United States Patent (19) 11 4,256,694 McAllister et al. 45 Mar. 17, 1981 3,755, 192 8/1973 Rottig et al. ................ 252/477 RX CARBON MONOXDE MONITORNG 54 3,847,552 11/1974 Hobgood et al................... 23/232 R SYSTEM 3,966,440 6/1976 Roberts ............. ... 422/86 X 75 Inventors: Jerome W. McAllister; Gunter A. 3,985,017 10/1976 Goldsmith ..................... 23/232 RX Kohler; Virtudes R. Lund, all of St. Paul, Minn. OTHER PUBLICATIONS 73) Assignee: Minnesota Mining and Katz et al., “Oxidation of Carbon Monoxide in Air by Manufacturing Company, St. Paul, Silver Permanganate', Ind. & Eng. Chenn., vol. 42, p. Minn. 345 (1950). Primary Examiner-Arnold Turk 21 Appl. No.: 912,344 Attorney, Agent, or Firm-C. Alexander; D. M. Sell; E. (22 Filed: Jun. 5, 1978 T. Okubo 51 Int. Cl...................... G01N 21/29; G01N 21/77; 57 ABSTRACT G01N 31/22 Colorimetric indicator material comprising alumina 52 U.S. C. ...................................... 422/58; 252/408; impregnated with permanganate ion and silver ion 422/60; 422/86 which changes color from purple to brown in the pres 58) Field of Search ....................... 422/55, 56, 58, 60, ence of carbon monoxide is disclosed. A personal moni 422/86; 23/232 R; 73/28; 252/408 tor containing permanganate ion and silver ion impreg (56) References Cited nated alumina which changes color completely when U.S. PATENT DOCUMENTS the carbon monoxide exposure over a given period of time exceeds a predetermined concentration is dis 2,408, 164 9/1946 Foster .......................... 252/477 RX 2,569,895 10/1951 Main-Smith et al. ... 23/232 RX closed. 2,961,303 11/1960 Wiswesser ............ - P - 422/58 X 3,112,999 12/1963 Grosskopf.............................. 422/57 17 Claims, 2 Drawing Figures U.S. Patent Mar. 17, 1981 4,256,694 3. 4/ 44 AA 42 Frog. a /O 4,256,694 2 pled CO, changing color from purple to brown at a rate CARBON MONOXIDE MONITORING SYSTEM proportional to the atmospheric CO concentration. BRIEF DESCRIPTION OF THE DRAWINGS BACKGROUND OF THE INVENTION 5 In the accompanying schematic diagrammatic draw The present invention relates to a system for monitor ings which illustrate the personal monitor forming a ing personal exposure to carbon monoxide. In the sys part of the present invention: tem of the present invention, carbon monoxide is oxi FIG. 1 is an isometric exploded view of the personal dized by alumina impregnated with silver ion and per monitor of the present invention; and manganate ion, the oxidation resulting in the impreg 10 FIG. 2 is a top plan view of the assembled personal nated alumina changing color from purple to brown. monitor. Commercial devices in the form of indicator tubes for monitoring personal exposure to various toxic gases or DETAILED DESCRIPTION OF THE vapors are well known. An indicator tube is a glass tube INVENTION containing a granular chemical and is worn by the user 15 The exposure of employees at their workplaces to in a position close to his breathing zone. A pump con carbon monoxide is greater than for any other chemical nected to the tube pulls air from the atmosphere or physical agent. Carbon monoxide in the ambient air through the tube. The granular material reacts chemi is commonly found in refineries, foundries, pulp mills, cally with the toxic gas and a color change occurs. The sintering mills, lampblack plants, formaldehyde manu color change progresses from the entrance to the exit of 20 facturing, arc welding, auto repair shops, traffic control the tube as the various cross sectional layers react. At operations and tunnel construction sites. Exposure to the end of any given sampling period, the length of the high concentrations of CO for even short periods of color change stain in the tube is proportional to the time can cause serious health hazards-1600 ppm of CO concentration of the toxic gas averaged over the sam in the air can cause headaches, dizziness, and nausea in pling period. 25 20 minutes, and in two hours collapse, unconsciousness Prior workers have reported in the literature that and possibly death. Exposure to low concentrations, on silver permanganate, when coated on various porous the order of 100 ppm, for extended periods of time can substrates, will produce materials which oxidize carbon result in behavioral changes, cardiovascular damage monoxide in the ambient atmosphere. See, for example, and brain damage. Although precautions are taken to 30 eliminate CO from the workplace air, CO can fre M. Katz and S. Halpern, "Oxidation of Carbon Monox quently be found in concentrations up to 200 ppm. The ide in Airby Silver Permanganate', Ind. & Eng. Chem., United States Government has established 50 ppm Vol. 42, p. 345 (1950). TWA for carbon monoxide as the official standard