Patent GB-1401056-A (GB)
Title: Gas detecting and measuring unit
IPC: G01N27/416
Filed: 1972-08-08
Abstract: 1401056 Electro-chemical analysis ENERGETICS SCIENCE Inc 8 Aug 1972 [17 Aug 1971] 36991/72 Heading G1N In a gas detecting unit in which the gas is drawn through an electro-chemical cell 20 at a controlled flow-rate, the cell 20 includes an anode which provides a catalytic site for electro-chemical reaction with the gas, a cathode and a reference electrode, the anode being maintained at a fixed potential relative to the reference electrode of +0.7 to +1.5 volts in order that only the gas being detected is electro-chemically reacted, precluding the possibility that other gases in the sample as well as an oxygen/water redox couple will influence the current produced. Cell construction, Fig. 4 and Fig. 3 (not shown). The gas to be detected is fed into a gas reaction chamber formed by recessed member 28a and PTFE substrate 24.1 carrying anode 24.2 of platinum black and PTFE particles. The anode is in contact with an electrolyte in a chamber defined by 28f the opposite side of which is closed by cathode 21 and reference electrode 26 on PTFE substrate 26/21. Alternatively the anode and cathode, (Fig. 3), may be mounted in facing relationship on PTFE carriers in contact with an electrolyte, a reference electrode of a platinum coated nickel structure being freely mounted in the electrolyte. If the gas being detected is alcohol the reference electrode may be lead oxide/lead sulphate or mercury sulphate/mercury. A sulphonated polystyrene ion exchange membrane may be inserted between the anode and reference electrodes. Alternatively a perm selective membrane may be mounted in the input to the cell. Detecting alcohol in breath. Multi position valve 12 is operated so that air passes through inlet 11 and is drawn through the cell by pump 30 and at the same time button 63 is pressed to allow a calibration sample from 60 to flow into sample collector 50, Fig. 5 (not shown) which includes a first helical tube mounted within a second tube and thermally conductive material therebetween. Valve 12 is then positioned to allow the calibration sample to pass from 50 to the cell. The flow is adjusted at 40 so that the read-out gauge gives the correct reading. The system is then flushed and inlet 12 connected to sample collector 50 so that the breath from the test person enters 50 that coming from the alveolae being the last into and hence first out of 50 when valve 12 is positioned to allow the sample to pass into the cell. If the reading is positive a verification sample may be taken and collected at 70. Two cells 20 may be used one of which measures alcohol and carbon monoxide and the other of which measures only carbon monoxide. The difference giving the amount of alcohol present. Detecting carbon monoxide. The inlet to the cell 20 is connected via a scrubber, Fig. 8 (not shown) which removes alcohols, aldehydes hydrocarbons but not carbon monoxide. A sump bottle may be included between the intake and cell to smooth out the curve obtained from the cell, Figs. 9 and 10 (not shown). The potential of the anode is maintained at the required voltage as described in Specification 1372245.