Accuracy in standards preparation for neutron activation analysis

Abstract

Errors in preparing standards, especially multielemental standards, are extremely important if accurate results are desired from neutron activation analysis (NAA). It is often convenient to prepare standards for NAA from single or multi-element solutions which are then deposited onto (or into) a suitable matrix, such as filter paper or quartz vials. There are many potential sources of error in preparing single-element standards including: impurities and non-stoichiometric composition of the element or compound used to prepare the standard solutions; evaporative losses of solvent; inaccuracy of calibration, and imprecision of the pipettes used; moisture content of elements or compounds used; contamination from reagents, equipment, laboratory environment, or final matrix of the standard; instability of standard solutions (i.e., to losses via precipitation or adsorption), and losses of volatile elements during dissolution and/or irradiation. Additional sources of error in preparing multielement standards includes: instability of mixed, multielement solutions, and cross-contamination of one element by the addition of a second element. Procedures previously used by the author at NIST to prepare multielement standards with concentrations accurate to about one percent are described. Additional techniques needed to prepare multielement standards with accuracies better than 1 percent will be discussed.