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Analytical and Bioanalytical Chemistry (v.368, #1)
Recent trends and developments in laser ablation-ICP-mass spectrometry by D. Günther; I. Horn; B. Hattendorf (pp. 4-14).
The increased interest in laser technology (e.g. for micro-machining, for medical applications, light shows, CD-players) is a tremendous driving force for the development of new laser types and optical set-ups. This directly influences their use in analytical chemistry. For direct analysis of the elemental composition of solids, mostly solid state lasers, such as Nd:YAG laser systems operating at 1064 nm (fundamental wavelength), 266 nm (frequency quadrupled) and even 213 nm (frequency quintupled) have been investigated in combination with all available inductively coupled plasma mass spectrometers. The trend towards shorter wavelengths (1064 nm– 157 nm) was initiated by access to high quality optical materials which led to the incorporation of UV gas lasers, such as excimer lasers (XeCl 308 nm, KrF 248 nm, ArF 193 nm, and F2 157 nm) into laser ablation set-ups. The flexibility in laser wavelengths, output energy, repetition rate, and spatial resolution allows qualitative and quantitative local and bulk elemental analysis as well as the determination of isotope ratios. However, the ablation process and the ablation behavior of various solid samples are different and no laser wavelength was found suitable for all types of solid samples. This article highlights some of the successfully applied systems in LA-ICP-MS. The current fields of applications are explained on selected examples using 266 nm and 193 nm laser ablation systems.
Mass spectrometry with plasma sources at atmospheric pressure – state-of-the-art and some developmental trends by J. A. C. Broekaert (pp. 15-22).
The state-of-the art and trends of development in ICP-MS are presented. Special reference is made to progress in plasma sources, which can be used as ion sources and, especially, the inductively coupled plasma and new microwave plasma sources. Further, progress in sample introduction for plasma mass spectrometry is discussed with special reference to new pneumatic nebulizers, enabling, e.g., work with microflows of solutions at high efficiency, new developments in ultrasonic nebulization, in electrothermal evaporation, laser ablation and hydride generation. Innovation in the types of mass spectrometers used is discussed with special reference to the use of reaction and collision cells, sector field mass spectrometry, time-of-flight mass spectrometry and multicollector mass spectrometers. Challenging applications in the field of speciation, especially in environmental samples with the example of the chromium speciation, and in materials analysis, with special reference to the analysis of ceramic powders with and without on-line matrix removal, are also discussed.
Precise and accurate isotope ratio measurements by ICP-MS by J. Sabine Becker; Hans-Joachim Dietze (pp. 23-30).
The precise and accurate determination of isotope ratios by inductively coupled plasma mass spectrometry (ICP-MS) and laser ablation ICP-MS (LA-ICP-MS) is important for quite different application fields (e.g. for isotope ratio measurements of stable isotopes in nature, especially for the investigation of isotope variation in nature or age dating, for determining isotope ratios of radiogenic elements in the nuclear industry, quality assurance of fuel material, for reprocessing plants, nuclear material accounting and radioactive waste control, for tracer experiments using stable isotopes or long-lived radionuclides in biological or medical studies). Thermal ionization mass spectrometry (TIMS), which used to be the dominant analytical technique for precise isotope ratio measurements, is being increasingly replaced for isotope ratio measurements by ICP-MS due to its excellent sensitivity, precision and good accuracy. Instrumental progress in ICP-MS was achieved by the introduction of the collision cell interface in order to dissociate many disturbing argon-based molecular ions, thermalize the ions and neutralize the disturbing argon ions of plasma gas (Ar+). The application of the collision cell in ICP-QMS results in a higher ion transmission, improved sensitivity and better precision of isotope ratio measurements compared to quadrupole ICP-MS without the collision cell [e.g., for 235U/238U ∼ 1 (10 μg L–1 uranium) 0.07% relative standard deviation (RSD) vs. 0.2% RSD in short-term measurements (n = 5)]. A significant instrumental improvement for ICP-MS is the multicollector device (MC-ICP-MS) in order to obtain a better precision of isotope ratio measurements (with a precision of up to 0.002%, RSD).CE- and HPLC-ICP-MS are used for the separation of isobaric interferences of long-lived radionuclides and stable isotopes by determination of spallation nuclide abundances in an irradiated tantalum target.
Bulk analysis by IR laser ablation inductively coupled plasma atomic emission spectrometry by Michel Hemmerlin; Dumont Somas; Cendrine Dubuisson; Fabrice Loisy; Emmanuelle Poussel; J.-M. Mermet (pp. 31-36).
