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The present paper describes the contribution of the Institute for Reference Materials and Measurements to the certification of B, Cd, Mg, Pb, Rb, Sr, and U amount contents in a natural water sample, in round 9 of the International Measurement Evaluation Programme (IMEP-9). The analytical procedure to establish the reference values for B, Cd, Mg, Pb, Rb, Sr, and U amount contents was based on isotope dilution inductively coupled plasma-mass spectrometry used as a primary method of measurement. Applying this procedure reference values, traceable to the SI, were obtained for the natural water sample of IMEP-9. For each of the certified amount contents presented here a total uncertainty budget was calculated using the method of propagation of uncertainties according to ISO and EURACHEM guidelines. The measurement procedures, as well as the uncertainty calculations are described for all seven elements mentioned above. In order to keep the whole certification process transparent and so traceable, the preparations of various reagents and materials as well as the sample treatment and blending, the measurements themselves, and finally the data treatment are described in detail. Explanations focus on Pb as a representative example. The total uncertainties (relative) obtained were less than 2% for all investigated elements at amount contents in the pmol/kg up to the high 7mol/kg range, corresponding to low 7g/kg and mg/kg levels.
The present paper describes the certification of the amount content of Cd, Cr and Pb in two different polyethylene materials within the third phase of the Polyethylene Elemental Reference Material (PERM) project. The analytical procedure to establish the reference values for Cd, Cr and Pb amount contents in these materials is based on isotope dilution mass spectrometry used as a primary method of measurement. Cd and Pb were measured with inductively coupled plasma-mass spectrometry and Cr with positive thermal ionization-mass spectrometry. The decomposition of the polymer matrix was carried out using a high pressure asher. Reference values for amount content, traceable to the SI-system, have been obtained for these three elements in both of the polyethylene samples of PERM. For each of the certified amount content values an uncertainty budget was calculated using the method of propagation of uncertainties according to ISO and EURACHEM guidelines. The measurement procedures, as well as the uncertainty calculations, are described for all three elements. In order to keep the whole certification process as transparent as possible, the preparations of various reagents and materials as well as the sample treatment and blending are described in detail. The mass spectrometry measurements and the data treatment are also explained carefully. The various sources of uncertainty present in the procedure are displayed in the uncertainty budgets. The obtained combined uncertainties for the amount content values were less than 2% relative (k=1) for all investigated elements. The amount contents were in the ?mol/kg range, corresponding to mg/kg levels.
A comparison of different isotope dilution mass spectrometric (IDMS) procedures using inductively coupled plasma mass spectrometry (ICPMS) and thermal ionization mass spectrometry (TIMS) was carried out to examine the degree of equivalence between the used procedures in terms of requirements for reference material certification. The comparison was based on the measurement results and their uncertainties. The sample used in this study is a pure zinc metal to be certified by the Bureau Communie de Référence (BCR) for amount contents of different trace elements. This study focuses on cadmium and thallium. The TIMS values contributed to the certified values. To guarantee identical conditions as far as possible for the procedures under investigation, the samples were split into subsamples after spiking and digestion took place. Thus, every IDMS procedure started with an identical set of samples. In total, four different IDMS procedures and one external calibration procedure using internal standardization as an example of routine analysis were applied. The IDMS procedures divide in a group with and a group without trace/matrix separation. Multicollector TIMS (TI-MC-MS) and multicollector ICPMS (ICP-MC-MS) were used in combination with trace/matrix separation, whereas quadrupole ICPMS (ICP-QMS) and ICP-MC-MS were also applied to nonseparated samples. All IDMS results agree well within their combined uncertainties, while some results from the external calibration procedure do not. IDMS results obtained by ICPMS without separation are comparable to those obtained by TI-MC-MS with separation regarding precision and accuracy. The smallest uncertainties were achieved using ICP-MC-MS in combination with trace/matrix separation.
The development and implementation of a method for the certification of cadmium in blood samples at low ng g-1 and sub ng g-1 levels is described. The analytical procedure is based on inductively coupled plasma isotope dilution mass spectrometry (ICP-IDMS) applied as a primary method of measurement. Two different sample digestion methods, an optimized microwave digestion procedure using HNO3 and H2O2 as oxidizing agents and a high-pressure asher digestion procedure, were developed and compared. The very high salt content of the digests and the high molybdenum content, which can cause oxide-based interferences with the Cd isotopes, were reduced by a chromatographic matrix separation step using an anion-exchange resin. All isotope ratio measurements were performed by a quadrupole ICP-MS equipped with an ultrasonic nebulizer with membrane desolvator. This sample introduction set-up was used to increase sensitivity and minimize the formation of oxides (less MoO+ interference with the Cd isotopes).
