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HIIRM final report

  • Accurate analytical results have become more and more an absolute essential tool for further progresses in technology and science. Precision however, often used in this context as a quality criterion for analytical methods, is not a replacement for accuracy in any way. Therefore, analytical procedures are necessary, which will generate reliable and accurate results and can be used for evaluation of other analytical procedures and certification of reference materials (RM). Especially the certification of reference materials for the amount content of trace elements requires highly accurate results with a small combined uncertainty. The best example for an analytical procedure having this capability is undoubtedly Isotope Dilution Mass Spectrometry, for inorganic as well as for organic applications. Applied on Thermal Ionization Mass Spectrometry (TIMS) isotope dilution provides results of highest quality and proven high accuracy especially in the field of RM certifications for more thanAccurate analytical results have become more and more an absolute essential tool for further progresses in technology and science. Precision however, often used in this context as a quality criterion for analytical methods, is not a replacement for accuracy in any way. Therefore, analytical procedures are necessary, which will generate reliable and accurate results and can be used for evaluation of other analytical procedures and certification of reference materials (RM). Especially the certification of reference materials for the amount content of trace elements requires highly accurate results with a small combined uncertainty. The best example for an analytical procedure having this capability is undoubtedly Isotope Dilution Mass Spectrometry, for inorganic as well as for organic applications. Applied on Thermal Ionization Mass Spectrometry (TIMS) isotope dilution provides results of highest quality and proven high accuracy especially in the field of RM certifications for more than 30 years. The major drawback of this approach often is the necessity for a complex chemical separation step. A major advantage of Inductively Coupled Plasma Mass Spectrometry (ICP-MS) is the potential to cope with a simplified or an on-line-carried-out sample preparation. A key requirement of isotope dilution analysis however is the accurate and precise determination of isotope ratios, because of its limiting factor for the accuracy and the total uncertainty of the result. Very precise isotope ratios can be determined in combination with a detection system that is capable of simultaneous detection of different isotopes, a so-called multi-collector system. The objective of the presented project is to evaluate the advantages of such a multi-collector ICP-MS for the application of IDMS in the field of trace elemental analysis in reference materials. The focus is on the development of simple and fast procedures for isotope ratio measurements in general and IDMS analysis in particular. Furthermore, it is an objective to develop and evaluate on-line spiking procedures. One of the first conclusions, which had a severe impact on the HIIRM project, arose during the early days of the project. Currently most certification experiments are accomplished by certification campaign based on a variety of participants’ results. The sample preparation, sending, analyzing and data evaluation however require lot of resources and the process may take a long time. An alternative way is given by using fewer participants with methods of higher metrological quality. For elemental amount contents such a method undoubtedly is isotope dilution analysis and multi-collector ICP-MS offers the necessary precision and matrix robustness and ruggedness as said above. Therefore, a multiple collector ICP-MS was manufactured as part of the project instead of the originally planned high-resolution instrument. Due to the novelty of the multicollector ICP-MS instrument, a lot of additional fundamental research became necessary. Especially interferences needed further attention. Fortunately, the IsoProbe is additionally equipped with a high-resolution option and with a brand new collison cell. The high-resolution option however can only be used to identify interferences but cannot be used to quantify them. On the other hand, the use of the collision cell proved to be a vital tool to overcome interferences. This is especially true because high resolution would have reduced the available sensitivity by a factor of ~100. Applying the collision cell technology the high sensitivity was maintained whilst most interferences were eliminated. However finding the right parameters of operation for the collision cell became a huge part of the method development process. A variety of gases like argon, helium, hydrogen, deuterium, nitrogen, krypton and xenon were tested for their suitability. Especially the tests accomplished for iron determinations revealed that carefully selected parameters have an incredible influence on the quality of the final results. Nonetheless collision cell technology will undoubtedly be widely used for newer ICP-MS instrumentation and contribute to eliminate wrong analytical values caused by interferences. The enhanced sensitivity of the instrument revealed also problems not detectable by other means. The control of contaminations seems to be one of the major analytical challenges in the future. Sector field based ICP-MS will give the user an opportunity to trace sources of