Two laser ablation systems dedicated to bulk analysis were evaluated for steel and PVC samples, using inductively coupled plasma atomic emission spectrometry detection. These systems were characterized by the use of a Nd:YAG laser operating at 1064 nm, the absence of observation device and a large laser spot size. The 1064 nm wavelength was selected to avoid the use of frequency-multiplying optics, and to be less critical to the sampling position. Calibration graphs and limits of detection are given for both types of materials. LODs were in the range 3–120 μg/g for steel, and in the range 0.07–15 μg/g for PVC. In the case of steel samples, similar calibration graph slopes were obtained between polished and unpolished samples.
Optimization of a laser ablation-inductively coupled plasma “time of flight” mass spectrometry system for short transient signal acquisition by Davide Bleiner; Kathrin Hametner; D. Günther (pp. 37-44).
Simultaneous ion sampling and sequential detection offered by inductively coupled plasma ‘time of flight’ mass spectrometry (ICP-TOFMS) provides advantages for the analysis of short transient concentration-variable signals as produced in laser ablation. In order to investigate the capabilities of ICP-TOFMS in combination with an excimer laser ablation system, ablation studies on reference materials and geological samples were carried out. Various ICP-TOFMS parameters were optimized for laser-induced aerosols. Transverse rejection ion pulse was used to extend the dynamic range in concentration. A reduced volume ablation cell was designed and used in order to increase the sample density in the ICP. Results for 63 simultaneously measured isotopes (SRM 610 from NIST) lead to limits of detection in the 1–100 μg/g range for a 80 μm crater diameter (10 Hz, 1.2 mJ pulse energy). The reproducibility of signal ratios was determined to be better than 2% RSD for transient signals using 102 ms integration time. These optimized parameters were then used for the analysis of tin-rich fluid inclusions. Preliminary results of multielement analysis and isotopic ratio determinations on individual fluid inclusions (63 isotopes, 102 ms integration time) demonstrate the capabilities of ICP-TOFMS in combination with laser ablation.
A possible steady state kinetic model for the atomization and excitation processes during inductively coupled plasma atomic emission spectrometry: Application to interference effects of lithium on calcium by M. F. Zaranyika; Albert T. Chirenje (pp. 45-51).
A possible steady state kinetic model is presented for the atomization and excitation processes during inductively coupled plasma atomic emission spectrometry. The model takes into account the relative rates of (a) thermal dissociation of analyte salt, (b) recombination of counter atom and analyte atoms, (c) charge transfer between analyte and interferent species, (d) charge transfer between analyte and argon species, and (e) ion/electron collisional de-ionization. Number density ratio data, nu′/nu, where nu denotes the excited state and the prime denotes the presence of an interferent element, are presented showing that the predictions of the model are consistent with the signal enhancement observed at low analyte concentrations when Ca is determined by ICP in the presence of excess Li.
A novel high-temperature (360 °C)/high-pressure (30 MPa) flow system for online sample digestion applied to ICP spectrometry by Stephan Haiber; H. Berndt (pp. 52-58).
A flow injection sample digestion system has been developed comprising an indirectly electrically heated Pt/Ir capillary. Such a capillary allows reaction temperatures of up to 360 °C and pressures of up to 30 MPa (300 bar) and withstands concentrated acids. This temperature is 130 °C to 160 °C higher compared to the operating temperatures of microwave heated flow systems. A combination of an ultrasonic nebulizer and membrane desolvator serves as an interface between the flow digestion system and an ICP/AES spectrometer. The membrane desolvator removes interfering gaseous digestion products so effectively before the sample stream enters the plasma that the measured residual carbon concentration falls in the region of the detection limit of ICP/OES measurements. Sewage sludge samples were digested using nitric acid and the elemental traces online determined. The detection limits related to the original dry substances amount to the lower μg/g range.
A simple co-precipitation inductively coupled plasma mass spectrometric method for the determination of uranium in seawater by Chiu L. Chou; John D. Moffatt (pp. 59-61).
Inductively coupled plasma mass spectrometry (ICP-MS) was used in the determination of 238uranium in seawater after concentration by a simplified co-precipitation with iron hydroxide. Ocean water and reference seawater were used in the study. The co-precipitation method required a smaller sample volume (10 fold less), and less column separation to recover the uranium from the seawater matrix, compared to the original iron hydroxide method. The direct seawater dilution technique requires only a small seawater volume (0.5 mL) and offers a rapid, reliable method for uranium analysis in seawater compared to traditional methods. Comparison of the results for simple co-precipitation, direct dilution of seawater, and theoretical uranium values based on salinity concentrations, yielded negligible differences. Data from this work show that the certified value for NASS-4 is low.
