperature program was investigated by means of the radiotracer⁷⁶As. The investigated matrix systems include 1 mol/l HCl, 0.2 mol/l HNO₃, 0.2 mol/l NaCl, urine, human serum and a tetramethylammonium hydroxide solution of hair. Significant stabilization effects can be achieved in the preatomization steps by using Ni, W, Mo, Pd, H₂O₂ as well as the mixtures H₂O₂ + Pd, HNO₃ + Pd and H₂O₂ + Ni as matrix modifiers. In sample solutions containing chloride, stabilization of As(III) is possible only in presence of nitric acid. The experimental conditions for the determination of As in urine, human serum and hair have been optimized.

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Radiotracer-Untersuchung des Verhaltens von Arsen im Graphitofen

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Dedicated to Prof. Dr. G. Tölg on the occasion of his 60th birthday     

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.     

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.     

Simultaneous determination of cadmium and lead in wine by electrothermal atomic absorption spectrometry

A method has been developed for the direct simultaneous determination of Cd and Pb in white and red wine by electrothermal atomic absorption spectrometry (ET-AAS) using a transversely heated graphite tube atomizer (THGA) with longitudinal Zeeman-effect background correction. The thermal behavior of both analytes during pyrolysis and atomization stages were investigated in 0.028 mol l⁻¹ HNO₃ and in 1+1 v/v diluted wine using mixtures of Pd(NO₃)₂+Mg(NO₃)₂ and NH₄H₂PO₄+Mg(NO₃)₂ as chemical modifiers. With 5 μg Pd+3 μg Mg as the modifiers and a two-step pyrolysis (10 s at 400°C and 10 s at 600°C), the formation of carbonaceous residues inside the atomizer was avoided. For 20 μl of sample (wine+0.056 mol l⁻¹ HNO₃, 1+1, v/v) dispensed into the graphite tube, analytical curves in the 0.10–1.0 μg l⁻¹ Cd and 5.0–50 μg l⁻¹ Pb ranges were established. The characteristic mass was approximately 0.6 pg for Cd and 33 pg for Pb, and the lifetime of the tube was approximately 400 firings. The limits of detection (LOD) based on integrated absorbance (0.03 μg l⁻¹ for Cd, 0.8 μg l⁻¹ for Pb) exceeded the requirements of Brazilian Food Regulations (decree #55871 from Health Department), which establish the maximum permissible level for Cd at 200 μg l⁻¹ and for Pb at 500 μg l⁻¹. The relative standard deviations (n=12) were typically <8% for Cd and <6% for Pb. The recoveries of Cd and Pb added to wine samples varied from 88 to 107% and 93 to 103%, respectively. The accuracy of the direct determination of Cd and Pb was checked for 10 table wines by comparing the results with those obtained for digested wine using single-element ET-AAS, which were in agreement at the 95% confidence level.     

Determination of bismuth, indium and lead in geological samples by electrothermal AAS Part 2. Comparative study of palladium and molybdenum containing chemical modifiers*

A comparative and systematic study has been carried out of the effects of palladium and molybdenum containing chemical modifiers, such as Pd + Rh, Pd + Pt, Pd + Ru, Pd + Rh + Pt, Pd + Rh + Ru, Mo + Pd, Mo + Rh, Mo + Ru and Mo + Pt and additionally tartaric acid (TA) as a reducing agent together with mixed modifiers for the thermal stabilization of Bi, In and Pb in a Zeeman electrothermal atomic absorption spectrometer (ETAAS). The effect of the mass ratios of the mixed modifier components on the maximum pretreatment temperature for the analytes has been determined. The modifier mixtures of Pd + Rh + Pt, Mo + Pd + TA and Mo + Pt + TA were found to be especially powerful for the determination of Bi, In and Pb. These mixed modifiers could increase the ashing temperatures of the analytes up to 1250–1400° C. They were applied to the determination of Bi and Pb in dissolved geological reference samples and accuracy and precision of the method were thereby enhanced. The percent relative error was decreased from 20.0 to 0.4 for Bi and from 10.5 to 0.3 for Pb, depending on the sample type. Received: 9 May 1997 / Revised: 19 August 1997 / Accepted: 20 August 1997     

Determination of bismuth, indium and lead in geological samples by electrothermal AAS Part 2. Comparative study of palladium and molybdenum containing chemical modifiers*

A comparative and systematic study has been carried out of the effects of palladium and molybdenum containing chemical modifiers, such as Pd + Rh, Pd + Pt, Pd + Ru, Pd + Rh + Pt, Pd + Rh + Ru, Mo + Pd, Mo + Rh, Mo + Ru and Mo + Pt and additionally tartaric acid (TA) as a reducing agent together with mixed modifiers for the thermal stabilization of Bi, In and Pb in a Zeeman electrothermal atomic absorption spectrometer (ETAAS). The effect of the mass ratios of the mixed modifier components on the maximum pretreatment temperature for the analytes has been determined. The modifier mixtures of Pd + Rh + Pt, Mo + Pd + TA and Mo + Pt + TA were found to be especially powerful for the determination of Bi, In and Pb. These mixed modifiers could increase the ashing temperatures of the analytes up to 1250–1400° C. They were applied to the determination of Bi and Pb in dissolved geological reference samples and accuracy and precision of the method were thereby enhanced. The percent relative error was decreased from 20.0 to 0.4 for Bi and from 10.5 to 0.3 for Pb, depending on the sample type. Received: 9 May 1997 / Revised: 19 August 1997 / Accepted: 20 August 1997     

