What is the recommended pre-start check for a UV-Vis spectrophotometer before turning it on?

• A. Check that the sample holder is empty before turning on.
• B. Keep the sample compartment open during measurement.
• C. Wipe any spills immediately.
• D. Let the instrument initialize after turning on.

Answer: (A)

Before turning on a UV-Vis spectrophotometer, the most important step is to ensure the sample holder is empty. Having an empty holder keeps the light path clear during lamp warm-up and baseline measurement, and prevents any liquid or solids from being introduced into the optical chamber as the system initializes. If a sample is left in place during startup, spills or residues could contaminate optics, alter the baseline, or even damage the lamp or detectors, leading to inaccurate readings. Wiping spills immediately and other safety or cleanup steps are important, but they’re general lab practices rather than the specific pre-start check this question is asking about. Allowing the instrument to initialize after turning on is part of the startup routine, but it doesn’t address the immediate need to clear the beam path before power-up.