Because of the very low Cd concentrations in the samples and the resulting need to minimize the procedural blank as much as possible, all sample-processing steps were performed in a clean room environment. Detection limits of 0.005 ng g-1 Cd were achieved using sample weights of 2.7 g. The method described was used to re-certify the cadmium content of three different blood reference materials from the Community Bureau of Reference (BCR) of the European Commission (BCR-194, BCR-195, BCR-196). Cadmium concentrations ranged between ~0.2 ng g-1 and ~12 ng g-1. For these materials, SI-traceable certified values including total uncertainty budgets according to ISO and Eurachem guidelines were established.
A thin-layer reference material for surface and near-surface analytical methods was produced and certified. The surface density of the implanted Sb layer was determined by Rutherford backscattering spectrometry (RBS), instrumental neutron activation analysis (INAA), and inductively coupled plasma isotope dilution mass spectrometry (ICP-IDMS) equipped with a multi-collector. The isotopic abundances of Sb (121Sb and 123Sb) were determined by multi-collector ICP-MS and INAA. ICP-IDMS measurements are discussed in detail in this paper. All methods produced values traceable to the SI and are accompanied by a complete uncertainty budget. The homogeneity of the material was measured with RBS. From these measurements the standard uncertainty due to possible inhomogeneities was estimated to be less than 0.78% for fractions of the area increments down to 0.75 mm2 in size. Excellent agreement between the results of the three different methods was found. For the surface density of implanted Sb atoms the unweighted mean value of the means of four data sets is 4.8121016 cm-2 with an expanded uncertainty (coverage factor k=2) of 0.0921016 cm-2. For the isotope amount ratio R (121Sb/123Sb) the unweighted mean value of the means of two data sets is 1.435 with an expanded uncertainty (coverage factor k=2) of 0.006.
The ?- branching ratio of 64Cu was determined by investigating the resulting decay products in copper doped by neutron transmutation. The numbers of 64Zn and 64Ni atoms were analyzed using isotope dilution analysis combined with thermal ionization mass spectrometry. A ?- branching ratio of (38.06±0.30)% was obtained, which agrees with the study of Kawada (Appl. Radiat. Isot. 37 (1) (1986) 7) to a higher accuracy. However, our result differs from the value cited in the NUDAT database of (39.0±0.3)%.
An ICP-MS equipped with collision cell, sector field and multi-collector technology has been applied to developing analytical procedures for Fe in terms of isotope ratio measurements and isotope dilution analysis. Therefore a detailed study on the reduction of molecular interferences by a variety of collision gases (He, Ar, Kr, H2, D2 and N2) was performed. The efficiency of the reduction has been checked by high resolution mass scans. The argon based interferences disturbing the determination of 54Fe and 56Fe could be completely removed when using Faraday detectors. The interferences on mass 57 could be reduced to a level which enables accurate measurements. Also, the 40Ar12C interference, which disturbs the chromium correction, could be completely removed. Reproducibilities of 0.01% could be reached for 54Fe/56Fe isotope ratios and 0.02% for 57Fe/56Fe isotope ratios. Under these measurement conditions a sensitivity of 1.2 V per 50 µg kg1 Fe is available. This corresponds to 1.5 × 109 cps per mg kg1. Based on these results highly accurate procedures for Fe isotope ratio determinations were set up, reaching a performance level superior to that of other ICP-MS instruments. Consequently, IDMS procedures were developed on this basis in order to perform certification measurements at the highest metrological level. The first application was the contribution to the Fe reference value by IMEP-12, an interlaboratory comparison with approximately 350 participants worldwide. The analysed Fe mass content is 0.2150 mg kg1 with its expanded uncertainty (k= 2) of 0.0012 mg kg1(0.56%), which is ten times less than the uncertainty of the second certification laboratory. Another application was the certification campaign of the two reference materials Tea Leaves and Polish Herbs. The results obtained with the ICP-MS procedure, 542 ± 11 mg kg1 and 543 ± 12 mg kg1, were compared with the results analysed by TIMS, 541 ± 12 mg kg1 and 541 ± 13 mg kg1, and agree very well within the stated uncertainties (k= 2). The results presented demonstrate quite well the suitability of the developed IDMS procedures for certification or reference measurements.