PURIFICATION OF REAGENTS AND SEPARATION OF ELEMENT TRACES BY ELECTRODEPOSITION ONTO A GRAPHITE TUBE CATHODE

The use of a commercially available AAS graphite tube atomizer as an electrode for the cathodic electrodeposition of element traces at constant-current in a hydrodynamic flow-through-system is described. After deposition the graphite tube is transferred into an atomizer unit for subsequent sensitive determination by atomic absorption spectrometry. The deposition yield of greater-than-or-equal-to 99% (2 h; 1.5 A) for Co was verified, using Co-60 as a radioactive tracer, by monitoring the concentration fall in the electrolyte solution down to less-than-or-equal-to 5 pg/ml, and the deposited material. The efficiency of the system for the purification of electrolyte solutions was found to be very high. For the determination of the residual impurities, e.g. in very concentrated NH4F-solutions, a simple ion-exchange procedure was worked out for Cu, Mn, Ni, Pb, Zn. To get back the high purity solid NH4F, the solvent was evaporated partly and the precipitated crystals were sucked off in a PTFE-funnel. To avoid contamination, crystallization was carried out in a closed container system using the principle of subboiling distillation. The purity of the recrystallized NH4F-salt increased by a factor of 2 to 3 (crystallization yield 50 - 70%) so that a solid product with an impurity level below 0.5 ng/g was obtained.