contamination back to their origin and eliminate them. Even lower limits of detection will be the result as well as an enhanced reliability for analysts dealing with higher amount contents. The analyst will also benefit in controlling blank levels when the method of isotopically spiked procedure blanks is used as demonstrated in this project. Another main part of the project was the validation of the developed procedures. The first validation step was successfully accomplished by applying these procedures on the standard solutions provided by NRG. The main part of this validation however consisted of the evaluation of the fundamental parameters of the isotope dilution process and related measurements. This approach turned out to be superior compaired to the first step as a highly reliable uncertainty calculation can be easily performed. The best reputation and acceptance of the methods can however only be accomplished by participating in certification campaigns or in interlaboratory comparisons on highest metrological level. The results of the participations in general were brilliant. Not only the results but also the obtained realistic uncertainties were of superior quality. Direct comparisons at BAM with the results obtained by a multicollector TIMS applying the same calculation schemes showed the benefits of using multicollector ICP-MS. The main benefits of ICP-MS were identified, of which the first one is the enhanced precision of the isotope ratio measurement. For a variety of elements the values obtained by multicollector ICP-MS are even more precise than the ones obtainable by multicollector TIMS. The second important advantage identified was the simplified sample preparation. The laborious and time consuming analyte-matrix-separation step as necessary for TIMS measurements can either be omitted or at least be drastically reduced. Therefore, the advantages regarding time and enhanced sample throughput will result in further spread of ICP-MS in general and multicollector ICP-MS in particular. The third major part in terms of the method development process was mainly focused on developing an online isotope dilution system. The volumetric instead of the gravimetric IDMS approach proved difficult, if the high demands necessary for RM definition measurements are to be fulfilled. The major obstacle in this case is the missing stability and precision in terms of mass flow. Consequently, the initial development failed as the system made up of two piezoelectric droplet injectors was unable to reach the required stability as well as precision. The thereupon-created system consisting of two HPLC pumps proved to be far more valuable regarding automation and particularly the quantification of transient signals. Nevertheless, such a system will probably be rarely used in certification campaigns, as the gain of time is too small compared to the loss of reliability. However, this system proved most valuable in terms of species-specific elemental analysis as preliminary investigations showed. In this context this system will be suitable for certification measurements, as the major uncertainty contributions derive from sampling, sample treatment and species distribution and as moreover all availabel methods demonstrate far beyond. During the whole project, one of the main concerns regarding the multicollector ICP-MS instrument were software issues caused by the early development state of the original control programs. A lot of effort was necessary to accomplish the necessary data manipulations externally. The development of a new software suite by Micromass for the HIIRM project has solved this issue almost completely. With the new software suite and the validated parameters of measurement a step forward for institutes dealing with reference material certifications was achieved. Future certifications campaigns for minor elemental contents in different matrices should be performed by a small number of participants from highly qualified institutes. These institutes should apply very reliable methods of measurement like the ones developed in the HIIRM project. Many resources may be saved that way while the outcome of the certifications may easily be improved. ICP-MC-MS has the potential to be an important method in this context. Stable isotope dilution analysis in combination with a multi-detector ICP-MS, equipped with a hexapole collision cell for the suppression of important spectral interferences and for enhanced sensitivity, proved to be an advanced method of elemental analysis with a high potential for matrix independent measurements. Since ICP mass spectrometers of this type have only recently been introduced, no systematic evaluation of the capabilities of this specific application of the ICP-IDMS method has yet been made.zeige mehrzeige weniger

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Metadaten
Autor*innen:Jochen VoglORCiD, P. Klingbeil, W. Pritzkow, Gundel Riebe, G. Wermann, P. Turner, N. Wortel, J. Woittiez
Dokumenttyp:Forschungsbericht
Veröffentlichungsform:Eigenverlag BAM
Sprache:Englisch
Jahr der Erstveröffentlichung:2002
Verlag:Bundesanstalt für Materialforschung und -prüfung (BAM)
Verlagsort:Berlin
Erste Seite:1
Letzte Seite:166
DDC-Klassifikation:Naturwissenschaften und Mathematik / Chemie / Analytische Chemie
Freie Schlagwörter:ICPMS; IDMS; collision cell; interferences
Verfügbarkeit des Dokuments:Datei im Netzwerk der BAM verfügbar ("Closed Access")
Datum der Freischaltung:29.03.2016
Referierte Publikation:Nein
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