Patent GB-1432613-A (GB)
Title: Fluorescence spectrophotometer
IPC: G01J3/44
Filed: 1973-04-09
Abstract: 1432613 Fluorescence spectrometers HITACHI Ltd 9 April 1973 16845/73 Heading G1A A fluorescence spectrophotometer comprises in series a light source, a first monochromator, a specimen under test, a second monochromator and a single photo-detector; the light is chopped after the first monochromator to give two beams, one of which passes to the sample and thence to the second monochromator while the other beam forms a reference which by-passes the sample and the second monochromator. This allows variations in light output to be eliminated. In Fig. 2, light from the source 30 is directed through the first monochromator 33 to a rotating disc chopper having alternate transmissive, opaque, reflective and opaque sections, Fig. 3 (not shown). Light transmitted through the chopper is directed to fluorescent specimen 40 and thence to the second monochromator 42 and detector 49. Light reflected from the chopper passes via mirrors 52, 53 to the detector.  As the chopper rotates, the photo-detector 49 produces in sequence a zero level when an opaque section is in the beam path, a reference level when the reflective section is present, a further zero level when the second opaque section is present, and a specimen level when the transmissive level is present. Fig. 5 shows the circuit connected to the detector. Switches 61-1 to 61-3 are operated in turn as the chopper rotates;.when the first opaque region is present the switch 61-3 is closed and the other two are open so that the signal from detector 49 passes through preamp 60 to the zero level hold circuit 74 where it is held. Next the transmissive section of the chopper is present so switch 61-2 is closed and the other two are open. With switches 64, 65, 69 in the positions shown the detector signal passes through preamp 60, reference hold circuit 68, and switch 69 to differential amp 70 where it is compared with standard cell 72. The output of amp 70 controls a high voltage source 73 to change the characteristics of the detector 49, which is a photomultiplier. In this manner the detector output is always the same for the beam reflected by the chopper and the dependance of the detector output on wavelength is removed. Next the zero signal is re-held as the second opaque section occurs, and finally when the transmissive section is present the switch 61-1 closes to pass the detector signal to amp 63 and thence to output 66. During this last step the detector 49 still receives the high voltage set by the reference beam reflected from the chopper, so that the final output at 66 is in effect a comparison of the specimen and reference beams. Using the circuit of Fig. 5 as above, another comparison can be made by placing a photon meter cpmprising a high concentration of Rhodamine B at 81 in Fig. 2 and a filter which passes only Rhodamine fluorescence at 82; in this manner the emission spectra of the specimen and the photon meter are compared in wavelength. By changing switches 64 and 69 to their other positions in Fig. 5, a subtraction measurement is possible; using a specimen at 40 and at 81, a filter is placed at 82 to pass only one wavelength while the second monochromator passes a different wavelength, so that the output of the specimen at two wavelengths are compared and the background due to the solvent removed.