Patent GB-1339475-A (GB)
Title: Chromatogrpahic spectrophotometric method of analysis and  equipment suitable for employing the method
IPC: G01N30/86
Filed: 1971-05-04
Abstract: 1339475 Monitoring a chromatographic process photo-electrically POLSKA AKADEMIA NAUK INSTYTUT CHEMII FIZYCZNEJ 4 May 1971 12937/71 Heading G1A The composition of a liquid or gas flowing through a cell 5 at the output of a chromatographic column 8 is monitored using a scanning monochromator II whose output beam passes through the test cell to a photo-cell 6. The light-source comprises the light-spot on a TV tube which is scanned repetitively across the tube by the application of a sawtooth voltage to the control electrodes. The waveform repetition time should be substantially less than the time of flow of any substance through the column. The grating monochromator output is divided at 4 to provide a reference beam, which passes through a reference liquid 10 to a photo-cell 11. The output from the measuring photo-cell 6 is utilized in four ways: (A) Absorption spectra of the sample fluid, each spectrum resulting from one complete scan by the light spot, are presented in sequence on a TV screen 13 whose sweep voltage is synchronized with the sawtooth voltage. (B) The absorption of the sample is recorded -19- at a number of discrete wavelengths during each scan. In this way a graphical picture of the change of absorption with time is obtained Fig.7, (not shown). To achieve this record, the output from photo-cell 6 is applied to a unit 15 including one gate/voltage discriminator pair (22/23) for each discrete wavelength required Fig.2, (not shown). Each gate receives the sawtooth waveform produced by generator 14 and each produces a gating pulse when this waveform reaches a pre-set level (U 1 ...U 3 ) determined by programming device 17. Each pulse from a gate actuates the corresponding discriminator which thereby produces an output pulse indicative of the radiation intensity received by the photo-cell at the wavelength corresponding to the gate trigger level. The respective discriminator outputs are recorded simultaneously for each scan Fig.7, (not shown) and the results for successive scans are printed one after the other. The outputs from the gates are also supplied to the TV screen to provide wavelength marking pulses. (C) For one or more selected pairs of wavelengths, the outputs from the corresponding discriminators (23) are ratioed in a quotient device (27). This ratio is recorded for each spectral scan to produce a curve. (D) The wavelengths at which absorption exceeds a pre-set value are determined and the absorption at these optimum wavelengths is recorded on each scan. To do this the photo-cell output is supplied to a threshold device (24). Each time the threshold is exceeded on a scan a pulse signal is produced which is combined with the sawtooth voltage (at 26) to produce a further pulse (U 5 ) whose timing relates the corresponding optimum wavelength to the spectral scan. Each pulse is fed to the control unit 17 which causes recording of the absorption at the optimum wavelengths during each scan. This gives a trace, Fig.7 (not shown) displaying how the absorption at the optimum wavelengths varies with time.