Speciation of antimony(III) and antimony(V) in cell extracts by anion chromatography/ inductively coupled plasma mass spectrometry by N. Ulrich; Pninit Shaked; Dan Zilberstein (pp. 62-66).
An analytical method for the separation and quantification of Sb(III) and Sb(V) using anion chromatography with ICP-MS is presented. The optimum conditions for the separation of the antimony species were established with 15 mmol/L nitric acid at pH 6 as eluent system on a PRP-X100 column. The retention times for antimony(V) and antimony(III) were 85 s and 300 s with detection limits of 0.06 μg/L and 0.29 μg/L, respectively. The proposed method was applied to cell extracts of Leishmania donovani, which were incubated with antimony(III) and antimony(V). Some metabolism seemed to occur within the cells.
A new HG/LT-GC/ICP-MS multi-element speciation technique for real samples in different matrices by U. M. Grüter; J. Kresimon; A. V. Hirner (pp. 67-72).
An improved speciation technique is presented for metal(loid)organic compounds, enabling identification and quantification of species from twelve elements: germanium, arsenic, selenium, molybdenum, tin, antimony, tellurium, iodine, tungsten, mercury, lead and bismuth. At this time it is possible to identify 29 species with boiling points between –88.5 °C and 250 °C in gaseous, liquid and solid samples in a few minutes. This study shows as an example results from measurements of soil samples from municipal waste deposits. The HG/LT-GC/ICP-MS-(hydride generation/low temperature-gas chromatography/inductively coupled plasma-mass spectrometry) apparatus contains a home-built gas chromatograph that enables satisfactory separation of various species with a boiling point difference of ≥ 14 °C. The absolute detection limits for the elements mentioned above were below 0.7 pg.
Automated in situ trace element analysis of silicate materials by laser ablation inductively coupled plasma mass spectrometry by Zhongxing Chen; Dante Canil; Henry P. Longerich (pp. 73-78).
This paper describes the automated in situ trace element analysis of solid materials by laser ablation (LA) inductively coupled plasma mass spectrometry (ICP-MS). A compact computer-controlled solid state Nd:YAG MerchantekTM EO UV laser ablation (LA) system has been coupled with the high sensitivity VG PQII S ICP-MS. A two-directional communication was interfaced in-house between the ICP-MS and the LA via serial RS-232 port. Each LA-ICP-MS analysis at a defined point includes a 60 s pre-ablation delay, a 60 s ablation, and a 90 s flush delay. The execution of each defined time setting by LA was corresponding to the ICP-MS data acquisition allowing samples to be run in automated cycle sequences like solution auto-sampler ICP-MS analysis. Each analytical cycle consists of four standards, one control reference material, and 15 samples, and requires about 70 min. Data produced by Time Resolved Analysis (TRA) from ICP-MS were later reduced off-line by in-house written software. Twenty-two trace elements from four reference materials (NIST SRM 613, and fused glass chips of BCR-2, SY-4, and G-2) were determined by the automated LA-ICP-MS method. NIST SRM 610 or NIST SRM 613 was used as an external calibration standard, and Ca as an internal standard to correct for drift, differences in transport efficiency and sampling yield. Except for Zr and Hf in G-2, relative standard deviations for all other elements are less than 10%. Results compare well with the data reported from literature with average limits of detection from 1 ng g–1 to 455 ng g–1 and less than 100 ng g–1 for most trace elements.
Determination of trace elements in zeolites by laser ablation ICP-MS by C. Pickhardt; I. B. Brenner; J. S. Becker; H.-J. Dietze (pp. 79-87).
