Determination Of Sr Isotope Ratios Research Articles

An improved separation scheme for Sr through fluoride coprecipitation combined with a cation-exchange resin from geological samples with high Rb/Sr ratios for high-precision determination of Sr isotope ratios

A new separation method for Sr involving HF coprecipitation combined with AG50 resin from samples with high Rb/Sr ratios.

Strontium carbonate precipitation as a sample preparation technique for isotope ratio analysis of Sr in mineral water and wine by quadrupole-based inductively coupled plasma mass spectrometry.

The defined origin of food products is nowadays often seen as a marker of quality. Stontium (Sr) isotope ratio determination can be used to verify the origin of such food products and it has thus become an important technique. Wine samples in particular are often investigated using this technique. Sr isotopic ratio measurements are often disturbed by isobaric Rb interference, making a separation procedure necessary. In this investigation a very simple and effective procedure for the separation of Rb+ and Sr2+ ions for Sr isotope ratio determination in mineral water and wine samples was developed. The classical Sr-carbonate precipitation reaction for the separation of Sr2+ ions from highly soluble Rb+ ions was used. For liquid samples, such as mineral water or wine, a prior digestion is not required. This sample preparation procedure was successfully applied for Sr isotope measurements on a widely available quadrupole-based inductively coupled plasma mass spectrometry (ICP-MS) device in combination with the Concentration-Gradient-Method (CGM). The separation achieved Sr/Rb concentration ratios of 50,000 to 150,000 in water and wine samples. The addition of Ca2+ ions to co-precipitate with the traces of Sr improved the Rb separation and the reproducibility of isotope ratio determination to an uncertainty of ±0.4 ‰ (single standard deviation). This sample preparation approach achieved 2 to 6 times better Rb separation than the commonly applied ion-exchange resin materials. The quality of the separation is only limited by the number of precipitation repetitions. Moreover, the applicability of quadrupole-based ICP-MS for the characterisation of samples with respect to their origin by means of Sr isotope ratio determination was demonstrated.

Calcium Carbonate and Phosphate Reference Materials for Monitoring Bulk and Microanalytical Determination of Sr Isotopes

In situ laser ablation analyses rely on the microanalytical homogeneity of reference materials (RMs) and a similar matrix and mass fraction between unknown samples and RMs to obtain reliable results. Suitable carbonate and phosphate RMs for determination of Sr isotope ratios in such materials are limited. Thus, we determined 87Sr/86Sr ratios of several carbonate (JCt‐1, JCp‐1, MACS‐1, MACS‐3) and phosphate (MAPS‐4, MAPS‐5, NIST SRM 1400, NIST SRM 1486) international RMs using dissolved samples and two different multi‐collector inductively coupled plasma‐mass spectrometers (MC‐ICP‐MS). Our Sr isotope data are in agreement with published data and have an improved measurement precision for some RMs. For MACS‐1, we present the first 87Sr/86Sr value. We tested the suitability of these materials for microanalytical analyses by LA‐MC‐ICP‐MS, with two different laser ablation systems: a conventional nanosecond laser and a state‐of‐the‐art femtosecond laser. We investigated the RMs micro‐homogeneity and compared the data with our solution data. Both laser ablation systems yielded identical 87Sr/86Sr ratios within uncertainty to the solution data for RMs with low interferences of REEs. Therefore, these carbonate and phosphate RMs can be used to achieve accurate and precise results for in situ Sr isotope investigations by LA‐MC‐ICP‐MS of similar materials.

Wine fingerprinting using a bio-geochemical approach

The wine sector is a billion euro business and therefore subjected to multiple attempts of fraudulent practices. This requires the development of rapid and reliable methods to detect such situations. Several methodologies have been developed based on the chemical profiles of the wines, but they are limited due to the environmental conditions that cannot be controlled. The use of DNA-based detection systems are an emergent research field that have been extended to a wide variety of food prod- ucts and are still the most reliable methods for varietal identification. However these methods are not suitable for geographical determination. Soil related fingerprints have a primary role considering that there is a relationship between the elemental compo- sition of wine and the composition of the provenance soil. WineBioCode is a project aiming to define the best strategy for wine authenticity based on a multidisciplinary approach. Two DNA-based strategies have been developed based on Real-time PCR and a label free optical biosensor platform. Both platforms enabled successful identification of specific DNA-targets when applied to Vitis vinifera L., and can be applied throughout the grape-wine chain. The methods are complementary and can be used in dif- ferent situations, according to the requirements. The geographical evaluation has been assessed by the strontium 87 Sr/86 Sr isotope ratio determination involving soil evaluation in the vineyards followed by its assay in the wine samples. The results are being integrated in order to establish the best procedure to be undertaken for wine fingerprinting, including varietal composition and geographical origin, therefore fulfilling the requirements of the geographical denominations in wine certification.

