Patent GB-900423-A (GB)
Title: Spectrographic analysis apparatus and process
Inventor: WEBB MAURICE STEPHEN WILLIAM
IPC: G01N21/69
Filed: 1959-04-06
Abstract: 900,423. Photo-electric spectrography. UNITED KINGDOM ATOMIC ENERGY AUTHORITY. March 29, 1960 [April 6, 1959], No. 11652/59. Class 40 (3). [Also in Groups XX and XL (a)] A process for the measurement of an element (e.g. beryllium, mercury, lead, chromium, manganese, silicon, arsenic, antimony, zinc and copper) contained in a gas or gas mixture (e.g. air), comprises feeding the gas or gas mixture at a known rate into an intermittent electric arc discharge and then withdrawing the gas or gas mixture from the discharge, splitting the radiation emitted by the discharge into a spectrum and measuring the intensity relative to its background of a line of the spectrum characteristic of the element to indicate the concentration of the element present. In the apparatus shown in Fig. 3 for carrying out the process, the motor 23A rotates a plate 25 so as to close a duct leading into the air filter unit 27 and allow contaminated air (e.g. containing beryllium) into a funnel 4 from the atmosphere through a port 26 in the plate 25. The radiation emitted while the contaminated air is passing through the intermittent arc 5 in the chamber 9 passes through a quartz window into the monochromator 32 and photomultipliers 33. The relative intensity of the beryllium doublet is recorded on a ratio-recorder and compared with the record obtained from a standard sample of filtered air to enable the concentration of the beryllium to be read directly. The standard sample is obtained by passing air through the filter 27 and tube 28 into a spark chamber 29 containing two copper-beryllium electrodes 30 and then through the tube 31 and funnel 4 into the arc chamber 9. The concentration of the beryllium in the sample is measured by spectrochemically analysing the beryllium deposited on a filter paper between plates 10 during the passage of a given volume of the sample. The air then passes through tubes 12, 35, a filter unit 36, flow control unit 37 including a flowmeter, and suction pump 38. The tubes 12 and 35 are joined by elements 34 so that the arc chamber 9 can be removed to replace the electrodes. Themonochromator-photomultiplier unit 32, 33 is shown in Fig. 2 in which radiation from the arc chamber 9 passes through slit 13 and as reflected from mirrors 14 and 15 on to a diffraction grating 16. The grating is arranged so that the part of the spectrum containing the beryllium doublet is reflected to mirror 15, to mirror 17, through a slit 18 in mirror 19 to mirror 20 and into the photomultiplier 22. Part of the background adjacent the beryllium doublet is reflected from mirror 19 into the photomultiplier 21. A modification (Fig. 5, not shown) is described in which the monochromator-photomultiplier unit is integral with remainder of the apparatus. The unit is shown in Fig. 4 in which radiation from the arc chamber is reflected by a plane mirror (not shown) underneath the slit 39 on to a concave mirror 40, the slit being at the focus of the mirror. The mirror 40 reflects parallel radiation on to diffraction grating 41 which reflects that part of the spectrum containing the beryllium doublet on to a concave mirror 42 which focuses the doublet through a slit in plane mirror 43 on to the plane mirror 45 and into the photomultiplier 46<SP>1</SP>, and the background on to the mirror 43 and into the photomultiplier 46.