1.6 Anorganische Referenzmaterialien
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Paper des Monats
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Society for Applied Spectroscopy (SAS) Atomic Section Student Award.
Magnesium is a major element in the hydrosphere and biosphere and plays important roles in (bio-) geochemical and physiological cycles. Mg has three stable isotopes, 24Mg, 25Mg and 26Mg. It is due to their relatively large mass difference (~8% between) that isotope fractionation leads to slight variations of isotope amount ratios in biological, environmental and geological samples. Traditionally, isotope ratios are measured by mass spectrometric methods. Their drawbacks include the high costs for instruments and their operation, experienced operators and elaborate time-consuming chromatographic sample preparation.
Recently, optical spectrometric methods have been proposed as faster and low-cost alternative for the analysis of isotope ratios of selected elements by means of high-resolution continuum source molecular absorption spectrometry (HR-CS-MAS), and laser ablation molecular isotopic spectrometry (LAMIS).
For the determination of Mg isotope ratios in selected rock reference materials, the molecular spectrum of the in-situ generated MgF and MgO molecules were studied and their results compared with MC-ICP-MS. By HR-CS-MAS, samples were dissolved by acid digestion and Mg isotopes analyzed with and without matrix. The absorption spectrum was recorded for MgF for the electronic transitions X 2Σ → A 2 Πi, and X 2Σ → B 2Σ+. In the case of LAMIS, we investigated the MgF molecule for the electronic transition A 2Πi → X 2Σ, as well as direct analysis by the MgO molecule for the electronic transition A 1Π+ → X 1Σ. The MgF and MgO spectra are described as the linear combination of their isotopic components or isotopologues: 24MgF, 25MgF, and 26MgF for the MgF and 24MgO, 25MgO, and 26MgO for the MgO. The isotope analysis was done by deconvolution of the MgF spectrum by partial least square regression (PLS) calibrated with enriched isotope spikes. Results were accurate with precisions ranging between 0.2 ‰ and 0.8 ‰ (2 SD, n= 10) for HR-CS-GFMAS. No statistically significant differences were observed for samples w/o matrix extraction. On the other hand, LAMIS allows the direct analysis of solid samples with the extended possibility of direct analysis, however the precision is lower due the lack of solid isotopic calibration standards.
The entire process involving the determination of Cl by molecular emission detection in Laser-Induced Breakdown Spectroscopy (LIBS) is thoroughly studied in this paper. This critical evaluation considers how spectra are normalized, how interferences from other molecular species signals are removed, and how signal integration is applied. Moreover, a data treatment protocol is proposed to achieve reliable and accurate Cl determination from the CaCl molecular spectral signal, not requiring the use of more complex numerical approaches. Calcium chloride dihydrate (CaCl2⋅2H2O) and high purity anhydrite samples (CaSO4) are used to optimize the acquisition conditions and data treatment of CaCl emission signal. Using the developed protocol, calibration curves for Cl, covering the concentration range from 0 μg/g to 60,000 μg/g of Cl, are successfully achieved. Finally, the suitability of the proposed methodology for Cl determination is successfully applied in industrial gypsum waste samples, where the results obtained by LIBS are validated using high-resolution molecular absorption spectroscopy (HR-CS-MAS) and potentiometric titration.
A method, based on electrothermal vaporization (ETV) coupled to inductively coupled plasma optical emission spectrometry (ICP OES), has been optimized for direct solid sampling analysis of soda-lime glass - the most common type of industrially manufactured glass. This method allows fast and reliable quantification of the main elements - Al, Ca, K, Mg, Na, and Si - and trace elements - As, Ba, Cd, Ce, Co, Cr, Cu, Fe, Mn, Mo, Ni, (P), Pb, Sb, (Se), Sn, Sr, Ti, V, Zn, and Zr. In the presented ETV-ICP OES method, calibration is performed predominantly with matrix-free synthetic samples. This metrological advantage is normally not achieved with direct solid sampling methods and is one of the goals of the present study. In a certification interlaboratory comparison for the soda-lime glass CRM BAM-S005c, 2 out of 16 laboratories employed the ETV-ICP OES method. An improved analytical performance was obtained compared with the results of laboratories that used conventional liquid ICP OES. For both methods, the average relative deviations between the laboratory results and certified values as well as the average values of relative standard deviation were with a few exceptions <10%, in most cases even <5%, which indicated high trueness and precision.
