Showing papers in "Journal of Analytical Atomic Spectrometry in 2004"

Comparing several atomic spectrometric methods to the super stars: special emphasis on laser induced breakdown spectrometry, LIBS, a future super star

Abstract: The “super stars” of analytical atomic spectrometry are electrothermal atomization-atomic absorption spectrometry (ETA-AAS), inductively coupled plasma-atomic emission spectrometry (ICP-AES) and inductively coupled plasma-mass spectrometry (ICP-MS). Many other atomic spectrometric methods have been used to determine levels of elements present in solid, liquid and gaseous samples, but in most cases these other methods are inferior to the big three super star methods. The other atomic methods include glow discharge emission, absorption and mass spectrometric methods, laser excited fluorescence emission and ionization methods, and flame and microwave plasma emission and mass spectrometric methods. These “lesser” methods will be compared to the “super star” methods based on a number of figures of merit, including detection power, selectivity, multi-element capability, cost, applications, and “age” of the methods. The “age” of the method will be determined by a modification of the well-known Laitinen “Seven Ages of an Analytical Method” (H.A. Laitinen, Anal. Chem., 1973, 45, 2305). Calculations will show that certain methods are capable of single atom detection, including several atomic absorption methods, as well as laser atomic ionization and fluorescence methods. The comparison of methods will indicate why the “super stars” of atomic spectrometric methods will continue to retain their status and what must be done for the lesser atomic methods to approach “super star” status. Certainly most of the lesser atomic spectrometric methods will have a limited place in the analytical arena. Because of the wide current interest and research activity, special emphasis will be placed on the technique of laser induced breakdown spectrometry (LIBS). Its current status and future developments will therefore be reviewed.

Metallomics as integrated biometal science

Abstract: In this paper, “metallomics” is proposed as a new scientific field in order to integrate the research fields related to biometals. Metallomics should be a scientific field in symbiosis with genomics and proteomics, because syntheses and metabolic functions of genes (DNA and RNA) and proteins cannot be performed without the aid of various metal ions and metalloenzymes. In metallomics, metalloproteins, metalloenzymes and other metal- containing biomolecules are defined as “metallomes”, in a similar manner to genomes in genomics as well as proteomes in proteomics. Since the identification of metallomes and the elucidation of their biological or physiological functions in the biological systems is the main research target of metallomics, chemical speciation for specific identification of bioactive metallomes is one of the most important analytical technologies to establish metallomics as the integrated bio-metal science. In order to rationalize the concept of metallomics, the distributions of the elements in man, human blood serum and sea-water, a challenge to all-elements analysis of one biological cell, and some other research topics are introduced with emphasis on recent development of chemical speciation of trace metals in some biological samples.

Multiwalled carbon nanotubes as solid-phase extraction adsorbent for the preconcentration of trace metal ions and their determination by inductively coupled plasma atomic emission spectrometry

Abstract: The potential of multiwalled carbon nanotubes (MWNTs) as a solid-phase extraction adsorbent for the preconcentration of trace Cd, Mn and Ni has been investigated. The studied metal ions can be adsorbed quantitatively on MWNTs at pH 8.0, then eluted completely with 0.5 mol L−1 HNO3. The adsorption capacity of MWNTs was found to be 7.42, 4.86 and 6.89 mg g−1 for Cd, Mn and Ni, respectively. A new method using a microcolumn packed with MWNTs as sorbent has been developed for the preconcentration of trace amounts of Cd, Mn and Ni prior to their determination by inductively coupled plasma atomic emission spectrometry (ICP-AES). Parameters influencing the preconcentration of the analytes, such as pH of the sample, sample flow rate and volume, elution solution and interfering ions, have been examined. The method has been successfully applied to the determination of trace elements in some environmental samples with satisfactory results.

Mass discrimination correction in multiple-collector plasma source mass spectrometry: an example using Cu and Zn isotopes

Abstract: Multiple-collector magnetic sector ICP-MS affords the possibility of applying instrumental mass discrimination corrections using a reference isotope ratio of an element (dopant) other than the analyte. Much attention has focused on the use of this approach for lead isotope analysis using a thallium dopant and the technique has also been applied to copper–zinc isotope analysis. The most successful applications of the doping approach have established empirical mass bias relationships between dopant and analyte isotope ratios but this often has to be done for single analytical sessions. Insufficient intra-session variation in mass discrimination often leads to poor constraints on these relationships. Moreover, with the Tl–Pb system there is some doubt over whether samples and standards exhibit the same relationship. Here we show that for the Cu–Zn system, two improvements on previous approaches lead to precise and accurate isotope ratios for unknowns. Firstly, addition of Sr to mixed Cu–Zn standard solutions generates extreme variation in mass bias so that empirical mass bias relationships between analyte and dopant are much better constrained. Secondly, we show that inadequate chemistry, specifically the inefficient removal of matrix Fe and Ti, seriously compromises the Cu–Zn isotope analysis of samples but that with clean chemistry, samples with complex matrices demonstrably yield similar mass discrimination relationships between Cu and Zn isotopes to standards. We also document previously unreported aspects of Cu–Zn isotope analysis: (1) that Cu–Zn mass bias relationships depend critically on the Cu/Zn ratio of the solution; (2) that for an introduction system with a desolvating membrane, the behaviour of standards is highly variable, perhaps due to variations in the oxidation state of Cu in the solution, and that this can be overcome by the passage of standards through the ion exchange procedure used to purify samples. Finally, we document chemical separation and mass spectrometric techniques that permit the isotopic analysis of order of magnitude smaller samples than previously achieved and report values for BCR-1 basalt standard of δ66Zn = 0.20 ± 0.09‰ (n = 12) and δ65Cu = 0.07 ± 0.08‰ (n = 6) at the 95% confidence level.

