Francisco Ardini

Determination of sub-nanomolar levels of iron in sea-water using reaction cell inductively coupled plasma mass spectrometry after Mg(OH)2 coprecipitation

A new procedure for the determination of iron in sea-water at sub-nanomolar concentration levels was developed. The method applied the low-blank magnesium hydroxide co-precipitation procedure in combination with quadrupole ICP-MS and used the dynamic reaction cell technique to resolve the polyatomic interferences arising from the residual matrix and the solvent. Although the interference-free determination at m/z = 56 could be obtained by using methane as the reaction gas, the best signal-to-background ratio was achieved by using ammonia and performing the measurements at m/z = 54. Accurate quantification of low levels of iron at m/z = 54 also required the mathematical correction for the isobaric interference due to the occurrence of chromium. The main analytical figures of the optimized method were evaluated, with special attention to the determination of the procedural, reagent and field blanks. A detection limit as low as 0.09 nM was achieved, using a pre-concentration ratio of 10. The accuracy of the analytical procedure was evaluated by the analysis of the sea-water reference materials CASS-4, NASS-5, SAFe D2 and SAFe S1, having certified concentration values ranging from 12.8 nM to about 0.1 nM. The analytical precision for replicated analyses of the CRMs ranged from 1.3% to 14% (n = 7). Finally, the developed procedure was applied to a number of open-ocean sea-water samples from the Ross Sea (Southern Ocean, Antarctica)

Comparison of inductively coupled plasma spectrometry techniques for the direct determination of rare earth elements in digests from geological samples

Inductively coupled plasma quadrupole mass spectrometry (ICP-QMS), ICP sector field mass spectrometry (ICP-SFMS) and ICP atomic emission spectrometry (ICP-AES) were compared with regard to the direct determination of rare earth elements (REEs) in geological samples. In order to reduce the polyatomic interferences occurring in ICP-QMS, the use of a cooled spray chamber was optimized, obtaining a significant decrease of the oxide ions formation (about 50%) and a consequent mitigation of the interfering effects. Precision and accuracy of the method were demonstrated by the analyses of sediment and soil certified reference materials. ICP-SFMS working in high-resolution mode also provided accurate results, with similar precision to ICP-QMS (RSD%: 3-8%) and comparable or better limits of detection. Quantification limits of the procedures were 18-52 ng g(-1) and 10-780 ng g(-1) for sector field- and quadrupole-ICP-MS, respectively. Accurate and precise determination of most REEs was also achieved by ICP-AES using both pneumatic and ultrasonic nebulization, after a careful selection of the emission lines and compensation for non-spectral interferences by internal standardization. The three techniques were finally applied to glaciomarine sediment samples collected in Antarctica, providing comparable analytical data on REE abundance and depth pattern.

Conversion of rare earth elements to molecular oxide ions in a dynamic reaction cell and consequences on their determination by inductively coupled plasma mass spectrometry

The behaviour of rare earth elements (REEs) ions within a dynamic reaction cell (DRC) pressurized with oxygen was investigated, in order to explore their determination at m/z +16 by inductively coupled plasma mass spectrometry (ICP-MS). Under the optimized conditions, the conversion of REEs to molecular monoxide ions was nearly quantitative (>96%), with the exception of Tm (78%), Eu (11%) and Yb (6%). Moreover, the formation of dioxide ions was generally lower than 1%. According to these results, a new method for the determination of REEs in digests from geological samples was developed. After microwave-assisted acid digestion, the solutions were directly analyzed by ICP-MS, determining REEs at m/z +16. The interferences due to dioxide and un-reacted ions were carefully evaluated by taking into account the actual concentration of REEs in sediment samples. In addition, the possible interferences due to other constituents of sediments (e.g. barium) were considered. The accurate determination of Y, La, Ce, Pr, Nd, Sm, Tb, Dy, Ho, Er and Tm was achieved, as demonstrated by the analysis of both certified reference materials and Antarctic marine sediment samples, using ICP sector field mass spectrometry (ICP-SFMS) for comparison. On the other hand, Eu, Gd, Yb and Lu could not be measured by the O-atom addition approach and their separate determination in the standard mode using mathematical correction is hence necessary to obtain the complete REE pattern. The quantification limits (10 times the standard deviation of 10 procedural blanks) were at least two orders of magnitude lower than the REEs concentrations in sediment samples. Precision of the procedure ranged from 1.6% to 6.4%.