Statistic process control as well as process capability demand for calibrated determination of layer thicknesses in various industries, e.g. automotive, aerospace, microelectronics manufacturing. Calibration requires well know and well characterized samples. A calibration laboratory accredited according to DIN EN ISO 17025 has the objective to distribute standards traceable to SI units to industrial laboratories for quality control of manufacturing of various products. Especially, the thickness determination of thin metallic coatings e.g. from galvanic processes or layer deposition using X-Ray Fluorescence can be significantly improved by customized calibration samples. This is essential as the measurement uncertainty directly correlates to the capability performing reliable control of processes with high yield. For calibration laboratories, the validation of results using round robins and the direct comparison to national metrology institutes is a prerequisite to demonstrate the competence to perform calibration services.
In this paper a strategy to obtain traceability and validation for thin alloy layers as well as first results are presented. The combined use of the accredited method for determination of mass per area from measurement of mass and area combined with standard free X-Ray Fluorescence as well as chemical analysis of dissolved samples with thin layers is deployed for material systems as NixZn1-x as well as NixP1-x. The obtained results are compared to reference free X-Ray Fluorescence at the BESSY II laboratories of Physikalisch-Technische Bundesanstalt. An excellent agreement of the obtained measured values as mass per unit area and alloy concentrations from the different applied methods within the measurement uncertainty was observed for NixP1-x showing the successful performed traceability of the calibration samples to SI units in combination with a validation of results by national metrology institutes and the round robin approach.
The analysis of Zinc layers on Iron sheets is one of the most essential application of Glow Discharge - Optical Emission Spectrometry (GD-OES). Since the year 2000 for this application calibration of GD-OES instruments mostly included the set of the six calibration samples CZ 2009-CZ 2014 from CKD. These CRMs are no longer available. Furthermore, in this application the analysis of Al and Mg became essential. To overcome this lack of calibration materials, the working group VDEh FA II.47 decided to organize the production and characterization of a new set of certified reference materials.
The analysis of Zinc layers on Iron sheets is one of the most essential application of Glow Discharge - Optical Emission Spectrometry (GD-OES). Since the year 2000 for this application calibration of GD-OES instruments mostly included the set of the six calibration samples CZ 2009-CZ 2014 from CKD. These CRMs are no longer available. Furthermore, in this application the analysis of Al and Mg became essential. To overcome this lack of calibration materials, the working group VDEh FA II.47 decided to organize the production and characterization of a new set of certified reference materials.
Advances and Applications of Molecular Absorption Spectrometry: from Non-Metals to Isotope Analysis
(2020)
The present work covers two main aspects of high-resolution continuum source graphite furnace molecular absorption spectrometry (HR-CS-GFMAS), an analytical technique for elemental trace analysis.
First, a comprehensive mechanistic study of molecule formation in graphite furnaces is presented, which is a key step into the recovery of analytical signals. For this, the molecule formation of CaF was studied, which is used for the indirect analytical determination of fluorine in HR-CS-GFMAS. A zirconium coating catalyzes the CaF formation, and its structure was investigated. The kinetics of this reaction was established by monitoring its molecular spectrum at different atomisation temperatures. An Arrhenius plot showed a pseudo-first order reaction with respect to fluorine (n = 1). An intermediate state was isolated, and its structure was elucidated by spectroscopic methods: scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX), X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XANES and EXAFS), and Raman microspectroscopy. Here a mechanism is proposed, where ZrO2 works as a heterogeneous catalyst: after a pyrolytic step, an intermediate state of ZrO(OCaF) is activated, and at higher temperatures, CaF(g) is released from the zirconium-coated graphite surface.
Second, analytical methods were developed by using HR-CS-MAS as detector for non-metals and isotope analysis. Therefore, the determination of organic absorbable chlorine in water, the quantification of fluorine in consume care products with declared perfluorinated ingredients, and the determination of sulfur content in crude oils were investigated. Finally, the high resolution of the instrumentation allows to measure isotopic shifts with high precision in some observed molecular spectra. Consequently, the molecular spectra of enriched isotopes of boron and magnesium were investigated, establishing so the potential of HR-CS-MAS for the accurate and precise determination of isotopic amount ratios.
Advances and Applications of Molecular Absorption Spectrometry: from Non-Metals to Isotope Analysis
(2019)
The present work covers two main aspects of high-resolution continuum source graphite furnace molecular absorption spectrometry (HR-CS-GFMAS), an analytical technique for elemental trace analysis.