Particle size distributions and compositions of aerosols produced by near-IR femto- and nanosecond laser ablation of brass

Abstract: Particle size distributions and compositions of primary aerosols produced by means of near-IR femtosecond laser ablation (λ = 775 nm) of brass in He or Ar at atmospheric pressure have been measured. Aerosols were characterized using a 13-stage low-pressure impactor covering a size range from 5 nm up to 5 μm and subsequently analyzed applying total reflection X-ray fluorescence spectrometry. The results indicate, that for femtosecond laser ablation in the low-fluence regime (<5 J cm−2) ultra-fine aerosols (mean diameter dp ≈ 10 nm/peak width wp ≈ 35 nm) are produced. Furthermore, the total Cu/Zn ratio of these aerosols corresponds to the composition of the bulk material. In contrast, ablation above 10 J cm−2 results in the formation of polydisperse, bimodal aerosols, which are distributed around dp1 ≈ 20 nm (wp1 ≈ 50 nm) and dp2 ≈ 1 μm (wp2 ≈ 5 µm), respectively, and whose total Cu/Zn ratio slightly deviates from the bulk composition. In order to examine the influence of pulse duration on particle size distribution and aerosol composition, comparative measurements by means of near-IR nanosecond ablation were also performed. The data show that nanosecond ablation generally leads to an intensified formation of particles in the micrometer range. Moreover, the composition of these aerosols strongly departs from the stoichiometry of the bulk. Aspects concerning the formation of particles during ablation as well as implications for the element-selective analysis by inductively coupled plasma spectrometry are discussed.

Transferrin binding and transferrin-mediated cellular uptake of the ruthenium coordination compound KP1019, studied by means of AAS, ESI-MS and CD spectroscopy

Abstract: Indazolium trans-[tetrachlorobis(1H-indazole)ruthenate(III)] (KP1019) shows particular promise as an antitumour agent against colorectal cancer. It is known that KP1019 reacts with human serum proteins, whereby the major amount binds to albumin (present in large excess) and a smaller amount to transferrin. It has been hypothesised that transferrin-mediated uptake by transferrin receptor expressing tumour cells may in part explain the apparent tumour selectivity of this compound. Circular dichroism spectroscopy and electrospray ionisation mass spectrometry studies demonstrate that two equivalents of KP1019 bind specifically to human apotransferrin, while additional amounts of the ruthenium complex bind unspecifically. Uptake studies in the transferrin receptor-expressing human colon carcinoma cell line SW480 revealed a higher cellular accumulation of KP1019 in comparison to a KP1019-transferrin adduct (2∶1), while the uptake of a KP1019–Fe(III)-transferrin conjugate (1∶0.3∶1) significantly exceeded that of KP1019, suggesting that iron binding is necessary to obtain a protein conformation which favours recognition by the transferrin receptors on the cell surface. Our study showed that KP1019 is transported into the cell by both transferrin-independent and transferrin-dependent mechanisms. Transferrin-mediated uptake is more efficient when transferrin is saturated with iron to a physiological degree (∼30%). Cell fractionation experiments demonstrated that after a 2 h treatment of human colon cancer cells with 10 µM KP1019 on average 55% of the intracellular ruthenium is located in the cellular nucleus, while 45% remain in the cytosol and other cellular components.

Collision and reaction cells in atomic mass spectrometry: development, status, and applications

Abstract: The development and utilization of collision and reaction cells in atomic mass spectrometry is reviewed. These devices have been used for decades in fundamental studies of ion–molecule chemistry and have only recently been applied in the GD-MS and ICP-MS fields. Such cells are used to promote reactive and non-reactive collisions, with resultant benefits in interference reduction, isobar separation, and thermalization/focusing of ions in ICP-MS. Novel ion–molecule chemistry schemes, using a variety of reaction gas reagents selected on the basis of thermodynamic and kinetic principles and data, are now designed and empirically evaluated with relative ease. These chemical resolution techniques can avert interferences requiring mass spectral resolutions of >600000 (m/Δm). Purely physical ion beam processes, including collisional dampening and collisional dissociation, are also employed to provide improved sensitivity, resolution and spectral simplicity. Collision and reaction cell techniques are now firmly entrenched in current-day ICP-MS technology, enabling unprecedented flexibility and freedom from many spectral interferences. A significant body of applications has now been reported in the literature. Collision/reaction cell techniques are found to be most useful for specialized or difficult analytical needs and situations, and are employed in both single- and multi-element determination modes.

