J. Ignacio García Alonso

Determination of fission products and actinides in spent nuclear fuels by isotope dilution ion chromatography inductively coupled plasma mass spectrometry

An Elan 5000 inductively coupled plasma mass spectrometry (ICP-MS) instrument was modified for its installation in a glove-box for the analysis of radioactive materials. An ion chromatographic system was coupled to the ICP-MS instrument. The chromatographic pump was set outside the box while the injection valve and separation column were installed inside the box coupled directly to the cross-flow nebulizer. Performance characteristics of the modified ICP-MS system were evaluated regarding long-term stability, optimum plasma and ion lens conditions, sensitivity and detection limits, polyatomic ions, mass discrimination, detector dead time and uranium matrix interferences. Chromatographic methods were developed for the separation of fission Cs from Ba, for the lanthanide elements (La to Gd) and for the actinides (U to Cm) in order to eliminate isobaric interferences. Isotope dilution analysis was applied for the determination of selected fission products and actinides in spent nuclear fuels after ion chromatographic separation.

Calcification rate and temperature effects on Sr partitioning in coccoliths of multiple species of coccolithophorids in culture

Five common placolith-bearing coccolithophorid algae—Gephyrocapsa oceanica, Coccolithus pelagicus, Calcidiscus leptoporus, Umbilicosphaera sibogae (var. sibogae and var. foliosa), and Emiliania huxleyi—were cultured to investigate controls on Sr partitioning in coccolith calcite. For identical temperature and media composition, Sr partitioning varies by more than 30% in exponential phase cultures of the five species and is linearly related to rates of calcite production/cell (ρ=0.91). Exponential phase culture experiments with three strains of C. leptoporus and six strains of G. oceanica at varying temperatures show variations in Sr partitioning of 20% and 30%, respectively. With C. leptoporus, Sr partitioning is equally correlated with temperature and calcification rate (ρ=0.8), which themselves are highly correlated; the slope of the relationship between DSr and calcification rate is comparable to that observed in all species at constant temperature. However, in G. oceanica, increased temperature appears to enhance Sr incorporation by up to 2% to 1.6% °C−1 in the range of 15 to 30 °C. The strong influence of calcification rate on Sr partitioning may be useful for inferring past variations in coccolithophorid productivity from Sr partitioning in coccolith sediments if the influence of temperature on Sr partitioning can be resolved. Because the relationship between calcite production and Sr partitioning is linear, a proportional change in calcification should be expressed much more strongly in the Sr/Ca ratio of large species with rapid calcite production than in smaller species, which produce calcite more slowly. Consequently, it may be possible to separate temperature and calcification influences on coccolith Sr/Ca by separately analyzing Sr/Ca in species that produce calcite rapidly and those that produce calcite slowly, if both undergo comparable relative changes in calcification rates.

A comparison between quadrupole, double focusingand multicollector ICP-MS instruments

A quadrupole-based instrument (HP-4500), a double focusing single collector instrument (Element) and a single focusing multicollector (IsoProbe) were all evaluated for the precise and accurate measurement of lead isotope ratios using Tl as internal isotope ratio standard. The isotope ratio accuracy was evaluated using NIST 981 Common Lead Isotope standard reference material and an enriched 204Pb spike. Mass bias correction was performed using an exponential model in all the three instruments and equations for the evaluation of the total combined uncertainty arising from the correction for the dead time and mass bias were developed. It was observed that, in the correction for mass bias, the uncertainty in the natural Tl ratio was the main source of uncertainty for the multicollector instrument while, for the quadrupole and double focusing single collector instruments, the measured isotope ratio was the main source of uncertainty.

An alternative GC-ICP-MS interface design for trace element speciation

The design, construction and performance characteristics of an easily removable interface to couple a gas chromatograph (GC) to an inductively coupled plasma mass spectrometer (ICP-MS) for trace element speciation is described. The interface is based on the use of a heated metallic tube where the last part of the capillary GC column is inserted. This metallic tube is connected to a metallic T-piece where a flow of argon carrier gas is introduced perpendicularly and externally to the metallic tube, creating a high velocity flow of intermediate sheath gas, which prevents condensation of the analytes eluting from the column on the walls of the T-piece or on the connection tubing to the ICP-MS torch. A flexible non-heated PTFE tube is used to connect the exit of the T-piece to the ICP-MS torch. This new interface has been applied to the separation and detection of different organometallic compounds of Se, S, Pb, Hg and Sn.

