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Although citrate is frequently used as a surface ligand for nanomaterials (NMs) such as metal, metal oxide, and lanthanide-based NMs in hydrophilic environments due to its biocompatibility and simple replacement by other more strongly binding ligands in postsynthetic surface modification reactions, its quantification on NM surfaces has rarely been addressed. Here, we present a multimethod approach for citrate quantification on iron oxide nanoparticles (IONPs) broadly applied in the life and material sciences. Methods explored include thermogravimetric (TGA) and elemental (CHN) analysis, providing citrate-nonspecific information on the IONP coating, simple photometry, and citrate-selective reversed-phase high-performance liquid chromatography (RP-HPLC) with absorption (UV) detection and quantitative nuclear magnetic resonance spectroscopy (qNMR). Challenges originating from the strongly absorbing magnetic NM and paramagnetic iron species interfering with optical and NMR Methods were overcome by suitable sample preparation workflows. Our multimethod approach to citrate quantification highlights the advantages of combining specific and unspecific methods for characterizing NM Surface chemistry and method cross-validation. It also demonstrates that chemically nonselective measurements can favor an overestimation of the amount of a specific surface ligand by signal contributions from molecules remaining on the NM surface, e.g., from particle synthesis, such as initially employed ligands and/or surfactants. Our results emphasize the potential of underexplored selective RPHPLC for quantifying ligands on NMs, which does not require a multistep sample preparation workflow such as qNMR for many NMs and provides a higher sensitivity. These findings can pave the road to future applications of versatile HPLC methods in NM characterization.
Untersuchungen zur ZnO-Reduktion beim Schmelzen von Filterstäuben im elektrischen Lichtbogenofen
(2008)
Certification of the mass fractions of Pt, Pd and Rh in a used car catalyst reference material
(2009)
The high economic value of catalysts containing the platinum group elements platinum, rhodium and palladium as active components causes the need to be able to measure the precious metal loading with small uncertainty and to have suitable certified reference materials fulfilling high demands on the quality of the certified values. In European Reference Material ERM®-EB504, a used cordierite-based car catalyst material, mass fractions of platinum, palladium and rhodium were certified. The raw material was milled, homogenised and annealed before analysis. Seventeen laboratories experienced in precious metals analysis participated in the certification interlaboratory comparison, most of them analysing with inductively coupled plasma optical emission spectrometry using different sample pretreatment techniques. Homogeneity testing was carried out using X-ray fluorescence spectrometry. The certified mass fractions of Pt, Pd and Rh and their expanded uncertainties (k = 2) in ERM®-EB504 are (1777 ± 15), (279 ± 6) and (338 ± 4) mg/kg respectively.
Einsatz der RFA bei der Zertifizierung von Referenzmaterialien
Der Bedarf an Referenzmaterialien für die chem. Analytik steigt stetig. Nur durch Einsatz moderner Analysenmethoden kann die Nachfrage gedeckt werden.
Die RFA als hochpräzises Verfahren, ist aufgrund der sehr geringen Verfahrensstreuung in der Lage, bei der Beurteilung der Homogenität des Kanditatenmaterials entscheidene Informationen über die Analytverteilung zu liefern.
Zur Zertifizierung von Referenzmaterial wird in der anorg. chem. Analytik häufig die ICP-OES eingesetzt.
Die RFA, in Kombination mit der Rekonstitutions- und Boratschmelztechnik, ist bei der Zertifizierung eine Analysenmethode, die sich in Bezug auf Probenvorbereitung und Messmethodik grundsätzlich von der ICP-OES unterscheidet.
Dadurch trägt sie zur analytischen Methodenvielfalt und damit zur Richtigkeit des zertifizierten Wertes bei und erfüllt zudem im vollsten Maße die Anforderung an metrologischer Rückführbarkeit.
Nichts wissen macht nichts? Erfahrungen mit dem "Standardlosen" Analyseprogramm IQ+.
Die moderne semiquantitative Röntgenfluoreszensanalyse bietet als feststoffanalytisches Verfahren die Möglichkeit, chem. Elemente einer völlig unbekannten Probe schnell und zerstörungsfrei qualitativ und quantitativ zu bestimmen. Im Gegensatz zur konventionellen Kalibration, die sich auf eine Elementauswahl beschränkt, wird bei der semiquantitativen RFA das gesamte mögliche Elementspektrum (5?Z?92, B-U) erfasst.
Nach einem Scan, der sich in anregungs- und erfassungsoptimierte Teilscans aufteilt, werden aus den Peaklagen zunächst die Elemente erkannt. Aus den Peakhöhen werden dann, über iterativ arbeitende Fundamentalparameter gestützte Rechenprogramme, die Elemente quantitativ bestimmt. Die gebräuchlichen semiquantitativen Programme basieren auf Universalkalibrationen wobei die Probenart (Metall, Glas, Pressling
) nicht berücksichtigt wird.
In der BAM wurde nun begonnen, probenspezifische Kalibrationen zu erstellen, so dass die Richtigkeit des Analyseergebnisses gesteigert werden konnte.
Ziel ist es, einen großen Teil der analytischen Fragestellungen an ständig wechselnd zusammengesetzten Proben feststoffanalytisch mit der RFA bearbeitbar zu machen.
The EU RoHS Directive (2002/95/EC of the European Parliament and of the Council) bans the placing of new electrical and electronic equipment containing more than agreed levels of lead, cadmium, mercury, hexavalent chromium, polybrominated biphenyl (PBB) and polybrominated diphenyl ether (PBDE) flame retardants on the EU market. It necessitates methods for the evaluation of RoHS compliance of assembled electronic equipment. In this study mounted printed circuit boards from personal computers were analyzed on their content of the three elements Cd, Pb and Hg which were limited by the EU RoHS directive. Main focus of the investigations was the influence of sample pre-treatment on the precision and reproducibility of the results. The sample preparation steps used were based on the guidelines given in EN 62321. Five different types of dissolution procedures were tested on different subsequent steps of sample treatment like cutting and milling. Elemental analysis was carried out using ICP–OES, XRF and CV–AFS (Hg). The results obtained showed that for decision-making with respect to RoHS compliance a size reduction of the material to be analyzed to particles ≤1.5 mm can already be sufficient. However, to ensure analytical results with relative standard deviations of less than 20%, as recommended by the EN 62321, a much larger effort for sample processing towards smaller particle sizes might be required which strongly depends on the mass fraction of the element under investigation.
Phosphorus (P) is an essential element for all living organisms and cannot be replaced. Municipal sewage sludge is a carrier of phosphorus, but also contains organic pollutants and heavy metals. A two-step thermal treatment is suggested, including mono-incineration of sewage sludge and subsequent thermochemical treatment of the ashes. Organic pollutants are completely destroyed by mono-incineration. The resulting sewage sludge ashes contain P, but also heavy metals. P in the ashes exhibits low bioavailability, a disadvantage in farming. Therefore, in a second thermochemical step, P is transferred into mineral phases available for plants, and heavy metals are removed as well. The thermochemical treatment was investigated in a laboratory-scale rotary furnace by treating seven different sewage sludge ashes under systematic variation of operational parameters. Heavy metal removal and the increase of the P-bioavailability were the focus of the investigation. The present experimental study shows that these objectives have been achieved with the proposed process. The P-bioavailability was significantly increased due to the formation of new mineral phases such as chlorapatite, farringtonite and stanfieldite during thermochemical treatment.