Effect of Graphite Furnace Degradation on Atomic Absorption Signals
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Journal of Applied Spectroscopy, Vol. 87, No. 4, September, 2020 (Russian Original Vol. 87, No. 4, July–August, 2020)
EFFECT OF GRAPHITE FURNACE DEGRADATION ON ATOMIC ABSORPTION SIGNALS A. N. Kulik,a* Yu. V. Rogulsky,a O. M. Buhay,a V. Yu. Illiashenko,b and A. N. Kalinkevicha
UDC 543.421
The time dynamics of degradation of the working characteristics of longitudinally heated furnaces for spectrometers with electrothermal atomization of a sample in the presence of tungsten, zirconium, and palladium compounds used as chemical modifiers were studied. Visual changes in the state of the investigated furnaces are discussed. The loss of carbon material during the experiment is shown. Atomic absorption signals of silver and copper recorded at different stages of degradation of unmodified and modified furnaces are analyzed. An explanation of the reasons for the accelerated damage to the pyrographite coating and subsequent destruction of the polycrystalline graphite base of furnaces subjected to modification is suggested. Keywords: graphite furnaces, pyrolytic graphite, degradation, chemical modifier, atomization. Introduction. Atomic absorption spectrometry with electrothermal atomization in a graphite furnace (ETAAS) is one of the most common and available of widely used spectroanalytical methods. The slow pace of ETAAS analysis is compensated by the high sensitivity, low elemental detection limits, reliable and simple instrument construction, and relatively inexpensive analytical equipment. The time dependence of the heating of a so-called "aged" furnace with a pyrographite coating (PGC) is known to change according to operators with long-term experience working with atomic absorption spectrometry (AAS) combined with electrothermal atomization (ETA) [1–3]. However, this phenomenon was explained by the decreased mass of the furnace and was not thoroughly studied. A furnace loses material to wear unevenly and can overheat in places where the wall crosssectional area is the smallest [4–7]. This aspect has been discussed before [8]. The difference between the set and actual temperature can adversely affect the accuracy and precision of the measurements. The wear rate of furnaces depends mainly on the impurity content of the protective gas, the temperature program, the volume and composition of the injected sample, and the used chemical modifiers (CM). The use of CM can increase [9] or decrease the service life of graphite furnaces [1, 3, 7]. CM are classified as permanent modifiers and platinum-group metals, in particular, tungsten (W), zirconium (Zr), and palladium (Pd), according to the mechanism of action. The parameters of the obtained atomization curves should change if they are added to a sample, i.e., the shape of the analytical signal should change and its initial appearance should shift. Silver (Ag) and copper (Cu) are typical test elements for AAS with ETA in studies of the kinetics, mechanism of atomization, etc. because Ag does not react with graphite and is easily atomized while Cu is held in the furnace-wall
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