In operating a UV-Vis spectrophotometer, the following shall be done, except for:

• A. Keep the sample compartment open during measurement.
• B. Before turning on the power, check if the sample holder does not contain anything.
• C. If there are any spills that gets onto the instrument, immediately wipe it away.
• D. After turning on, allow the spectrophotometer to initialize and stabilize according to its user manual.

Answer: (B)

When operating a UV-Vis spectrophotometer, safe handling and proper startup sequencing ensure accurate measurements and protect the instrument. A key point is that the optical path must be stable and free from stray light during measurement, so the sample compartment is kept closed while taking measurements. Spills on the instrument must be wiped away promptly to prevent damage and contamination, and after turning the instrument on, you should let it initialize and stabilize according to the manual to allow the lamp and detectors to reach their proper operating conditions.

The step of checking the sample holder is not required before turning on the power. You don’t need to verify emptiness prior to powering up; loading cuvettes and preparing samples is typically done as part of the setup after initialization.