Samples with very low concentrations are difficult to measure accurately due to the radioactive atoms unexpectedly depositing on surfaces.  Sample loss at trace levels may be due to adhesion to container walls and filter surface sites by ionic or electrostatic adsorption, as well as metal foils and glass slides.  Sample loss is an ever present concern, especially at the beginning of the analysis path where sequential steps may compound these losses.  
Various solutions are known to circumvent these losses which include adding an inactive carrier or adding a tracer.  Research has also shown that pretreatment of glassware and plastic surfaces can reduce radionuclide sorption by saturating the sites.