Multi-elemental trace analysis of human serum by double-focusing ICP-MS

A method is described for the determination of a selected range of trace and ultratrace elements in human serum, using a double-focusing ICP-MS instrument (ELEMENT, Finnigan-MAT). Serum samples were diluted 1+4 with ultrapure water and addition of Sc, Ga, Y and Tl as internal standards, to a final concentration of 10 µg L –1 , was used for matrix interference correction. Low and medium resolution scans were performed on the instrument for the analyses, the first scan, at m/Δm=300, for the determination of Rb, Sr, Mo, Cd, Pb and U and the second scan, at m/Δm=3000, for the determination of those elements subject to interference at low resolution: Al, Ca, Cr, Mn, Fe, Co, Cu, Zn and Se. A SRM, 1598 Inorganic Constituents in Bovine Serum (NIST), was analysed for validation of the multi-element analysis method. Good agreement was achieved between the found levels and the certified values. The method was also applied to the multi-analysis of trace elements in serum samples from healthy subjects and from uraemic patients. Preliminary experiments carried out with both quadrupole and double-focusing ICP-MS instruments proved to be invaluable for the study of spectral and non-spectral interferences in ICP-MS detection.

Accurate determination of iron, copper and zinc in human serum by isotope dilution analysis using double focusing ICP-MS

The development of an ICP-MS method for the determination of three essential trace elements, Fe, Cu and Zn, in human serum by isotope dilution analysis is described. A double focusing ICP mass spectrometer (ELEMENT) working at a nominal resolution of 3000 allowed the complete resolution of polyatomic ions overlapping the main isotopes of these elements. The isotope ratios measured for the determination of Fe, Cu and Zn were 57 Fe/ 56 Fe, 65 Cu/ 63 Cu and 67 Zn/ 64 Zn, respectively. Instrumental parameters of the mass spectrometer were optimised for optimum precision, while keeping the total time of analysis under 6 min (2 min per element). The RSD values obtained for the isotope ratios of Fe (57/56), Cu (65/63) and Zn (67/64) were 0.7, 0.2 and 0.8%, respectively, for a natural standard aqueous solution of 50 µg l –1 . The measured isotope ratios were corrected for dead time on the detector and mass discrimination errors. The sample to spike ratio was optimised to minimise the relative error on the isotope ratio measurement. Serum samples were diluted 1+19 with ultrapure water after the addition of the 57 Fe, 65 Cu and 67 Zn spikes. The proposed method was validated by the analysis of NIST SRM 1598 Inorganic Constituents in Bovine Serum, the levels found being in agreement with the certified values. Finally, the method was applied to the analysis of 21 serum samples from healthy blood donors.

Development of a triple spike methodology for validation of butyltin compounds speciation analysis by isotope dilution mass spectrometry

The triple spike GC-ICP-MS methodology developed in Part 1 of this paper has been applied here to study and validate different extraction procedures previously reported in the analytical literature for speciation analysis of biological materials in the determination of butyltin compounds. Microwave assisted extraction, mechanical shaking, alkaline hydrolysis with tetramethylammonium hydroxide (TMAH) and enzymatic digestion have been evaluated under different conditions for the determination of these species in mussel tissue CRM-477. The results obtained showed extensive degradation of the species using alkaline hydrolysis with TMAH and also a lack of isotope equilibration when using enzymatic digestion. The use of microwave assisted extraction with methanol–acetic acid showed the best results in terms of low degradation, rapid isotope equilibration and quantitative recoveries. Quantitative extraction was also obtained, however, by mechanical shaking at 37 °C using methanol–acetic acid as extractant, with no degradation of the species. The developed triple spike methodology was able to correct for as much as 50% degradation of DBT to form MBT during sample pre-treatment. Moreover, isotope equilibration studies performed using different extraction procedures have shown that the required complete isotope equilibration is achieved only after the naturally occurring organotin compounds are completely released to the solution from the solid matrix.

