To obtain the spectrum of a compound from 190 to 500 nm, which item is not necessary?

• A. Tungsten light source
• B. Deuterium light source
• C. Double-beam spectrophotometer
• D. Quartz cuvettes

Answer: (A)

Measuring a spectrum that starts at 190 nm requires a light source that emits in the UV region. A deuterium lamp provides strong UV output down to about 190 nm, which is essential for the 190–500 nm range. Quartz cuvettes are necessary because UV light would be absorbed by ordinary glass, so only a UV-transmitting material can let you observe the spectrum in this range. A double-beam spectrophotometer is common for accurate measurements across a broad range, but a single-beam instrument can still obtain the spectrum. The tungsten light source is not needed for this task because it mainly emits in the visible region and contributes little to the UV part of the spectrum.