Silver in selected, predominantly biological, reference materials (NIST SRM 1515, 1547, 1549, 1566a, 1571, 1577b, 2704, CTA-OTL-1,
and Bowen’s Kale) was determined using neutron activation analysis (NAA) in two different analytical modes: instrumental NAA
with epithermal neutrons (ENAA), and NAA with radiochemical separation (RNAA). The ENAA mode was based on long-time 5-hour
irradiation of samples in a special Cd lined box with counting after 8-month decay. The RNAA procedure consisted in 20-hour
irradiation of samples, their decomposition/dissolution by alkaline-oxidative fusion, and precipitation of AgCl including
several purification steps. Both methods provided Ag contents in the analyzed reference materials consistent with certified
and/or literature values down to the ng·g−1 level.