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A set of 59 ancient magical artefacts, mainly made of lead, was selected from the collections of the Staatliche Museen zu Berlin in order to unravel their origins. All the selected artefacts have been studied for their Pb isotope compositions, which covered the whole range of the Mediterranean ore deposits. However, the majority (≈86%) were made of lead matching the small compositional range of the Laurion ore deposits. Only eight out of the 59 artefacts were made of recycled lead or lead from other ore deposits.
Additionally, all but two were approximately dated based on their inscriptions. The lead isotopic composition together with information obtained from the inscriptions, the resulting dating, the context of the find and the known history of each item allowed us to gain more detailed information about the origins of these magical artefacts. The Attic provenance of 36 curse tablets was confirmed, whereas for 11 curse tablets previously classified as non-Attic, the provenance was either confirmed and specified (six artefacts) or changed to Attic (five artefacts). Surprisingly, the majority (six out of eight) of the analysed curse tablets from the Egyptian collection showed a lead isotopic composition closely matching that of Laurion.
A Laurion-like lead isotopic composition was also observed for three of the four analysed oracular tablets from Dodona. Together with the dating information, this points to Laurion as the major and dominant lead source in the Aegean, at least during the fourth–third century B.C. The few curse tablets from earlier than the fourth–third century B.C. point to the use of multiple and thus isotopically more variable lead sources compared with the Roman times.
For the first time, an international comparison was conducted on the determination of the purity of a high purity element. Participants were free to choose any analytical approach appropriate for their institute’s applications and services. The material tested was a high purity zinc, which had earlier been assessed for homogeneity and previously used in CCQM-K72 for the determination of six defined metallic impurities. Either a direct metal assay of the Zn mass fraction was undertaken by EDTA titrimetry, or an indirect approach was used wherein all impurities, or at least the major ones, were determined and their sum subtracted from ideal purity of 100 %, or 1 kg/kg. Impurity assessment techniques included glow discharge mass spectrometry, inductively coupled plasma mass spectrometry and carrier gas hot extraction/combustion analysis. Up to 91 elemental impurities covering metals, non-metals and semi-metals/metalloids were quantified. Due to the lack of internal experience or experimental capabilities, some participants contracted external laboratories for specific analytical tasks, mainly for the analysis of non-metals. The reported purity, expressed as zinc mass fraction in the high purity zinc material, showed excellent agreement for all participants, with a relative standard deviation of 0.011 %. The calculated reference value, w(Zn) = 0.999 873 kg/kg, was assigned an asymmetric combined uncertainty of + 0.000025 kg/kg and – 0.000028 kg/kg. Comparability amongst participating metrology institutes is thus demonstrated for the purity determination of high purity metals which have no particular difficulties with their decomposition / dissolution process when solution-based analytical methods are used, or which do not have specific difficulties when direct analysis approaches are used. Nevertheless, further development is required in terms of uncertainty assessment, quantification of non-metals and the determination of purity of less pure elements and/or for those elements suffering difficulties with the decomposition process.
Previously applied methods for the quantification of sulphur in copper and other pure metals revealed a lack of SI-traceability and additionally showed inconsistent results, when different methods were compared.
Therefore, a reference procedure is required which allows SI-traceable values accompanied by a Sound uncertainty budget. In this study a procedure was developed for the quantification of total sulphur in copper at low concentration levels using inductively coupled plasma-isotope dilution mass spectrometry (ICP-IDMS). The major part of the copper matrix was separated by adding ammonia which forms a complex with the copper while releasing the sulphur followed by chromatographic separation using a weak cation resin. After that the sulphur fraction was further purified by chromatographic means using first an anion exchange method and second a chelating resin. The developed procedure shows high performance, especially concerning high efficiency in matrix removal (>99.999%) while keeping the recovery of sulphur above 80%. Procedure blanks are in the order of 3–53 ng resulting in LOD and LOQ values of 0.2 mg g1 and 0.54 mg g1, respectively. The procedure is sufficient to facilitate value assignment of the total sulphur mass fraction in reference materials. Additionally, relative measurement uncertainties were calculated to be below 1% and the measurement results were traceable to the SI. The procedure reported in this study is a new reference procedure for sulphur measurement in copper, being fit for two major purposes, certification of reference materials and assignment of reference values for inter-laboratory comparison.
Boron isotope amount ratios n(10B)/n(11B) have been determined by monitoring the absorption spectrum of boron monohydride (BH) in a graphite furnace using high-resolution continuum source molecular absorption spectrometry (HR-CS-MAS). Bands (0→0) and (1→1) for the electronic transition X1Σ+ → A1Π were evaluated around wavelengths 433.1 nm and 437.1 nm respectively. Clean and free of memory effect molecular spectra of BH were recorded. In order to eliminate the memory effect of boron, a combination of 2% (v/v) hydrogen gas in argon and 1% trifluoromethane in argon, an acid solution of calcium chloride and mannitol as chemical modifiers was used. Partial least square regression (PLS) for analysis of samples and reference materials were applied. For this, a spectral library with different isotopes ratios for PLS regression was built. Results obtained around the 433.1 nm and 437.1 nm spectral regions are metrologically compatible with those reported by mass spectrometric methods. Moreover, for the evaluated region of 437 nm, an accuracy of 0.15‰ is obtained as the average deviation from the isotope reference materials. Expanded uncertainties with a coverage factor of k = 2 range between 0.15 and 0.44‰. This accuracy and precision are compatible with those obtained by mass spectrometry for boron isotope ratio measurements.
