6 9 The significant role of trace elements present at the Jlgfg (10- gig), ngfg (10- gig) 12 and pgfg (10- gig) levels in geological, biological, environmental and industrial materials has increasingly been recognized in science and technology. To detect and determine trace elements, we usually use modern optical, electrochemical and nuclear analytical techniques. Althouih most of them are highly sensitive and selective, preliminary enrichment techniques are required to extend the detection limits, improve precision and accuracy of analytical results, and to widen the scope of the determina...