P. Tschöpel

Aufschluß biologischer Matrices für die Bestimmung sehr niedriger Spurenelementgehalte bei begrenzter Einwaage mit Salpetersäure unter Druck in einem Teflongefäß

For the determination of trace elements (< 10−4%) in biological materials (e.g. tissue, food, sewage muds) in samples ≤ 500 mg a pressure decomposition with nitric acid or a mixture of nitric and hydrofluoric acid in a teflon tube is described. The recoveries for the volatile elements, e.g. Hg, Se and I, in the ng-range were investigated by the tracer method and were found to be ≥ 98%.ZusammenfassungFür die Bestimmung von Spurenelementgehalten (< 10−4%) in biologischen Matrices (Gewebe, Nahrungsmittel, Abwasserschlämme u. a.) bei begrenzten Einwaagen (≤ 500mg) wird ein Druckaufschluß mit HNO3 bzw. HNO3-HF in einem Teflongefäß beschrieben. Radiochemische Messungen ergaben, daß die Verluste selbst bei Nanogramm-Mengen flüchtiger Elemente (Hg, Se, J u.a.) unter 2% liegen.

Preconcentration of palladium, platinum and rhodium by on-line sorbent extraction for graphite furnace atomic absorption spectrometry and inductively coupled plasma atomic emission spectrometry

A flow system combined with a segmentation technique was used to develop an efficient on-line sorbent extraction preconcentration system for palladium, platinum and rhodium for graphite furnace atomic absorption spectrometry (GFAAS) and inductively coupled plasma atomic emission spectrometry (ICP-AES). The investigated metals were preconcentrated as their bis(carboxylmethyl)dithiocarbamate (CMDTC) chelates on a microcolumn packed with XAD-4 after the off-line addition of solid CMDTC to the sample solution containing SnCl2 and hydrochloric acid. The sample, rinsing and eluent solutions were segmented by air to prevent dispersion. The eluate was collected on-line in a PTFE loop and was forced either into the graphite tube by nitrogen or into the ICP by using a carrier solution. The time duration of one preconcentration cycle was about 10 min. The influence of the acidity of the synthetic sample solution, the concentration of the complexing reagent and reducing agent, the flow-rate for preconcentration, the efficiency of the desorption and the influence of various matrices were also investigated. The detection limits (3σ) were 0.03, 0.1 and 0.01 ng/ml for Pd, Pt and Rh, respectively, using GFAAS detection. The method was applied for the analysis of polluted biological materials.

Zur Ursache und Vermeidung systematischer Fehler bei Elementbestimmungen in wäßrigen Lösungen im ng/ml- und pg/ml-Bereich

SummaryConsiderable discrepancies have been found between theoretically derived detection limits in literature for the determination of elements in the extreme trace range and actually found results for high-purity materials. This caused us to study the systematic errors (blanks, adsorption and desorption) of solution procedures. The sources of systematic errors by contamination are demonstrated by example of the determination of magnesium and zinc at pg/ml levels by AAS with electrothermal atomization. These sources of the blanks mainly determine the actual detection limits of solution procedures and appear even in very simple operations, e.g., preparation, measuring, storage, filtration and evaporation of solutions. Possibilities for eliminating these errors are: selection of suitable vessel materials and reagents and their effective cleaning resp. purification as well as working in clean rooms under extreme conditions. The exemplary studies show the actual obtainable detection abilities, which may differ — depending on the element — from the idealized and unrealistic values of the literature.ZusammenfassungErhebliche Diskrepanzen zwischen theoretisch abgeleiteten, in der Literatur angegebenen Nachweisgrenzen von Elementbestimmungsverfahren im extremen Spurenbereich und den real gefundenen Ergebnissen im Rahmen der Reinststoffanalytik gaben Anlaß, systematische Fehler (Blindwerte, Adsorption und Desorption) bei Lösungsverfahren grundlegend zu untersuchen. Am Beispiel der Bestimmung von Magnesium und Zink im pg/ml-Bereich durch AAS mit elektrothermischer Atomisation werden die Quellen für Kontaminationen nachgewiesen, die in erster Linie die realen Nachweisgrenzen der Lösungsverfahren bestimmen und schon bei den einfachsten Operationen wie Bereitung, Abmessen, Aufbewahren, Filtrieren und Eindampfen von Lösungen auftreten. Möglichkeiten zu ihrer Ausschaltung sind: Auswahl geeigneter Gerätematerialien und Reagentien und deren Reinigung sowie das Arbeiten in staubarmen Laboratorien (Reinen Räumen) unter extremen Reinheitsbedingungen. Die exemplarischen Untersuchungen zeigen die praktisch erreichbaren Grenzen des Nachweisvermögens, das sich elementabhängig z. T. wesentlich von den idealisierten und unrealistischen Literaturwerten unterscheiden kann.

