Klaus Dittrich

Shadow spectral fiming: a method of investigating electrothermal atomization. Part 2. Dynamics of formation and structure of the absorption layer of aluminium, indium and gallium molecules

The shadow spectral filming method suggested in Part 1 of this paper is used to study the dynamics of formation and structure of the absorption layers of Ga, In and Al molecules. The molecules of these elements are confined to the central part of the graphite atomizer and their distribution is strongly non-homogeneous with a pronounced decrease in concentration near the graphite walls. The cross-sectional distribution of these molecules, along with other experimental evidence, suggests that the molecular species recorded were Ga2O, In2O and Al2O. During the atomization of In, Ga and especially Al, these suboxides and their heterogeneous reactions with the graphite surface play an important role. The process of vaporization of aluminium-containing salts consists of two pronounced stages. Firstly, the sample is vaporized as a gaseous suboxide and secondly, the suboxide is oxidized to form finely dispersed, condensed alumina, Al2O3(s,l). The cloud of condensed alumina has a ‘doughnut’ structure that mimics the inner surface of the graphite tube.

Comparative study of injection into a pneumatic nebuliser and tungsten coil electrothermal vaporisation for the determination of rare earth elements by inductively coupled plasma optical emission spectrometry

Injection into a pneumatic nebuliser and vaporisation using a tungsten coil electrothermal vaporisation system, with a 3-kW argon-nitrogen inductively coupled plasma (ICP), are compared for the determination of the rare earth elements. The sampling efficiency and thus also the absolute power of detection of the tungsten coil ICP optical emission spectrometric (ICP-OES) technique are better by two orders of magnitude, than the injection technique. The absolute detection limits for the rare earth elements are at the pg level; for the refractory rare earth elements (Er, La, Lu and Y), they are lower than those obtained by graphite furnace atomic absorption spectrometry, whereas for the other rare earth elements (Eu, Sc, Tm and Yb), the detection limits are comparable. With injection of samples into a pneumatic nebuliser and ICP-OES, matrix effects are low and absolute amounts of the order of mg of the rare earth matrix can be tolerated, giving relative detection limits down to 1 µg g–1. The amount of rare earth matrix that can be tolerated with the tungsten-coil atomiser is two orders of magnitude lower. Thus the relatively detection limits of the two methods are of the same order, although the matrix effects are considerably higher with the tungsten coil.

Laser-excited atomic fluorescence spectrometry as a practical analytical method. Part I. Design of a graphite tube atomiser for the determination of trace amounts of lead

Tube atomiser designs for the laser-excited atomic fluorescence spectrometric (LAFS) technique were investigated. Commercially available cuvettes of the Beckman 1268 type and Perkin-Elmer HGA-500-EA 3 type that had been modified for use with LAFS were used. The fluorescence was measured within the tube. These tube atomisers were tested and compared with a home-made rod atomiser by measuring the fluorescence of lead. The detection limits, sensitivities and reproducibility obtained by tube atomisation were greatly improved compared with rod atomisation. The influence of some metal nitrates and sodium sulphate on the fluorescence intensity of lead was investigated. With tube atomisation the interferences were reduced.

Analytical applications of furnace atomic non-thermal excitation spectrometry (FANES) and molecular non-thermal excitation spectrometry (MONES). Part. 5. Study of the MONES of PO and HPO for the determination of trace amounts of phosphorus

A method for the determination of phosphorus by the molecular non-thermal excitation spectrometry (MONES) of PO and HPO has been developed. The phosphorus was introduced into the furnace atomic non-thermal excitation spectrometry (FANES) source as a solution of sodium dihydrogen phosphate. The measurements were carried out at the bands that gave the maximum signals, for PO at 246.4 nm and for HPO at 507 nm. The electrical, thermal and chemical conditions were optimised and are discussed. In addition, the influence of La3+ as a chemical modifier on the MONES of PO and HPO was investigated. The best values for the detection limit were 700 pg of P (MONES of PO) and 3400 pg of P (MONES of HPO). By comparison with the best values obtained with commercial electrothermal atomisation atomic absorption spectrometry instruments, these values are better by factors of 8 and 1.6, respectively. However, the determination of P by FANES at 213.5/213.6 nm is the best method for investigations of phosphorus using the FANES source, in the presence of La3+ as a chemical modifier.