for SUMMARY OF THE INVENTION industrial air (Federal Register, Vol. 36, No. 105, May 35 29, 1971). The TWA is the time-weighted average con The present invention relates to a system for monitor centration for a normal 8-hour workday or 40-hour ing personal exposure to carbon monoxide and utilizes work week, to which nearly all workers may be repeat alumina impregnated with permanganate ion and silver edly exposed, day after day, without adverse effect. ion as the active material in a personal monitor. Thus, worker health and federal regulations dictate that The permanganate-silver impregnated alumina is for employers with a potential CO hazard monitor the ex mulated by immersing the alumina in a solution of per posure of their workers to determine if their average manganate and silver, draining the excess solution, and exposure exceeds 50 ppm. drying under vacuum. The solution is comprised of The impregnated activated alumina of the present water soluble salts of silver and permanganate with invention is prepared by immersing alumina in a water noninterfering counter ions. The resulting purple mate 45 solution of permanganate ion and silver ion followed by rial oxidizes carbon monoxide at a rate proportional to draining excess solution and drying under vacuum. The the ratio of Ag to MnO4 concentrations. The oxida alumina can be any form of porous, high surface area tion reaction causes the purple material to change color alumina which is referred to as activated alumina. The from purple to brown. The impregnated alumina is activated alumina can be powdered, granular, extruded utilized in a personal monitor for carbon monoxide. The 50 or molded into shapes. monitor samples the ambient atmosphere at a diffusion The activated alumina utilized in a preferred embodi controlled rate. If the atmosphere contains a predeter ment of a monitor of the present invention is in the form mined concentration, say 50 ppm of carbon monoxide, of 30 mm. diameter by 1.6 mm. thick discs which are the impregnated alumina will change color completely made according to the following procedure. The discs from purple to brown in a predetermined time. The rate 55 are cut from rods made up of equal weights of two types of color change of the impregnated alumina in the moni of aluminas; RA-1, an activated alumina from the tor is independent of the relative humidity and the pres Chemical Division of Reynolds Metal Company, and ence of organic vapors in the atmosphere. A300, a partially calcined alumina hydrate from Kaiser The present invention provides a permanganate-sil Chemicals. RA-1 alumina is received in an 8X 14 mesh ver impregnated alumina wherein the rate of carbon distribution, but is ball milled and classified to minus 150 monoxide oxidation and hence, the rate of color change mesh. A300 alumina is used as received (minus 325 is proportional to the ratio of the silver concentration to mesh). 100 g of RA-1 is mixed with 100 g of A300. The the permanganate concentration. alumina mixture is thoroughly combined with 115 ml of The present invention also provides a personal moni a 10% hydrogen peroxide solution to form a slurry. The tor for carbon monoxide containing permanganate-sil 65 slurry is poured into a 30 mm.x80 mm. Whatman Ex ver impregnated alumina wherein the monitor samples traction Thimble Cellulose Single Thickness which is the CO from the atmosphere at a diffusion controlled contained in a glass tube. The glass tube and the con rate and the impregnated alumina reacts with the sam tents are placed in a closed container which also con 4,256,694 3 4. tains an amount of water. The alumina slurry is cured in closed system, and the rate constant k2 was measured this closed container for 18 hours at a temperature of for each sample. 90° C. After the curing period, the alumina is a solid rod 30 mm.X80 mm. of activated alumina. After removing the thimble, the rod is sawed into discs 1.6 mm thick, KMnO4 AgNO3) k2 and the discs are heated under vacuum at 450° C. for 1 SAMPLE moles/1 moles/1 min A 1.58 x 10-2 0.74 X 10-2 0.025 hour. The H2O2 is vaporized from the rod during the B 1.58 x 10-2 1.48 x 10-2 0.0372 90° C. heating step. The vaporization causes macro C 1.58 x 10-2 2.96 x 10-2 0.2030 scopic pores to form throughout the alumina rod result ing in a molded alumina that is open to the diffusion of 10 gases or vapors. EXAMPLE 2 The activated alumina discs are then impregnated with permanganate ion and silver ion by the following Treated alumina samples were prepared and tested general process. Water soluble salts of permanganate exactly as described in Example 1 except that silver and silver are selected; the counter ions must be chemi 15 permanganate (AgMnO4) was used in the coating solu cally non-interfering.