Question

Explain the principles of double-focusing and why it is required in some instruments?

Answer 1

In double beam focusing instruments, the energy emitted by the radiation source is split by the instrument into two beams, which are energetically and optically identical. One of the beam passes through the sample and the other through the reference sample. The two half-beams are recombined and pass along the optical path to the detector.

The double focusing is required in some instruments becuase when the sample is analyzed in solution, the bands of solvent appear in the spectrum. In this case, the spectrum of the sample is obtained by subtracting the spectrum of the solvent from the resultant spectrum, the former must be recorded under identical conditions.