In reflectance spectrophotometry using a dry reagent slide, which statement is true?

In reflectance spectrophotometry using a dry reagent slide, which statement is true?

• A. Light projected to the slide at 180-degree angle
• B. Dye concentration directly proportional to reflectance
• C. Unabsorbed, reflected light detected by photodetector
• D. Reflectance values are linearly proportional to transmission values

Answer: (C)

In reflectance spectrophotometry, light is incident on the dry reagent slide and the detector measures the light that's reflected from the surface. The dye absorbs part of the light, so as dye concentration increases, more light is absorbed and less is reflected. The photodetector therefore responds to the unabsorbed, reflected light, producing a signal that decreases as the dye concentration goes up. This is why the statement about detecting unabsorbed, reflected light is the correct description. The other ideas don’t fit: the detection geometry isn’t about projecting light back along the incident path at a 180-degree angle; dye concentration and reflectance are not directly proportional—increasing dye lowers reflectance; and reflectance is not simply linearly proportional to transmission, since reflectance and transmission involve different optical paths and interactions with scattering and absorption.

In reflectance spectrophotometry, light is incident on the dry reagent slide and the detector measures the light that's reflected from the surface. The dye absorbs part of the light, so as dye concentration increases, more light is absorbed and less is reflected. The photodetector therefore responds to the unabsorbed, reflected light, producing a signal that decreases as the dye concentration goes up. This is why the statement about detecting unabsorbed, reflected light is the correct description.

The other ideas don’t fit: the detection geometry isn’t about projecting light back along the incident path at a 180-degree angle; dye concentration and reflectance are not directly proportional—increasing dye lowers reflectance; and reflectance is not simply linearly proportional to transmission, since reflectance and transmission involve different optical paths and interactions with scattering and absorption.