Laser ablation-ICP-MS: particle size dependent elemental composition studies on filter-collected and online measured aerosols from glass

Abstract: In laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), the term elemental fractionation is normally used to summarize all non-stoichiometric effects occurring during sample ablation, aerosol transport and vaporization, atomisation and ionisation within the ICP. Nevertheless, there are different types of elemental fractionation occurring between different sized particles within an aerosol, as previously shown for metal alloy ablations. In the present work, laser generated aerosols from glass samples were filter collected before entering the ICP to study their total and particle size dependent composition. Furthermore, elemental concentrations in different particle size fractions on filters were compared with their response measured in the ICP. For the NIST SRM 610 glass, elemental fractionation effects between small particles (<125 nm and <340 nm), and the total aerosol containing all particle sizes up to 1 µm or even larger, were measured for 42 major and trace elements using a 266 nm Nd∶YAG laser and scanning ablation conditions to produce the aerosol. Particles above 125 nm and 340 nm were separated from the aerosol by a particle separation device and the remaining particles were collected on a filter, digested and measured using solution nebulization ICP sector field MS (SFMS). Results show an enrichment of certain elements such as Cu, Zn, Ag, Tl, Pb and Bi of up to 90% relative to Ca within the small particle size fraction of an aerosol in comparison with the total composition of the aerosol. The same elements are depleted in large aerosol particles measured from deposited particles within the ablation cell. However, the total transportable aerosols produced using different laser wavelengths (193/266 nm), and gas environments (He/Ar), which were also filtered and digested show no significant deviation in their overall stoichiometry from the original sample (except Be, Fe, Cd for all lasers and gases) within the uncertainty of the measurements. Therefore, the composition of filter collected aerosol of glass samples indicates that the elemental fractionation in LA-ICP-MS, detected at the beginning of a 266 nm single hole ablation, is predominantly caused by incomplete vaporization of large particles within the ICP and is not dominated by non-stoichiometric ablation of the glass.

Laser assisted plasma spectrochemistry: laser ablation

Abstract: This paper presents a brief overview of the current research issues in laser ablation for chemical analysis, discusses several fundamental studies of laser ablation using time-resolved shadowgraph and spectroscopic imaging, and describes recent data using femtosecond ablation sampling for ICP-MS and LIBS. This manuscript represents a summary of the plenary lecture presented at the 2004 Winter Conference on Plasma Spectrochemistry.

Application of strontium isotope abundance ratios measured by MC-ICP-MS for food authentication

Abstract: Naturally occurring isotopes of such elements as strontium (Sr) have proved to be good tools for detecting trends in the soil-vegetation system and the tracing of a variety of objects. Multiple-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) has been used for the precise determination of variations in the isotopic composition of Sr. The method described has been applied to the establishment of the potential and limits to determine the geographical origins of different Emmental-type cheese samples. The sample preparation consists of (i) a freeze-drying procedure to remove water, (ii) an extraction step to eliminate the fat components and to obtain the cheese casein fraction, (iii) a thermal decomposition of the latter, and (iv) a chromatographic matrix separation of the redissolved residue. The determination of the isotope abundance ratios 88Sr/86Sr, 87Sr/86Sr and 84Sr/86Sr resulted in precisions of 0.002–0.01%. Simultaneously, the ion currents for krypton (83Kr, 82Kr) and rubidium (85Rb) were measured to correct for interferences with the Sr isotopes 84, 86 and 87. These and further (argide) spectral interferences causing bias effects to the Sr isotope abundance ratios have been investigated and an adequate computational correction procedure has been assessed. The whole set of validation data has been used for the calculation of the combined standard measurement uncertainty of the isotopic abundance ratio, resulting in a value of 0.016%. Comparison of the measured 87Sr/86Sr data with thermal ionisation mass spectrometric (TIMS) results, determined on the same cheese samples, agreed within the stated measurement uncertainties, thus indicating that both the validation of the sample preparation procedures and the mass spectrometric measurements cause no evident bias effect with respect to the Sr isotope abundance values. The 87Sr/86Sr isotope abundance ratios in cheese originating from different regions (alpine, pre-alpine, Bretagne, Finland, Canada, Australia) accorded to local geological properties. No difference was found between “casein-bound” and “whole-cheese” Sr isotope abundance ratios within the stated measurement uncertainties.

Remote LIBS with ultrashort pulses: characteristics in picosecond and femtosecond regimes

Abstract: Using a container-integrated mobile femtosecond terawatt laser system with integrated detection unit (Teramobile), we have demonstrated remote laser-induced breakdown spectroscopy (R-LIBS) on copper and aluminium samples with targets located at 25 m away from the container. The ability of our laser system to generate pulses in the femtosecond, picosecond and nanosecond regimes allowed us to perform direct comparisons between these three pulse durations. The dependence of the fluorescence signal on laser pulse energy showed a nonlinear behavior with a threshold, which is consistent with the previous observations for laser ablation. Such nonlinear behavior leads to a dependence of the LIBS signal on the temporal-spectral shape of the laser pulse. We showed especially that the transform-limited pulse does not optimize the fluorescence. A properly applied chirp allows an increase of the LIBS signal. Understanding and optimization of the chirp effect would improve the detection limit of the LIBS using a femtosecond laser (Femto-LIBS) and lead to a larger detection distance. Furthermore the use of pulse shaping should enhance the detection specificity for the cases of spectral overlapping between several elements to be identified.

