Patent GB-1057905-A (GB)
Title: Gas chromatograph detector
IPC: G01N27/70
Filed: 1964-02-17
Abstract: 1,057,905. Electrophysical measurements. BECKMAN INSTRUMENTS, Inc. Feb. 17, 1964 [Feb. 20, 1963], No. 6586/64. Heading G1N. [Also in Division H1]. A detector for a gas chromatograph comprises a chamber 13 including an anode 22 and a radiant energy passing cathode 18, means for flowing a gas stream through the zone between the anode and cathode, and a light source 14 for directing light on to the cathode 18 for releasing photoelectrons into the chamber. In the single cell embodiment shown the source 14 is an ultraviolet lamp, and an additional needle anode 21 is provided. Connection to a mesh screen cathode 18 is made via a terminal 19 and wire 20. A stream of sample gas is passed through chamber 13 via pipes 23, 24 and a reference or carrier gas is passed through the cathode 18 from a pipe 25 to prevent contamination of the cathode by the sample gas. The cathode is preferably made of or plated with a metal of low work function such as silver, gold or copper. The anodes are preferably made of or plated with a metal of high work function such as platinium or stainless steel. Alternatively, the cathode may be made of solid material such as quartz with the surface facing the chamber 13 covered with a silver grid or with a uniform metal film of a density such as to transmit a portion of the incident light. The detector may be connected in a circuit (Fig. 3) in which the cathode 18 is connected through a load resistor 31 and voltage source 30 to earth, and the anode 22 is connected to an electrometer amplifier 32 having an output resistor 33 feeding a voltage recorder 34. The anode 21 is removed from the chamber 13 and the opening plugged. With the source 30 adjusted to a low value analysis of halogenated compounds, certain pesticides and herbicides, and other materials which show affinity for low voltage electrons may be effected by electron capture detection using nitrogen as a carrier gas. With a higher value of source 30, hydrocarbons and other organic compounds may be analyzed by ionization detection, using argon as a carrier. By employing anode 21 connected in parallel with anode 22, and connecting amplifier 32 as a voltmeter, Fig. 4 (not shown), breakdown voltage detection may be utilized in the measurement of H 2 , O 2 , N 2  and CO in helium carrier gas. In further modes of operation, a rectified A. C. supply is employed to detect diatomic and polyatomic gases such as nitrogen and propane in argon and helium carriers, or the electron energy spectrum of a sample is measured by varying the supply voltage over the electron capture range sufficiently rapidly to complete a cycle during the presence of a particular constituent in the chamber. A double cell form of detector, Fig. 2 (not shown), utilizes identical sample and reference chambers each having an apertured anode and cathode, and is connected in circuit arrangements, Figs. 5 and 6 (not shown), which either compensate for lamp output and amplifier operation, or vary the light intensity to keep the cell current constant. The light source 14 may be a mercury, hydrogen, xenon or other discharge lamp. The housings 10, 12 are preferably made of insulating material such as P. T. F. E., but may be of metal.