Maite Aramendía

High-resolution continuum source graphite furnace atomic absorption spectrometry for direct analysis of solid samples and complex materials: a tutorial review

The purpose of this review is to examine the literature devoted to direct sample analysis using high-resolution continuum source atomic absorption spectrometry in a tutorial way, in an attempt to provide guidelines on the most critical issues to consider when developing a new method. This review discusses in detail the advantages and limitations of this technique, highlighting its benefits in comparison with classic line source atomic absorption spectrometry instrumentation in the context of direct analysis of solid samples, slurries and complex liquid samples, trying to establish in which situations the use of this technique can be particularly beneficial. Some of the aspects that are addressed comprise: (i) the improved potential to detect and correct for spectral interferences; (ii) the different options to adjust the sensitivity to the analyte content; (iii) strategies to minimize matrix effects and calibrate with aqueous standard solutions; (iv) possibilities to carry out multi-element analysis.

Laser ablation-inductively coupled plasma-dynamic reaction cell-mass spectrometry for the determination of lead isotope ratios in ancient glazed ceramics for discriminating purposes

The potential of laser ablation-single collector-inductively coupled plasma-mass spectrometry for discrimination among Spanish antique lead-glazed ceramics according to age and workshop has been investigated. In order to obtain the required precision, pressurizing the dynamic reaction cell (DRC) with Ne proved to be a significant help. In this way, it was feasible to obtain RSD values in the range 0.15–0.25% (internal precision) for the ratios calculated using the most abundant Pb isotopes (206Pb, 207Pb and 208Pb), under optimized conditions. These values are 2–3 times lower than those that could be achieved in standard (vented) mode and proved to be sufficient for distinguishing between the different groups of samples under study. The method finally proposed was demonstrated to show interesting features, such as the potential to obtain spatially resolved isotopic information in approximately 30 min measurement time per sample, with negligible (ng level) sample damage. On the other hand, it has to be mentioned that the use of the DRC results in an undesired enhancement in the mass discrimination that has to be corrected for. Only by using a perfectly matrix-matched standard (in the current work, one sample of each group that was analyzed by an alternative procedure in order to obtain a suitable reference value), accurate correction for this effect became possible. Obviously, this is somewhat inconvenient, but the possibility of analyzing the vast majority of the samples in a fast, quasi non-destructive, spatially resolved and cost-effective way (particularly when comparing with the use of dedicated techniques for isotopic analysis) may be appealing for archaeological laboratories.

Direct determination of Cu isotope ratios in dried urine spots by means of fs-LA-MC-ICPMS. Potential to diagnose Wilson's disease

This work investigates the potential of a 257 nm femtosecond (fs) laser ablation (LA) device operating at a high repetition rate (10 000 Hz) coupled to a multicollector (MC)-ICPMS to develop a method for the direct determination of Cu ratios in dried urine spots, prepared by deposition of urine (300 μL) onto precut clinical filter paper discs (16 mm diameter). The sampling capabilities offered by the fs LA system, permitting ablation of 150 μm thick coronas in the rim area of the filter, together with the use of admixed Ni as an internal standard, the proper optimization of the MC-ICPMS conditions (e.g., use of pseudo high-resolution mode to avoid interferences) and the use of a data processing approach particularly suitable for short transient signals (linear regression fit) enabled analysis of real urine samples with precision values around 500 ppm (RSD) for urinary Cu contents of a few hundred μg L−1. The methodology developed could prove to be useful for implementing screening protocols to detect Wilsons disease (WD), a well-known disorder related to Cu metabolism. In fact, the use of this analytical methodology permitted us to observe significant differences between (i) untreated WD patients and (ii) WD patients that are under treatment and control samples. This work represents the first time that determination of 65Cu/63Cu ratios has been used in the context of WD research, and serves as a proof of principle, suggesting that Cu isotope analysis could help in developing earlier and more reliable means to diagnose WD.

Direct multi-element analysis of a fluorocarbon polymer via solid sampling-electrothermal vaporization-inductively coupled plasma mass spectrometry

This paper reports on the performance of solid sampling-electrothermal vaporization-inductively coupled plasma mass spectrometry for the direct multi-element analysis of two different perfluorosulfonic acid/TFE copolymer samples, which were selected in order to test the potential of this technique for routine control of fluorocarbon polymers. Careful selection of the most suitable isotopes permits the reliable monitoring of the analytes of interest: Cr, Cu, Fe, K, Mn, Pb and Zn. The use of Pd as chemical modifier allows stabilization of all of these analytes during the pyrolysis step (at 800 °C), enabling adequate matrix removal, while the use of a high vaporization temperature (2700 °C) is required for the efficient simultaneous vaporization of these elements. Moreover, the 105Pd+ signal can be used as internal standard, correcting for possible sensitivity drifts. Under these conditions, straightforward calibration with aqueous standard solutions was feasible for all of the elements investigated. The method thus developed exhibits interesting features, such as a low detection limit (ng g−1 range) for most elements, a high sample throughput (15 min per determination), a low sample consumption (a few milligrams only), precision values usually in the 7–12% RSD range and the absence of any sample pretreatment, with the subsequent lower risk of analyte losses or contamination. Therefore, it seems to offer a promising alternative for the laborious procedures currently in use for analysis of these complex samples.

