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Different dental alloys are used for producing prostodontics appliance. The nonprecious alloys are the most commonly used for metal-ceramics bridges and crowns. They are developed by modification of the steel composition. Iron as a minor component segregates on grain boundaries of alloy surface and create chemical bonding between metal and ceramic. Six alloys of different composition were analysed. The analysis was performed by anodic sampling in water-HCl (conc.) solution in a 10:1 volume ratio [1]. Alloy sampling was timing and voltage controlled (20 s, 4.5 V) and transfer of dissoluted cations to the chromatographic plates took 15 s. Metal cations were separated and identified by Thin Layer Cromatography [2]. Standard solutions (FeSO4 0.1 mg/ml and FeCl3 0.1 mg/ml) and alloy samples were applied to TLC plates (Merck, Darmstadt, Germany) 10 x 10 cm, precoated with cellulose. For the cromatography the standard solutions (10 μ l volume) and the alloy samples were applied 1 cm from the lower edge of the plates. Plates were developed in the saturated glass chamber (DESAGA) to the distance of ca 8 cm with iso-amyl alchohol (3-methyl-1-butanol HPLC grade, SIGMA-ALDRICH) - HCl (36.5%, p.a., KEMIKA) - acetonitrile (p.a. Merck, Darmstadt) 8.8 + 0.7 + 0.5. The developing time was ca 2 hours and the temperature 23˚ C. After separation the plates were dried in a steam of warm air for aproximately 1 minute and the spots were visualised by spraying with the saturated ethanolic solutions of alizarin, diphenylcarbazide and quercetin [3]. The plates were dried and exposed to NH3 vapour. Pink (identifacation solution - diphenylcarbazide), purple (identifacation solution – alizarin) and brown (identifacation solution – quercetin) spots of iron were visible at the distance of 6.8 cm from the start (Rf value was 0.85). The difference between Rf value and the colours of the standard solutions (FeSO4 and FeCl3) spots could not be found. The method described is suitable for the separation and identification of iron cations no matter of charge. |