Arsenic–glutathione complexes—their stability in solution and during separation by different HPLC modes

Abstract: Complexes of arsenic compounds and glutathione are believed to play an essential part in the metabolism and transport of inorganic arsenic and its methylated species. Up to now, the evidence of their presence is mostly indirect. We studied the stability and chromatographic behaviour of glutathione complexes with trivalent arsenic: i.e. AsIII(GS)3, MAIII(GS)2 and DMAIII(GS) under different conditions. Standard ion chromatography using PRP X-100 and carbonate or formic acid buffer disintegrated the complexes, while all three complexes are stable and separable by reversed phase chromatography (0.1% formic acid/acetonitrile gradient). AsIII(GS)3 and MAIII(GS)2 were more stable than DMAIII(GS), which even under optimal conditions tended to degrade on the column at 25 °C. Chromatography at 6 °C can retain the integrity of the samples. These results shed more light on the interpretation of a vast number of previously published arsenic speciation studies, which have used chromatographic separation techniques with the assumption that the integrity of the arsenic species is guaranteed.

Space- and time-resolved dynamics of plasmas generated by laser double pulses interacting with metallic samples

Abstract: Significant improvements to the analytical performance of laser-induced breakdown spectrometry (LIBS) were achieved by the use of laser double pulses to ablate and excite the sample material to be analysed. To clarify the underlying physical phenomena the dynamics of the laser-induced plasma in air is studied using a high-speed electro-optic camera to observe the spatial and temporal development of the plasma geometry. A Mach–Zehnder interferometer was set-up to detect the spatio-temporal changes of the refractive index of the plasma. The velocities of the luminous plasma front and shock waves after the impact of the first laser pulse are consistent with the prediction of Sedov's model for spherical expansion. The dynamics caused by the second laser pulse of the double pulse differ significantly, indicating a modified state of the local atmosphere in the interaction region. Electron densities determined interferometrically amount to about 3 × 1018 cm−3 at the center of the hemispheric plasma geometry at a delay time of 2 µs. Whereas the electron density for single or double pulses is approximately the same, the volume of the plasma is greater by more than a factor of 3 after the interaction with the double pulse of the same total energy.

LIBS limit of detection and plasma parameters of some elements in two different metallic matrices

Abstract: In the present work a detailed study has been performed on the effect of the matrix on the limit of detection (LOD) and the plasma parameters of the laser induced breakdown spectroscopy (LIBS) technique The LOD of magnesium, silicon, manganese and copper as minor elements was evaluated in aluminium standard sample alloys compared to the values of the LOD of the same elements in standard steel alloys The effect of changing the matrix on the laser induced plasma plume parameters, namely the plasma temperature Te and the electron density Ne, has been also studied Calibrations were achieved for the four elements with linear regression coefficients between 98–99% on average According to the obtained results Mn and Cu have the lowest LOD in the steel alloy matrix, while Mg has much lower LOD in the aluminium alloy matrix These results may be interpreted in view of the compatibility of the physical properties of the elements existing in the same matrix Approximately similar electronic structure and values of melting point, density, atomic weight, etc, may facilitate better conditions for energy transfer within the matrix From the application view point, it is possible for LIBS in the on-line industrial process control to follow up only a single element (that with the lowest LOD in such matrix) as a marker for the correct alloying in metals and mixing in pharmaceuticals

Development of signal smoothing device for precise elemental analysis using laser ablation-ICP-mass spectrometry

Abstract: A new signal smoothing device (stabilizer) has been developed for elemental and isotopic ratio analyses of solid samples from small crater sizes obtained by a laser ablation-ICP-mass spectrometry. With the stabilizer developed in this study, no oscillation of signal intensity was found, even with the repetition rate of 2 Hz. The effectiveness of the stabilizer was evaluated by vigorous testing of the stability in signal intensity and the relationship between signal smoothing efficiency and signal decay time. The precision of elemental and isotopic ratio measurements was evaluated by the repeated analysis of 7 isotopes from NIST SRM 610 glass standard. The resulting repeatability in elemental ratio and isotopic ratio was as low as 2–4% (2 SD, n = 10). Another important advantage of using the stabilizer is that the elemental fractionation, which was a large source of analytical error, was successfully reduced by the laser ablation with low repetition rate ablation approach.

High-precision Cu and Zn isotope analysis by plasma source mass spectrometry: Part 2. Correcting for mass discrimination effects

Abstract: Two approaches to correct for mass discrimination effects associated with Cu and Zn isotopic measurements on two different MC-ICP-MS instruments (a Micromass IsoProbe and a VG Axiom) have been compared and assessed in detail: (1) sample-standard bracketing (SSB), and (2) the 'empirical external normalisation' (EEN) whereby a second element is used to simultaneously correct for mass discrimination. This has provided new insights into the mass discrimination behaviours of Cu and Zn under varying instrumental set-ups, and has allowed improvements to be made to the existing correction procedures. With the SSB approach, mass bias stability is a prerequisite, and matrix components must be removed from the analyte to avoid matrix-related mass discrimination effects. By comparison, the EEN approach requires a degree of mass bias instability, and automatically corrects for matrix-related mass discrimination effects. The EEN correction may therefore appear more robust. However, while the EEN correction yields high-precision 6 5 Cu/ 6 3 Cu and 6 6 Zn/ 6 4 Zn data, an as yet unidentified source of systematic drift in the 6 7 Zn and 6 8 Zn signals through time hinders analyses of ratios incorporating these isotopes. Using the EEN correction where analyte and spike ratios were measured sequentially within a peak-switching protocol led to a three-fold deterioration in precision relative to static measurements. This is consistent with mass bias drift on the scale of a single five-second-measurement integration. For relative 6 5 Cu/ 6 3 Cu and 6 6 Zn/ 6 4 Zn ratio measurements, the SSB and EEN corrections give long-term reproducibilities of less then ′0.07‰ (2SD) for pure Cu and Zn reagents. This is sufficient for resolving mass-dependent isotopic variability in natural and anthropogenic materials.