Determination of toxic trace impurities in titanium dioxide by solid sampling-electrothermal vaporization-inductively coupled plasma mass spectrometry

This paper reports on the performance of solid sampling-electrothermal vaporization-inductively coupled plasma mass spectrometry (SS-ETV-ICPMS) for the direct multi-element determination of six toxic trace impurities (As, Cd, Hg, Pb, Sb and Zn) in three different TiO2 samples. Careful selection of the most suitable target nuclides for the different analytes and temperature program optimization permit the reliable monitoring of the analytes of interest, while avoiding the occurrence of potentially relevant spectral interferences. A pyrolysis-free program, in which simultaneous vaporization of all the analytes is carried out at a relatively low temperature (1700 °C), was used. In this way, sample matrix and analyte co-vaporization is avoided, considerably reducing matrix effects and allowing the determination of Zn, which would otherwise be hampered by a spectral overlap with TiO+ ions. Calibration against aqueous standards was found to be feasible. Addition of 50 ng Pd as carrier agent improved the linearity of the calibration curves. Two different internal standards (105Pd+ and 125Te+) were used to compensate for matrix effects. The method thus developed exhibits interesting features: low limits of detection (ng g−1 range) for all of the elements, at least an order of magnitude lower than those for digestion-based procedures; high sample throughput (maximum 35 min per determination), contrasting with the 2 h required for sample digestion and subsequent analysis; low sample consumption (a few milligrams only); precision values usually in the 9–13% RSD range; and last but not least, the absence of any sample pre-treatment, with the subsequent lower risk of analyte losses, contamination or personal and instrumental harms derived from the necessity of using hazardous reagents for sample digestion. SS-ETV-ICPMS therefore seems to be a promising alternative for industrial control analysis of TiO2 samples with analyte contents ranging from a few ng g−1 to several hundreds of µg g−1.

Direct trace-elemental analysis of urine samples by laser ablation-inductively coupled plasma mass spectrometry after sample deposition on clinical filter papers.

Collection of biological fluids on clinical filter papers shows important advantages from a logistic point of view, although analysis of these specimens is far from straightforward. Concerning urine analysis, and particularly when direct trace elemental analysis by laser ablation-inductively coupled plasma mass spectrometry (LA-ICPMS) is aimed at, several problems arise, such as lack of sensitivity or different distribution of the analytes on the filter paper, rendering obtaining reliable quantitative results quite difficult. In this paper, a novel approach for urine collection is proposed, which circumvents many of these problems. This methodology consists on the use of precut filter paper discs where large amounts of sample can be retained upon a single deposition. This provides higher amounts of the target analytes and, thus, sufficient sensitivity, and allows addition of an adequate internal standard at the clinical lab prior to analysis, therefore making it suitable for a strategy based on unsupervised sample collection and ulterior analysis at referral centers. On the basis of this sampling methodology, an analytical method was developed for the direct determination of several elements in urine (Be, Bi, Cd, Co, Cu, Ni, Sb, Sn, Tl, Pb, and V) at the low μg L(-1) level by means of LA-ICPMS. The method developed provides good results in terms of accuracy and LODs (≤1 μg L(-1) for most of the analytes tested), with a precision in the range of 15%, fit-for-purpose for clinical control analysis.

Isotope ratio determination by laser ablation-single collector-inductively coupled plasma-mass spectrometry. General capabilities and possibilities for improvement

In this paper, the general capabilities of laser ablation-single-collector-inductively coupled plasma-mass spectrometry (LA-SC-ICP-MS) for isotope ratio determination are discussed. Some new approaches for improving the quality of the results have been investigated, and the results are presented here and compared with previously published data. In this way, an attempt is made to promote the use of this accessible technique in those contexts for which it is fit-for-purpose. Starting from a general exposition of the main factors affecting the combined uncertainty for isotopic analysis when using this technique, some general hints for method development are given and some methodological approaches permitting the results to be improved presented. In this regard, proper selection of the type of mass spectrometer, of the ICP-MS acquisition parameters, and of the detection mode used (i.e. pulse counting or analog mode) are first discussed. Secondly, different methodological approaches for stabilizing the LA-ICP-MS signal and/or filtering out large particles that would not be properly digested in the plasma are presented and critically compared in terms of precision improvement and the effect they exert on the observed mass discrimination. The use of Ne in a collision/reaction cell leads to precision improvement due to the so-called collisional damping effect, but, at a cost of strongly matrix-dependent mass discrimination. The insertion of a dual-pass spray chamber in-between the LA system and the ICP torch with simultaneous admixture of (i) a nebulized aerosol or (ii) a flow of N2 leads to improved precision while providing more robust plasma conditions, reducing the matrix-dependence of the mass discrimination effect. After evaluation of the results presented, some general hints for achieving optimal isotopic data by means of LA-SC-ICP-MS are summarized in the conclusions section. These recommended conditions provide considerable improvements with respect to the typical precision values reported for this technique (e.g., ∼0.1% RSD external precision for glass samples), such that valuable information can be obtained in many application fields.