Application of Metalfix Chelamine prior to the determination of noble metals by the inductively coupled plasma atomic emission spectrometry

Metalfix Chelamine chelating resins of two different bead sizes (150-300 and 40-80 μm) were examined and compared regarding their application for sorption of Au, Ir, Pd, Pt, Rh and Ru ions from medium of HCl, HNO₃ and mixtures of HCl and HNO₃. The quantitative enrichment of Au, Ir, Pd and Pt was established for the resin of 150-300 μm particle size and for solutions acidified with HCl and HNO₃ (3:1) up to the concentration of 0.50 mol l⁻¹. In the case of Rh and Ru, the uptake of these metals by the resin was lower than 50%. For the elution, solutions of different reagents, i.e. HCl, HNO₃, KCN, KI, KSCN and (NH₂)₂CS, were studied with respect to the complete release of the analytes retained by the resin. In addition, influence of various base metals, i.e. Al, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb and Zn, on the retention of the noble metals was investigated. Under the selected conditions for the retention and elution of Au, Ir, Pd and Pt, the analytical performance of the proposed pre-concentration procedure was evaluated and it was applied to the determination of these noble metals in anodic sludge sample.     

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     

Vaporization and atomization of the platinum group elements in the graphite furnace investigated by electrothermal vaporization-inductively coupled plasma-mass spectrometry

The mechanisms by which the platinum group elements (PGEs) are vaporized in the graphite furnace have been investigated using electrothermal vaporization-inductively coupled plasma-mass spectrometry (ETV-ICP-MS). The results suggest that live of these elements (Ru, Rh, Pd, Ir and Pt) are reduced to their metallic state in the graphite furnace and then vaporized by direct sublimation of the metal. For Os, the vaporization mechanism is different. In the presence of HNO₃, two distinct vaporization processes are observed. Volatile oxides of Os are released at low temperatures, but some of this oxide is reduced to relatively involatile Os metal which is then vaporized when the temperature is increased above 2000°C. The addition of TeCl₂ chemical modifier was found to have minimal effect on the vaporization mechanism and sensitivity for determination for five of the PGEs. For Os, however, the analytical sensitivity and limit of detection was improved when Te modifier was used in conjunction with a lower vaporization temperature of 1400°C. Optimum conditions for the determination of the PGEs by ETV-ICP-MS are reported, along with their absolute limits of detection; these range from 0.015 pg for Ir to 0.25 pg for Os.     

Determination of boron in blood,urine and bone by electrothermal atomic absorption spectrometry using zirconium and citric acid as modifiers

A comparative study of various potential chemical modifiers (Au, Ba, Be, Ca, Cr, Ir, La, Lu, Mg, Ni, Pd, Pt, Rh, Ru, Sr, V, W, and Zr), and different ‘coating’ treatments (Zr, W, and W+Rh) of the pyrolytic graphite platform of a longitudinally heated graphite tube atomizer for thermal stabilization and determination of boron was undertaken. The use of Au, Ba, Be, Cr, Ir, Pt, Rh, Ru, Sr and V as modifiers, and of W+Rh coating produced erratic, and noisy signals, while the addition of La, Ni and Pd as modifiers, and the W coating had positive effects, but with too high background absorption signals, rendering their use unsuitable for boron determination even in aqueous solutions. The atomic absorption signal for boron was increased and stabilized when the platform was coated with Zr, and by the addition of Ca, Mg, Lu, W or Zr as modifiers. Only the addition of 10 μg of Zr as a modifier onto Zr-treated platforms allowed the use of a higher pyrolysis temperature without analyte losses. The memory effect was minimized by incorporating a cleaning step with 10 μl of 50 g l⁻¹ NH₄F HF after every three boron measurements. The addition of 10 μl of 15 g l⁻¹ citric acid together with Zr onto Zr-treated platforms significantly improved the characteristic mass to m₀=282 pg, which is adequate for biological samples such as urine and bone, although the sensitivity was still inadequate for the determination of boron in blood of subjects without supplementary diet. Under optimized conditions, the detection limit (3σ) was 60 μg l⁻¹. The amount of boron found in whole blood, urine and femur head samples from patients with osteoporosis was in agreement with values previously reported in the literature.     

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.     

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.     

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.     

Preatomization behaviour of Se(-II), Se(IV), and Se(VI) in the graphite furnace without and with matrix modifiers

Summary Using ⁷⁵Se as a radiotracer, the preatomization behaviour of selenium in the graphite furnace was studied. The selenium forms investigated included Se(-II)-methionine, selenite, and selenate in a 0.2% HNO₃ solution, and in a 0.2% HNO₃ solution containing 1% NaCl. The effect of nickel nitrate and of the mixture of palladium/magnesium nitrates as matrix modifiers and of boron nitride coating of the graphite tube on the behaviour of selenium was investigated. The best stabilization effect for all oxidation states of selenium in the conventional graphite tube was achieved by using the mixture Pd/Mg. A considerable degree of modifier-free stabilization of selenuium could be achieved in boron nitride coated tubes. After the conversion of Se(IV) to a volatile piaselenol, a quantitative preatomization separation of Se(IV) from Se(VI) in the boron nitride coated tube was possible. However problems with these newtype tubes still to be solved include the need to increase the thermal stability of the coating.