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A metrological approach to improve accuracy and reliability of ammonia measurements in ambient air
(2016)
The environmental impacts of ammonia (NH3) in ambient air have become more evident in the recent decades, leading to intensifying research in this field. A number of novel analytical techniques and monitoring instruments have been developed, and the quality and availability of reference gas mixtures used for the calibration of measuring instruments has also increased significantly. However, recent inter-comparison measurements show significant discrepancies, indicating that the majority of the newly developed devices and reference materials require further thorough validation. There is a clear need for more intensive metrological research focusing on quality assurance, intercomparability and validations. MetNH3 (Metrology for ammonia in ambient air) is a three-year project within the framework of the European Metrology Research Programme (EMRP), which aims to bring metrological traceability to ambient ammonia measurements in the 0.5–500 nmol mol−1 amount fraction range. This is addressed by working in three areas: (1) improving accuracy and stability of static and dynamic reference gas mixtures, (2) developing an optical transfer standard and (3) establishing the link between high-accuracy metrological standards and field measurements. In this article we describe the concept, aims and first results of the project.
Metalloproteins, which represent about 30 % of the total proteome, are often important markers for distinguishing between healthy and diseased states of patients. As such markers have become increasingly important in clinical diagnostics, some of these proteins are routinely analysed in clinical laboratories. Reliable and comparable results are the basis for the investigation of changes in the proteome due to different health conditions. Nevertheless, for many proteins the results achieved with different routine measurement procedures or in different laboratories vary widely, thus hampering medical insights and the development of treatments. Reference measurement procedures with results traceable to the International System of Units (SI) will also help to greatly improve the performance of routine measurement procedures and, this way, they support the understanding of changes in the metallome.
Previously on sulfur determination in metal revealed a lack of traceability and inconsistent results. Solving the problems a reference procedure for sulfur measurement in metal are required to build up a reliable reference value. In this study a procedure was developed for quantification of total sulfur at low concentration (in sub ppm level) in metal using inductively coupled plasma-isotope dilution mass spectrometry (ICP-IDMS). The ion exchange method and complexing agent were applied in this procedure to avoid loading large amount of metal into the instrument. Adding ammonia as a complexing agent into sample solution to reduce sulfur-metal co-elute. The procedure shows high performance and it is expressed in % recovery of sulfur (> 90%) and % metal elimination (>99 %). Additionally, relative measurement uncertainties were calculated less than 1.5 % and the results are traceable directly to SI units. This study would establish as reference procedure for sulfur measurement in metal sample which fit for these purpose as follows; for certified reference material and assigned value for inter-laboratory comparison.
Ellipsometry is a valuable surface analysis tool with an unmatched sensitivity towards surface layer properties. In this presentation, an initiative is discussed to make ellipsometry also a metrological tool. This is usually seen as very difficult due to the model-based nature of the analysis process. By establishing standardisation and reference materials, ellipsometry can be made traceable and can also become a valuable part of the traceable thin film metrology landscape. This is important because this technique has much potential to determine complex material parameters much needed in the production of high-tech products.
Characterization of bio-molecular nano-layers by means of reference-free X-ray Spectrometry
An increasing field of application, e.g. in biotechnology is the dedicated adjustment of surface properties by functionalization with organic molecules. For a detailed understanding and further development of such nano-layers, a quantitative determination of the surface density of molecular species is required.
By means of reference-free X-Ray Fluorescence (XRF) spectrometry such surfaces can be analyzed quantitatively by detecting specific marker elements. Using calibrated instrumentation and a quantification approach based on atomic fundamental parameters a SI-traceable quantitative analysis without any calibration sample or reference material is possible. A chemical analysis of molecular bonds can be accomplished by X-Ray Absorption Spectroscopy in the Near-Edge region (NEXAFS). Especially in the soft X-ray range an access to relevant light elements like Carbon C, Nitrogen N and Oxygen is possible.
Here, aminated surfaces with varying densities of amino groups prepared from binary mixtures of silanes were investigated. In a complementary analysis by X-Ray Photoelectron Spectroscopy (XPS) and Fluorescence measurements based on laser-excitation in the optical light spectrum the functional-group density of silane monolayers were determined. The nitrogen atom in the head-group of the silane-molecule could be used as specific marker for the reference-free quantitative XRF analysis and were used for traceable calibration of XPS and Fluorescence Spectroscopy.
X-ray fluorescence (XRF) analysis is a well suited methodology for thin film analysis. With XRF the mass deposition of elements can be non-destructively determined. By knowledge of the density of the thin film as well the thickness can be given. In the field of industrial thin film manufacturing various material systems and layer structures are used. the analysis relies on well-known calibration samples or even reference materials to determine absolute analytical results from the measurement values recorded. Within this concept of chemical traceability the calibration sample has to be as similar as possible to the industrial thin film sample with respect to the spatial distribution of elemental composition in order to minimize matrix effects or analysis related uncertainties. The procurement of such certified similar calibration samples or reference materials including their required traceability is a challenge due to limited number of available calibration samples or reference materials, in particular at the nanoscale. There are only few providers of calibration standards for layer or coating thicknesses which are suitable for XRF analysis. The limited number of available certified reference materials (CRMs) for XRF thin film analysis and in parallel the growing market of novel thin film materials induces a growing gap of required calibration samples for XRF analysis.
The exploitation of process-near samples benefits from a leverage effect: on one hand reference materials are needed for calibration and alignment procedures for X-ray fluorescence devices. They are customized for the special need of the end-user, e.g. a company producing thin film solar cells. On the other hand the market for EDXRF devices develops positively by providing novel thin film calibration samples for industry and end user-related production processes or application. Two aspects are hereby being addressed; the improvement of product quality which in certain sectors like aerospace and automotive industry directly translates to product safety as well as the expansion of the sales potential of EDXRF measuring devices.
The overall objective of project Improved traceability chain of nanoparticle size measurements is to improve the traceability chain for nanoparticle size measurements. The main impact will be achieved by manifold contributions to standard documents for CEN/TC 352 “Nanotechnologies”, which directly addresses the research needs of CEN, CENELEC and ETSI mandated by EC to develop standards for methods and reference materials to accurately measure the size and size distribution of nanoparticles. This will take place in collaboration with ISO/TC229 ‘Nanotechnologies’, ISO/TC24/SC4 ‘Particle characterization’ and ISO/TC201 ‘Surface analysis’/ SC9 ‘Scanning probe microscopy’.