High-precision Cu and Zn isotope analysis by plasma source mass spectrometry part 1. Spectral interferences and their correction

Abstract: Spectral interferences originating from instrumental and sample-matrix components continue to present a major analytical challenge to high-precision isotope ratio measurements by multiple-collector inductively coupled plasma mass spectrometry (MC-ICP-MS). This is particularly true when measuring stable isotopic variability of Cu and Zn, where instrumental and sample-matrix related spectral components may obscure the very small isotopic anomalies that typify these metals in terrestrial materials. We present a systematic characterisation and quantification of spectral interferences across the mass range 63Cu to 70Zn using two MC-ICP-MS instruments: a Micromass IsoProbe and a VG Axiom. Significant instrumental Ni backgrounds of up to 40 mV total Ni occur on the IsoProbe, reflecting streaming off the Ni-sampler and/or skimmer cones. This Ni contribution, however, is insufficient to account for the excess peak contribution at 64amu, suggestive of an as yet unidentified interference contribution at this mass. By contrast, Ni backgrounds on the Axiom are roughly one order of magnitude lower, and no comparable interference occurs at 64amu. High-resolution mass scans on the Axiom have identified 40Ar12C16O+ and 40Ar14N14N+ species at 68amu and 40Ar14N16O+ at 70amu. Also, HNO3-related 1H1H14N16O16O16O+ and 1H1H14N16O16O18O+ species at 64amu and 66amu respectively were observed on the Axiom using solution nebulisation. None of these species were observed on the IsoProbe, possibly reflecting the effect of an Ar-bled hexapole collision cell that reduces molecular interferences through ion-molecule reactions. Instrumental backgrounds have been successfully corrected using an on-peak acid blank subtraction procedure. Zinc hydride adducts occur on the Axiom using solution nebulisation. These interferences are eliminated using a desolvated plasma, and have been corrected by monitoring the 64Zn1H+/64Zn ratio on a pure Zn solution and applying an offline peak subtraction. No Zn hydride interferences were observed on the IsoProbe, suggesting differences in instrument design influence the formation and/or persistence of these species. Matrix-induced interference contributions on the Axiom and IsoProbe show increasing significance from argides (NaAr+, MgAr+, AlAr+) to oxide/hydroxide (TiO+, TiOH+, VO+, VOH+, CrO+, CrOH+) to double-charged species (Ba2+, Ce2+). Switching from solution nebulisation to a desolvated plasma enhances argide and double-charge species, and concurrently depresses oxides and hydroxides, reflecting changing conditions within the ICP-source. These results highlight the importance of removing problematic matrix components prior to Cu and Zn MC-ICP-MS isotope ratio measurements.

Quantitative analysis of silicates using LA-ICP-MS with liquid calibration

Abstract: For more than a decade liquid calibration has been proposed and selectively applied as a calibration strategy for laser-generated aerosols. However, matrix independent calibration is not a well-accepted technique for quantification in direct solid analysis using LA-ICP-MS. In this study three synthetic calibration solutions were used for the analysis of three silicate reference materials (BCR-2G, ATHO, and NIST 610). The calibration solutions were introduced into the ICP using an Aridus liquid sample introduction system with aerosol desolvation, while argon was used as the carrier gas. A 193 nm ArF excimer laser ablation system generated sample aerosols using helium as carrier gas. The argon carrier gas containing the solution nebulization aerosols was mixed, using a sheath gas adaptor in front of the ICP, with the laser aerosol carried in helium. Two different calibration strategies were applied for the multielement quantification of three geological reference materials. The first calibration technique used internal standardization with Ca as the internal standard. The second approach used synthetic calibration solutions containing all major, minor, and trace elements, in which the concentration ratios and concentrations of the elements were known. A normalization algorithm was used which calculated the sum of all of the determined element concentrations as oxides to 100%. The data shown for Ca indicate that both procedures are well suited for multi-element determinations. The 100% oxide normalization strategy allowed the calculation of the Ca concentration based on the total matrix used as internal standard. This Ca concentration was then used for the determination of the trace element composition of the sample. The advantage of this calibration is the possibility of element analysis in silicates without knowing the element concentration of at least one internal standard element prior to analysis. However, this study also shows that the composition of the solution used for the calibration can lead to losses of some elements during the desolvation process in the Aridus or during aerosol transfer to the ICP, which will be shown for Cu.

