Fig. 1.

A schematic of the Perkin Elmer dual beam Lambda 850 spectrophotometer sample holders. Holder 1 represents the normal cuvette holder. Holder 2 locates the cuvette in front of the entrance port of the integrating sphere (IS) detector. Holder 3 places the cuvette inside the IS detector. For all cuvette positions, the same reference beam enters the IS detector through a reference port and hits the wall of the IS detector. In practice, the same ‘auto zero’ is used for all cuvette holders. The reference beam also has a holder which is not shown in the diagram.