First, a comprehensive mechanistic study of molecule formation in graphite furnaces is presented, which is a key step into the recovery of analytical signals. For this, the molecule formation of CaF was studied, which is used for the indirect analytical determination of fluorine in HR-CS-GFMAS. A zirconium coating catalyzes the CaF formation, and its structure was investigated. The kinetics of this reaction was established by monitoring its molecular spectrum at different atomisation temperatures. An Arrhenius plot showed a pseudo-first order reaction with respect to fluorine (n = 1). An intermediate state was isolated, and its structure was elucidated by spectroscopic methods: scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX), X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XANES and EXAFS), and Raman microspectroscopy. Here a mechanism is proposed, where ZrO2 works as a heterogeneous catalyst: after a pyrolytic step, an intermediate state of ZrO(OCaF) is activated, and at higher temperatures, CaF(g) is released from the zirconium-coated graphite surface.
Second, analytical methods were developed by using HR-CS-MAS as detector for non-metals and isotope analysis. Therefore, the determination of organic absorbable chlorine in water, the quantification of fluorine in consume care products with declared perfluorinated ingredients, and the determination of sulfur content in crude oils were investigated. Finally, the high resolution of the instrumentation allows to measure isotopic shifts with high precision in some observed molecular spectra. Consequently, the molecular spectra of enriched isotopes of boron and magnesium were investigated, establishing so the potential of HR-CS-MAS for the accurate and precise determination of isotopic amount ratios.
Zusammenfassung
Die vorliegende Arbeit befasst sich mit zwei zentralen Aspekten der High-Resolution-Continuum-Source-Molekülabsorptionsspektrometrie mit Graphitrohrtechnik (HR-CS-GFMAS), einer Analysetechnik für elementare Spurenanalyse.
Der erste Teil der Arbeit umfasst eine mechanistische Studie zur Molekülbildung auf Graphitoberflächen. Dies ist ein wichtiger Schritt, um analytische Signale zu entdecken. Dazu wurde die Molekülbildung von CaF analysiert, welches für die indirekte, analytische Bestimmung von Fluor in HR-CS-GFMAS genutzt wird. Die CaF Bildung wurde mittels einer Beschichtung aus Zirconium katalysiert und deren Struktur analysiert. Die Kinetik dieser Reaktion wurde durch Beobachtung des jeweiligen Molekülspektrums bei verschiedenen Atomisierungstemperaturen beobachtet. Ein Arrheniusplot zeigte für Fluor (n = 1) eine Reaktion Pseudo-erster Ordnung. Ein Übergangszustand wurde über die mit Zirconium überzogene Grafitoberfläche isoliert und seine Struktur mittels spektroskopischer Methoden Energiedispersive Rasterelektronenmikroskopie / Röntgenspektroskopie (REM-EDX), Röntgenphoto¬elektronenspektroskopie (XPS), Röntgenabsorptionsspektroskopie (XAS) und Raman Spektroskopie untersucht. Auf Grundlage dieser Ergebnisse wird ein Mechanismus vorgeschlagen, bei dem ZrO2 als heterogener Katalysator fungiert; in Folge einer Pyrolysestufe wird ein Übergangszustand des ZrO(OCaF) aktiviert, welcher bei höheren Temperaturen CaF(g) an der Zirconium-Graphitoberfläche freisetzt.
Im zweiten Teil der Arbeit werden Analysemethoden entwickelt, in dem HR-CS-MAS als Detektor für Nichtmetalle und Isotopanalyse angewandt wird. Hierfür wurde organisch gebundenes Chlor im Wasser bestimmt, der Fluorgehalt in Pflegeprodukten mit perfluorierten Inhaltsstoffen quantifiziert und der Schwefelgehalt in Erdöl untersucht. Weiterhin ermöglicht die hohe Auflösung der Messgeräte eine präzise Bestimmung der Isotopenverschiebung einiger untersuchter Molekülspektren. Daher wurden die Molekülspektren angereicherter Bor- und Magnesiumisotope untersucht. Auf diese Weise wurde das Potential von HR-CS-MAS für die akkurate und präzise Bestimmung von Isotop-Mengenverhältnissen nachgewiesen.
The climate and energy crisis are extreme challenges. One possible solution could be hydrogen technology. Safety is a big concern. Steel used for pipelines and storage is under permanent stress from low temperatures and high pressures. The content of different alloyed metals determines the performance of the steel. Nitrogen microwave inductively coupled atmosphere pressure plasma mass spectrometry (N2-MICAP-MS) is a promising method for trace metal analysis in steel. Nitrogen is cheap and can be generated on site. It has fewer interferences than argon. Additionally, MICAP-MS is very matrix tolerant, proving the matrix-matched calibration expendable. Safety in technology and chemistry is the mission of BAM. Providing reference methods and materials can create trust in future technologies like hydrogen.