The CCQM-K123 key comparison was organized by the Inorganic Analysis Working Group (IAWG) of CCQM to assess and document the capabilities of the national metrology institutes (NMIs) or the designated institutes (DIs) to measure the mass fractions of sodium, calcium, potassium, magnesium phosphorous and sulfur in biodiesel fuel (BDF). The National Metrology Institute of Japan (NMIJ) and National Institute of Standards and Technology (NIST) acted as the coordinating laboratories.
Results were submitted by 11 NMIs and DIs. The participants used different measurement methods, though most of them used inductively coupled plasma-mass spectrometry (ICP-MS), isotope dilution technique with ICP-MS and inductively coupled plasma-optical emission spectrometry (ICP-OES) with microwave acid digestion.
The material was quite challenging and a number of questions were raised at the IAWG meeting. Concerning S, the variation in S results between participants, particularly those using IDMS methods was discussed at the IAWG meeting. BAM, NIST and NMIJ reviewed their experimental conditions, results and/or uncertainty calculations for IDMS. According to the additional evaluation and investigation, the variances between the revised results became smaller than the original one, the revised results were overlapping between IDMS measurements of S content at the k=2 level. It is not possible to calculate a KCRV with values being modified after submission. It was concluded that this KC does not support S measurements.
Accounting for relative expanded uncertainty, comparability of measurement results for each of Na, Ca, K, Mg and P was successfully demonstrated by the participating NMIs or DIs. It is expected that sodium, calcium, potassium, magnesium and phosphorus at mass fractions greater than approximately 0.1 mg/kg, 0.1 mg/kg, 0.05 mg/kg, 0.05 mg/kg and 0.1 mg/kg respectively in biodiesel fuel and similar matrices (fuels and oils etc.) can be determined by each participant using the same technique(s) employed for this key comparison to achieve similar uncertainties mentioned in the present report. Furthermore, the results of this key comparison can be utilized along with the IAWG core capability approach.
For the first time, an ab initio calibration for absolute Mg isotope ratios was carried out, without making any a priori assumptions. All quantities influencing the calibration such as the purity of the enriched isotopes or liquid and solid densities were carefully analysed and their associated uncertainties were considered. A second unique aspect was the preparation of three sets of calibration solutions, which were applied to calibrate three multicollector ICPMS instruments by quantifying the correction factors for instrumental mass discrimination. Those fully calibrated mass spectrometers were then used to determine the absolute Mg isotope ratios in three candidate European Reference Materials (ERM)-AE143, -AE144 and -AE145, with ERM-AE143 becoming the new primary isotopic reference material for absolute isotope ratio and delta measurements. The isotope amount ratios of ERM-AE143 are n(25Mg)/n(24Mg) = 0.126590(20) mol/mol and n(26Mg)/n(24Mg) = 0.139362(43) mol/mol, with the resulting isotope amount fractions of x(24Mg) = 0.789920(46) mol/mol, x(25Mg) = 0.099996(14) mol/ mol and x(26Mg) = 0.110085(28) mol/mol and an atomic weight of Ar(Mg) = 24.305017(73); all uncertainties were stated for k = 2. This isotopic composition is identical within uncertainties to those stated on the NIST SRM 980 certificate. The candidate materials ERM-AE144 and -AE145 are isotopically lighter than ERM-AE143 by 1.6 ‰ and 1.3 ‰, respectively, concerning their n(26Mg)/n(24Mg) ratio. The relative combined standard uncertainties are ≤0.1 ‰ for the isotope ratio n(25Mg)/n(24Mg) and ≤0.15 ‰ for the isotope ratio n(26Mg)/ n(24Mg). In addition to characterizing the new isotopic reference materials, it was demonstrated that commonly used fractionation laws are invalid for correcting Mg isotope ratios in multicollector ICPMS as they result in a bias which is not covered by its associated uncertainty. Depending on their type, fractionation laws create a bias up to several per mil, with the exponential law showing the smallest bias between 0.1 ‰ and 0.7 ‰.
We report an appropriate preparation of binary isotope calibration mixtures of the three stable isotopes of magnesium to be used in the ab initio calibration of multicollector mass spectrometers (ICPMS and TIMS). For each of the three possible combinations of binary mixtures ("24Mg" + "25Mg", "24Mg" + "26Mg", and "25Mg" + "26Mg"), three individual setups have been prepared under gravimetric control, each of them with an isotope ratio close to unity, and a total magnesium mass fraction close to 20 mg kg-1. The preparation was designed to occur via an intermediate dilution of a parent solution of a highly purified specimen of the isotopically enriched magnesium materials. For the application as calibration mixtures, a complete uncertainty budget was set up, and is presented and discussed in detail, including the aspects that went into the design of the dilution and mixing approach to minimize uncertainty. The principle parameters for the purpose of the later calibration of the mass spectrometers are the absolute masses of isotopically enriched magnesium materials in the primary calibration mixtures. For the first time relative expanded uncertainties U (k = 2) for these masses of ≤0.005% could be achieved for all mixtures.