Laser ablation inductively coupled plasma mass spectrometry using a quadrupole-based mass spectrometer (LA-ICP-QMS) was applied for the analysis of powdered zeolites (microporous aluminosilicates) used for clean-up procedures. For the quantitative determination of trace element concentrations three geological reference materials, granite NIM-G, lujavrite NIM-L and syenite NIM-S, from the National Institute for Metallurgy (South Africa) with a matrix composition corresponding to the zeolites were employed. Both the zeolites and reference materials were fused with a lithium borate mixture to increase the homogeneity and to eliminate mineralogical effects. In order to compare two different approaches for the quantification of analytical results in LA-ICP-MS relative sensitivity coefficients (RSCs) of chemical elements and calibration curves were measured using the geostandards. The experimentally obtained RSCs are in the range of 0.2-6 for all elements of interest. Calibration curves for trace elements were measured without and with Li or Ti as internal standard element. With a few exceptions the regression coefficients of the calibration curves are better than 0.993 with internal standardization. NIM-G granite reference material was employed to evaluate the accuracy of the technique. Therefore, the measured concentrations were corrected with RSCs which were determined using lujavrite reference material NIM-L. This quantification method provided analytical results with deviations of 1–11% from the recommended and proposed values in granite reference material NIM-G, except for Co, Cs, La and Tb. The relative standard deviation (RSD) of the determination of the trace element concentration (n = 5) is about 1% to 6% using Ti as internal standard element. Detection limits of LA-ICP-QMS in the lower μg/g range (from 0.03 μg/g for Lu, Ta and Th to 7.3 μg/g for Cu, with the exception of La) have been achieved for all elements of interest. Under the laser ablation conditions employed (λ: 266 nm, repetition frequency: 10 Hz, pulse energy: 10 mJ, laser power density: 6 × 109 W/cm2) fractionation effects of the determined elements relative to the internal standard element Ti were not observed.
Ion chromatography inductively coupled plasma mass spectrometry (IC-ICP-MS) and radiometric techniques for the determination of actinides in aqueous leachate solutions from uranium oxide by D. Solatie; P. Carbol; M. Betti; F. Bocci; T. Hiernaut; V. V. Rondinella; J. Cobos (pp. 88-94).
The choice of the analytical method for the determination of actinide isotopes in leachate solutions has to be made considering several parameters: detection limit for each isotope, sample preparation procedure in terms of duration and complexity, counting time and interferences. A leachate solution obtained by keeping a pellet of UO2 doped with 238Pu in contact with distilled water was investigated for the content of U and Pu isotopes by radiometric methods (α-, γ-spectrometry and liquid scintillation counting). The results of the radiometric methods were compared with those obtained from the analysis performed by inductively coupled plasma mass spectrometry on-line to a system for chromatographic separation (IC-ICP-MS). The comparison confirmed that IC-ICP-MS is a powerful method for the detection of long-lived radionuclides. The radiometric methods have a detection limit two orders of magnitude lower than IC-ICP-MS in the case of short-lived radioisotopes mostly due to the low background in the detector. On the other hand, the sample preparation and the analysis duration are more time-consuming compared to IC-ICP-MS; moreover, not all isotopes can be determined by using only one radiometric technique.
Comparison between the use of direct current glow discharge mass spectrometry and inductively coupled plasma quadrupole mass spectrometry for the analysis of trace elements in nuclear samples by L. Aldave de las Heras; F. Bocci; M. Betti; L. O. Actis-Dato (pp. 95-102).
The quantitative determination of trace elements in nuclear samples by GDMS and ICP-MS is presented and compared. Spectral interferences, matrix effects, detection limits, precision and accuracy are discussed. Results for selected samples demonstrated that both techniques are complementary. The use of a multi-standard solution provides the most accurate results in ICP-MS, whereas in GDMS this is achieved by relative sensitivity factors (RSF) matrix matched. Nevertheless, the use of standard RSF allows a fast screening.
Development of an ICP-IDMS method for accurate routine analyses of toxic heavy metals in polyolefins and comparison with results by TI-IDMS by Jürgen Diemer; K. G. Heumann (pp. 103-108).
An inductively coupled plasma isotope dilution mass spectrometric (ICP-IDMS) method was developed as a suitable method – with respect to its sensitivity, precision, accuracy, and time-consumption – for the analysis of toxic heavy metal traces (Pb, Cd, Cr, and Hg) in polyolefins. Results for Pb, Cd, and Cr were compared with those obtained by thermal ionization isotope dilution mass spectrometry (TI-IDMS), which was used as a reference method. Because of its high first ionization potential and its high volatility mercury could not be determined by TI-IDMS. A multi-element spike solution, containing isotopically enriched 206Pb, 116Cd, 53Cr, and 201Hg, was used for the isotope dilution step. Decomposition of the polyolefin samples was carried out with concentrated HNO3 at temperatures of about 300 °C in a high pressure asher (HPA). This procedure decomposes polyolefins completely and allows isotopic equilibration between sample and spike isotopes. Detection limits of 16 ng/g, 5 ng/g, 164 ng/g, and 9 ng/g were obtained for Pb, Cd, Cr, and Hg by ICP-IDMS using only sample weights of 0.25 g. In different commercially available polyethylene samples heavy metal concentrations in the range of < 5 ng/g to 4 × 103 ng/g were analyzed. Both mass spectrometric methods were applied within the EU project “Polymeric Elemental Reference Material (PERM)” for the certification of two polyethylene reference materials. The ICP-IDMS results agreed very well with those of TI-IDMS which demonstrates the accuracy of the ICP-IDMS method also suitable for routine analyses.
