Which of the following is NOT listed as a use of fluorometers in the source material?

• A. Calcium
• B. Porphyrins
• C. Catecholamines
• D. Cholesterol

Answer: (D)

Fluorometers work by detecting fluorescence from molecules that either glow on their own or after being tagged with a fluorescent probe. That makes them especially useful for substances that can be visualized through fluorescent signals.

Calcium fits because there are fluorescent calcium indicators that light up when they bind calcium, allowing precise monitoring of calcium levels in cells and tissues. Porphyrins are well-known for their strong intrinsic fluorescence due to their conjugated ring structure, so they’re readily observed with fluorometry. Catecholamines can also be detected fluorometrically, either through intrinsic fluorescence under suitable conditions or after derivatization to produce a fluorescent product, enabling sensitive measurements in biological samples.

Cholesterol, on the other hand, is typically quantified using enzymatic colorimetric assays or other non-fluorescent methods, and it doesn’t appear as a standard fluorometric use in the source material. So cholesterol is the item not listed as a fluorometer use.