Illustration showing how slit orientation changes the volume from which fluorescence is measured: (a) vertical slit orientation; (b) horizontal slit orientation. Suppose each slit’s dimensions are 0.1 mm × 3 mm. In (a) the dimensions of the sampling volume are 0.1 mm × 0.1mm × 3 mm, or 0.03 mm3. For (b) the dimensions of the sampling volume are 0.1 mm × 3 mm × 3 mm, or 0.9 mm3, a 30-fold increase in the sampling volume.
Sampling volume is important because the sensitivity of a fluorescent or phosphorescent method is proportional to the number of analyte particles that absorb and emit radiation.