Total introduction of microsamples in inductively coupled plasma mass spectrometry by high-temperature evaporation chamber with a sheathing gas stream

A systematic study on the high-temperature Torch Integrated Sample Introduction System (TISIS) for use in Inductively Coupled Plasma Mass Spectrometry (ICP-MS) has been performed. The investigation included the optimization of the relevant parameters (chamber temperature, sheathing gas flow rate, nebulizer gas flow rate, sample uptake rate), the evaluation of its performance characteristics (sensitivity, limits of detection, stability, memory effects, use with the dynamic reaction cell) and representative applications to environmental, biological and clinical samples. Under the optimal conditions (T=150°C; nebulizer gas flow rate of 0.7Lmin(-1) along with sheathing gas flow rate of 0.35Lmin(-1) and a sample uptake rate of 20μLmin(-1)), the sensitivity was from 2 to 8 times higher than that measured using a conventional micronebulizer/mini-spray chamber system, due to the enhanced analyte mass transport toward the plasma and the solvent introduction in the vapour form. In addition, for several elements, TISIS provided lower limits of detection than the conventional system, even when the latter worked at 5-fold higher sample uptake rate. Short-term and long-term precision was better than 5%. Spectroscopic interferences arising from common matrices were efficiently removed by the dynamic reaction cell technique. The application of TISIS/ICP-MS to representative certified reference samples (spinach leaves, marine plankton, bone tissue, human blood) proved the suitability of this system for the accurate analysis of limited-size samples.

Determination of ultratrace levels of dissolved metals in seawater by reaction cell inductively coupled plasma mass spectrometry after ammonia induced magnesium hydroxide coprecipitation.

A method for the determination of ultratrace amounts of Cr, Fe, Mn, Pb and Zn in seawater has been developed. It combined the low-blank magnesium hydroxide coprecipitation procedure with quadrupole inductively coupled plasma mass spectrometry and used the dynamic reaction cell technique to resolve the polyatomic interferences arising from the residual matrix, the solvent and plasma gases. Detection limits (3σ(B), n=10) for Cr, Fe, Mn, Pb and Zn were 0.02, 0.10, 0.01, 0.002 and 0.19 nM, respectively, using 50 mL of seawater sample. The accuracy of the analytical procedure was verified by the analysis of the seawater reference materials CASS-4, NASS-5, SAFe D2 and SAFe S. The analytical precision ranged from 3% to 16% (n=6), with a sample throughput of about 6 samples h(-1).

High temperature liquid chromatography–inductively coupled plasma mass spectrometry for the determination of arsenosugars in biological samples

The potential of high temperature liquid chromatography (HTLC) with detection by inductively coupled plasma mass spectrometry (ICP-MS) for the determination of arsenosugars in marine organisms was examined for the first time. The retention behavior of four naturally occurring dimethylarsinoylribosides was studied on a graphite column using plain water as mobile phase. An aqueous solution of pH 8, ionic strength 13.8mM and containing 2% (v/v) of methanol, along with a column temperature of 120°C and a liquid flow rate of 1.0 mL/min, were selected as the optimal conditions, as they allowed the separation of the four arsenosugars in less than 18 min, without any interferences due to other common arsenic species (arsenite, arsenate, dimethylarsinate, methylarsonate and arsenobetaine). The run time could be further decreased to 12 min by working at 1.5 mL/min, although with a 3-4 times loss of sensitivity. The procedural limits of detection were 0.03-0.04 μg As/g dry mass, and the precision of the procedure ranged from 4% for arsenosugar glycerol to 18% for arsenosugar sulfate (RSD%, n=5). The developed method was applied to a number of representative biological samples, such as algae and crustaceans, providing results consistent with previous studies. In the red algae samples, the most of extracted arsenic was as arsenosugars (81-97%), mainly arsenosugar phosphate (56-94%). On the other hand, lower concentrations of these compounds were found in the crustacean, accounting for about 15% of the extracted arsenic.

Improving the analytical performances of ICP-AES by using a high-temperature single-pass spray chamber and segmented-injections micro-sample introduction for the analysis of environmental samples

A new method based on the use of a high-temperature single-pass spray chamber and the injection of a sample plug into an air carrier gas stream was developed to mitigate non-spectral interferences caused by inorganic concomitants and to reduce plasma loading in inductively coupled plasma atomic emission spectrometry (ICP-AES). The evaluated sample introduction systems were a 10 cm3 inner-volume single-pass spray chamber (also called the Torch Integrated Sample Introduction System, TISIS) with and without heating and a cinnabar spray chamber, taken as a reference device. The temperature of the spray chamber was raised up to 350 °C. Sensitivity, memory effects, limits of detection and non-spectral interferences were evaluated. The results proved that the higher the chamber walls temperature, the higher the peak height and the lower the memory effects. The single-pass spray chamber heated at 350 °C provided lower limits of detection (0.3–2.3 μg l−1) compared with the reference spray chamber (1–33 μg l−1) and a significant reduction of matrix effects. This device was successfully applied to the analysis of environmental certified reference materials, such as marine sediments and animals. The calibration curve was obtained by modifying the mass of the analyte injected, thus requiring only one standard solution. The results were also compared with those obtained by external calibration (both at room temperature and at 350 °C) and single-point standard addition. The analytical bias was lower than 5%, showing that this sample introduction system is adequate to remove the matrix effects due to inorganic concomitants, allowing the accurate analysis of environmental samples.