Determination of cadmium in environmental and biological reference materials using isotope dilution analysis with a double focusing ICP-MS: a comparison with quadrupole ICP-MS

A detailed examination of the performance of a double focusing (DF) sector field ICP-MS (Element, Finnigan MAT) for the ID-ICP-MS determination of cadmium in biological and environmental samples is described and compared with a quadrupole-based instrument (HP4500, Hewlett Packard). Experimental parameters governing the instrumental precision and accuracy for isotope ratio measurements of cadmium in the DF-ICP-MS are first characterized. Systematic errors, including dead time, mass bias effects and spectroscopic interferences, can be easily corrected in the two instruments studied. Detector dead time has only to be taken into account using the DF-ICP-MS. Typical isotope ratio precisions of 0.2-0.3% can be obtained routinely with both instruments. However, the precision of the measurements in the DF-ICP-MS can be improved (<0.1%) by increasing the number of scans. Moreover, for very low cadmium concentrations the DF-ICP-MS at low resolution setting (R=300) can provide better isotope ratio precision than the quadrupole ICP-MS because of its higher sensitivity. Both ICP-MS instruments were successfully applied to the determination of very low levels of cadmium by ID-ICP-MS (by both conventional and on-line ID modes) in biological and environmental certified reference materials, including Freeze-Dried Urine NIST SRM-2670, Horse Kidney IAEA H-8, Lichens BCR TP-25, Marine Sediment PACS-1 and Riverine Water SLRS-3. Combined uncertainty associated with the determinations is addressed.

Recent advances in isotope dilution analysis for elemental speciation

Following the concepts and applications included in our tutorial review published in 2005, this review presents and critically discusses new concepts, methodologies and trends that have appeared during the last five years of scientific development in the field of isotope dilution analysis for elemental speciation. Although general concepts have been detailed previously in several high quality reviews, we will highlight selected applications that, in our opinion, have significantly contributed to the improvement of the state of the art in this field. Methodological advances, such as the irruption of the Isotope Pattern Deconvolution theory, are commented in detail. Important metrological achievements, such as the organisation of international comparisons by the Comite consultatif pour la quantite de matiere (CCQM) or the certification of new reference materials using Isotope Dilution Analysis are also included. Particular attention has been paid to the developments in the field of bioanalytical chemistry. The application of enriched stable isotopes in metallomics, clinical chemistry and quantitative proteomics are covered in this review. Also, metabolic applications of enriched isotopes are included when speciation work is carried out. Finally, future trends are identified together with the extension of concepts and applications typical of elemental speciation to other scientific fields.

Single and multiple spike procedures for the determination of butyltin compounds in sediments using isotope dilution GC-ICP-MS

The combined use of single and multiple spike solutions for the determination of butyltin compounds in sediments by species-specific isotope dilution mass spectrometry has been evaluated in this work in order to validate an analytical procedure proposed for routine determinations. For this purpose, a test sediment sample was analysed during the course of an intercomparison exercise using both a single isotope spike solution (a mixture of mono-, di- and tributyltin enriched in 119Sn) and a triple spike solution containing each butyltin species enriched with a different tin isotope. The triple spike methodology (able to correct for interconversion reactions) was employed for the optimisation of the microwave assisted extraction procedure that was subsequently applied for the analysis of the test sediment. The determination of butyltin compounds in the test sediment was performed using both spike solutions under the same extraction conditions. An excellent agreement between the results obtained using both approaches and those provided by all laboratories participating in the intercomparison exercise was obtained, validating in this way the methodologies employed in this work. Uncertainty budgets were calculated for both spiking methodologies. The complexity of the triple spike methodology, in which the simultaneous measurement of nine tin isotope ratios must be carried out, provided additional sources of error in obtaining degradation-corrected concentrations of the three butyltin species. Additionally, uncertainty budgets were obtained also for the calculation of degradation factors F1 (degradation of TBT to DBT) and F2 (degradation of DBT to MBT). The results demonstrated that their uncertainty was independent of the uncertainty of the measurement of the concentration of the butyltin species, both in the spike solution and in the sample, when using a multiple spiking approach, and depended only on the measured isotope ratios and on the uncertainty in the isotopic composition of the spike.