An alternative method for lithium isotope analysis by using high-resolution atomic absorption spectrometry (HR-CS-AAS) is proposed herein. This method is based on monitoring the isotope shift of approximately 15 pm for the electronic transition 22P←22S at around the wavelength of 670.8 nm, which can be measured by state-of-the-art HR-CS-AAS. Isotope analysis can be used for (i) the traceable determination of Li concentration and (ii) isotope amount ratio analysis based on a combination of HR-CS-AAS and spectral data analysis by machine learning (ML).
In the first case, the Li spectra are described as the linear superposition of the contributions of the respective isotopes, each consisting of a spin-orbit doublet, which can be expressed as Gaussian components with constant spectral position and width and different relative intensity, reflecting the isotope ratio in the sample. Precision was further improved by using lanthanum as internal spectral standard. The procedure has been validated using human serum-certified reference materials. The results are metrologically comparable and compatible with the certified values.
In the second case, for isotope amount ratio analysis, a scalable tree boosting ML algorithm (XGBoost) was employed and calibrated using a set of samples with 6Li isotope amount fractions ranging from 0.06 to 0.99 mol mol−1. The training ML model was validated with certified reference materials. The procedure was applied to the isotope amount ratio determination of a set of stock chemicals and a BAM candidate reference material NMC111 (LiNi1/3Mn1/3Co1/3O2), a Li-battery cathode material. These determinations were compared with those obtained by MC-ICP-MS and found to be metrologically comparable and compatible. The residual bias was −1.8‰, and the precision obtained ranged from 1.9‰ to 6.2‰. This precision was sufficient to resolve naturally occurring variations. The NMC111 cathode candidate reference material was analyzed using high-resolution continuum source atomic absorption spectrometry with and without matrix purification to assess its suitability for technical applications. The results obtained were metrologically compatible with each other.
To establish the SI traceability of the element content w(Hg) of a gravimetrically prepared 1 g/kg mercury solution, the latter was compared to a primary reference solution by means of high accuracy inductively coupled plasma optical emission spectrometry (ICP OES) measurements. For this purpose, the ICP OES bracketing method previously described [1] was improved to yield a relative expanded uncertainty of the mercury element content of Urel(w(Hg)) = 0.5 % (with k = 2) associated with the comparison of two monoelemental solutions. In case of mercury, such a small uncertainty was achieved for the first time. Before, in general, such small uncertainties were only reported applying isotope dilution methods performed with MC-ICP-MS. However, for mercury solutions at this concentration range, several dilution steps are necessary to prepare the samples for ID-MC-ICP-MS. The sum of the uncertainty contributions stemming from the dilution steps, as well as the intrinsic difficulties of measuring mercury at low concentrations, result in an overall uncertainty of the ICP-MS measurements, which is comparable to or even larger than those, achieved with the ICP OES method applied. We will present details of the sample preparation as well as of the dedicated ICP OES measurement approach, which were crucial to achieve such a small measurement uncertainty.
The newly developed method was successfully applied in the context of the development and production of elemental solution chemical reference standards (CRS), which are distributed by the EDQM. The CRS are intended to support measurements required by the European Pharmacopoeia, which has recently incorporated a new international guideline for the control of elemental impurities in medicinal products.
The isotopic analysis of lithium is also relevant to the study of geological phenomena.1 In this work we propose improvements to the method for the isotopic analysis of lithium using a high-resolution continuum source atomic absorption spectrometer (HR-CS-AAS) coupled to a double echelle modular spectrometer (DEMON). 2 This tool for isotopic ratio determination is based on monitoring the isotopic components of lithium by their spin-orbit coupling and its isotopic shift of about 15 pm for the 22P←2 2S electronic transition around 670.788 nm. The data analysis was carried out by using a decision-tree-based ensemble machine learning (ML) algorithm. For the training of the algorithm (XGBoost), a set of samples with 6Li isotope amount fractions ranging from 0.06 to 0.99 mol-1 was used. Subsequently, the procedure was validated of a set of stock chemicals (Li2CO3, LiNO3, LiCl and LiOH) and a BAM candidate reference material, the cathode material LiNi1/3Mn1/3Co1/3O2 (NMC111). Finally, the ML model was applied to the set of geological samples, previously digested, for the determination of their isotope ratio. The optical resolution was improved from 140,000 to 790,000 to better deconvolution the lithium isotopic components in the atomic spectrum. And the method was compared with multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS). The results are metrologically comparable.
