Analytische Chemie
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Messergebnisse in der chemischen Analyse müssen vergleichbar sein. Dies wird durch die metrologische Rückführbarkeit (traceability) auf SI realisiert. In der Chemie dienen Reinststoffe als Primärnormale, deren Reinheit mit einer Unsicherheit von < 0.01% ermittelt werden soll. Ein eleganter Weg, die Reinheit eines realen Materials mit hoher Präzision zu bestimmen, ist, alle Verunreinigungen zu messen, diese aufzusummieren und von der idealen Reinheit von 100 Prozent abzuziehen. Die metallischen Verunreinigungen in Metallen lassen sich mittels hochauflösender Massenspektrometer ermitteln. Eine weit größere Herausforderung ist die Bestimmung von Nichtmetallen wie Sauerstoff, Wasserstoff und Stickstoff im Metall, zumal diese auch oft die Hauptverunreinigung darstellen. Für die quantitative Bestimmung von Verunreinigungen wurden mit Standards dotierte Pulverpresslinge und mit H, O und N dotierte, gesinterte Materialien auf ihre Eignung als Kalibrierstandards für die GD-OES und GD-MS untersucht. Dabei kamen unterschiedliche Plasmabedingungen (pulsed/ continuous mode; verschiedene Plasmagase) zum Einsatz. Ein Überblick über analytische Kenngrößen und Grenzen der verwendeten Kalibrierstrategien wird gegeben.
A plethora of innovative materials are produced by depositing thin and ultrathin coatings on different substrates. For instance, hard disks able to store terabytes of information are based on multiple magnetic and non-magnetic nano-layers. Moreover, protectives coatings might be used to enhance the mechanical properties of substrate materials; for instance Zn-based coatings are used in the Al industry.
In this context, solid analytical techniques are required to provide fast multi-elemental chemical analyses with high depth resolution (to monitor the different layers) and high sensitivity (to detect major, minor and trace elements). Direct solid analytical techniques, including Secondary Ion Mass Spectrometry, Secondary Neutral Mass Spectrometry, Auger Electron Spectroscopy or X-Ray Photoelectron Spectroscopy provide very valuable information about the atomic chemical composition of the surfaces/coatings; however, they also have some major drawbacks, such as high operating costs, complex sample pre-treatment and handling, low sample throughput and/or severe matrix effects that result in difficult quantification procedures. In order to overcome some of these drawbacks Glow Discharge Mass Spectroscopy (GD-MS) is proposed as a complementary methodology that provides an ideal solution for fast and accurate bulk and layer analyses. In this work, we evaluate the advantages and limitations of this technique and we discuss about recent progresses and new applications.
Innovative material with outstanding physical and chemical properties are produced upon the deposition of thin and ultrathin coatings on different substrates. For instance, hard disks able to store Tera-bytes of information are based on the deposition of multiple nano-layers, which include magnetic and non-magnetic layers. Many other analogous examples, including photovoltaic cells, coated Al substrates, oxidized thin film composite membranes, coated glasses, coated polymers, etc. could be cited. The physical performance of these emerging materials is directly related to their chemical properties, including the elemental distribution within the different layers and at the layer-interfaces, or the presence of critical non-desired trace elements. Therefore, quality control and R+D advances require the development of direct solid analytical techniques able to provide fast multi-elemental chemical analysis of these materials, with high depth resolution (to monitor the different layers) and high sensitivity (to detect major, minor and trace elements).
Atomic spectrometry techniques have long been used for direct elemental chemical characterization. Techniques, such as Secondary Ion Mass Spectrometry or Auger Electron Spectroscopy provide very valuable information about the chemical composition of the surfaces/coatings; however, they also have some major drawbacks, such as high operating costs, complex sample pre-treatment and handling, low sample throughput and/or severe matrix effects that result in difficult quantification procedures. To overcome some of these drawbacks Glow Discharge Mass Spectroscopy is proposed as a complementary methodology that provides an ideal solution for fast and accurate bulk and layer analyses. In this work, we evaluate the advantages and limitations of this technique and we discuss about recent progresses and new applications.
Reference materials are essential, when the accuracy and reliability of measurement results need to be guaranteed in order to generate confidence in the analysis.
These materials are frequently used for determining measurement uncertainty, for validation of methods, suitability testing and quality assurance. Especially direct solid sampling methods require reference materials for calibration.
They guarantee that measurement results can be compared to recognized reference values.
This presentation gives an overview about the use of GDMS in various certification procedures. Because it represents a fast, sensitive, multielement analyses technique without extensive sample preparation it plays a special role for the purity determination of high purity standards. Various calibration strategies and the preparation of traceable matrix matched calibration standards will be discussed.
For the certification of analyte content in matrix materials mainly techniques with solvent sample preparation are used. Here GD-MS is used to identify possible loss or contamination with analytes during the sample preparation step. Typically used acids to dissolve matrices lead to interferences in the ICP- mass spectrometric detection of various analytes and their quantification. Here GD-MS as direct method can also add an important contribution in the certification process.
Purity statements of high purity materials serving as primary standards by GDMS.
Primary standards are materials known for their total purity and therefore appropriate to realise the link with the International System of Units (SI). The realisation and dissemination of primary standards is of fundamental importance for comparability of measurement results through traceability in all fields of chemical analysis.
To serve as a primary standard for element determination the total purity of a high purity material needs to be measured. In order to achieve a sufficiently small uncertainty (i.e. < 0.01%) this involves determining all possible impurity contributions and to subtract their sum from the ideal purity of 100%.
GD-MS has the potential to reduce the effort for purity determination, as a fast sensitive multi-element analysis without extensive sample preparation. Similar to other solid sampling techniques, glow discharge
requires calibration link the measured signal and the content of the impurities in the matrix.
The use of the concept Relative Sensitivity Factors (RSFs) provides good approximations especially for high purity materials. However, it only works with a wide uncertainty of the results.
The preparation of synthetic pressed powder samples by different modifications of liquid and powder doping used for the determination of both metallic and none-metallic impurities are described. Efficient determination of metallic impurities by GD-MS via differential and absolute measurements with a significantly reduced target uncertainty of 20 % for absolute measurements using liquid doped pressed powder calibration could be achieved. The determination of impurities has been evaluated by independent analytical methods such as HR-ICP-MS, ETAAS; CGHE and combustion analysis