Three synthetic multi element standards (SMELS I, II and III) and two reference materials (RMs), SL-3 and Soil-7 of IAEA were analyzed for validation of the k₀-based  internal mono standard neutron  activation analysis (IM-NAA) method utilizing in-situ relative detection efficiency. The internal mono standards used in SMELS and RMs were Au and Sc, respectively. The samples were irradiate din 
Apsara and Dhruva reactors, BARC and radioactive assay was carried out using a 40% relative efficiency  HPGe detector coupled to an 8kMCA. Concentrations of 23 elements were determined in both SMELS  and  RMs. In the case of RMs, concentrations of a few elements, whose certified values renotavailable, could  also be determined. The % deviations for the elements determined in SMELS with respect to the assigned values and RMs with respect to certified values were within ±8%.The Z-score values at 95% confidence level for most of the elements in both the materials were within  ±1.