Different sample introduction systems for the multaneous determination of As, Sb and Se by microwave-induced plasma atomic emission spectrometry

Abstract The determination of hydride-forming elements using different sample introduction procedure into microwave-induced plasmas (MIPs) has been studied. For the determination of As, Sb and Se analyte introduction was accomplished with a pneumatic concentric glass nebulizer,a graphite furnace, or with thydride generation followed by cold-trapping or hot-trapping in a graphite furnace. The detection limits obtained with different types of low power MIPs (toroidal, 1 or 3 filament MIPs) operated in a TM 010 cavity according to Beenakker also were investigated. The contruction of the flow system used for preconcentration and the effects of reagent concentration, gas flow rates as with MIP-atomic emission spectrometry (AES) were investigated. The trapping of the hydrides followed by their vaporization showed substantial advantages over the other introduction systems investigated, especially with respect to power of detection. Further, mutual interferences being a big problem in atomic absorption spectrometry are widely absent in MIP-AES. Under compromise operating conditions the detection limits for As, Sb and Se are 0.4; 0.35; 0.25 ng ml −1 respectively, while the sample volume can be varied from 0.05 ml up to several millilitres.

Analysis of advanced ceramics and their basic products

SummaryA review on the analysis of the most important ceramic materials and their basic substances is given. The importance of minor and trace elements in the bulk as well as their distribution on the microscale in both classes of substances is discussed by the example of Al2O3, AlN, TiO2, Si3N4, SiO2, SiC, Y2O3, ZrO2-based and some other ceramics and of their basic substances. The state-of-the-art and trends of development in modern atomic spectrometric methods for bulk analysis of the basic substances subsequent to sample dissolution, such as plasma emission and mass spectrometry, but also of direct methods such as slurry nebulization for plasma spectrometry, inorganic mass spectrometry and X-ray spectrometry are discussed. Further, first approaches for the in-depth analysis of powders and trends in direct methods for compact ceramics based on laser evaporation as well as on electron and ion probe techniques are presented. The latter are illustrated with selected examples from the literature.

Characteristics of nebulized suspensions of refractory oxide powders used for the production of ceramics and their evaporation behaviour in an inductively coupled plasma

Abstract The capabilities of ICP-spectrometry using slurry atomization with a Babington nebulizer for the analysis of refractory oxide powders having a grain size of up to 20 μm were studied. First, aerosol droplet size distributions for the case of Al2O3 slurries (1 % w v ) were measured with a cascade impactor. Further, solid particles in the aerosol were collected on membrane niters at the top of the aerosol injector in the absence of an ICP discharge and were found to have diameters below 17 μm. Electron microscopic examinations of the aerosol collected after its passing through a 2.4 kW argon ICP allowed it to distinguish two different particle morphologies, namely sub-μm condensates and partially remolten larger particles. A simple physical model describing the evaporation of solid particles in the ICP was presented and results predicted with this model are compared to those experiments performed with suspensions of Al2O3 and SiO2 powders.