Flow injection on-line preconcentration of palladium by ion-pair adsorption in a knotted reactor coupled with electrothermal atomic absorption spectrometry

Abstract: A flow injection (FI) method for the preconcentration/separation of palladium, coupled with electrothermal atomic absorption spectrometry (ETAAS), is presented. The preconcentration was performed by on-line formation of an ion-pair between the positively charged potassium complex of 1,4,7,10,13,16-hexaoxacyclooctadecane (K+18-crown-6) and the palladium thiocyanate anion (Pd(SCN)42−) and its sorption on the inner walls of a PTFE knotted reactor (KR). The elution was achieved by methanol acidified with 1% (v/v) HNO3. An enhancement factor of 29 and a sampling frequency of 14 h−1 were obtained for a preconcentration time of 90 s and a sampling flow rate of 4.4 ml min−1. The detection limit (3σ) is 16 ng l−1 and precision (RSD) for 0.4 µg l−1 Pd is 2.3%. The method was validated by recovery measurements on spiked blood and road dust samples.

Quantitative laser induced breakdown spectroscopy analysis of ancient marbles and corrections for the variability of plasma parameters and of ablation rate

Abstract: White marble samples from ancient quarries have been analyzed by Laser Induced Breakdown Spectroscopy (LIBS) both on the bulk material and surface encrustations. With the aim to achieve quantitative results by LIBS, until now not reported on marble materials, calibration standards with CaCO3 matrices doped with certified soils were realized. Very different emission intensities and plasma parameters were observed on the standards and natural marbles. In order to compare so different spectra, a method for data analysis was developed, which takes into account variability of the ablation rate, plasma temperature and electron density. It was experimentally demonstrated that ablated volume is well correlated to the emission intensity of plasma continuum for a wide range of laser energies. LIBS signal normalization on the adjacent continuum level, together with introduction of correction factors dependent on plasma parameters, allowed the measuring of concentrations both for major and trace elements in marbles. The analytical procedure was validated by comparative SEM-EDX and ICP-OES measurements. Quantitative LIBS analyses were also performed during encrustation removal and could be applied to control laser-cleaning processes. The quantification of metal contents in the encrustations supported the occurrence of sulfates in the outer layers exposed to environmental agents via a catalytic process.

Optimization of mixed Pb–Tl solutions for high precision isotopic analyses by MC-ICP-MS

Abstract: Measurements of SRM 981 Pb isotope standard mixed with Tl for mass bias corrections were conducted with a MC-ICP-MS (Nu Plasma) using a Nu Instruments desolvating nebulizer. During the initial experiments, Pb and Tl from single-element, concentrated stock solutions were mixed in 2% HNO3 prior to isotope ratio measurements. The results revealed relatively poor precision and accuracy of the Pb isotope measurements, large variations in e205Tl in the same standard (ranging from −3.9 to +30.1), and large variations in the observed Pb/Tl intensity ratios. When analyses were restricted to freshly mixed (<1 hour) Pb–Tl solutions, however, highly precise isotopic ratios were obtained for lead (206Pb/204Pb = 16.9373 (±0.0011, 2σ), 207Pb/204Pb = 15.4907 (±0.0012, 2σ), and 208Pb/204Pb = 36.6935 (±0.0039, 2σ)) and for thallium (e205Tl = 1.5 (±0.8, 2σ)). In addition, Pb/Tl intensity ratios were constant and corresponded to the mixing ratios of the prepared solutions. A series of experiments revealed that the poor precision and accuracy observed for the initial set of isotope ratio measurements resulted from variable photoxidation of Tl+ to Tl3+, which occurs in the presence of Pb and solar UV radiation. This reversible reaction generates Tl3+, which behaves distinctly from Tl+ during desolvation and leads to consistently higher measured Pb/Tl and 205Tl/203Tl ratios. The extent of the interaction between Pb and Tl and the subsequent effect on isotope ratio measurements is sensitive to a combination of factors, including differences in the acid matrix and molarity, desolvation conditions, and UV light exposure. It appears that the observed e205Tl variations in the Pb–Tl3+-bearing solutions dominantly result from mass-dependant differential diffusion of Tl during desolvation. These experiments suggest that great care must be exercised during isotopic analyses of systems utilizing one element for mass-bias correction on another, such as Pb–Tl, Cu–Zn and Mo–Zr, which readily undergo redox reactions under laboratory conditions.

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

Abstract: 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.

γ-MPTMS modified nanometer-sized alumina micro-column separation and preconcentration of trace amounts of Hg, Cu, Au and Pd in biological, environmental and geological samples and their determination by inductively coupled plasma mass spectrometry

Abstract: Nanometre-sized alumina was chemically modified with γ-mercaptopropyltrimethoxysilane (γ-MPTMS). The modified nanometer-sized alumina was characterized by X-ray power diffusion (XRD), X-ray photoelectron energy spectrometer (XPS) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) before it was used as solid phase adsorption material for the inductively coupled plasma mass spectrometry (ICP-MS) determination of trace amounts of Hg, Cu, Au and Pd. The effects of pH, sample flow rate and volume, elution solution and interfering ions on the recovery of the analytes have been investigated. Under the optimized conditions, the adsorption capacity of modified nanometer-sized Al2O3 was found as 10.4, 16.3, 15.3, and 17.4 mg g−1 for Hg, Cu, Au and Pd, respectively. The limits of detection were as low as 0.066 and 0.49 ng L−1 for Cu and Hg with a concentration factor of 100 times, and 0.46 and 0.26 ng L−1 for Au and Pd with a concentration factor of 200 times. The developed method has been applied to the determination of trace Hg and Cu in biological and environmental certified materials and Au and Pd in geological certified materials, and the determined values were in a good agreement with the certified values.

