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For determination of silicon in aqueous solutions by electrothermal atomic absorption spectrometry methane/argon mixtures as a gaseous modifier were applied during the pyrolysis step to improve the analytical performance. The beneficial effects observed on thermal stabilization, signal enhancement and shape of absorbance signals were attributed to the thermal decomposition products of methane, which were hydrogen and carbon black (soot). Using a 5% CH4 mixture with argon, the optimized pyrolysis and atomization temperatures were 1350 °C and 2450 °C, respectively. A flushing step following the pyrolysis was mandatory to avoid background absorption and accelerated deposition of pyrolytic graphite. Characteristic masses of 50 and 30 pg were obtained for standard transversely heated graphite atomizer (THGA) tubes and end-capped THGA tubes, respectively, which were lower than with other previously applied modifiers. A limit of detection of 0.2 µg L- 1 (3 s, n = 10) has been obtained. In addition, this gaseous modifier did not contribute to contamination which often was significant when a liquid modifier solution was co-injected. The proposed method has been applied to the determination of silicon in ultrapure water, nitric and hydrochloric acids.
The Bundesanstalt für Materialforschung und -prüfung (Federal Institute for Materials Research and Testing) (BAM) is establishing a system of primary reference materials to meet the demands for metrological traceability and to act as national standards in the field of elemental analysis. For all elements of the periodic table - except those that are gases or radioactive - two different kinds of reference materials are being certified. One is for analyte calibration (Type A) and one for problems concerning matrix matching (Type B). These substances are of very high purity and of defined stoichiometry. As far as possible, pure elements and metals rather than pure compounds are used. The certification of both types of material requires most elements of the periodic table to be certified at very low levels using trace element analysis methods. The application of these methods is described and examples of the certification of copper and iron are given.
Certification of the mass fractions of trace elements in a medium purity graphite reference material
(2018)
The increasing application of graphite materials in various fields of technology and science enhances the demand for strictly controlled properties which are often directly correlated to the contents of trace element impurities. Therefore, the availability of powerful, rapid and reliable analytical methods for the determination of trace impurities is essential for process and quality control. Certified reference materials, indispensable for the development and validation of appropriate trace analytical methods for the characterization of special purity graphite materials are still lacking. Therefore, BAM in co-operation with the working group “Special Materials” of the committee of chemists of GDMB (Gesellschaft der Metallurgen und Bergleute e.V.) certified an industrially sourced graphite material with genuine elemental impurities.
The candidate material was a commercial product (NBG 18) taken from the customary production line of the producer SGL CARBON, Chedde (France). The homogeneity of the powdered material was assessed by means of ETV-ICP OES and DC Arc-OES. Certification of the candidate reference material was based on an inter-laboratory comparison involving 17 expert laboratories from Germany, France, Slovenia, USA, South Africa. A variety of different mineralization, digestion, leaching, fusion and combustion techniques prior to ICP OES and photometry, methods without sample preparation (INAA, k0-INAA) as well as typical solid sampling methods (ETV-ICP OES, ETV-ICP-MS, SS-ET AAS, DC Arc-OES, MF-DC Arc-OES) were used to characterise the material. Certified mass fractions and their expanded uncertainties (k = 2) were assigned for 27 elements (Al, B, Ba, Be, Ca, Co, Cr, Cu, Fe, K, Li, Mg, Mn, Mo, Na, Ni, P, Pb, S, Si, Sr, Ti, V, W, Y, Zn, Zr), ranging from (0.00050 ± 0.00027) mg/kg for Be to (41 ± 6) mg/kg for Si. Additionally, informative values are given for the: trace element contents of Ag, As, Au, Bi, Cd, Cs, Dy, Eu, Ga, Gd, Hg, In, La, Nb, Rb, Re, Rh, Sb, Sc, Se, Sm, Sn, Ta, Tb, Te, Th, U; method specific values obtained by ETV-ICP OES (BETV and SiETV) and the ash content of the material.
The certified material “BAM-S009 Medium Purity Graphite Powder” is available for purchase from BAM.
Certification of the mass fractions of trace elements in a medium purity graphite reference material
(2018)
The increasing application of graphite materials in various fields of technology and science enhances the demand for strictly controlled properties which are often directly correlated to the contents of trace element impurities. Therefore, the availability of powerful, rapid and reliable analytical methods for the determination of trace impurities is essential for process and quality control. Certified reference materials, indispensable for the development and validation of appropriate trace analytical methods for the characterization of special purity graphite materials are still lacking. Therefore, BAM in co-operation with the working group “Special Materials” of the committee of chemists of GDMB (Gesellschaft der Metallurgen und Bergleute e.V.) certified an industrially sourced graphite material with genuine elemental impurities.
The candidate material was a commercial product (NBG 18) taken from the customary production line of the producer SGL CARBON, Chedde (France). The homogeneity of the powdered material was assessed by means of ETV-ICP OES and DC Arc-OES. Certification of the candidate reference material was based on an inter-laboratory comparison involving 17 expert laboratories from Germany, France, Slovenia, USA, South Africa. A variety of different mineralization, digestion, leaching, fusion and combustion techniques prior to ICP OES and photometry, methods without sample preparation (INAA, k0-INAA) as well as typical solid sampling methods (ETV-ICP OES, ETV-ICP-MS, SS-ET AAS, DC Arc-OES, MF-DC Arc-OES) were used to characterise the material. Certified mass fractions and their expanded uncertainties (k = 2) were assigned for 27 elements (Al, B, Ba, Be, Ca, Co, Cr, Cu, Fe, K, Li, Mg, Mn, Mo, Na, Ni, P, Pb, S, Si, Sr, Ti, V, W, Y, Zn, Zr), ranging from (0.00050 ± 0.00027) mg/kg for Be to (41 ± 6) mg/kg for Si. Informative values are given for further parameters: trace element contents of Ag, As, Au, Bi, Cd, Cs, Dy, Eu, Ga, Gd, Hg, In, La, Nb, Rb, Re, Rh, Sb, Sc, Se, Sm, Sn, Ta, Tb, Te, Th, U; method specific values obtained by ETV-ICP OES (BETV and SiETV) and ash content.
The new certified material is available as BAM Reference Material BAM-S009 Medium Purity Graphite Powder.
Boron isotope amount ratios n(10B)/n(11B) have been determined by monitoring the absorption spectrum of boron monohydride (BH) in a graphite furnace using high-resolution continuum source molecular absorption spectrometry (HR-CS-MAS). Bands (0→0) and (1→1) for the electronic transition X1Σ+ → A1Π were evaluated around wavelengths 433.1 nm and 437.1 nm respectively. Clean and free of memory effect molecular spectra of BH were recorded. In order to eliminate the memory effect of boron, a combination of 2% (v/v) hydrogen gas in argon and 1% trifluoromethane in argon, an acid solution of calcium chloride and mannitol as chemical modifiers was used. Partial least square regression (PLS) for analysis of samples and reference materials were applied. For this, a spectral library with different isotopes ratios for PLS regression was built. Results obtained around the 433.1 nm and 437.1 nm spectral regions are metrologically compatible with those reported by mass spectrometric methods. Moreover, for the evaluated region of 437 nm, an accuracy of 0.15‰ is obtained as the average deviation from the isotope reference materials. Expanded uncertainties with a coverage factor of k = 2 range between 0.15 and 0.44‰. This accuracy and precision are compatible with those obtained by mass spectrometry for boron isotope ratio measurements.