Viliam Krivan

Multielement analysis of green coffee and its possible use for the determination of origin

Using instrumental neutron activation analysis (INAA), graphite furnace atomic absorption spectrometry (GFAAS), flame atomic absorption spectrometry (FAAS) and combustion elemental analysis, green coffees of the Arabica species produced in crop year 1987/88 in Colombia, Costa Rica, Cuba, El Salvador, Mexico, Nicaragua, Panamá and Papua New Guinea were analysed for the elements Ba, Br, C, Ca, Co, Cr, Cu, Cs, Fe, H, K, La, Mg, Mn, N, Na, Rb, Sc, Sr and Zn. In accordance with the concentrations determined, the elements could be ranked into five groups: Sc (sub-ppb level); Br, Co, Cr, Cs and La (ppb level); Ba, Cu, Fe, Mn, Na, Rb, Sr and Zn (ppm level); Ca and Mg (%o level); and C, H, K and N (% level). On the basis of the results obtained, an attempt was made to establish the origin of the green coffee via its elemental composition. Among the investigated elements, manganese was found to be best suited as an indicator for this purpose. However, the elements C, Co, Cs, Na and Rb proved to be of interest too.

A graphite furnace electrothermal vaporization system for inductively coupled plasma atomic emission spectrometry

An improved graphite furnace electrothermal vaporization device equipped with an autosampler for inductively coupled plasma atomic emission spectrometry is presented. The transport losses of eight selected analytes in the individual segments of the device were determined by means of the radiotracer technique by applying amounts traced comparable to those to be determined in real samples. The results obtained from the radiotracer study were the basis for further improvement of the interface design, leading to considerable increase of the total transport efficiency, which finally was found to be between 26 (for Cr) and 57% (for Ga). The whole system consists of a graphite furnace vaporizer, a power supply, a gas flow box, and an autosampler with incorporated microbalance. The temperature program, gas flows, and autosampler functions are controlled by a data station which also provides the data acquisition and processing of the transient signals. The performance parameters of the developed system were evaluated using aqueous standard solutions. Absolute limits of detection for most analytes were between 0.1 and 1 ng, and for As, K, Ni and Pb, they were between 2 and 3.2 ng.

Comparison of various forms of palladium used as chemical modifiers for the determination of selenium by electrothermal atomic absorption spectrometry

The efficiencies of various chemical modifiers based on palladium for the determination of selenium in the presence of sodium chloride by electrothermal atomic absorption spectrometry were investigated. Palladium nitrate proved to be superior to palladium chloride for selenium only in pure solutions. In the presence of a chloride matrix, these two chemical modifiers are of similar and rather low effectiveness, whereas ammonium dioxalatopalladate(II), colloidal palladium and a mixture of palladium nitrate and diammonium hydrogen citrate were found to be more effective. Using these latter modifiers, the chloride matrix does not prevent the formation of metallic palladium at relatively low temperatures. However, maximum modification efficiency was obtained with prereduced (at 1000 °C) palladium. Using this form of palladium as a chemical modifier, up to 330 µg of sodium chloride do not interfere in the determination of 2 ng of selenium. The relatively low effectiveness of colloidal palladium, which was stabilized with a polymer compound, could be explained by the formation and partial loss of volatile organoselenium compounds. Also, the surface of colloidal palladium is screened off by the polymer causing a rather low accessibility for selenium species.

Solid sampling electrothermal atomic absorption spectrometry for analysis of aluminium oxide powders

An atomic absorption spectrometer with a transversely heated graphite tube and a solid sampling system based on the boat technique was used for the direct determination of Co, Cr, Cu, Fe, K, Mg, Mn, Ni and Zn in high-purity aluminium oxide powders. The high background absorption caused by gaseous aluminium and aluminium suboxides could be eliminated by optimization of the atomization temperature and integration time, and by pyrolytic recoating of the graphite tube. Sample amounts of up to 6 mg per atomization were applied. Calibration was performed by using aqueous solutions. Limits of detection between 0.25 ng g–1 (Mg) and 25 ng g–1 (Co) were achieved. The accuracy was checked by comparison of the results with those obtained by instrumental and radiochemical neutron activation analysis and by other independent methods.

Determination of trace impurities in high-purity quartz by electrothermal vaporization inductively coupled plasma mass spectrometry using the slurry sampling technique

A method has been developed for the determination of 14 relevant trace impurities in high-purity quartz based on ETV-ICP-MS using slurry sampling. The ETV device consisted of a double layer tungsten coil. Experimental conditions were optimized with respect to the temperature program, the carrier gas flow, the i.d. of the aerosol tubing, ICP-MS measurement parameters and internal standardization. Excluding U, calibration had to be carried out by the standard additions method because of non-spectral matrix interferences. For U, simple quantification via calibration curves, recorded with aqueous standards, was possible. The observed interferences also aggravated the background evaluation, which seriously limited the determination of Al and Fe. The method was applied to the determination of Al, Ba, Co, Cr, Cu, Fe, Li, Mg, Mn, Na, Pb, Sr, U and Zn in two quartz samples of different grades of purity. The accuracy of the results was checked by their comparison with those obtained by independent methods including instrumental neutron activation analysis. The achievable detection limits are between 2 ng g -1 (Li, U) and 70 µg g -1 (Al).

