COLORIMETRY-SPECTROPHOTOMETRY 



119 



Gary spectrophotometer, a motor-driven shutter-beam-splitter combina- 

 tion provides a time sequence of "dark interval-through reference-dark 

 interval-through sample-dark interval-through reference, etc." Later these 

 two beams are recombined and directed to the same phototube. The two 

 beams are compared by means of an electronic system synchronized with 

 the rotating mirror which splits the beams. This arrangement avoids the 

 possible mismatch of two phototubes but moves the detector farther away 

 from the sample and reference containers. 



Tungsten 

 lamp 



Of- 



H2 lamp 



[h- 



Qr 



-^-- 



Grcting-* 



Slit 2 



^ 



Reference 



\ Motor 



I Phototube 



j^ Tungsten 

 lamp" 



Fig. 9-5. Optical Schematic Diagram of Gary Model 14 Recording Spectrophotome- 

 ter, for comparison with Fig. 9-4. Note that the spHt beam, after passing through 

 the reference and sample, is recombined in a single phototube. (Courtesy Applied 

 Physics Corp.) 



Ultraviolet and infrared spectrophotometers 



Measurements in the ultraviolet region require a special source of 

 energy and an optical system which will transmit ultraviolet. Usually 

 quartz optics are used, and the cuvettes or tubes which hold the solu- 

 tions are made of quartz or fused silica. Otherwise operation in the ul- 

 traviolet is the same in principle as operation in the visible region. Ultra- 

 violet spectrophotometers are important in biology because a number of 



