Patent GB-1455886-A (GB)
Title: Method of analysis
IPC: G01N35/00
Filed: 1974-03-05
Abstract: 1455886 Gas analysis by chemiluminescence SYBRON CORP 5 March 1974 [5 March 1973] 9922/74 Headings G1A and G1B A method of calibrating apparatus to measure the concentration of either one of two components that react together to produce a signal representing the concentration of one component if the other is supplied at a constant rate, comprises: supplying a mixture containing a known concentration of the first component in a first stream, and supplying a second component in a second stream, to a reactor at respective constant rates, and calibrating the apparatus to measure concentrations of the first component; then, while continuing to supply the first component in the first stream, bleeding a quantity of the first component into the second stream upstream of the reactor, and increasing said quantity until the reactor signal is minimized; whereby, when this said quantity of the first component alone is provided in the second stream, the apparatus is effective to measure concentrations of the second component present, in the first stream. Equimolecular proportions of NO and O 3  will react together to produce NO 2  and 02, and will emit luminescence which, if one reactant is supplied at a constant rate and in high enough concentration to ensure that only a small fraction of it is consumed, is proportional in intensity to the concentration of the other. Apparatus calibrated to measure concentrations of a first component in a first stream by reaction with a more highly concentrated second component in a second stream will be equally effective to measure concentrations of the second component present in the first stream, if the second component in the second stream is replaced by an equally highly concentrated first component. A cylindrical reactor 10, having a light filter 11 adjacent the photocathode 12 of a photomultiplier 13, communicates with first and second inlets 15, 20 having calibrated orifices 16, 21, and with an outlet coupled to an exhaust pump 27. The apparatus is first calibrated for a stable component, e.g. NO, by feeding it in a known concentration at a constant rate into the first inlet 15, while air enters at a constant rate through a dryer 23, an ozonator 22 and the second inlet 20. Then, while the supplies of NO and O 3  are maintained, further NO is bled in through a line 24 to react with the O 3  upstream of the second inlet 20, the rate of bleed being adjusted to bring the apparatus to minimum reading, indicative of the condition of equimolecular proportions of NO and 03 upstream of the reactor necessary to cause complete consumption of the O 3 . If this rate of bleed is then maintained while the ozonator is cut off, the apparatus is thereby rendered effective to measure concentrations of O 3  present in the first inlet 15, and the need for a calibrating sample of O 3  in a known concentration is thus avoided. The ozonator may be an electric discharge type producing 1 to 3 per cent of O 3  in an air-stream, or a photolytic type providing about 0.1 per cent O 3  in air on up to 0.5 per cent in oxygen. At an air flow-rate of 10 ml/sec into the ozonator, the 03 and NO will have time to react completely if a volume of about 20cc is provided upstream of the second inlet 20.