indicator

1. In chemical analysis, a substance that changes color within a certain definite range of pH or oxidation potential, or in any way renders visible the completion of a chemical reaction; e.g., litmus, phenolsulfonphthalein. 2. An isotope that is used as a tracer. 3. The labeled substance whose distribution between reactants of a system is used to determine the amount of analyte present. [L. one that points out]

- alizarin i. a solution consisting of 1 g sodium alizarin sulfonate dissolved in 100 mL distilled water; used as an i. for free acidity in gastric contents.

- clinical i. a measure, process, or outcome used to judge a particular clinical situation and indicate whether the care delivered was appropriate.

- health i. variable, susceptible to direct measurement, that reflects the state of health of persons in a community.

- oxidation-reduction i. a substance that undergoes a definite color change at a specific oxidation potential. SYN: redox i..

- redox i. SYN: oxidation-reduction i..

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in·di·ca·tor 'in-də-.kāt-ər n a substance (as a dye) used to show visually usu. by its capacity for color change the condition of a solution with respect to the presence of free acid or alkali or some other substance (as in detecting the end point of a titration) <litmus and phenolphthalein are acid-base \indicators>

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in·di·ca·tor (inґdĭ-ka″tər) [L.] 1. the index finger (index [TA]). 2. the extensor muscle of the index finger (musculus extensor indicis [TA]). 3. a substance, usually a dye or intermediate, that shows the concentration of a substance, the completion of a reaction, or the attainment of a particular pH range by a change in color or other visible sign.