Gas Chromatography - Tandem Techniques - The Fluorescence Spectrometer > Page 21

This toroidal mirror focuses the portion of incident light onto the reference photocell, providing an output that is proportional to the strength of the incident light. The path of the fluorescent light is largely on the right hand side of the diagram. Fluorescent light from the cell is focused by an ellipsoidal mirror on to a spherical mirror at the top right-hand side of the diagram. This mirror focuses the light onto a grating situated at about center right of the figure. This grating can scan the fluorescent light and provide a fluorescent spectrum. Light from the grating passes to a photoelectric cell which monitors its intensity. The instrument is quite complex and, as a result, rather expensive; however, from the point of view of measuring fluorescence it is extremely versatile. Again the cell and all conduits must be heated to prevent any condensation of eluted vapor from building up in the sensor cell.

The fluorescence signal (If) is given by