Patent GB-1181682-A (GB)
Title: Analysis Apparatus
IPC: G01N31/00
Filed: 1967-02-01
Abstract: 1,181,682. Photo-electric absorption measurements. BAUSCH & LOMB Inc. Feb. 1, 1967 [Feb. 24, 1966], No.4992/67. Heading G1A. The kinetics of physical or chemical processes are investigated by absorption analysis using photo-electric apparatus which includes servocontrolled movable attenuator means in the radiation path. In a system using two radiation paths, Fig.2, the sample 24 the kinetics of which are to be investigated, is positioned in the same radiation path as the movable attenuator means 74, 76. The other path provides a reference intensity level set manually by a jaw 70. The sample and reference beams are produced by means of a source 10 and a shutter 42 having two opposed arcuate slots, which rotates in the cylindrical cavity 45 of a block 44 past two exit slits 46, 48. This produces chopping of the beams and arranges that they reach a photo-multiplier 26 alternately. The beam paths both include mirrors 50, 62, collimators 52, 64, interference filters 54, 66, condensers 56, 68 and a common ultraviolet filter 58. Before a measurement is taken, the reference beam intensity is set to allow testing of the most absorbent sample. Also, a switch (122, Fig. 3, not shown) is set to arrange the direction of initial movement of the attenuator means (74, 76). This is decided by whether the absorption coefficient of the sample increases or decreases during the measurement as a result of the chemical reaction (or physical process) which is to be investigated. The attenuator means comprises an optical wedge (76) which is moved across the beam by a servomotor (30) through a screw (92) and an opaque occluder (74) having an opening shaped in the form of a logarithmic function, which can be moved by servomotor (30) only when the wedge (76) is driven beyond the limits provided by extension members (94, 96) on the mounting of the wedge (16). The occluder (74) provides coarse, and the wedge (74) fine, intensity adjustments of the sample beam. The attenuator means is described and claimed in Specification 1,181,681. To start a measurement, a push button (120) is depressed. This starts the timing sequence control mechanism and connects power through the preset switch (122) to a solenoid (114 or 116) to cause movement, by means of a pivoted push arm (108), of the occluder (74) producing a large unbalance in the system. This unbalance in intensity between the sample and reference beams is detected by the photo-multiplier, the output of which is amplified and fed back to the servomotor (30) which drives the wedge (76) in a direction such as to null the detector output. The wedge (76) may also carry with it the occluder (74) to attain an intensity balance, the gain of the servo-system being increased to provide for this. Overshoot will probably occur, but this is desirable since as the wedge (76) is backtracked from the maximum overshoot position to the initial balance position for the system, back-lash in mechanical system is taken up. Once an initial balance is obtained, the chemical reaction or physical process is started and as it proceeds, the movement (in a single direction only) of the wedge (76), necessary to maintain a balance, is measured. This is done in analog fashion by a potentiometer (31), whose wiper arm (95) is coupled to the screw (92) and which feeds a recorder, or digitally using an apertured wheel 102 and a photo-electric counting device, Fig. 3, and also Figs. 6-8 (not shown). In alternative two-path systems, either the attenuator means 74, 76 is in the reference path instead of the sample path, or the occluder 74 is in the reference path, and the wedge 76 in the sample path. Single path systems are described in which instead of a reference radiation path, an electrical reference signal is used. The D. C. output of the photo-multiplier is applied with that from the reference signal source in opposite polarity to a summing circuit, Figs. 9, 10 (not shown), the output of which supplies the servomotor. The radiation beam may be chopped, in which case an A.C. reference signal is provided by a electromagnetic generator synchronized with the radiation chopper, Fig. 11 (not shown), and a summing circuit adapted for A. C., Fig. 12 (not shown), is provided. Applications of the apparatus are to investigation, on series of discrete samples or even fluidflow samples, of chemical reactions e.g. reactions involving enzymes as catalysts in oxidization processes, and physical processes e.g. diffusion, evaporation &c.