THE INSEPARABLE TRIAD - ANALYTICAL SENSITIVITY, MEASUREMENT UNCERTAINTY, AND QUANTITATIVE RESOLUTION

The formal definition of sensitivity associates the term with the chan ge in the response of a system for a small change of the stimulus caus ing the response, i.e., the ratio of the response of a system to the s timulus causing it. One interpretation of sensitivity associates the r ate of change of the response for a small change of the stimulus as th e slope of a calibration plot of response vs stimulus. An alternative interpretation associates sensitivity with the smallest value of the s timulus that can be resolved with a given degree of confidence, i.e., the detection limit. Applications of the first usage to analytical che mistry date at least to the beginning of this century; applications of the second interpretation are of more recent origin. The accompanying paper argues in favor of the second interpretation on the basis that, among of her things, the ''slope'' interpretation conflicts with the formal definition of sensitivity and is meaningless as a descriptor of the performance of a measuring system. In this paper I offer argument s to support my belief that the slope definition of sensitivity is con sistent with both formal definitions and accepted usage in analytical chemistry and, more importantly, that it is an invaluable descriptor o f one of the most important characteristics of any analytical method, I include information to support my belief that proper use of the slop e definition yields much more information than is available in the ''d etection limit'' interpretation.