Isotope dilution inductively coupled plasma quadrupole mass spectrometry in connection with a chromatographic separation for ultra trace determinations of platinum group elements (Pt, Pd, Ru, Ir) in environmental samples by M. Müller; K. G. Heumann (pp. 109-115).
An isotope dilution inductively coupled plasma quadrupole mass spectrometric (ID-ICP-QMS) method was developed for the simultaneous determination of the platinum group elements Pt, Pd, Ru, and Ir in environmental samples. Spike solutions, enriched with the isotopes 194Pt, 108Pd, 99Ru, and 191Ir, were used for the isotope dilution step. Interfering elements were eliminated by chromatographic separation using an anion-exchange resin. Samples were dissolved with aqua regia in a high pressure asher. Additional dissolution of possible silicate portions by hydrofluoric acid was usually not necessary. Detection limits of 0.15 ng g–1, 0.075 ng g–1, and 0.015 ng g–1 were achieved for Pt, Pd, Ru, and Ir, respectively, using sample weights of only 0.2 g. The reliability of the ID-ICP-QMS method was demonstrated by analyzing a Canadian geological reference material and by participating in an interlaboratory study for the determination of platinum and palladium in a homogenized road dust sample. Surface soil, sampled at different distances from a highway, showed concentrations in the range of 0.1–87 ng g–1. An exponential decrease of the platinum and palladium concentration with increasing distance and a small anthropogenic contribution to the natural background concentration of ruthenium and iridium was found in these samples.
Arsenic metabolism in seaweed-eating sheep from Northern Scotland by J. Feldmann; Katie John; Paramee Pengprecha (pp. 116-121).
Cation exchange and anion exchange liquid chromatography were coupled to an ICP-MS and optimised for the separation of 13 different arsenic species in body fluids (arsenite, arsenate, dimethylarsinic acid (DMAA), monomethylarsonic acid (MMAA), trimethylarsine oxide (TMAO), tetramethylarsonium ion (TMA), arsenobetaine (AsB), arsenocholine (AsC), dimethylarsinoyl ethanol (DMAE) and four common dimethylarsinoylribosides (arsenosugars). The arsenic species were determined in seaweed extracts and in the urine and blood serum of seaweed-eating sheep from Northern Scotland. The sheep eat 2–4 kg of seaweed daily which is washed ashore on the most northern Island of Orkney. The urine, blood and wool of 20 North Ronaldsay sheep and kidney, liver and muscle from 11 sheep were sampled and analysed for their arsenic species. In addition five Dorset Finn sheep, which lived entirely on grass, were used as a control group. The sheep have a body burden of approximately 45–90 mg arsenic daily. Since the metabolism of arsenic species varies with the arsenite and arsenate being the most toxic, and organoarsenic compounds such as arsenobetaine the least toxic compounds, the determination of the arsenic species in the diet and their body fluids are important. The major arsenic species in their diet are arsenoribosides. The major metabolite excreted into urine and blood is DMAA (95 ± 4.1%) with minor amounts of MMAA, riboside X, TMA and an unidentified species. The occurrence of MMAA is assumed to be a precursor of the exposure to inorganic arsenic, since demethylation of dimethylated or trimethylated organoarsenic compounds is not known (max. MMAA concentration 259 μg/L). The concentrations in the urine (3179 ± 2667 μg/L) and blood (44 ± 19 μg/kg) are at least two orders of magnitude higher than the level of arsenic in the urine of the control sheep or literature levels of blood for the unexposed sheep. The tissue samples (liver: 292 ± 99 μg/kg, kidney: 565 ± 193 μg/kg, muscle: 680 ± 224 μg/kg) and wool samples (10 470 ± 5690 μg/kg) show elevated levels which are also 100 times higher than the levels for the unexposed sheep.