An analytical approach to Sr isotope ratio determination in Lambrusco wines for geographical traceability purposes

Geographical origin and authenticity of food are topics of interest for both consumers and producers. Among the different indicators used for traceability studies, 87Sr/86Sr isotopic ratio has provided excellent results. In this study, two analytical approaches for wine sample pre-treatment, microwave and low temperature mineralisation, were investigated to develop accurate and precise analytical method for 87Sr/86Sr determination. The two procedures led to comparable results (paired t-test, with t<tcrit). Furthermore, the precision of the whole analytical procedure was evaluated by using a control sample (wine sample), processed during each sample batch (calculated Relative Standard Deviation, RSD%, equal to 0.002%. Lambrusco PDO (Protected Designation of Origin) wines coming from four different vintages (2009, 2010, 2011 and 2012) were pre-treated according to the best procedure and their isotopic values were compared with isotopic data coming from (i) soils of their territory of origin and (ii) wines obtained by same grape varieties cultivated in different districts. The obtained results have shown no significant variability among the different vintages of wines and a perfect agreement between the isotopic range of the soils and wines has been observed. Nevertheless, the investigated indicator was not enough powerful to discriminate between similar products. To this regard, it is worth to note that more soil samples as well as wines coming from different districts will be considered to obtain more trustworthy results.

785 nm femtosecond laser ablation for improved precision and reduction of interferences in Sr isotope analyses using MC-ICP-MS

The femtosecond (fs) laser ablation (LA) MC-ICP-MS Sr isotope analysis of calcium-rich materials is reported. Independent Sr isotope ratio determination using solution nebulization (SN) MC-ICP-MS after chromatographic separation of Sr was also conducted. Material studied includes a marine carbonate saggital otolith certified (for trace metals) reference material FEBS-1, and igneous fluorite. Analyses of the FEBS-1 using LA analyses at repetition rates of 5 to 200 Hz with energies from 0.1 to 0.6 mJ pulse−1 and SN analyses demonstrate that fs LA Sr isotope analysis produced similar within-run precision to the SN Sr isotope analysis when the same total number of ions was collected in an analysis. The results demonstrate that the precision for fs LA Sr isotope analyses is more controlled by Poisson counting statistics than for nanosecond (ns) LA analyses, and improvements (≥ 2 fold) in external precision, within-run precision, and accuracy can be obtained in comparison with reported ns LA-based results. Good external precision (1SD, n = 17) ± 0.000007, good within-run precision (1SE) ± 0.000010, as well as good accuracy (0.000006) determinations of Sr isotope ratios in carbonate materials can be obtained in situ with a spatial resolution of 60 to 90 μm when using a Faraday detector signal intensity at mass 88 of greater than 10 V and a total integration time of 151 s. In this contribution, it is further shown that an accurate 84Sr/86Sr ratio of 0.056560 ± 0.000015 to 0.056525 ± 0.000007 can be measured in fs LA Sr isotope analysis of FEBS-1. Previously reported Ca argide and Ca dimer polyatomic ion interferences were not observed to be significant in this study. In addition, this study reports the criteria necessary for effective interference corrections from doubly-charged ions of Er and Yb in LA Sr isotope analysis of fluorite samples, which have Sr concentrations > 650 ppm, and a rare-earth element (REE) Er/Sr or Yb/Sr concentration ratio of less than 0.01.

