| 摘要 |
1,205,249. Spectrophotometry. DOW CHEMICAL CO. Oct.4, 1967 [Oct. 5, 1966], No.45106/67. Heading G2J. [Also in Division G1] Apparatus for determining a plurality of components of a mixture by measuring the radiation affecting properties of each of the components at a pair of mono-chromatic wavelengths comprises a mono-chromator with a plurality of entrance slits and shutter means for selectively masking and unmasking the entrance slits. Infrared radiation from a resistance wire, nernst glower or a piece of heated silicon carbide, 10 is focused by a mirror 11 on to a plurality of entrance slits 13, 14, 15. Slits, 13 and 15 are so positioned that light entering through them reaches the exit slit 28 of the grating mono-chromator 25, 26, 27 as measuring wavelengths for two components of a mixture in flow cell 30 and slit 14 is positioned to provide a reference wavelength. A filter 29 removes higher orders of diffraction. The pneumatically operated shutter 16 alternately exposes slits 13 and 14 and slits 14 and 15 to estimate the components in turn. A chopper 22 chops radiation passing through slit 14 at frequency f 1 and through slits 13, 15 at frequency f 2 . The radiation passing through the flow cell 30 and falling on detector 32 contains measuring and reference components modulated at frequencies f 2 and f 1 respectively. These components in the detector output are separated by tuned amplifiers and detected by rectifiers synchronized with the rotation of chopper 22 by photodiodes 42, 43. The rectifier outputs are compared in self balancing potentiometer and recorded. When shutter 16 is operated by the instrument programmer to test the other component, a mark is made on the record or a different pen is brought into use. The output may be used for process control. The flow cell may be a reflectance cell using the attenuated total reflectance principle, and the grating may be replaced by a Na Cl crystal prism. The apparatus may be used to determine ethylbenzene and vinylcyanide (acrylonitrile) in styrene monomer. The apparatus may be used in the visible spectrum using glass lenses and front surface mirrors and in the ultraviolet spectrum using quartz lenses and front surface mirrors. |