Influence of chemical species on the determination of arsenic using inductively coupled plasma mass spectrometry at a low liquid flow rate

The effect of common arsenic species on the ICP-MS signal working at a low liquid flow rate was investigated, taking into account the influence of the analytical concentration and of the matrix, comparing various sample introduction systems. Significant decrease (up to 65%) in the relative sensitivity of arsenite compared to arsenate was found, while methylarsonate, dimethylarsinate and arsenobetaine gave the same response (within 6%) as arsenate, throughout the 20–1000 μL min−1 liquid flow rate range. The effect was independent of the analytical concentration in the 1–100 μg L−1 range, and it was ascribed to processes related to both the sample introduction system and the ion generation and transport. Ion defocussing due to dissimilar kinetic energy of the arsenic ions generated from arsenite and arsenate was ruled out. Results obtained by various micronebulizer/spray chamber configurations showed that the temperature of the spray chamber is relevant in determining the relative responses of the arsenic species: heating the spray chamber at 60 °C caused a decrease in relative sensitivity of arsenite and dimethylarsinate compared to arsenate, while the arsenite-to-arsenate signal ratio was improved by cooling at 4 °C. The relative response of arsenite and arsenate was also significantly influenced by the presence of ammonium phosphate, which mitigated the difference between the species using conventional sample introduction devices. The influence of the chemical species on the ICP-MS signal was also investigated for species of other elements, finding significant differences in sensitivity for Hg, Se and Sn compounds when working at a low liquid flow rate. The results proved to have an effect on the accurate quantification of total concentration, as well as for arsenic speciation analysis by μHPLC/ICP-MS.

Ionomic profiling of Nicotiana langsdorffii wild-type and mutant genotypes exposed to abiotic stresses

AbstractTo provide a new insight into the response of plants to abiotic stresses, the ionomic profiles of Nicotiana langsdorffii specimens have been determined before and after exposure to toxic metals (chromium) or drought conditions. The plants were genetically transformed with the rat glucocorticoid receptor (GR) or the gene for Agrobacterium rhizogenes rolC, because these modifications are known to produce an imbalance in phytohormone equilibria and a significant change in the defence response of the plant. Elemental profiles were obtained by developing and applying analytical procedures based on inductively coupled plasma atomic emission and mass spectrometry (ICP–AES/MS). In particular, the removal of isobaric interferences affecting the determination of Cr and V by ICP–MS was accomplished by use of a dynamic reaction cell, after optimization of the relevant conditions. The combined use of ICP atomic emission and mass spectrometry enabled the determination of 29 major and trace elements (Ba, Bi, Ca, Cd, Co, Cr, Cu, Eu, Fe, Ga, K, Li, Mg, Mn, Mo, Na, P, Pb, Pt, Rb, S, Sb, Sn, Sr, Te, V, W, Y, and Zn) in different parts of the plants (roots, stems, and leaves), with high accuracy and precision. Multivariate data processing and study of element distribution patterns provided new information about the ionomic response of the target organism to chemical treatment or water stress. Genetic modification mainly affected the distribution of Bi, Cr, Mo, Na, and S, indicating that these elements were involved in biochemical processes controlled by the GR or rolC genes. Chemical stress strongly affected accumulation of several elements (Ba, Ca, Fe, Ga, K, Li, Mn, Mo, Na, P, Pb, Rb, S, Sn, Te, V, and Zn) in different ways; for Ca, Fe, K, Mn, Na, and P the effect was quite similar to that observed in other studies after treatment with other transition elements, for example Cu and Cd. The effect of water deficit was less evident, mainly consisting in a decrease of Ba, Cr, Na, and Sr in roots. FigureRoots, stems and leaves of different Nicotiana langsdorffii genotypes exposed to abiotic stresses were analysed by ICP-AES and ICP-MS, obtaining information on the distribution of 29 major and trace elements in the samples

Trace elements in surface sediments from Kongsfjorden, Svalbard: occurrence, sources and bioavailability

ABSTRACT Concentration levels, potential sources and bioavailability of trace elements in marine sediments from Kongsfjorden (Svalbard Islands, Norwegian Arctic) were assessed and discussed. Surface sediments were collected by a Ponar grab and characterised in terms of mineralogical composition, grain-size distribution, total organic carbon and nitrogen percentage contents, and major and trace elements concentrations. Anthropogenic and natural sources of trace elements were inferred from lead isotope ratios, while the potential metal bioavailability was evaluated by size-fractionation and solid-phase speciation studies and by the analysis of acid-volatile sulphides (AVS) and simultaneously extracted metals (SEM). Concentrations of metals, their enrichment factors and solid speciation patterns collectively indicated that the anthropogenic impact of trace elements in the fjord is generally low, with a minor enrichment with respect to crustal values (by a factor of 2–11) for As, Cr, Ni and V. The lead isotope ratios (208Pb/207Pb: 2.474–2.498 and 206Pb/207Pb: 1.206–1.212) were close to the natural signature except in the outer fjord, due to the influence of the Atlantic marine circulation. Many elements of toxicological concern (e.g. Pb, V, Zn) were enriched in the finest sediment fraction, which was by far the preponderant one, especially in the inner fjord. However, less than 15% of most trace elements (exceptions Cd and Mn) in the finest fraction was actually associated with easily leachable sediment phases. Finally, the high SEM/AVS ratios determined on samples from sites close to the glacier fronts (11–15), due to low AVS content, highlighted that the sediment in that zone cannot remove additional inputs of heavy metals by sulphide precipitation.