Assays provide quantitative determinations of elements in non-processed geological materials. Assays are usually required when samples are known or suspected to contain higher levels of metals.
Accuracy is typically in the 1-3% range as long as the analyte is greater than 100 times the detection limit of the method. For some elements more difficult to analyze, this may stretch to 5%. Analyses can be purely instrumental (INAA or Delayed Neutron Counting (DNC)) or can be produced by chemical treatment such as fusion or acid digestion with final analyses commonly by AA, XRF, ICP-OES, ICP-MS, titration or gravimetric methods.
Usually higher levels of dilution and use of internal standards help minimize matrix effects. All dilutions are done either volumetrically or gravimetrically to ensure minimal error.