Precise determination of Sr isotope ratios in igneous rock samples and application to micro-analysis of plagioclase phenocrysts

A two-step chemical procedure to separate Sr from whole igneous rock sample has been developed for the analysis of Sr isotopes by thermal ionization mass spectrometry (TIMS). Firstly, a Sr-bearing fraction and a REE fraction are separated from the major elements of a decomposed sample solution using H+ form cation-exchange chromatography. Then the Sr fraction is purified in a second column using extraction chromatography and a Sr specific resin. For small amounts of sample (< 0.1 mg) obtained by micro-milling, only the second step of column separation is applied, directly separating the Sr fraction from the decomposed sample solution. The total procedural blank of these chemical separation procedures are very low, comparable to the lowest blank levels ever reported. The purified Sr is loaded on to a single Re-filament with a Ta ionization activator and measured using TIMS in static multi-collection mode. The mean value and reproducibility for standard 87Sr/86Sr in NIST SRM 987 with Sr loads of 100 ng and 5 ng are 0.710240 ± 0.000012(2σ, n = 12) and 0.710248 ± 0.000022 (2σ, n = 7), respectively. These values agree well with those from previous studies. Additionally, Sr isotope ratios measured in GSJ igneous rock reference materials JB-2, JA-1 and JR-1 are within error of values from previous studies, verifying the versatility of the technique reported in this study.

Automation and miniaturization of an on-line flow injection Sr/matrix separation method for accurate, high throughput determination of Sr isotope ratios by MC-ICP-MS

In this work we present a fully automated Sr/matrix separation method, based on flow injection (FI) hyphenated to a multiple collector-inductively coupled plasma-mass spectrometer (MC-ICP-MS). Our method compares favourably to the common, manual, batch Sr/matrix separation procedure, with respect to labour and reagent investment. We validated the system analyzing NIST SRM 987 Sr isotope reference material and digests of Asparagus officinalis at Sr concentrations of approximately 30–40 ng g−1 total Sr using separation columns containing approximately 40 μL of Sr specific resin. 33 consecutive runs of the NIST SRM 987 Sr isotope reference material could be repeated with 0.03% (2 RSD), yielding an average 87Sr/86Sr isotope ratio of 0.71030 which is well within the certified range. 5 Hungarian and 5 Austrian samples were determined to have 87Sr/86Sr isotope ratios ranging from 0.70504–0.70746 and 0.70884–0.70923 respectively. 87Sr/86Sr isotope ratios of single elutions could be measured with typical precisions of 0.02–0.1% (2 RSD) depending on signal intensities. 6 successive measurements could be repeated with 0.006–0.04% (2 RSD). Results presented in this work are in agreement with results previously obtained via off-line Sr/matrix separation and subsequent measurement of 87Sr/86Sr isotope ratios by MC-ICP-MS. We were able to use a single 40 μL column for Sr/matrix separation of 66 samples.

Development of an On-Line Flow Injection Sr/Matrix Separation Method for Accurate, High-Throughput Determination of Sr Isotope Ratios by Multiple Collector-Inductively Coupled Plasma-Mass Spectrometry

This work introduces a newly developed on-line flow injection (FI) Sr/Rb separation method as an alternative to the common, manual Sr/matrix batch separation procedure, since total analysis time is often limited by sample preparation despite the fast rate of data acquisition possible by inductively coupled plasma-mass spectrometers (ICPMS). Separation columns containing approximately 100 muL of Sr-specific resin were used for on-line FI Sr/matrix separation with subsequent determination of (87)Sr/(86)Sr isotope ratios by multiple collector ICPMS. The occurrence of memory effects exhibited by the Sr-specific resin, a major restriction to the repetitive use of this costly material, could successfully be overcome. The method was fully validated by means of certified reference materials. A set of two biological and six geological Sr- and Rb-bearing samples was successfully characterized for its (87)Sr/(86)Sr isotope ratios with precisions of 0.01-0.04% 2 RSD (n = 5-10). Based on our measurements we suggest (87)Sr/(86)Sr isotope ratios of 0.713 15 +/- 0.000 16 (2 SD) and 0.709 31 +/- 0.000 06 (2 SD) for the NIST SRM 1400 bone ash and the NIST SRM 1486 bone meal, respectively. Measured (87)Sr/(86)Sr isotope ratios for five basalt samples are in excellent agreement with published data with deviations from the published value ranging from 0 to 0.03%. A mica sample with a Rb/Sr ratio of approximately 1 was successfully characterized for its (87)Sr/(86)Sr isotope signature to be 0.718 24 +/- 0.000 29 (2 SD) by the proposed method. Synthetic samples with Rb/Sr ratios of up to 10/1 could successfully be measured without significant interferences on mass 87, which would otherwise bias the accuracy and uncertainty of the obtained data.