Referenzmaterialien sind unter anderem ein wichtiges Werkzeug zur Qualitätskontrolle von Messungen bestimmter Merkmalswerte. Dabei ist zu berücksichtigen, dass zertifizierte Merkmalswerte immer eine gewisse Unsicherheit haben. Die Ermittlung dieser Unsicherheitsbeiträge ist Gegenstand des Vortrags. Referenzmaterialien sind gleichzeitig ein wertvolles Werkzeug zur Ermittlung der Unsicherheit von Messverfahren und -Analysen unbekannter Proben. Die Vorgehensweise bei der Ermittlung der Messunsicherheit mit Hilfe eines Referenzmaterials wird beschrieben.
Referenzmaterialien sind unter anderem ein wichtiges Werkzeug zur Qualitätskontrolle von Messungen bestimmter Merkmalswerte. Dabei ist zu berücksichtigen, dass zertifizierte Merkmalswerte immer eine gewisse Unsicherheit haben. Die Ermittlung dieser Unsicherheitsbeiträge ist Gegenstand des Vortrags. Referenzmaterialien sind gleichzeitig ein wertvolles Werkzeug zur Ermittlung der Unsicherheit von Messverfahren und -Analysen unbekannter Proben. Die Vorgehensweise bei der Ermittlung der Messunsicherheit mit Hilfe eines Referenzmaterials wird beschrieben.
Die metallischen Verunreinigungen in Metallen lassen sich mittels hochauflösender Massenspektrometer relativ einfach ermitteln. Die Glimmentladungs-Massenspektrometrie (GD-MS) stellt hierfür eine schnelle Multielementmethode dar. Aufgrund ihrer höheren Anregungs- und Ionisationsenergien ist die Bestimmung von Nichtmetallen eine weit größere Herausforderung. Außerdem fehlt es an für die direkte Feststofftechnik notwendigen Kalibrierstandards z.B. in Form zertifizierter Referenzmaterialien. Für die quantitative Bestimmung von Verunreinigungen wurden mit Standards dotierte Pulverpresslinge und dotierte, gesinterte Materialien auf ihre Eignung als Kalibrierstandards für die GD-MS untersucht. Dabei kamen unterschiedliche Plasmabedingungen (gepulster/ kontinuierlicher Betrieb; verschiedene Plasmagase) zum Einsatz. Ein Überblick über analytische Kenngrößen und Grenzen der verwendeten Kalibrierstrategien wird gegeben. Zur Validierung des Verfahrens wurde die hochauflösende Continuum Source Absorptionsspektrometrie (HR-CS-MAAS) verwendet. Die analytische Nutzung der Molekül-absorptionsspektrometrie zur Bestimmung von Halogenen basiert auf der Bildung insitu-generierter zweiatomiger Moleküle (AlCl, GaF). Die entstehenden Molekülspektren werden im Echelle-Spektrometer aufgespalten und mittels CCD-Array detektiert, was eine sehr empfindliche Messung und präzise Quantifizierung ermöglicht.
Die metallischen Verunreinigungen in Metallen lassen sich mittels hochauflösender Massenspektrometer relativ einfach ermitteln. Die Glimmentladungs-Massenspektrometrie (GD-MS) stellt hierfür eine schnelle Multielementmethode dar. Aufgrund ihrer höheren Anregungs- und Ionisationsenergien ist die Bestimmung von Nichtmetallen eine weit größere Herausforderung. Außerdem fehlt es an für die direkte Feststofftechnik notwendigen Kalibrierstandards z.B. in Form zertifizierter Referenzmaterialien. Für die quantitative Bestimmung von Verunreinigungen wurden mit Standards dotierte Pulverpresslinge und dotierte, gesinterte Materialien auf ihre Eignung als Kalibrierstandards für die GD-MS untersucht. Dabei kamen unterschiedliche Plasmabedingungen (gepulster/ kontinuierlicher Betrieb; verschiedene Plasmagase) zum Einsatz. Ein Überblick über analytische Kenngrößen und Grenzen der verwendeten Kalibrierstrategien wird gegeben. Zur Validierung des Verfahrens wurde die hochauflösende Continuum Source Absorptionsspektrometrie (HR-CS-MAAS) verwendet. Die analytische Nutzung der Molekül-absorptionsspektrometrie zur Bestimmung von Halogenen basiert auf der Bildung insitu-generierter zweiatomiger Moleküle (AlCl, GaF). Die entstehenden Molekülspektren werden im Echelle-Spektrometer aufgespalten und mittels CCD-Array detektiert, was eine sehr empfindliche Messung und präzise Quantifizierung ermöglicht.