Analytical applications of furnace atomic non-thermal excitation spectrometry (FANES) and molecular non-thermal excitation spectrometry (MONES). Part 4. Determination of trace amounts of phosphorus by FANES

A method of determining phosphorus by furnace atomic non-thermal excitation spectrometry (FANES) has been developed. The phosphorus is introduced into the FANES source as a solution of sodium dihydrogen phosphate. The measurements are carried out at 213.5/213.6 and 253.3/253.5 nm, the transition at 213.5/213.6 nm being the more sensitive one. The thermal and chemical conditions were optimised, the best chemical modifier being La3+ ions as they stabilise phosphate ions as LaPO4. Using the optimum amount of lanthanum (2 µg) the pre-treatment temperatures could be increased considerably (300 to 800 °C at normal pressure and 350 to 400 °C at low pressure). The best detection limit obtained is 90 pg of phosphorus, which is an improvement by a factor of 60 in comparison with the best values obtained with commercially available electrothermal atomisation atomic absorption spectrometric (ETAAS) instruments. Examples for real analyses with associated matrix interferences are given.

Investigations on the determination of chloride and bromide by furnace atomic non-thermal excitation spectrometry and furnace ionic non-thermal excitation spectrometry

The determination of chloride and bromide by non-thermal excitation spectrometry in a graphite furnace using both atomic and ionic spectral lines was investigated. The most sensitive determinations could be made at the ionic lines Cl II 479.545 nm and Br II 470.486 nm. The addition of an ionization buffer provided constant plasma conditions resulting in improved linearity of the calibration function. Under optimum conditions and in the presence of appropriate buffers detection limits of 0.6 ng for chloride and 2 ng for bromide were obtained.

Determination of nitrogen and oxygen and species containing nitrogen by molecular non-thermal excitation spectrometry (MONES) using microwave-induced plasma (MIP) and furnace atomization non-thermal excitation spectrometry (FANES) sources

A microwave-induced plasma (MIP) source produced through a surface-wave propagation process (surfatron) and a furnace atomization non-thermal excitation spectrometry source have been used to determine N and O in gaseous and aqueous samples, respectively, through the formation and emission of NH and OH radicals. Water is removed through liquid nitrogen cold trapping and hydrogen is added to the He plasma gas. The spectral characteristics of the two sources have been compared.

Elimination of interferences in the electrothermal atomisation of manganese in atomic absorption spectrometry

The effects of inorganic acids and salts which may be present in samples as the result of mineralisation of manganese during wall and platform atomisation have been studied. It was found that the influence of chlorides on manganese in atomic absorption spectrometry (AAS) cannot be eliminated completely using platform atomisation. The proposed chemical modifier consists of an acidic component (phosphoric acid) and a basic component (calcium ions) which improves the sensitivity for the determination of manganese with both wall and platform atomisation. The combination of chemical modifier and platform atomisation gives the greatest sensitivity. Chemical modification increases the sensitivity more than if platform atomisation is used. The accuracy of the determination of manganese by AAS with both wall and platform atomisation are also improved by chemical modification because interferent anions, e.g., chloride, are removed at the pyrolysis stage. The same effect for manganese is seen for other divalent metals, such as magnesium and zinc, in combination with phosphoric acid.

Analytical applications of furnace atomisation non-thermal excitation spectrometry (FANES) and molecular non-thermal excitation spectrometry (MONES). Part 2. Determination of technetium-99 by FANES and electrothermal atomisation atomic absorption spectrometry

The determination of trace amounts of 99Tc was performed using electrothermal atomisation atomic absorption spectrometry (ETA-AAS) and furnace atomisation non-thermal excitation spectrometry (FANES). The thermal and chemical conditions were optimised. Tube-wall atomisation and matrix modification with 0.05 M Ni(NO3)2 in 0.1 M HNO3[forming Ni(TcO4)2] gave the best analytical results. The detection limits for 99Tc were 85 and 90 pg by ETA-AAS and FANES, respectively.

Analytical applications of furnace atomisation non-thermal excitation spectrometry (FANES) and molecular non-thermal excitation spectrometry (MONES). Part 3. Determination of rare earth elements by electrothermal atomisation atomic emission spectrometry (ETA-AAS), FANES and furnace Ionisation non-thermal excitation spectrometry (FINES)

The application of two methods of trace analysis of microsamples, electrothermal atomisation atomic absorption spectrometry (ETA-AAS) and furnace atomisation non-thermal excitation spectrometry (FANES) to rare earth elements (REE) was studied. The evaporation and atomisation could be improved in both methods by the introduction of a tungsten platform into the graphite tubes to prevent the formation of REE carbides. Depending on the boiling-points of the REE, the absolute detection limits for both methods are in the picogram range. The thermal conditions for evaporation and atomisation were optimised. It was found that in ETA-AAS only the use of maximum heating conditions is successful. In FANES determinations on pure solutions the heating conditions can be reduced with the use of a vacuum, but in the presence of inorganic matrices it is again advantageous to use maximum heating. A new variation of FANES, furnace ionisation non-thermal excitation spectrometry (FINES), was developed for easily ionisable elements and was applied successfully to the determination of Eu, Sc and Sm. The limits of determination of REE in other REE are 1–100 p.p.m., depending on the conditions used, which were mainly influenced by the volatility of the elements.