Real-time toxic metals monitor device and method

• US 5,481,181 A
• Filed: 08/01/1994
• Issued: 01/02/1996
• Est. Priority Date: 08/01/1994
• Status: Expired due to Term

• Current Assignee: OL Security LLC (Intellectual Ventures LLC)
• Original Assignee: Hughes Aircraft Company (Rtx Corporation)
• Inventors: McHardy, John, Townsend, Carl W., Megerle, Clifford A.
• Primary Examiner(s): Wieder, Kenneth A.
• Assistant Examiner(s): DO, DIEP N
• Application Number:
  US08/283,457
• Time in Patent Office: 519 Days
• Field of Search: 324/71.1, 324/425, 204/153.1, 204/400, 204/412, 204/431, 204/432
• US Class Current: 205/794.5
• CPC Class Codes: G01N 27/49 Systems involving the determination of the current at a single specific value, or small range of values, of applied voltage for producing selective measurement of one or more particular ionic species
• CPC Class Codes: G01N 33/0011 Sample conditioning preparing specimens for investigation G01N1/28

Abstract

An device for monitoring workplace air comprises a monitor cell comprising a base and a removable assembly. The removable assembly comprises (1) a flat, electrically insulating substrate having a first surface, (2) an electrolyte cell having an anode and a cathode disposed on the first surface, the anode and cathode spaced apart to define a controlled volume for holding a quantity of an electrolyte, and (3) means for applying a controlled electrical potential to the cathode. The base comprises (1) an air inlet portion for sampling air, (2) an air outlet portion connected to an air sampling pump, (3) a channel connecting the air inlet and the air outlet and adapted to introduce air to the electrolyte in the electrolyte cell, (4) a reservoir for storing the electrolyte for the electrolyte cell, and (5) a wick for supplying electrolyte from the reservoir to the electrolyte cell.

Claims

1. A device for monitoring the concentration of toxic metals in workplace air, comprising a monitor cell comprising a base and a removable assembly, wherein

(a) said removable assembly comprises (1) a flat, electrically insulating substrate having a first surface, (2) an electrolyte cell having an anode and a cathode disposed on said first surface, said anode and cathode spaced apart to define a controlled volume for holding a quantity of an electrolyte, and (3) means for applying a controlled electrical potential to said cathode of said electrolyte cell;

and

(b) said base comprises (1) an air inlet portion for sampling air, (2) an air outlet portion connected to an air sampling pump, (3) a channel connecting said air inlet and said air outlet and adapted to introduce said air to said electrolyte, (4) a reservoir for storing said electrolyte for said electrolyte cell, (5) wick means for supplying said electrolyte from said reservoir to said electrolyte cell and (6) wick means for providing contact between said air and said electrolyte in said channel whereby said toxic metals dissolve in said electrolyte.

2. The device of claim 1 wherein said toxic metals comprise at least one metal selected from the group consisting of cadmium, lead, mercury, and thallium.

3. The device of claim 1 wherein said cathode comprises a metal selected from the group consisting of iron and silver and said anode comprises a material selected from the group consisting of non-consumable metals, electronic conductors, noble metals, and noble metal oxides supported on metal substrates.

4. The device of claim 3 wherein said anode is selected from the group consisting of graphite, platinum, palladium, and iridium.

5. The device of claim 1 wherein said electrolyte comprises an aqueous acidic solution of an acid selected from the group consisting of acetic acid, nitric acid, perchloric acid, o-phosphoric acid, and sulfuric acid.

6. The device of claim 1 wherein said means for supplying said electrolyte and said means for providing contact between said air and said electrolyte are identical and comprise a wick material comprising interlocking hydrophilic and hydrophobic pores.

7. The device of claim 1 wherein said controlled electrical potential to said cathode ranges from 0 to about -2 volts versus a saturated calomel reference electrode.

8. The device of claim 1 wherein said controlled volume ranges from about 0.1 to 10 milliliters.

9. A method for monitoring the concentration of toxic metals in workplace air breathed by personnel comprising:

(a) obtaining a sample of said workplace air;

(b) providing a monitor cell comprising (1) an electrolyte cell having an anode and a cathode spaced apart a controlled volume filled with an electrolyte, (2) an electrolyte reservoir for storing said electrolyte and means for supplying said electrolyte to said electrolyte cell, and (3) means for applying a controlled electrical potential to said cathode of said electrolyte cell;

(c) forming a solution of any said toxic metals in said electrolyte;

(d) controlling said electrical potential of said cathode of said electrolyte cell such that hydrogen is evolved at said cathode at a current between about 10^-4 and 1 amp per square centimeter;

(e) poisoning at least one catalytic site on said cathode for said evolution of hydrogen by an amount of at least one toxic metal atom plating out of said solution in said electrolyte cell onto said cathode;

(f) monitoring in real time said amount of said toxic metal plating out of said solution onto said cathode by detecting a change in said current flow;

(g) determining a measure of said toxic metals from said change in said current flow and comparing said measure to a safety standard for airborne levels of said toxic metals.

10. The method of claim 9, further comprising generating a warning signal when said measure is at least equal to the level of said standard.

11. The method of claim 10, further comprising communicating said warning signal to said personnel.

12. The method of claim 9 wherein said solution is formed by:

(a) flowing said electrolyte by capillary action from said electrolyte reservoir through a wick into said electrolyte cell; and

(b) pumping said sample through said wick.

13. The method of claim 12 wherein said wick comprises interlocking hydrophilic and hydrophobic pores.

14. The method of claim 9 wherein said toxic metals comprise at least one metal selected from the group consisting of cadmium, lead, mercury, and thallium.

15. The method of claim 9 wherein said cathode comprises a metal selected from the group consisting of iron and silver and said anode comprises a material selected from the group consisting of non-consumable metals, electronic conductors, and noble metals.

16. The method of claim 15 wherein said anode is selected from the group consisting of graphite, platinum, palladium, and iridium.

17. The method of claim 9 wherein said electrolyte comprises an aqueous acidic solution of an acid selected from the group consisting of acetic acid, nitric acid, perchloric acid, o-phosphoric acid, and sulfuric acid.

18. The method of claim 9 wherein said controlled electrical potential ranges from about 0 to -2 volts versus a saturated calomel reference electrode.

19. The method of claim 9 wherein said controlled volume ranges from about 0.1 to 10 milliliters.