Al determination in whole blood samples as AlF via high-resolution continuum source graphite furnace molecular absorption spectrometry: potential application to forensic diagnosis of drowning

In this work, a new methodology for direct determination of Al in whole blood samples by means of high-resolution continuum source graphite furnace molecular absorption spectrometry has been developed, based on the formation of the AlF diatomic molecule in the graphite furnace and the subsequent monitoring of its molecular absorption. The proposed methodology provides an alternative method to conventional atomic absorption, solving most of the problems related to the latter technique, particularly matrix effects, providing a straightforward alternative for blood analysis. The addition of NH4F·HF, which is required for promotion of the AlF molecule, was found to improve sample matrix removal for whole blood samples, whether they contain EDTA or heparin as anticoagulant agents. Besides minimizing residues in the graphite platform, this circumstance enabled the use of aqueous standards to build a calibration curve, avoiding the need for the cumbersome method of standard additions, while not affecting significantly detection capabilities (1.8 μg L−1 LOD). The method developed was also used for exploring the possibilities of Al as a chemical marker assisting forensic diagnosis of death-by-drowning. For this purpose, a set of samples (water and blood) obtained from 8 drowning suspects and two controls were analysed for their Al levels. Although additional studies with a large number of samples would be needed in order to draw definitive conclusions from a forensic point of view, a positive correlation between Al concentration in the drowning water and Al concentration in the blood of drowning suspects was found, supporting the validity of Al as a marker for drowning diagnosis.

Chlorine isotope determination via the monitoring of the AlCl molecule by high-resolution continuum source graphite furnace molecular absorption spectrometry – a case study

This work investigates the possibility of obtaining isotopic information via the monitoring of the absorption spectra of a gaseous diatomic molecule generated in a graphite furnace and using a high-resolution (approx. 1.5 pm per pixel) monochromator (HR CS GFMAS). To test this concept, Cl was chosen as the analyte and AlCl as the target species. The results demonstrate that, unlike what occurs with atomic spectra, under optimum conditions it is possible to acquire isotopic information by HR CS GFMAS in a straightforward way, as it is feasible to observe band heads for each Cl isotope (actually, for Al35Cl and Al37Cl) that are separated, i.e., they act like two different molecules absorbing at different wavelengths. The method proposed, based upon the addition of both Pd and Al and the selection of peak height values, enables Cl isotopic analysis with precision values around 2% RSD for solutions with Cl contents at the mg L−1 level. Accurate values, within this uncertainty, can be directly obtained without requiring any method for mass bias correction. The potential of isotope dilution for calibration is also explored, and it is proven how this approach can help in providing accurate results in situations where the occurrence of chemical interferences, a case frequently encountered for the HR CS GFMAS technique, hampers the use of other calibration approaches, as demonstrated for water analysis.

Isotope ratio mapping by means of laser ablation-single collector-ICP-mass spectrometry : Zn tracer studies in thin sections of Daphnia magna

In this paper, the possibilities of LA-single collector-ICP-mass spectrometry for obtaining isotope ratio images of thin sections of Daphnia magna specimens exposed to isotopically enriched Zn tracers were evaluated. Zn was selected considering its importance in ecotoxicological studies. All aspects of the analytical methodology deployed were carefully studied and optimized for obtaining the best isotope ratio precision and accuracy. The development of this methodological approach consisted of: (i) evaluation of the performance of two different medium mass resolution exit slits, a conventional one providing a mass resolution of m/Δm ≈ 4000 and triangular shaped peaks, and another (wider) one, offering a lower mass resolution (m/Δm ≈ 2000), but providing enhanced ion transmission and flat-topped peaks; (ii) the use of a wet plasma for improving plasma robustness; (iii) thorough optimization of the ablation conditions (such as laser spot size, repetition rate, scan speed and laser fluence) and data acquisition parameters (such as scan mode, the number of nuclides monitored, mass window, the number of samples per peak and dwell times); and (iv) adequate data treatment including the use of the moving average of 5 individual values. With the methodology developed, isotope ratio images with 30 micrometer spatial resolution scale were obtained for exposed and unexposed Daphnia magna individuals. The typical overall uncertainty of the measurements was approximately 5% RSD for the 66Zn/64Zn and 68Zn/64Zn ratios, which can be considered as satisfactory taking into account that the amount of Zn present per 30 μm × 30 μm pixel only reached a few picograms in the most favourable cases (giving rise to 10 000–20 000 counts per s for 64Zn). These results open the possibility for tracer studies with stable isotopes to be carried out using single collector instrumentation, a much more widespread analytical technique than multi-collector ICP-MS.