A radiotracer study on effectiveness of platinum metals as chemical modifiers in electrothermal atomic absorption spectrometry: behaviour of selenium in a graphite furnace

Abstract The effect of palladium, platinum, rhodium and iridium on the behaviour of selenium in the graphite furnace for electrothermal atomic absorption spectrometry (ETAAS) has been investigated by the radiotracer technique. These chemical modifiers have been used both in the chloride and in a reduced form, the latter being achieved by preliminary pyrolysis at 1000°C. The losses of selenium were observed during the pyrolysis stage for every modifier studied. For prereduced Pd, Pt, Rh and Ir as chemical modifiers, at the pyrolysis temperature of 600°C these losses amount up to 13%, 32%, 41% and 65%, respectively. In most instances, the effectiveness of chlorides of the platinum metals is lower than that of the pre-reduced modifiers. It is postulated that the dissolution of elemental selenium in palladium and platinum at relatively low temperatures diminishes losses of selenium in the pyrolysis stage.

Cross-interferences of hydride-forming elements in hydride-generation atomic absorption spectrometry

Abstract A systematic study was made of interferences of As(V), Bi(III), Se(IV), Sb(III), Sn(IV) and Te(IV) in the determination of As(V), Sb(III, Se(IV) and Sn(IV) by hydride-generation atomic absorption spectrometry. The interfering elements were applied in concentrations between 1 ng ml−1 and 100 μg ml−1. The effect of potassium iodide on the interferences by bismuth, selenium and tellurium on the antimony absorption signal and the interferences of antimony, arsenic, bismuth, tellurium and tin on the selenium absorption signal by addition of oxygen and a mixture of oxygen and ozone were also investigated. A time versus absorption diagram with superimposed recordings of the absorption signals of the elements antimony, arsenic, bismuth, selenium, tellurium and tin is given.

Direct determination of impurities in powdered silicon carbide by electrothermal atomic absorption spectrometry using the slurry sampling technique

A direct method of analysis of powdered silicon carbide for the determination of Al, Cd, Cr, Cu, Fe, Mg, Mn, Ni, Ti, V and Zn based on electrothermal atomic absorption spectrometry (ETAAS) using the slurry sampling technique is described. Possible spectral interferences caused by the refractory matrix components were studied. The technique was optimized with regard to sample preparation, dispensing, thermal pre-treatment and atomization parameters. The accuracy was checked by comparison of the results with those obtained by ETAAS and inductively coupled plasma atomic emission spectrometry involving decomposition of the sample, and by instrumental neutron activation analysis. For most of the elements investigated the achievable limits of detection are at the sub-microgram per gram level.

Determination of uranium, thorium, and 18 other elements in high-purity molybdenum by radiochemical neutron activation analysis

A radiochemical neutron activation analysis technique for the determination of uranium and thorium in high-purity molybdenum via the indicator radionuclides {sup 239}Np for U and {sup 233}Pa for Th has been developed. Simultaneously, the elements Ag, Co, Cr, Cs, Cu, Fe, Ga, In, Ir, K, Mn, Na, Ni, Rb, Ru, Sc, Se, and Zn can be determined, too. The elements Hf, Sb, Ta, Sn, and W were determined by instrumental neutron activation analysis. The radiochemical separation is performed by anion exchange on a Dowex 1 {times} 8 column from a 20 M HF/3% H{sub 2}O{sub 2} medium. A limit of detection of 4 ng/g for uranium and 40 pg/g for thorium can be achieved. For the other elements, the limits of detection are between 1 pg/g and 100 ng/g. A modified more selective separation of the indicator radionuclide of Th, {sup 233}Pa, allows improvement of the limit of detection for Th by a factor up to 5. This technique was applied to the analysis of high-purity molybdenum, and the results of a number of elements were compared with those of other techniques.

Behaviour of Selenium(iv) in a Transversely Heated GraphiteAtomizer for Electrothermal Atomic Absorption Spectrometry in the Presenceof Platinum Metals as Chemical Modifiers

The effect of Pd, Pt, Rh, Ru and Ir on the behaviour of selenium in a transversely heated graphite atomizer for ETAAS was investigated. The chemical modifiers were used mainly in a thermally pre-reduced form. For all modifiers studied, the maximum pyrolysis and optimum atomization temperatures for selenium were approximately the same (about 1200 and 1600–1800 °C, respectively). There does not appear to be any correlation between these parameters and the melting-points of the modifiers used. Under optimized conditions, losses of about 10% of selenium at pyrolysis temperatures of 400–800 °C were observed for the pre-reduced Rh and Ru modifiers. The characteristic mass for selenium in the presence of pre-reduced Pt metal modifiers varied from 27.5 pg with the Pd modifier in a new graphite tube to 38.6 pg with the Pt modifier in a ‘used’ tube. All pre-reduced platinum group metals studied enabled the negative influence of up to 500 µg of chloride ion (as NaCl) on the determination of selenium to be eliminated. The efficiency of modification of chlorides of the platinum metals studied is very low, except for RhCl 3 . In general, they can even act as an additional source of interference.