Atomic emission and atomic absorption spectrometric analysis of high-purity powders for the production of ceramics

SummaryDirect analysis methods and multistage combined analytical procedures for the determination of impurities at the μg/g level and the upper ng/g level in high-purity powders of Al2O3, AlN, Si3N4 and SiC are described. Results obtained with a novel direct slurry-atomization technique using a Babington nebulizer and inductively coupled plasma optical emission spectrometry (ICP-OES) are presented. A comparison of analysis results of combined analytical procedures including wet chemical decomposition and determinations with graphite furnace atomic absorption spectrometry (ETAAS) or ICP-OES with those of slurry-atomization ICP-OES show the capabilities of this technique for routine analysis in production control. Detection limits for Al, B, Ca, Co, Cu, Fe, Mg, Mn, Si, Ti, W, V, and Zn in the matrices mentioned are between 0.03 and 2.5 μg/g. For elemental concentrations ⩾ 10 μg/g relative standard deviations of the measurements are generally below 10%. The technique is shown to be a powerful tool for trace determinations in powder samples. This is shown by its use for analysis of a series of the ceramic powders mentioned and comparative results of other direct techniques such as total reflection X-ray fluorescence spectrometry and instrumental neutron activation analysis.

Determination of impurities in silicon carbide powders

SummaryThe analysis of SiC powders used for the production of high-performance ceramics was investigated by combined procedures as well as by a direct technique including atomic spectrometric detection. For the combined chemical procedure, SiC powders (0.25 g) were completely dissolved in a mixture of HNO3, HF and fuming H2SO4 in an autoclave at 240°C within 8 to 20 h. In the final 0.5% w/v solution 13 elements were determined by electrothermal atomic absorption spectrometry (ETAAS) and by inductively coupled plasma atomic emission spectrometry (ICP-AES). With acid decomposition the detection limits for Ca, Cd, Cr, Cu, Mg, Mn and Zn were found to be in the range of 0.1–1 μg/g; those for Al, B, Fe, Ni, Ti and V are at the 1–5 μg/g level. With a Babingtontype nebulizer 1% slurries of SiC can be directly analyzed by ICP-AES. Calibration was performed by standard addition of aqueous solutions of the elements to be determined and the detection limits are close to those of ETAAS subsequent to pressure decomposition. The required analysis time was reduced from approx. 24 h to 30 min. First results for Ca, Cr, Cu, Mg, Mn, Ti and V as well as the needs to overcome systematic errors of this method, e.g. for Fe, are communicated.

Optimization of slurry nebulization inductively-coupled plasma atomic emission spectrometry for the analysis of ZrO2-powder

SummaryThe optimization and use of ICP-AES with slurry nebulization for the direct analysis of ZrO2-powder is described. The powder samples are dispersed in water, acidified to pH 2 and the slurry is fed into a Babington nebulizer. The effects of grain size, pH of the suspending medium and standing time on the stability of the slurry are discussed. For the optimization of the ICP operating conditions, a simplex technique is applied and for this purpose three types of objective functions were examined. Identical behaviour of slurries and solutions with the same matrix concentrations in the ICP-AES is achieved for powders with particle sizes lower than 10 μm; in the latter case calibration can be performed by standard addition with aqueous solutions. The detection limits for Al, B, Ca, Cu, Fe, Mg, Mn, Na, Ti, V. Y are 0.03 μg/g to 10 μg/g and the standard deviation is generally lower than 10%. Six commercially available ZrO2 powders are analyzed by slurry nebulization ICP-AES and the results were found to agree well with those obtained by ICP-AES after chemical decomposition of the samples.

Determination of platinum in biotic and environmental samples by graphite furnace atomic absorption spectrometry after its electrodeposition into a graphite tube packed with reticulated vitreous carbon

SummaryTobacco, beans, slag and dust samples were digested with nitric and hydrochloric acids in high-pressure PTFE bombs. Pt in the sample solutions was electrochemically deposited at −0.9 to −1.2 V in a flow system incorporating a 3-electrode flow-through cell with a graphite counter and Ag/AgCl reference electrodes. A pyrolytically coated graphite tube packed with reticulated vitreous carbon (RVC) served as the working electrode with the RVC filling axially bored to let the light beam pass through the tube during the AAS measurements. This opening was plugged with a glass rod during the preconcentration step. After the electrodeposition the tube was placed into the graphite furnace and an atomization temperature of 2700°C was applied. The geometry of the cell, flow rate for electrodeposition, deposition potential and electrolyte composition were optimized. The absolute detection limit was found to be about 0.3 ng Pt.