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Organisationseinheit der BAM
Isotope reference materials are essential to enable reliable and comparable isotope data. This article reviews the work in this field within the past years. The focus is on all stable elements, except for classical stable isotopes (H, C, N, O, S) and for radioactive elements. Currently available isotope reference materials are listed. The limitations of synthetic isotope mixtures being used to characterize these materials are discussed, as well as the limitations of the isotope reference materials, such as uncertainty and homogeneity. The needs for present research on isotope variations are being considered and are compared to the limitations of current isotope reference materials. This disagreement between both can only be solved by providing isotope reference materials defining a δ-scale for each element of interest. Such materials should be provided with additional data on isotope abundances whenever possible. As an outlook a possible outline for a new program on isotope reference materials is discussed.
In this study, an analytical procedure for multi-element screening of 40 elements in milk and feed samples was developed. Three different digestion and two different calibration methods were tested for the best suitability. The analytical procedure for the quantification of minor and trace elements is based on sector field ICP-MS (SF-ICP-MS). The method validation revealed good agreement between the determined elemental mass fractions and the certified values of two milk and three feed reference materials. Milk samples of dairy cows at different feeding regimes were collected from two different farms. The results of our study showed significant differences of nine elemental mass fractions (Li, P, Mn, Co, Cu, Rb, Sr, Br, I) between milk from the two locations. Further, a correlation between the elemental mass fractions of milk and the ingested feed and water was observed.
The quantitative analysis of toxic metals in plastics is very important for different sectors of industry and daily life. Many routine procedures have been established based on X-ray fluorescence or inductively coupled plasma atomic emission spectrometry. However, all of them require suitable reference materials to calibrate or validate. These reference materials ideally are being certified by reference procedures. The development of such reference procedures for sulfur and the four toxic elements cadmium, chromium, mercury and lead in plastics is described here. The procedures are based on double isotope dilution mass spectrometry including analyte–matrix separation. The applied mass spectrometric techniques are thermal ionization mass spectrometry as well as inductively coupled plasma mass spectrometry. Memory effects of mercury and dissolution of chromium(III) oxide have been considered especially. The expanded uncertainties have been improved from the percent range down to the per mill range during the development of the procedure from the early analysis of BCR-680/681 to the recent analysis of CCQM-P106. With the fully developed procedures expanded uncertainties (k = 2) between 0.1 and 0.4% for cadmium, chromium, lead and sulfur and around 1% for mercury can be achieved. The so developed procedures have been successfully applied to the certification of reference materials as well as to intercomparisons organized by CCQM.
Boron isotope studies on technical materials and geological and environmental samples are one hot topic in nowadays isotope research. Provenance studies of artefacts, food and other products might become another one, as several recent studies demonstrate. Typically boron isotope determinations have been carried out by TIMS. To open up this research field to a broader scientific community we developed two analytical procedures for boron isotope determinations based on single collector SF-ICPMS combined with a sample preparation procedure consisting of dry-ashing and a three step ion chromatographic boron-matrix separation. The developed procedures consist of one low resolution (LR) and one medium resolution (MR) procedure. The repeatability for the δ11B determination in three independently measured aliquots lies between 0.2 and 0.8‰ for the LR procedure and between 0.3 and 1.5‰ for the MR procedure. The expanded uncertainties with a coverage factor of k=2 range between 1.4 and 1.6‰ for the LR procedure and between 2.9 and 3.2‰ for the MR procedure. The accuracy, expressed as average deviation from the reference values, is 0.43‰ for the LR procedure and 0.33‰ for the MR procedure. To test the practicability of the procedures the matrix tolerance has been investigated as well and was found to be up to 2 mg kg-1 of alkaline and alkaline earth elements in the final measurement solution containing 100 µg kg-1 boron. Thus a highly efficient matrix separation for SF-ICPMS boron isotope determinations is required, similar to TIMS.
Development and validation of a method to determine the boron isotopic composition of crop plants
(2011)
We present a comprehensive chemical and mass spectrometric method to determine boron isotopic compositions of plant tissue. The method including dry ashing, a three-step ion chromatographic boron–matrix separation, and 11B/10B isotope ratio determinations using the Cs2BO2+ graphite technique has been validated using certified reference and quality control materials. The developed method is capable to determine δ11B values in plant tissue down to boron concentrations of 1 mg/kg with an expanded uncertainty of ≤1.7‰ (k = 2). The determined δ11B values reveal an enormous isotopic range of boron in plant tissues covering three-quarters of the natural terrestrial occurring variation in the boron isotopic composition. As the local environment and anthropogenic activity mainly control the boron intake of plants, the boron isotopic composition of plants can be used for food provenance studies.
The encyclopedia of mass spectrometry, Volume 5: Elemental and isotope ratio mass spectrometry covers the subject almost entirely and serves as a reference work with links to specialist literature if more details are required.
Therefore, this book can be recommended to all beginners, students, and experts working in this broad field.