Metallobiomolecules. The basis of life, the challenge of atomic spectroscopy

Abstract: An outline of recent advances in metalloproteomics (structural and functional characterization of metal-binding proteins and their structural metal-binding moieties) and metallomics (characterization of the entirety of metal and metalloid species within a cell or tissue type) is presented. ICP-MS allows the specific detection of heteroelements after separation using techniques traditionally associated with biochemistry, such as gel electrophoresis or capillary chromatography. The element specificity, independence of matrix effects, and wide linear range make ICP-MS an attractive complementary technique to ESI/MALDI-MS for the analysis of sulfur-, selenium- and phosphorus-containing proteins, metal-complexes with nucleic acids, carbohydrates and proteins, and metal-tagged biomolecules in general.

Sources of mass bias and isotope ratio variation in multi-collector ICP-MS: optimization of instrumental parameters based on experimental observations

Abstract: In this work, several contributing factors to the observed mass bias in inductively coupled plasma mass spectrometry (ICP-MS) have been identified. Analyses of the isotopic compositions of B deposited on sampler and skimmer cones demonstrate enrichment of 10B on the former and 11B on the latter. Grounding the capacitive discharge system to enhance sensitivity also magnified the level of 11B enrichment on the skimmer cone more than four-fold. This supersonic expansion of the ion beam behind the sampler is confirmed to be an important source of mass bias. Isotopic analyses of the Fe, Zn and Tl leached from used extraction lenses yielded a linear relationship between the levels of lighter isotope depletion and mass ratio. Although consistent with the space-charge effect, the fact that isotopically-heavy deposits were found demonstrates that the ion beam diverges into a relatively wide solid angle in the field-free region behind the skimmer. This severely impairs transmission of, in particular, the lighter isotopes. For a wide range of elements (Li, B, Fe, Ni, Cu, Sb, Ce, Hf and Re), the magnitude of the mass bias was found to be affected by the sample gas flow rate, as well as the distance between the sampler and the end of the torch, i.e., the sampling depth, employed in the Neptune multi-collector ICP-MS instrument. Mathematical analysis of the profiles of intensity variations as a function of these instrumental parameters revealed that the response peaks closer to the torch for the heavier isotopes of all studied elements. Owing to this spatial non-coincidence, tuning for maximum intensity on either isotope will result in sampling from a region where even slight plasma instabilities will be translated into substantial variations in mass bias. Therefore, in-plasma processes also contribute to the degree and temporal stability of mass bias. In light of these findings, recommendations for optimizing multi-collector ICP-MS with respect to obtaining the highest possible precision are presented.

Fast, simple and reliable routine determination of 23 elements in urine by ICP-MS

Abstract: The paper presents a method for the fast, simple and reliable routine determination of As, Ba, Be, Co, Cd, Cu, Cr, In, Li, Mn, Mo, Ni, Pb, Pt, Rh, Sb, Se, Sn, Tl, U, V, W and Zn in urine by inductively coupled plasma mass spectrometry (ICP-MS) with an octopole based collision cell. The complete method validation for all elements is described, including the evaluation of short- and long-term stability, the analysis of different reference materials and the discussion of precision and accuracy in internal and external quality assurance. The urine samples were analysed directly after a 1/5 (v/v) dilution with 1% (v/v) nitric acid. The sample introduction system consisted of a robust Babington nebulizer for sample introduction into the ICP and a torch with an injector tube with an inner diameter of 2.5 mm. Combined with a low sample aspiration rate (0.4 ml min−1) these applied ICP operating conditions enable the analysis of 500 samples without clogging of the nebulizer and deposition of particles in the injector tube. Limits of detection are in the range 0.4 ng l−1 (for U) to 143 ng l−1 (for Se) calculated to the undiluted urine. Spectral interferences from polyatomic ions were removed by adding 3.2 ml min−1 helium (for As, Ba, Cd, Cr, Cu, Mo, Mn, Ni, Rh, V, Zn) or 3.4 ml min−1 hydrogen (for Se) as collision gas. The analysis results of 63 real urine samples from non-exposed human subjects are presented. ICP-MS fitted with a collision cell enables the simultaneous determination of all 23 elements either in their essential concentration range or at concentration levels relevant for occupational and environmental health. For some elements (Rh, Pt, W, Mn) most of the concentrations in urine are below the limit of quantification, for other elements (Li, Pb, Co, Tl Cu, Zn, Se) good agreement with previous studies was found, while for a further group of elements (Be, Cr, Ni, Cd) new results or useful statistical data are presented.

High precision calcium isotope ratio measurements using a magnetic sector multiple collector inductively coupled plasma mass spectrometer

Abstract: Calcium isotope abundances were measured using a Finnigan Neptune magnetic sector multiple collector inductively coupled plasma mass spectrometer capable of resolving all molecular isobaric interferences from 42Ca, 43Ca, 44Ca, 46Ca and 48Ca. Scattering events caused by the intense 40Ar+ ion beam did not contribute to the uncertainty in the baseline of the calcium mass spectrum. Quantitative separation of the calcium from the sample matrix was carried out to ensure that the measurements were independent of the sample type. In addition, thorough desolvation of the aerosol was found to have a significant effect on the stability and sensitivity of the method. The stable mass bias of the instrument enabled normalization of the measured isotope abundance ratios relative to standard reference materials. Delta values including δ44Ca/43Ca, δ44Ca/42Ca and δ48Ca/42Ca were measured with external reproducibilities better than ±0.2‰ (2s) from 10 ppm solutions of calcium-containing materials, including sea-water and biogenic and non-biogenic marine carbonates.

