Radiochemical Methods of Analysis: Evaluation

Evaluation

Radiochemical methods are routinely used for the analysis of trace analytes in macro- and mesosamples. The accuracy and precision of radiochemical analyses are generally within the range of 1–5%. Precision is limited by the random nature of ra- dioactive decay and is improved by counting the emission of radioactive particles over as long a time as is practical. If the number of counts, M, is reasonably large (M >= 100), and the counting period is significantly less than the isotopes half-life, then the percent relative standard deviation for the activity, (σ_A)_rel, is estimated as

For example, when the activity is determined by counting 10,000 radioactive parti- cles, the relative standard deviation is 1%. The analytical sensitivity of a radiochemi- cal method is inversely proportional to the standard deviation of the measured ac- tivity and, therefore, is improved by increasing the number of particles that are counted.

Selectivity rarely is of concern with radiochemical methods because most sam- ples contain only a single radioactive isotope. When several radioactive isotopes are present, differences in the energies of their respective radioactive particles can be used to determine each isotope’s activity.

In comparison with most other analytical techniques, radiochemical methods are usually more expensive and require more time to complete an analysis. Radio- chemical methods also are subject to significant safety concerns due to the analyst’s potential exposure to high-energy radiation and the need to safely dispose of ra- dioactive waste.