Selenium speciation in human urine samples by LC- and CE-ICP-MS—separation and identification of selenosugars

Abstract: Human urine samples were analysed by a reversed-phase chromatographic system and an ion-pair chromatographic system The chromatographic system was connected to the ICP-MS either by a microconcentric nebulizer (MCN) in combination with a cyclonic spraychamber or by a modified direct injection nebulizer (MDIN) The sensitivity of the latter was better than the sensitivity of the MCN, which on the other hand was more robust for the analysis of samples with high concentrations of dissolved solids Urine sample composition did not seem to change when urine was exposed to evaporation under nitrogen at ambient temperature and methanol extraction A pre-concentration factor of 10 was achieved with this procedure On occasions when a pre-concentration factor of 100 was obtained by lyophilsation and methanol extraction, at least 10 selenium compounds were separated in the urine sample Urine samples were collected from two healthy volunteers who had been supplied with 1000 µg and 2000 µg of selenium, respectively, in the form of selenized yeast When samples were spiked with 8 different standards, only two standards co-eluted with compounds in urine in both chromatographic systems: the major urinary metabolite Se-methyl-N-acetylgalactosamine and Se-methyl-N-acetylglucosamine The presence of Se-methyl-N-acetylglucosamine in urine was verified by co-migration with the standard in capillary electrophoresis after fractionation by preparative reversed-phase chromatography Se-methyl-N-acetylglucosamine is only a minor metabolite as its concentration was less than 2% of the concentration of Se-methyl-N-acetylgalactosamine The presence of this metabolite in urine has, to our knowledge, not been suggested before Trimethylselenonium, selenomethionine, Se-methylselenocysteine, Se-methylselenomethionine and selenocystamine were not detected in these samples

Element and molecular mass spectrometry—an emerging analytical dream team in the life sciences

Abstract: The recent literature on the combined applications of element (ICP, inductively coupled plasma) mass spectrometry and molecular (ESI, electrospray ionisation and MALDI, matrix assisted laser desorption ionisation) mass spectrometry in the life sciences is reviewed. Emphasis is put on investigations where both techniques have been used in a synergistic way with the aim of an analytical result with molecular specificity. Multi-element specificity and quantification are the key features of element MS, whereas molecular weight determination and structural information are those contributed by ESI and MALDI MS. The analytical applications cover the study of selenoproteins, phosphoproteins, metalloproteins, unmodified proteins, metallothioneins, phytochelatins, nucleic acids, arsenosugars, thyroid hormones, cobalamines, drugs and drug metabolites. Supported by on-line or off-line coupling to chromatographic or electrophoretic separation methods, the combined application of element and molecular mass spectrometry in all these studies has created the basis for new structural and/or quantitative insights, demonstrating the analytical excellence of this approach.

The application of collision/reaction cell inductively coupled plasma mass spectrometry to multi-element analysis in variable sample matrices, using He as a non-reactive cell gas

Abstract: The development of collision and reaction cells for inductively coupled plasma mass spectrometry (ICP-MS) has extended the capability of the technique by allowing the selective attenuation or removal of previously problematic spectral interferences. However, many of the reported applications of collision and reaction cell ICP-MS have required the adoption of operating conditions that are so specific to the selected analyte and/or target interference that the multi-element capability of the instrument has been compromised, or the conditions have been applicable only to a well-defined and consistent sample type. This work demonstrates the application of an ICP-MS, fitted with a collision/reaction cell, to perform multi-element analysis at the single ng ml−1 level in multiple sample types. A single set of operating conditions was used for all selected analytes across a diverse range of sample matrices. The capability of an octopole-based collision/reaction cell ICP-MS, operated using He as the inert collision gas, was demonstrated for the removal of unidentified polyatomic species arising from variable Cl−, S− and C-based synthetic matrices and round-robin samples comprising a range of clinical matrices. Compared to the standard (no cell gas) mode, the He cell gas mode improved the accuracy of spike recoveries at the 5 ng ml−1 level for all the measured isotopes of all the transition metals investigated (Ti, V, Cr, Mn, Fe, Co, Ni, Cu and Zn) in the synthetic matrix samples, using the same cell gas and voltage conditions for all analytes in all matrices. Where reference values were available for the clinical samples, analyte recoveries were typically within the range of the expected concentrations, when calibrated using simple (not matched for sample matrix) calibration standards and using operating conditions that were constant for all analytes and all matrices. Additional benefits of using an inert cell gas such as He were the complete absence of newly formed interfering product ion species and freedom from analyte signal reduction through loss by reaction. This is in contrast to the reported generation of new, cell-formed polyatomic ions and the loss of some analytes by reaction, which can occur when highly reactive cell gases are used, and suggests that the use of an inert collision gas may be suitable for the analysis of complex and variable sample matrices, where the identity of any potential interfering species is not known in advance.